Electric on-demand, tankless water heaters have significant pros and cons.
Electric tankless water heaters can be placed very near the point of use, resulting in exceptionally short wait times for hot water.
- They are small and will easily fit under a sink.
- Most don't require a separate pressure/temperature (PT) valve and dedicated drain line.
- They are easy to plumb in.
They are very quiet.
The small ones, such as for a single sink, cost only a few hundred dollars to purchase. The annual cost to use a small model may be less than the cost of running a full size electric tank unit, without the long wait time for hot water that a distant tank unit may have.
Electric tankless water heaters require a dedicated circuit run from the main circuit breaker box, which can be a significant expense.
- One large enough to handle a shower will require a heavy (more expensive) wiring and circuit breaker.
- An older circuit breaker box of under 200 amps will likely not be able to handle the extra load of an electric water heater.
The smaller units, that draw less than 20 amps, are fit only for a single sink use and may struggle to give you hot water at anything over 0.5 gallons per minute (gpm), equivalent to a low-flow bathroom sink faucet. A larger unit capable of 3 gpm or so can cost $400 to $800 plus installation, or $1000 - $2000 installed. If you live in an area with tiered, time-of-use, or expensive electricity supply, or if you opt for a larger unit capable of a shower and sink, the annual cost can be surprisingly high.
Consider these issues as you think about adding a water heater.
Recirculation pump. If you have an existing water heater in good condition but have long wait times for hot water in your shower and vanity, an electric on demand water heater under your vanity sink can solve that problem. So can, however, an on-demand hot water recirculation pump like the Metlund, which may be less than half the cost of a new electric water heater large enough to handle a shower.
Ask a friend. If your electricity is relatively cheap, less than 15 cents a kilowatt/hour and you or a friend can handle the installation, the electric tankless becomes attractive.
How much heat. Electric on-demand water heaters are sized by the temperature rise in degrees at a certain number of gpm. Google 'electric on-demand water heater' and see what you can find.
- For a vanity sink, you will need 0.5 to 1.0 gpm at a 40 degree temperature rise in the far South where the water temperature entering your home is reasonably warm.
- Or if you live in the North with its snowy winters, you may need 0.5 to 1.0 gpm at a 60 degree temperature rise.
- For a shower in the winter in the Wisconsin, you may need a much larger unit that can provide 3 gpm at a 80 degree temperature rise.
For more information:
Read "Is installing a tankless hot water heater worth it?" a Q&A answered by Michael Holcomb.
Also,Squidoo has a page with a description of what these terms mean here.