Tankless Electric WH not performing as advertised.

[GWT500]

Furnace started acting up so it was neccesary to install an alternative means of heating water. Winter is over and furnace will be replaced later this year. Anyway I got the biggest tankless WH they sell. It has 3 copper heaters and requires 3 double pole 40Amp breakers. It supposed to turn on with only a quarter GPM flow. I had 1 GPM at the kitchen faucet and it was not turning on. Called their service dept and they said remove all the airators in all the faucets. Did so and it turned on at every faucet except the 2nd floor one. I imagined this might have increased the flow another quarter gallon a minute. I got the WH temp set to 140 def F and the water still isn't hot enough at any of the faucets. But on a hot day once it was hot enough to take a shower. I suppose this was because the cellar was warmer. The heater is about 20 feet from the water pump inlet through the foundation. So as it stands, the heater's flow switch is no where sensitive enough to turn the thing on at under 1 GPM. And when it does turn on. The faucet has to be wide open. The heater does not heat the water sufficiently even when set to 140 degrees F. I could increase the flow by changing the 1/2" 20' pipe supplying the heater to 3/4" pipe. Also I can insulate all the pipes going in and out. But darn- the fact that the flow switch won't activate the thing until 4 + the advertised flow rate is flowing through it? The heater is wired correctly and passes all the electrical tests the manual says to check with a voltmeter. The unit is a EcoSmart 27. Any help is greatly appreciated.

[jadnashua]

This time of year, your incoming well water could be very close to freezing. Tankless systems are sort of like waving your hand through a candle flame. The faster you do it, the less heat your hand gets. It really doesn't matter what you've set the outlet temp to, at typical flows with frigid incoming water, it can only add so much heat as the water passes by the heat plates. 120A at 240vac is just under 100KBTU, which is quite small for a tankless system as a more typical sized unit in say gas is closer to 200K. Assuming it actually turns on, at say 2.5gpm, it should be able to raise the water temp around 80-degrees. That's a theoretical max, but it isn't a perfect system, so it's probably closer to 70-degrees. Now, if the incoming water is at say 35, add 70, then lose some in the distance from the heater to your shower, and it might reach body temp IF your valve will let you use all hot (many won't!). Smaller flow, potentially higher delta Temp, but there's a limit on how hot it will let it get.

Electric tankless systems are rarely a good choice for a whole home water heater.

[Dana]

The EcoSmart 27 is a 27kw unit, which is about 92,000BTU/hr. That will support one 2gpm (~1000lbs per hour) shower with Massachusetts-style mid/late winter 70F rise in water temperature between the water entering the heater (35F) and the shower head (105F) but barely squeak a 2.5gpm shower at that rise. With a low flow shower head and a shower mixer that will allow 100% hot-side flow, no mixing, you should be able to take a truly hot shower as long as there are no other draws occurring.

Setting it to 140F is a mistake, since that just lowers the flow rate through the unit as you're forced to mix-in cold to avoid scalding. Try setting it to 110-115F, which is about as hot as it would ever need to be to fill a cast-iron tub.

I suspect the flow sensor is shot (not a rare thing with tankless units) if it takes a 4gpm flow to get it to turn on. At 4gpm (~2000lbs/hr) you'd only be able to sustain a 92000/2000= 46F delta-T on it. So if the water coming in from the street is say 40F, you have only tepid 86F water at the taps. When the water coming in from the street is 60F in late summer you can take a 4gpm shower at a decently hot 106F.

So, if you fix the flow meter so it will really activate at a sub-2gpm flow, and crank the temp down- you can probably live with it. It should not take anything like 4gpm just to get it to turn on.

BTW: By "furnace", do you mean "boiler" (pumped hot water heating)?? If yes, when you replace a boiler is an opportunity moment to "right size" it for the load, which results in higher efficiency and better comfort levels. Most existing boilers in MA are at least 3x too big for the space heating load (just in case there's a cold snap when it gets down to -117F, I suppose, :-) ) Scaling it down to the right size produces longer burn times, lower standby losses, steadier interior temperatures. There are several methods of calculating the right size, but most old-schoolers are into the "Lessee, 2300 square feet times 35 BTU/foot gives ya 80,500BTU, let's call it 100K, just to be sure" kind of methods, which reliably oversizes, usually by more than 2x. It heats the house, sure- the contractor never gets the 5AM call from the shivering irate customer, but it costs more up front, and every year thereafter in reduced efficiency and higher maintenance costs. Comparing fuel use against weather data for your zip code it's possible to put a reliable hard upper bound on the boiler output requirements to avoid that gross-error in sizing.

[GWT500]

It seemed to me that tankless was the way to go. But I see it is not. Guess I'll keep it. Warranty no good because I installed it myself. Will try and at least get a replacement flow switch out of them, It activates the heater at about 1 GPM. But it supposed to activate it at .25 GPM. Boiler still works so we do still have HW. I have no doubt that the incoming water temp must be around 40 degs F, it's COLD. I'll try to improve the things perfomance over the summer with bigger pipes, insulation and anything else I can think of. I'll lower the set temp now and see what happens. I think perhaps finding a way to heat the cold supply water, maybe 25 degrees before it reaches the tankless would be a good idea. But once the new boiler is in. We will use it as the primary source for HW. If I can't get the ECOSMART to work better. Won't be using the boiler for much else as we heat the whole house with a pellet stove. 3 tons ($600) gets us through the winter. Thinking of getting a Buderus boiler. I'll make sure not to get one thats oversized. Thanks for your insight guys. I'll continue to follow the forums.

[johnjh2o1]

Why do people keep getting sucked into these things?

John

[Dana]

It's a chunk o' change, but a drainwater heat exchanger pre-heating the incoming flow to both the water heater and the cold side of the shower would improve the shower-flow situation entirely, but not batch draws. Heating water with electricity (or oil, or propane) at typical MA pricing the payback is under 5 years for a 3 person showering (not tub-bathing) family even if you paid somebody to install it. (But it's a fairly straightforward DIY project if you're handy with plumbing.)

The PowerPipe series is on the approved list for installation in MA. It takes a section of VERTICAL drain to work, and fatter & longer==higher return/faster payback, despite higher cost. I have 4x48" unit in my house, and the wintertime output of the HX while someone is showering is well into the 70s F- literally half the total delta-T between the water meter and the showerhead.



If your's is an oil-fired boiler, note that oil boilers are ALL oversized for typical MA house heat loads by virtue of the fact that the burner nozzles only go so low. For less than the installed cost of a Buderus you could buy a decent mini-split/multi-split air source heat pump, and the cost of operation would be about half that of oil, at current oil prices, and comparable to wood pellets. And, they are super-high efficiency in air conditioning mode in summer. With a careful analysis of both boiler-fuel + pellet use over a season and your zip code (for weather and design temp info) it's possible to put an upper bound on what your whole house heat load is, and whether a heat pump would even be an option.

In small to mid-sized tight houses it can work here though, and in VERY well-insulated houses in coastal MA it's cheaper than heating with natural gas in a mid-efficiency boiler. This guy on Martha's Vinyard yanked out a fairly new oil-fired Buderus and dropped in a small mini-split to handle the whole shebang, but most houses would need something somewhat bigger. Open floor plans with good air communication between rooms helps too, but it's not that different than point-source heating from a pellet stove in just one main room. (I've read of one guy who insulated his basement and just overheated the basement with a mini-split to get the "radiant floor" effect for distriuting heat to the first floor, but that's probably not the way to do it at MA electricity prices. :-) )