Another Tankless Water Heater Question


Can you clever folks tell me about this one? My husband did an excellent job installing our tankless water heater. I was out of town that weekend, but given his record for thoroughness, handiness with tools, & researching how exactly to do something right, I believe he put it all in right. It is this one right here: http://www.hotwaterheater.com/model-h-28-4.htm
However, now I can't get a hot shower!! I had nice long hot showers with the tank system, but now, nope!! It starts off and builds up to scalding water pretty quickly, if I crank it all the way up. Then I push it back down to the correct temperature. But then it quickly tapers off after a minute or two, and the rest of the shower is lukewarm! It will get a little hotter & then colder in turns, which is also annoying; but never gets hot, even if I push it all the way back to the maximum. It's definitely not a comfortable showering temperature, even.
Any ideas?
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If it's wired correctly, this sucker is supposed to pull 116 Amps and deliver 3.3 gal/min with a 60 deg rise in temp, or 3 gal/min with a 65 deg rise. If you're incoming water is around 40, which is a typical incoming winter temp in colder parts of the country, then it should be capable of giving you around 105, which is typical shower range.
But, one has to wonder about how practical this really is. Typical service for a new house today is 200 Amp. And this one load is gonna suck up 116 of that. If you start to figure in AC, cooking, dryer, (maybe you have gas for cooking/dryer, but I'm guessing not, otherwise you probably would have used a gas tankless), the avail capacity could be pretty much maxed out.
Back to your problem. Is it wired up correctly with two 60 amp breakers? Measure the incoming and outgoing water temps and flow rate and compare it to the flow chart in the spec sheet. Make sure your shower head is less than 3 gal a min. My guess is that it's not wired up for max output.
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Turn down the temperature on the water heater. What is happening is that as you blend cold water to get the temperature right, the flow of water through the heater slows to the point where it has insufficient flow and shuts off. by turning down the temperature more water is permitted to flow through the heater, as less cold is required to blend with the hot.
--

Roger Shoaf

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Start taking baths. <g>
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former tankless owners say the 2 best days........
the first day its installed
the day its replaced with a standard tank.
Did you hubby upsize the gas line all the way to the meter? too small a input line can cause this.
besides standard tanks like mine are 75K BTU
Your tankless is only 95K BTU
You my have ongoing hassles, sorry to give you bad news.
PLEASE REPORT BACK WETHER YOUR HAPPY O)R UNHAPPY WITH THIS TANKLESS LONG TERM!
if your unhappy, consider using it as a pre heater for a standard tank, by prte heating the incoming water to a standard tank you can have a endless supply of nice hot water, at no extra fuel cost.
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Thanks so much for all the advice!
I asked my husband how HE managed to get such nice warm showers as he claimed. Apparently I had the routine wrong. I am supposed to crank it to very hot, and then VERY SLOWLY, in small amounts, nudge it back colder. If I just crank it back quickly, then it won't work. Does that sound right to you folks?
It is an electric heater, not gas. Everything here is electric. The old tank was ancient, and needed to be replaced. It was eating up a TON of electricity- and never mind the sludge that was probably in the bottom of that tank! Hahaha-
Anyway I will definitely find a low-flow shower head to put on it. I just hope that our washing machine and especially the dishwasher is getting the hot water they need- but, we also replaced the old, extremely non-efficient units with brand spanking new LG ones. It was self-defense mostly; we have a well that before simply did not produce enough water to take care of everything like was needed. Do 2-3 loads of laundry, a couple showers, and a couple loads of dishes and you're risking running out of water until morning. Not anymore, though. I'm banking on the LG efficiency to be o.k. with the Tankless.
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Caya writes:

No it wasn't. The fraudulent sales pitch just said so.
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I take back what I said about the house being all-electric- the heat is oil. Duh.
I forget just what calculations my husband used to determine that the water heater was the electricity-hog- it might have been the plumber we had come in that told him this, but also I think he arrived at this conclusion himself. He is Mr. Mathematics & so likely his figures are correct. Yes, I'm pretty clueless on all this. I'll have to go & ask, I'm curious now.
But I can bake a mean pie, or bake most anything else you name :-D And quilt, crochet, sew, cook, garden, etc etc, none of which HE can do :-D
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Caya writes:

28 KW (37.5 HP) and weighs 30 lbs? Are you mad? That's energy density comparable to a jet engine. Not something I want running in my house.
To heat water to 120 deg F in a Yankee winter (delta_T = 80 deg F) takes 40,000 BTUs/hour for each gallon per minute. That's 11.7 KW per gallon/minute with perfect efficiency. So a 28 KW unit (if that much is to be believed) will get you 2.4 gallons/minute of hot water. After tempering to bath temperature with cold water, you will be just over the piddling water-saving "shower" rate of 2.5 gal/min, which will waste many minutes of your time every day (or however often a rube who is foolish enough to buy tankless bathes) for the rest of your miserably shower-impoverished, life.
Also consider that electric demand rates are typically $12 per KW each month. So to just turn on this 28 KW fantasy costs you $336 per month! Or it would if your residential electricity weren't subsidized for free demand. This is after you have paid $1000s to upgrade your electric service by 100+ amps to operate this rocket engine gadget that runs like a tricycle with a bent wheel.
Tankless heaters are more expensive to buy, more expensive to own, and more expensive to operate. Anyone who selling you a different story is a fraud. This is not a case of sales puffery or exaggeration. This is outright flim-flam baloney that flies in the face of physics. The reason the Web sites and newspaper ads look like they were designed by hillbillies after a quick buck is, they were.
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I agree and was struck by this:
"The old tank was ancient, and needed to be replaced. It was eating up a TON of electricity"
Physics would suggest otherwise. Whatever electricity the tank water heater was using was all turned into heat. Exactly the same as the tankless. The only difference is that the tank water heater lost some of that heat through loss from the insulated tank to the surrounding air while the water is sitting there, waiting to be used. That amount isn't a ton, especially in an electric unit that doesn't have an exhaust flue running up the middle. New tanks have more insulation and you can add a cheap extra insulation blanket if you want. I agree with Richard, that I doubt you will ever recover the increased upfront cost of a tankless in future energy savings.
And I would be very surprised if you see any significant change in your electric bill. BTW, in some areas, electric companies offer off peak service meters and rates for water heaters. Meaning they charge a significantly lower rate since the water heater won't heat during peak day time hours, which is something many people find possible with a tank heater. If available, you can't take advantage of that with a tankless, so a tankless could cost a TON more to opperate
In my view, the main advantage of tankless is when you have a unit of sufficient capacity to meet all your needs and have a usage pattern where you would run out of hot water frequently even with any reasonable size tank heater.
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