Monday, June 27, 2011

Hot Water Recirculation VS Tankless Water Heaters – Not Compatible?

Typically, hot water recirculation systems with a few exceptions aren’t compatible with tankless hot water heaters.

Hot water circulating systems were designed to work with storage type


water heaters. Without the tank full of water the burners would be cycling on and off constantly trying to maintain the temperature in the piping. Since the piping is continuously losing heat the heat must be replenished continuously.

Tankless water heaters are much more complex than a traditional storage heater. The tankless heater has to put much more heat into the water much more quickly than a storage unit in order to get the water up to the desired temperature before it leaves the heater.

It sounds simple but it is not. Putting all that heat energy into the heat exchanger means that if the water stops flowing or even if the flow just drops significantly the heat exchanger can be quickly destroyed. That is why tankless heaters need so many sensors. Tankless water heaters monitor the gas supply, the exhaust, and the inlet and outlet temperatures.

The minimum flow that tankless water heaters require is typically ½ to ¾ gallon per minute. Most hot water circulating pumps will not produce enough flow through tankless heater to turn on the heater.

Let’s suppose that we get a good big pump and pump enough water to turn on the heater. With a traditional tank type storage water heater the outcome would be easy to predict. When the hot water in the tank falls below the burner set point the burners will come on and heat the water until it hits the upper set point, and then the burners will shut off. The cycle will repeat over and over.

What happens with the tankless water heater is a lot more difficult to predict. The tankless heater is trying to maintain a constant outlet temperature. It doesn’t just turn the burners on and off, it regulates or modulates the gas flames (or electric current) to try and maintain a very accurate outlet temperature. Some heaters even modulate the flow of water through the unit.

Remember, the tankless heater is measuring things like inlet water inlet temperature and exhaust temperature and taking appropriate actions to keep the heater running correctly and keeping the outlet temperature at the set point.

Tankless heaters weren’t designed to raise the water temperature only a few degrees. When the inlet water gets up near the set point, which it will rather quickly, then the heater won’t know quite what to do. The Exhaust temperature might not ever stabilize, and thus could cause headaches for the tankless electronics. Tankless heaters for the most part just weren’t designed to work with circulating pumps. All sorts of strange malfunctions could pop up with such an arrangement.

Demand hot water systems are compatible with tankless heaters

A demand system is a system that acts like a circulating pump, circulating water through the hot water piping and then through the cold pipe back to the water heater. But a demand system shuts the pump off when hot water reaches the last fixture. Therefore no hot water ever gets sent to the water heater inlet.

As far as the water heater is concerned it just thinks someone turned on a faucet. As long as your demand system pump is capable of creating enough flow to turn on the water heater it will work fine with a tankless water heater.

More about hot water recirculation.  Hot Water Recirculation – What Are the Benefits and Pitfalls?

Thursday, June 16, 2011

Hot Water Flow Rates with Tankless Water Heaters and Storage Heaters

Hot Water Flow Rates with Tankless Water Heaters and Storage Heaters


The flow rate of the water in a pipe, and the diameter of the pipe determine the velocity of the water
traveling in the pipe, and thus the amount of waiting time for hot water to arrive at the fixture.

Increasing the flow rate and decreasing the pipe diameter have the same affect; increasing the velocity of the water in the pipe. Flow rates that are too high can produce noise and vibration in the piping, and can cause water hammer problems. High flow rates can cause pipe erosion especially in the elbows and T fittings.

Often building codes limit the water velocity in hot water piping to 5 feet per second. At five feet per second the hot water should reach a fixture connected to the water heater with a 100 foot pipe in about 20 seconds.

The table below gives the flow velocity in feet/second for a number of flows in g/m with typical pipe sizes.



 

 



Pressure Drop Affects Flow Rate












To push for instance, 4 gallons per minute through a 100 foot long ½” diameter Type L copper tubing would require a pressure of 10.6 psi. No problem if your source of water is more than 10.6 psi, but if you are circulating water with a hot water circulating pump then you have more of a challenge.

At 1 gallon per minute the drop would be less than 1 psi but the wait would be about 112 seconds.

At 5 gallons per minute the pressure drop would be 16.1 psi. (37.1 feet of head)


Hot Water Circulating Pumps

Here is a graph showing the pump curves for TACO hot water circulating pumps and are virtually the same as all the other brands. (1 psi = 2.3 feet of head and 1 foot of head = .434 psi.)



