I posted recently about our tankless water heater failure and I have now replaced it. Here are some of my observations on this experience:
- Go more powerful than you think you need. We have 12 kw(220VAC 50 amp)units on our bathroom and kitchen(sink, dishwasher, guest shower and washer.)
- Inspect the circuit diagram before you buy. Both sides of the element power should be switched. Otherwise, the element can short to ground halfway through the pipe and go full on with no flow, resulting in superheated water and live steam spraying out of your faucet. (Examples: Bosch Powerstar has one side connected to power with no safety. Stiebel Elton has both sides switched with a relay
and thermal safety cutoff
.) This actually happened twice before it self destructed. It has been reported to UL labs.
- The heater you choose should have as low a turn on rate as possible. One with a higher rate can turn off if the flow is a trickle(especially if you use a mixer, which tends to have a lower flow because it is mixing in cold) Typical turn on rates are .5 to .7 gpm. The Stiebel digital models have a turn on rate of .26 gpm. (It's not pleasant to have your shower either scalding hot or ice cold with nothing in between!)
- Install maintenance valves . These allow the water to be shut off, a pump connected to pump cleaning fluid (basically vinegar) to remove deposits. (deposits can clog the heating chamber, decrease heating efficiency, and cause corrosion and shorting.
- Add a mixer valve. Tankless heaters tend to have fluctuating temperatures. With a mixer, you can set your heater temperature higher(typically 140F). This goes to the mixer that mixes cold water with it to hold an exact temperature, and never goes above it. (We keep our kitchen sink at 107F) Our old heater had to be adjusted at least twice a year because of ambient temperature changes from summer to winter. A mixer makes this unnecessary.
- Whole house models replace a single traditional tank heater, but you still have to wait for the heat to reach the faucet. Smaller units mounted at bathroom, kitchen, etc. will deliver hot water within seconds. The smaller units are less expensive per unit, but have to be wired with 220v 40 or 50 amp service.
(Some of the smaller ones don't need this)
- They are small, but do require space near the faucet. We were able to install ours in the crawl space directly under the floor. With service valves, mixer and plumbing, it fills up about a 2 x 2 x 1 foot space.
- I've heard good things about natural gas models, but don't have gas.
- Tankless heaters hold less water than a tank heater, but if either ruptures, they are going to leak out as long as the water is connected. Either kind of heater should be mounted where leaks will not cause problems. Either outside, in a room with drains or with a drain pan under it that drains outside.
- Most tankless heaters do not specify a GFCI breaker. But if our first tankless heater had had a GFCI, it would have tripped and not allowed hot live steam to spew out of my kitchen faucet.The new Stiebel I have has a dual thermal emergency shutoff that switches both legs of the power. The old Bosch did not.)
- Hard water - If your water supply is above 11 "grains per gallon", you should probably do something about softening your water. A home water softener can be a couple thousand dollars or so. Yearly maintenance of pumping vinegar can help. I compromised with the service valves and a 3M Aquapure cartridge that claims to reduce hardness. I think they recommend changing the cartridges twice a year, but I think you can monitor the water with a handheld TDS meter and get more mileage from them.
Cost for main parts:- 12kw heater $300- service valve set - $80- Mixer $100
- 3M Aquapure water treatment to reduce water hardness $70, replacement cartridges are about $30 each.
- misc fittings, tubing, about $100
- a 220v high power service to each heater is required(50 amp for 12kw).
- If you have a traditional tank heater, your plumbing will have to be modified at each heater location. I suspect total cost with labor for each unit like this would be around at least a thousand dollars. YMMV
Another discussion on this here:http://www.diychatroom.com/articles/2015/11/the-benefits-of-tankless-water-heaters/#comment-618
Tankless Water Heaters
Re: Tankless water heaters
