Someone needs to invent a better tankless water heater! Tankless water heaters are very popular these days due to the popularity of “going green”. They save energy since they don’t have standby losses like storage type water heaters. Another big incentive are the tax rebates being offered when you install one.
On the positive side tankless water heaters offer endless amounts of hot water and high efficiency, are relatively small so they can save some space, and they can last longer than tank type units that have a tank that can rust and leak.
However, there are some problems. I like to use a small flow of hot water for various things, and to do this you simply adjust the hot and cold water faucets until you get the flow and temperature that you want. This works fine for storage type water heaters, but with tankless heaters it’s a bit more difficult.
Because a tankless water heater needs a minimum flow of water to turn on and to stay on, you must run that amount of hot water no mater what… otherwise the heater just turns off. Most tankless hot water heaters require ½ gallon per minute with smaller models and as much as ¾ gallons per minute for the larger models designed for whole-house applications.
That minimum flow is at the full outlet temperature of the water heater. So if you want a lower temperature you need to mix cold water with that hot water at the faucet. Let’s assume for a moment that to obtain the desired temperature you need to mix the cold and hot water in equal amounts. Now you have to run one gallon per minute from your fixture to obtain that warm water. This can be a big waster of water.
Another problem is that it takes a tankless water heater time to heat water, and thus it takes longer to deliver hot water to the fixture and hence more water gets run down the drain while you wait.
Some one needs to invent a tankless water heater that solves either or both of these problems. If the turn on flow required was only say 0.1 gallons per minute that would put the tankless unit pretty much on par with a tank type water heater when low flows of warm water are desired.
Tankless water heaters are more energy efficient than tank type units due to the large amount of heat loss from a large tank of hot water. But if you insulated the heat exchanger in a tankless heater which holds only about a quart or two of water, why couldn’t you keep it hot and ready to eliminate the delay tankless units have when they start up? With standby energy losses related to the surface area of the tank, one would think a tank or heat exchanger holding less than a gallon of water would lose far less energy than a tank that holds 40 or 50 gallons.
Something to think about anyway.
So all you would-be inventors out there put your thinking caps on and figure out how to invent the perfect tankless water heater!