From the graph it is easy to see that none of the pumps will be able to create a 5 g/m flow and only two a 4g/m flow.


Hot Water Return Line

If you have a hot water circulating system then you need a return line from the furthest end of the hot water supply pipe back to the pump and water heater. If you are using a hot water demand system then the cold water piping is typically used as the return line. When calculating the wait time for the hot water the return line isn’t included, but for purposes figuring pressure drop and flow rates it will need to be included.


Tankless Water Heater Pressure Drops

Storage water heaters (Tank type heater) typically have insignificant pressure drops when water flows through them. Below is a graph showing the pressure drop through various models of Rinnai tankless water heaters. Tankless hot water heaters do have significant pressure drops.






From the graph it can be seen that the larger the heater the lower the pressure drop at any given flow rate.
To find the pressure required to push a certain flow through the piping system requires one to add the pressure drops from the piping and from the water heater.

Reading from the graph with the largest model (lowest pressure drop) we find that at 4 gallons per minute the pressure drop will be approximately 5 psi, and at 5 g/m the drop will be about 8 psi. On the other end of the scale, the smallest tankless water heater has a pressure drop at 4 g/m of about 9psi and at 5 g/m it’s close to 12 psi.

Armed with the above charts and graphs it should be fairly easy for you to get a good idea of how long the wait for hot water will be for any given plumbing layout and pump combination. Basically you want to minimize pipe diameters and lengths to minimize the total volume contained in the hot water piping to have
the most efficient hot water plumbing system.

Sunday, June 12, 2011

Using a Chilipepper with a Dedicated Hot Water Return Line

Hot Water Demand Systems and Dedicated Return Lines Are Compatible

For home owners who have a residential hot water circulating system and would like to convert the system to a demand system to save energy, reduce their carbon foot print and be green as far as water and energy conservation go, here is how to do it.

Traditional residential hot water circulating or recirc systems waste a lot of energy. The cost of heating water is generally substantially higher than the cost of the water itself.



With a hot water demand system you will have a wait for the hot water, and although the wait is shorter than with a non-pump residential plumbing system, there is still a waiting period before the hot water reaches the fixture. Once that wait is over then when you turn on the tap you will have nearly instant hot water. The length of the wait depends on two things, the plumbing layout, and the power of the pump being used.

Installing a Demand System with a Dedicated Hot Water Return Line

Typically a traditional hot water return line consists of a pipe connected from the hot water supply pipe at the last fixture to the inlet of the water heater. Usually the pump is located at the water.

Replacing the existing pump with a Chilipepper hot water demand pump is very easy to do. Remove the old pump and plumb in the Chilipepper. Use hoses to connect the Chilipepper inlet to the same fitting that was hooked to the old pump's inlet and do the same with the outlet.

You can then either hard wire the buttons to the various fixtures, or if you don't want to string wire in your attic or crawl space or there are other impediments to hard wiring start buttons, use an X10 remote control system for starting the pump from any location. Insteon remote control can also be used but Insteon stuff is pretty pricey.

What to Expect - Operating Your Hot Water Demand System with a Dedicated Return Line

There are differences in the way a hot water demand system and a hot water recirculation system work. .

Since hot water is continuously circulating the loop stays full of hot water. Since a hot water circulating system wastes so much heat energy lots of home owners use timers and or temperature controls to reduce the operating hours and thus reduce the energy wastage.

A timer can be used with the circulating pump to shut if off during periods of no or little use. This does of course save oodles of energy, but is quite inconvenient if you happen to need hot water during one of those periods that the system is turned off.

Another method used to reduce the energy wastage of recirc systems is to have the pump turn on when the temperature drops below a set point and turn off when it reaches an upper set point. The problem is that if you reduce the temperature low enough to realize significant energy savings you don't end up with hot water in the loop, just warm.

With a hot water demand system, when you want hot water you must push the start button and then wait for the hot water to arrive. The hot water will of course, reach the first fixture in the loop first, and then each fixture along the loop until the pump senses the arrival of hot water.

When the Chilipepper detects a temperature increase of 3 to 12 degrees, depending on the sensitivity setting, it shuts off. If you again push the button the pump will again shut off when it sees a second temperature increase... which typically would only be a second or two because the hot water has arrived.

Once the temperature hits 96 degrees or above the pump locks out and won't restart until the water temperature in the pump drops below 96 degrees.

