Tankless water heaters have become very popular over the last few years, but most people don’t know much about them, or storage water heaters either for that matter. Hopefully after reading this blog you will be able to make an intelligent decision about whether you should convert to a tankless or stick with a storage tank type water heater.
Let’s take a look at storage type water heaters. Basically you have a big pot of water (water heater) over a hot fire (burner or electric heating element). A thermostat turns on the burner when the water in the tank begins to get cold and turns it off when the water temperature reaches the set temperature. When you want hot water for something there is a big tank just waiting for you to turn on a hot water faucet.
When the burners are off, the tank will slowly cool off, even if it is well insulated. The water in a storage water heater is always changing temperature; either being heated by the flames (or by an electric heating element), or cooling off. The outlet water temperature varies widely.
As the user of the hot water you probably don’t notice the difference in actual water temperature. You are usually using a mixed flow of cold and hot and just adjust the water flows for the temperature you desire.
As you use the hot water cold water is flowing into the heater and after a while the temperature begins to drop until it’s no longer considered “hot” water.
Tankless Water Heaters
Tankless hot water heaters are quite popular these days and with the energy tax credits you can save money over the life of the heater. Tankless heaters don’t have a big tank full of water cooling off all the time, so they don’t have standby losses.
They won’t run out of hot water either. If you need a continuous supply of hot water and a storage heater won’t handle it, then a tankless heater may be the preferred choice. The alternative I suppose would be to use multiple storage heaters.
Heating water on the fly is much more difficult than it first looks. Rather than a big pot of water you now have to picture a coil of copper tubing (heat exchanger) in the flames (burner or heating element) with water flowing through it.
It sounds simple, but consider what happens if you put the copper tubing in the flames without running water through it. It melts. Ok, so we run water through the pipe. If we run the water too slowly it turns to steam in the pipe and possibly blows the pipe up. If we run the water through the pipe too quickly then the water doesn’t get very hot.
Changing the size of the flames has the same affect as changing the water flow, the lower the flame the longer it takes to heat the water.
Tankless water heaters therefore have valves to adjust the size of the flame (or the amount of electricity being directed to the heating elements) and/or the amount of water flowing through the heat exchanger.
They also have a flow switch that turns the heater on only if a minimum flow rate is achieved… typically ½ or ¾ gallons per minute. They have microprocessor in them and monitor the water inlet temperature, outlet temperature, exhaust temperature, gas pressure, gas flow, and water flow in order to keep the output temperature constant.
They are far more complex than standard storage type water heaters.
Because there is a minimum and maximum flow rate one has to choose the set point outlet temperature carefully. Set it too low or too high and you will experience problems with the heater shutting down unexpectedly or not being able to deliver hot enough water.
Installation and Maintenance
Proper installation of a gas tankless water heater is more important than storage type heaters. Tankless units need much bigger burners than storage heaters and they require a lot more ventilation as well as bigger exhaust pipes. Storage heaters are typically supplied by ½” gas pipes, but tankless units require at least ¾ and often 1” pipes.
If the exhaust condensation drain isn’t installed properly the corrosive liquid can destroy the heat exchanger after a couple of years.
Electric Tankless Heater Installation – Potential Problems
Whole house electric tankless hot water heaters require very heavy 220 volt electric wiring and usually they need their own circuit breakers. Often times the service to the home isn’t heavy enough to handle a tankless heater and will have to be upgraded with a higher power transformer and heavier gauge wire from the pole.
With a storage tank type heater when minerals precipitate out of the hot water they fall to the bottom of the tank and are referred to as sediment.
In tankless heaters the minerals form scale in the copper piping which restricts the flow of water. This can damage the heat exchanger. Often tankless heaters need to have the scale cleaned out every year, especially if you live in an area with hard water. Some warranties will be void if your water is too hard. Some require you to use a water softener if your water is too hard. You should read the owner’s manual before you buy anything.
Repairing a storage water heater is pretty easy and any plumber can easily handle a repair or replacement. Not so with a tankless heater. They are complex with valves, sensors, and microprocessor chips. They have displays that show error codes, and many even have remote controls for changing the temperature.
The installation of a tankless water heater should be handled by a trained professional with the brand of heater being installed. That is probably the most important aspect of a tankless heater… correct installation.
Storage type heaters can be useful in some situations such as:
If there is a natural disaster and the water gets shut off your storage water heater tank is a source of clean drinkable water…
In a power outage your gas storage water heater will still work and an electric will still have hot water for a while… most gas tankless heaters won’t work if the power goes out.
Most tankless water heaters will not work with hot water circulating systems, however they will work with hot water demand systems.
For information about tankless water heaters visit: Tankless Water Heaters
For details about using a demand pump with your tankless water heater: Tankless Water Heater Pump
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