Electric point of use water heaters have some real benefits, but there can be substantial problems when it comes to the installation including potentially high installation costs, so plan your plumbing layout carefully.
Small Tank Type Point of Use Water Heaters
Installing a point of use water heater can be difficult when installing them where there is not much power available like in bathrooms where there is usually only a 15 Amp circuit somewhere near the sink. To run the power down below the sink is sometimes hard but usually it’s a simple task to drop a wire down from the existing outlet.
Electric Water Heating Takes Lots of Power
Once we get the power down under the sink, we still have only about 15 amps to work with. A small point of use heater takes about 1,500 Watts, which draws about 12.5 amps. That doesn’t leave much current for a hair dryer for example, which typically draws about 1500 Watts.
Point-of-use water heaters actually have a small 2.5 to 4 gallon tank; they can’t heat any real volume of water quickly with only 1,500 watts power input to the heating elements. You certainly couldn’t use one to take a shower.
To heat hot water fast, as with a tankless water heater we would need at least 40Amps or more. The cost of heating the water can also go up very quickly. Some parts of the country use a tiered electricity rate system. The electricity starts at 12 cents per kw/h and goes up to as much as 50c per kw/h.
Even though electric water heaters are very efficient, typically 99% or higher, delivering electricity to your home is very inefficient. Only about 30 percent of the electricity generated makes it to your home. The rest is used up in the transmission lines and transformers. As electricity flows it heats the wires losing energy to the conversion of heat and other losses.
Another problem with putting a point of use water heater in a bathroom is that there are usually only 110 volt circuits available in bathrooms. 220 Volts would be much better, providing twice as much water heating power as 110 Volt service.
Getting Enough Power Can Be Very Expensive
A typical house has a 100A service coming into it. The lines go through the main panel and usually through another sub panel. With today’s life style, 100 Amps it is not nearly enough. An upgrade to 200 amp service is feasible if the power lines come in from overhead. (From a transformer on a pole nearby), but if your utilities are buried underground it’s another story altogether.
In cases where the wire is buried underground the costs to install a point of water heater can become enormous very rapidly, often requiring crossing under the street to get to the transformer. Your utility company will not pay for the upgrade either.
Running an extra circuit from the sub panel or main panel of the house to the bathroom is. Obtaining a service upgrade from 100 amp service to 200 amp service can cost around $ 2000 – $2,500 not including hookup to the water heater.
The kitchen often has a 20 amp service with 20 amp circuit breakers that are only used for the garbage disposal. The garbage disposal electrical service can be used to power a small point of use water heater, but it is often against local building codes because it can overload the circuit if the garbage disposal is used while the water heater is heating water.
Much of this material was provided by JustTankless the place for tankless water heaters.