Due to the time it takes hot water to cool off in the piping and the pump there can be short periods of time where the occupant would like to use the demand system to get hotter water than what is in the loop but the pump won't respond because the water is just above 96 degrees. 96 degree water is lower than human body temperature and therefore will feel cool, not hot. Typically that time period would be 20 minutes or so.

That's all there is too it. Be a little more green, conserve water, save time, and install a hot water demand system in your home today!

Thursday, April 7, 2011

Why Are Tankless Water Heaters So Expensive?

A friend of mine who installs tankless water heaters recently wrote an article that I think many of you might find interesting. You can find the original article here: Tankless Expenses


Tankless water heaters are hi tech appliances with multiple microprocessors, electro mechanical valves, temperature sensors, flow regulators and more. The unit cost is about the same as a good storage tank water heater, maybe 10%-15% more. But when you get a quote from your neighborhood plumber for a tankless unit it is often 3x or more than the storage tankless water heater.



So where is the cost difference coming from? It comes from the INSTALLATION. Now how difficult is it to install a tankless water heater you ask. The answer is actually very simple, in some ways simpler than a traditional tank water heater.

The problem lies with overly conservative calculations and the resulting additional requirements. The biggest being the fuel, the gas supply.

Gas Supply requirements

Most whole house tankless water heaters require a 199,000 Btu/h gas supply. Now, that is only required when it runs full power. It is like driving your car at maximum speed. Most building departments require you to run a separate gas line for the tankless, which can become very expensive and drives up the cost of the installation.

Their argument is that one should be able to supply the full 199,000 Btu/h all the time regardless of the gas usage of other gas appliances in the home.

They want you to add up for example :

1- Furnace 80,000 Btu/h

2- Gas Dryer 50,000 Btu/h

3- Gas Stove 60,000 Btu/h

4- Fireplace 50,000 Btu/h

5- Gas Cooktop 50,000 Btu/h (let’s say six burner model)

Total : 290,000 Btu/h

The regular water heater uses about 40,000 Btu/h

Based on these calculations and a worst case gas volume/pressure table for gas line diameter requirement you will be forced to install a new gas line for the tankless water heater.

This method ensures that in case your:

Furnace is full on and

Gas Dryer is running and

Gas Stove is on full power and

Fireplace is on and

Gas Cooktop is on with all its 6 burners full power you can run the tankless unit at full power with its 199,000 Btu/h. and typically the 199,000 btu/h is running when 2 people are taking shower at the same time and the washer is running and you are washing dishes by hand (Dishwasher heats its own water electrically).

Now, is this a realistic situation? NO NO NO, but they make you pay for that.

Let’s take another example. A typical home has an electric supply service of 100 Amperes, provided by the utility company. Now when you open up your electrical box and add up all the breakers you have there it will be 200 amperes or 300 amperes. This means that if your run all your electrical appliances, lights and plugs you’ll be in the dark because the main breaker of 100 Ampere will trip and cut the electricity off. That is because the electric utility company is limiting the total power you can draw at anytime.

That is not a problem most the time. Sometimes when you have your electric dryer and air conditioner and other high power appliance running at the same time you’ll be forced to compromise so that the breaker will not trip.

The same should be through with gas supply too. The gas meter with its attached regulator limits how much gas you can draw, rightfully so. In the above example we need almost 500,000 Btu/h and this is above what the meter/regulator is set to supply.

But this over design in installing a separate gas line for the tankless drives up the installation cost without a real benefit.

In most situations the existing gas line is sufficient for the tankless with some limitations on total gas usage at once.

Exhaust Venting

Here is another situation that drives up the cost, separate venting. Without going too much into the details of it here is a summary.

Newer tankless water heaters are highly efficient, 92% and more and therefore their exhaust temperature is very low, about 120 F. They can be vented with PVC instead of stainless steel models that have a 300 F exhaust temperature.

These new models are condensing units and there is condensation in the venting. That condensation fluid is lightly acidic and should flow back into the unit where it is neutralized and drained.

When replacing the storage tank heater the existing venting is often of galvanized sheet metal that CAN oxidize or rust over long period of time when and if condensation collects inside of it.

A properly installed tankless vent is sloped towards the unit and any condensate fluid would flow back into the tankless unit and is then neutralized and drained and is not collected in the galvanized sheet metal vent.

Here again the requirement for a separate venting for the tankless drives up the installation cost.

