Tankless water heaters can save you energy and provide you with a virtually endless supply of hot water.
You do need to be aware of a few differences between the way tankless water heaters work and the way standard storage tank type water heaters work.
Tankless waterheaters are not quite as simple as standard water heaters, having sophisticated microprocessor based electronic controllers, temperature sensors, flow switches, modulating gas valves, and even remote controllers.
Most of the time if you have a tank water heater the only time you think about it is when you either run out of hot water, or if the tank springs a leak and you find you need a new one.
Occasionally a gas water heater may need a new thermocouple because the pilot light won’t stay lit, or the high limit switch may need replacement in an electric water heater, but other than that they are pretty darned reliable appliances. You set the temperature and forget about it.
With tankless waterheaters there are some differences. Tankless water heaters have both a minimum flow rate and a maximum flow rate to be able to maintain a constant outlet temperature. If the water flows too slowly through the heater the water cannot carry the heat away from the heat exchanger rapidly enough and the heat exchanger can overheat and become damaged.
To prevent the overheating of the heat exchanger tankless water heaters have a flow switch that will only turn on the water heater if the minimum flow rate is reached. Typically tankless heaters require 1/2″ to 3/4 gallons of water per minute to initiate operation. Keep in mind, this means you can’t use “just a trickle” of hot water.
Since you will need to mix hot and cold water at the fixture to get a usable water temperature from the faucet, and you must maintain the hot water part to at least 1/2″ gallon per minute or 3/4 gallons per minute for larger models, then you could end up needing to use at least a gallon per minute for the right temperature water.
On the other end of the spectrum, tankless water heaters have a maximum flow rate for which they can heat water to any specific temperature rise. Use a higher flow rate and the water temperature will drop.
When choosing a specific model of tankless hot waterheater it’s critical to choose the size correctly. It needs to be able to heat enough gallons per minute for your expected usages and at the coldest that the incoming water will be… typically in winter.
Look through the owners manual before you buy… some models require periodic maintenance and many models will void the warranty for extremely hard water. Scale buildup from hard water can be a serious problem. Usually the owner’s manual will tell you how to clean the scale out of your tankless water heater if it needs it. However, you may need a water softener if you are going to use a tankless water heater and you water is too hard.
Installing a tankless water heater should not be attempted unless the installer knows what he is doing. Improper installation can lead to things like carbon monoxide poisoning, a fire hazard, or unstable heater operation. Venting is very important as well as proper gas line sizing.
Tankless hot water heaters require some time to heat the water, so they deliver hot water to the fixtures typically 10 to 20 seconds later than a standard tank heater. That translates to more water run down the drain waiting for hot water. Tankless heaters are compatible with hot water demand pumps, and combined with such a system are truly green saving both energy and water.
If you have a need for large volumes of hot water tankless waterheaters are the way to go. Just make sure you size it correctly and have it installed correctly. And if applicable add a hot water demand system as well.