Most plumbers like to do the additional work; it is more revenue for them.

Would it not be for the separate venting and separate gas supply line a tankless installation and total cost would be much lower and slightly higher than a regular tank water heater. Because of its longevity and energy saving tankless water heaters would be actually the less expensive solution.

It seems a more practical and realistic approach would bring down the cost of a tankless water heater significantly and make it more of a mainstream approach like in many other countries. It would reduce our energy cost, provide the convenience of endless and clean (no chance of bacteria growth)and help the environment not only in harmful emissions but also in the reduction of disposal of roughly 9 million tank water heaters in landfills annually.

Wednesday, March 23, 2011

Control Your Hot Water Demand System with a Flow Switch

I’ve had a number of customers inquire about using a flow switch to control their Chilipepper hot water demand systems. Many of them also have tankless water heaters.


The idea is that you could briefly turn on the hot water tap and immediately shut it off, which would turn the Chilipepper on and then you wouldn’t need to press a button. When you hear the pump shut off you know you will have instant hot water when you turn on the hot tap. Personally I don’t think a pressing a button is any more difficult than turning the hot water on and then off.



You could, I suppose, turn the hot water on and just leave it on until the water gets hot, but with the Chilipepper pump it won’t get the hot water to the faucet quicker and you won’t save any water.

In fact, the Chilipepper requires a momentary contact between its control wires to activate it. The Chilipepper comes with a pushbutton, pretty much a doorbell button. When you push the button the contact is made between the two wires, and when you release the button the contact is broken. It’s not until the contacts are broken that the Chilipepper pump turns on.

This means that if you turn the faucet on and then off the Chilipepper will start and shut off when hot water gets there. Next, you turn on the hot water faucet, and begin using your hot water. But the flow switch will keep the contacts closed for as long as you are using the hot water.

In the meantime, if the Chilipepper sees the control wires make contact and they remain in contact for more than 15 seconds, the microcontroller in the Chilipepper thinks there is a short circuit on the control wires. In response the Chilipepper will turn on for two brief spurts about every 15 seconds until the contact between the control wires is broken.

We can overcome this problem by using a capacitor and a resistor. Placing a capacitor in series with the switch contacts creates a momentary short on the control wires. When the switch closes, the cap allows a rush of current to flow and causes a voltage drop on the input pin of the microcontroller. As the capacitor charges up and the voltage rises above about 2.5 volts the microcontroller sees it as an open contact and starts the pump.

After the flow switch opens its contacts when you shut off the faucet, the capacitor needs a way to discharge. Placing a resistor in parallel with the capacitor provides a discharge path. The control wires consist of a hot wire and a ground wire. A resistor in parallel with the cap discharges the cap when the contacts open.

A 1uf capacitor in parallel with a 10k resistor works good. Use a non polar capacitor so you don’t need to worry about which lead is positive and which is negative.

It’s a nice solution to eliminate the need for a button if that is the kind of thing you want to do. However, flow switches are pretty expensive. Trying to use flow switches for several sinks would be very expensive and you would need to do a lot of plumbing and wiring as well.

I will cover using a “whole house” flow control for the Chilipepper hot water demand system in my next blog.

Related Articles:

Motion Sensing for Residential Hot Water Demand Systems

Freeze Protection with a Chilipepper?

Friday, March 11, 2011

Living With A Tankless Hot Water Heater

Living With a Tankless Hot Water Heater


Using hot water from a tankless water heater is not the same as a using hot water from a tank type water heater. If you haven’t experienced living with a tankless water heater, it may take some getting used to.

Hot Water Temperature Characteristics of Storage Water Heaters

With storage water heaters when you turn on the tap the hot water begins flowing through the hot water piping on its way to the faucet. As the hot water flows toward the fixture it gives up some of its heat to the piping material. The faster the water flows the less heat it gives up on the way.



Depending on the ambient temperature, pipe run length, and piping material it can take up to 40% or more gallons of water to get hot water at the fixture than the pipe holds.
Temperature Stability

The temperature of the hot water in the tank is always changing. When the burner is on the water temperature is increasing, and when the burners are turned off the water temperature will be decreasing since heat is being lost through standby losses. To obtain the desired hot water temperature the user mixes hot and cold water together at the fixture.

The burners aren’t big enough to keep up with flowing water, so when you use the hot water the temperature drops fairly quickly at the bottom of the tank, and as the hotter water at the top of the tank exits the tank and the colder water begins rising to the top to replace the consumed hot water, the temperature begins to drop rapidly . At this point you have to begin re-adjusting the hot and cold water valves to keep the temperature where you want it and not long after there is no more hot water.

You never really know what the actual hot water temperature will be coming from a tank type water heater since the temperature is constantly going up or down depending on whether the burners are on or not.

Storage water heater reliability

Storage tank type water heaters are simple devices. A tank of course, a burner with pilot light and thermocouple, a combination thermostat gas valve, anode rode, PTR valve, drain valve, and that’s about it. No electronics or sensors other than the thermostat. Parts are easy to get and inexpensive. Any plumber can fix or replace them.

Tankless Water Heaters

Tankless water heaters are highly complex with many more parts than a storage heater. They have sensors to monitor water flow rate, gas pressure, exhaust temperature and more. They have computers built into them to control the burners and modulating gas valves to control the flame size. More parts means that there are more things that can fail. More complexity means more trouble fixing them.

You can think of a tankless water heater, (gas), as a coil of copper piping in the flames over a burner. If you run water through the tubing with the flames on, the water coming out of the other end will be hotter than the water going in the inlet.

A longer coiled pipe will result in hotter water and a shorter coil will provide lower temperature water at the outlet. That is because a longer pipe will keep the water the flames for a longer time.

Higher flow rates will result in less time in the flames and the water won’t be heated as much and lower flow rates expose the water to the heat longer and thus the water will get hotter. Any change in inlet temperature will result in a corresponding change in outlet temperature as well.

With storage hot water heaters a change in inlet temperature does not result in a change in the outlet temperature, nor will a change in flow change the outlet temperature.

With a tankless water heater you set the hot water outlet temperature the water heater controls the size of the flames to keep the outlet temperature at the set point.

Tankless water heaters have a minimum flow rate that must be achieved to turn on and keep the heater on. They also have a maximum flow rate that if exceeded causes the outlet temperature to drop as flow further increases.

Bathroom sink faucets are often have a flow rate of one gallon per minute. That means that to just keep the tankless heater on you need to run the hot water faucet at almost full blast. If you want only warm water you have to add more cold water to the mix and run the risk of reducing the flow rate enough that the heater shuts off.

In order to supply continuous hot water tankless hot water heaters have to have much bigger burners than storage heaters and need larger gas supply lines. If the tankless heater is electric it will probably need its own extra heavy wiring and possibly require a service upgrade from your utility company.

With gas tankless water heaters the exhaust vent will need to be substantially larger than the vent for a storage water heater.

Sediment Vs Scale buildup

If you live in a hard water area then you probably get sediment buildup in your water heater. Over a few years you can get quite a bit of sediment and it will begin to reduce the amount of hot water available from the heater. At some point you may have to drain the heater and flush out the sediment.

With a tankless water heater the hard water will cause scale buildup in the heat exchanger. The scale buildup increases the pressure drop through the heater and causes the flow rate to lower which leads to overheating and heat exchanger damage. Tankless water heaters in hard water areas usually need to be flushed out and de-scaled once a year.

Operating a tankless water heater with very hard water can void the warranty. In extremely hard water areas tankless water heaters can only be used if they have a water softener supplying the cold inlet water. Check the owner’s manual for the maximum water hardness can be without voiding the warranty.


Trouble Shooting Electric Water Heaters

Trouble shooting gas water heaters

Comparing Tankless Water Heaters

Comparing Storage Heaters to Tankless Heaters

Thursday, March 3, 2011

Understanding Your Residential Hot Water Plumbing System

httYesterday I received the following email about how to plumb the hot water in his house and here are his questions along with my answer which is a bit long.


I'm about to build a 3 bath home in the Knoxville, TN area.
Down there, they use PEX plumbing.
I've been wanting recirculating hot water ever since I spent time in Santa
Fe NM where it's required.
How many Chilipepper pumps would I want...


What's best to design and build...a typical manifold system with hot water
return?
Eventually there will be two more baths on the lower level.
I'm planning for a GE GeoSpring heat pump hot water heater, based upon
little knowledge.

This seems like a great time to be asking you…

HELP?

John Doe (ok… not his real name)



Mr. Doe,

How you plumb your house will depend on things like whether you want to maximize water savings, or energy savings, or convenience for the user etc. The floor plan is the other biggy. Without seeing the floor plan I am clueless as to how to plumb the hot water.

I would really rather not tell someone how to plumb a new home, however, perhaps I can give you enough information for you to make some informed decisions about how to plumb your new home to reach whatever your goals may be.

I shall limit my perspective to typical residential homes… not 25,000 square foot mansions. I will assume that the bathrooms are not equipped with multiple shower heads and that kind of thing.


Hot Water Plumbing Basics

Let’s take a look at some plumbing basics for residential hot water plumbing.

The plumbing is the distribution system. In regards to hot water recirculating systems the type of water heater generally doesn’t make any difference. Tankless water heaters take longer to deliver hot water since they don’t have any hot water ready and waiting to go… they must heat it first and so typically it will take 10 to 20 seconds longer to deliver hot water than with a tank type water heater. Many tankless heaters are incompatible with hot water circulating systems.

Hot water distribution systems are capable of wasting both energy and water. They can also be irritating and stressful. Having to stand there on a cold morning with your hand in the shower waiting for the hot water can make a one minute wait seem like a 10 minute wait. Not the best way to start your day!

If you stop to think about it cold water plumbing doesn’t have the capability of wasting water or energy unless you have a leak or something. You don’t have to run the water down the drain waiting for cold water and you don’t lose heat energy since you didn’t add any energy to begin with. It’s only the hot water plumbing that can lead to wasted energy and wasted water.

Pipe Size and Water Flow

Pipe size is an important factor and must be carefully considered. Many home owners want to use the biggest pipe they can because they believe that larger pipes will provide a higher flow rate. This may have been true to an extent in the days before low flow fixtures, but not anymore.

The Federal Energy Policy Act of 1992 required all faucet / shower fixtures made the USA to have a flow rate of no more than 2.2 GPM at 60 PSI. Before 1992, older fixtures used much more.

Prior to 1992 fixtures could deliver 5, 6, even as high as 8 gallons per minute or more. With such high flow rates running more than one fixture at a time could create such a high pressure drop through the main pipe run that the flow could drop when a second fixture was opened. In that case a larger pipe would fix the problem.

With a typical water pressure of about 60 psi, a ½” diameter pipe should be able to deliver over 20 gallons a minute. But your flow rate is limited to what your fixture or fixtures can deliver. Let’s say you had two 2.2 gallon per minute fixtures running full blast with just hot water. That would be a piece of cake for a ½” pipe. But fixtures are seldom run full blast with only hot water.

There is a cost to using larger pipe though… water velocity. The larger the pipe diameter the more water the pipe can hold and the slower the water will travel at a given flow rate.

For example, a ½” diameter type K copper pipe holds about .012 gallons per foot. That works out to approximately 80 feet of pipe per gallon, or 1.2 gallons in a 100 foot pipe run. So if your fixture is running at 2 gallons per minute, it will take about 36 seconds for the hot water to reach the fixture. The water won’t necessarily still be hot when it gets there since the water loses heat to the piping material along the way.

A ¾” pipe holds about .025 gallons per foot, which is approximately 40 feet of pipe. At the same flow rate of 2 gallons per minute it will take the water one minute and 15 seconds to reach the fixture through a 100 foot pipe run.

A 1”diameter pipe holds about .043 gallons per foot, or 4.3 gallons per 100 feet. At 2 gallons a minute it would take over 2 minutes for the water to reach the fixture.

The slower the hot water travels through the pipe the more heat it gives up on the trip until the pipe warms up. That adds more time waiting for hot water and running water down the drain.

For the fastest hot water delivery and consequently the least amount of wasted water one would use half inch diameter pipe (when allowed by the local plumbing codes). Always follow the plumbing codes.

If you have one of those fancy showers with 8 shower heads and a steam generator you may need to run that 1” pipe, but for most homeowners the green way to go is with small diameter piping for the plumbing layout.


Hot Water Plumbing

There are a variety of methods used when plumbing a house. There are looped , branched, home run, point of use, and combinations of these used. Typically when a new home is designed there is no plumbing diagram, or plumbing layout. The plumber just uses the blue prints that show where the fixtures are.

Let’s take a brief look at the pros and cons of the different kinds of residential plumbing layouts.


Looped Plumbing

Looped plumbing is where the hot water piping goes from the water heater outlet to the first fixture, and from there goes to the next fixture, and from there the next, etc. As you might suspect, this can lead to pretty long pipe runs.

Looped plumbing is traditionally used for hot water circulating systems. One pump with a low flow rate running constantly will provide you with hot water instantly at every fixture. It will also radiate a lot of heat energy and drive up your utility bill.

This type of plumbing saves the maximum amount of water since you never have to run water down the drain to get your hot water.


Branched Plumbing

Branched plumbing is when you run a main hot water line to the furthest fixture and tap off of the main line with short branch lines to each fixture. This is a very common method of plumbing. Using a recirc pump to circulate the hot water will only fill the main pipe with hot water, so to get hot water at the other fixtures requires running the water contained in the branch line down the drain. If the branch line is short it’s not a problem, but for longer branch runs you can waste a lot of water.


Home Run Plumbing

Home run plumbing is when each fixture has a separate pipe leading back to the water heater outlet. It’s the most difficult plumbing system to equip with hot water circulating systems for obvious reasons. Not much else to say about it.

Manifold plumbing systems

Manifold type plumbing is where a main hot water line runs from the water heater to a manifold where smaller lines are plumbed to the fixtures near the manifold. Manifold plumbing layouts are usually associated with PEX plastic pipe.

I don’t see the advantage to a manifold system other than cost of installation I suppose. You usually end up with a ¾ inch main run and probably 3/8 inch runs from the manifold to the fixtures. As you can imagine the flow velocity through the small lines will be quite high while the main supply run to the manifold will be slow.

A hot water circulating pump can be connected at the manifold or one of the fixtures. If it connects to the fixtures it will need to have enough pressure capability to produce a decent flow through the small piping. Small diameter piping like 3/8” can produce large pressure drops. Most hot water recirc pumps will not work with such small tubing.

Point of Use Hot Water Plumbing

Point of use typically means you design your home with a floor plan that allows the water heater to supply all of the fixtures with no fixtures being very far from the water heater. If you can pull it off then it is the greenest possible plumbing system. You waste very little water, your hot water arrives fast without a pump, you lose very little heat from the piping since the lines are short etc.

Locating a small tankless water heater at each location such as the kitchen and bathrooms is also considered point of use, but can get a little pricey. This is a common application for tankless hot water heaters.

Pipe Insulation

Pipe insulation is important! Pipe insulation obviously reduces the amount of heat lost from the pipe while the hot water is being used. In most cases pipe insulation will reduce the amount of time it takes to get hot water, reducing the amount of wasted water. Since the insulation will keep the pipe warmer, less heat is sucked out of the water as it travels to the fixture, thus reducing the time it takes for hot water to reach the faucet.

Pipe insulation can also reduce or eliminate thermo siphoning effects, further reducing the energy required to keep the hot water hot.

What kind of plumbing system would be best for my new home?

The best kind of plumbing system is entirely subjective. What are your main concerns? Obtaining maximum energy efficiency, water savings, convenience, having a green plumbing system, minimum installed cost, or something else?

Point of use systems are very green eliminating nearly all lost energy and wasted water and having the lowest installation cost assuming you can use one water heater.

Looped plumbing layouts are very good at conserving water but contribute slightly to energy loss due to the longer pipe run. For instance, a hot water demand system located at the end of the looped system will get instant hot water to every fixture, (after the pump shuts off), but will always fill the entire pipe no matter with fixture is used. It is a very small amount, but it is there, and could be noticeable if the length of the hot water piping is very long.

Pex manifold systems are easy and quick to install, and with a proper floor plan could offer some water and or energy savings over a branched or home run system.

Home run plumbing layouts are generally wasteful of energy and water. Avoid locating your water heater in the middle of your home if possible when you want hot water recirculation.


Common Sense Plumbing Layouts

Layout your residential plumbing system based on your floor plan and use common sense when planning the system. Keep your pipes as short as possible. If you have a guest bath that is far from any other hot water locations that have fixtures and the location will seldom be used, perhaps using a single home run from that fixture and looping the other fixtures would be the best combination. Maybe branched would be better. It just depends on your homes floor plan.

If you are stuck with a heater in the middle of the house with multiple fixtures on both ends of the house then your best bet might be two loops, or maybe one loop for high usage locations like the master bath and the kitchen, and a branched system for a couple of low usage locations such as spare bathrooms and laundry rooms.


Hot Water Circulating Systems

There are a number of residential hot water circulating systems being marketed and there are substantial differences in how the systems work. Many systems claim to provide the user with “instant” hot water, but that isn’t usually quite true. Let’s take a look at the various types of systems and the pros and cons of each.


Traditional Hot Water Recirculation

In the old days before energy and water conservation became such a concern, large homes often had hot water circulating systems usually referred to as recirc systems and recirc pumps. The plumbing layout consisted of looped plumbing with a return line connected to the far end of the hot water loop returning to the water heater inlet. The circulating pump was typically located between the circulating pump and the water heater inlet.

Originally the pumps would simply run continuously twenty four hours a day. That was great for convenience because you had truly instant hot water whenever you needed it. It’s also great for water conservation. However, it consumes a lot of heat energy and significantly raises your utility bill. It’s like a giant radiator hooked to your water heater.

These days when you run across a traditional hot water circulating system it has a timer to turn it off during periods when there will be no usage to reduce the energy loss. Some systems also control the pump with an aqua-stat, (water thermometer), which turns the pump on when the water temperature drops below a pre-set temperature and off at another higher temperature. This reduces the losses from the system marginally but not much energy is lost from the motor. You’ve simply lowered the average temperature of the water in the hot water piping which reduces the energy losses slightly.

For convenience and water savings you can’t beat the old traditional hot water recirc system.

Warm Water Circulating Systems

Since it is usually prohibitively expensive to convert a typically plumbed house to a traditional hot water circulating system a new class of systems popped up… the warm water circulating system. The Laing Autocirc and The Watts Premier, are examples of such systems.

These systems circulate water through the hot water pipe and use the cold water line as the return line. The temperature of the turn on for the pump is around 95 degrees and the shut off at about 100 degrees or something like that. So you end up with tepid water in your hot cold water pipes instead of cold water. You also once again waste a lot of energy keeping the piping full of above ambient temperature water.

These systems are typically advertised as “Instant Hot Water Systems”, in my opinion they are not. If you really want HOT water you still have to wait. The wait is shorter since the pipes are already warm, but it certainly is not instant hot water.


Demand Hot Water Systems

The newest innovation in hot water distribution systems are the hot water demand systems. These systems only deliver hot water when the user “demands” hot water by pushing a button to start the system. Examples of demand hot water systems are the Metlund D’mand System and the Chilipepper Pump.

Demand hot water systems are typically installed at the sink furthest from the water heater and connect up to the hot and cold water supply lines. A push button is typically provided to start the pump but other types of activation are sometimes used such as motion sensors or door switches.

When the system is activated by pushing the button, the pump begins pumping hot water through the pipes to the fixture returning the cooled off hot water left in the pipes from the last run back to the water heater through the cold water piping.

When hot water reaches the pump it turns off to prevent filling the cold water lines with hot water. This system saves the same amount of water as the traditional circulating system and uses no more energy than a non-circulating system uses. The energy used by the pump itself is very small since it only runs for a few seconds and not for long periods of time. Typically the electricity consumed for an entire year is only $1 to $2.

The hot water typically reaches the fixture faster since the pumps can pump at a higher flow rate than low-flow fixtures can emit. No wasted energy, water conservation and added convenience for the user makes it one of those rare win win win situations.

Traditional hot water circ systems can be easily converted to a demand system by replacing the traditional hot water circulating pump with a demand pump. This allows the demand pump to be mounted at the water heater inlet instead of under the sink.

For branched or home run plumbing layouts multiple demand pumps can be used and won’t interfere with each other.

Hot water demand systems are green products.


Heat Pump Water Heaters

Before purchasing a heat pump water heater there are a few things to be aware of. Heat pump water heaters are slow. They take longer to heat water than electric resistance water heaters. They are however, the least expensive method of electrically heating water if you do not have access to gas.

Heat pumps need some heat in the air around them in order to heat the water. This means you need plenty of ventilation. Putting one in a small room will refrigerate the room and there won’t be enough heat to heat the water.

Heat pumps struggle at the ambient temperature drops and around 45 degrees or so they stop working and require back up heating elements.

I reviewed a Geospring heat pump water heater in an article not too long ago. Here is a link to the GeoSpring hybrid water heater article.

I hope I have answered your questions sufficiently for you to proceed with your project.

Bill
Tech Staff
Chilipepper Sales

More information about:
Water Heaters
Tankless Water Heaters
Hot Water Recirc Systems
Solar Water Heating
Metlund D'mand System