Noisy tankless heater

D_E_G

I've installed a hydronic on slab system in my basement and I'm adding zones to my main floor. My heat source is a natural gas tankless water heater. I've found the heater to be extremely noisy at start-up. After it fires it begins to moan and howl like a banshee. I made a call to the manufacturer and they told me you cannot use their water heater in hydronic systems because the incoming water has to be cold. When I pointed out that they don't specify this in the owners guide they acknowledged this but stated that they can't list every application that isn't proper.



My questions: Has anyone else heard of such nonsense? What could be causing the noise and how do I eliminate it? Should I ditch tankless?



Thanks in advance.

DG

AMH112181

Yes

Yes ditch it. That's why they call it a water heater and not a boiler.

lchmb

I would

replace it with a boiler. Use the proper tool for the job....

Gordy

Ditto

Ditto

kcopp

Poor application....

I would not recommend using a tankless for radiant ... get the right tool for the job.... a boiler. Wall hung versions would be a good fit. Biasi, Embassy and Triangle tube are good choices.

 Did you get the suggestion from an Internet radiant floor company?

Jack

Square peg/round hole

disconnect the radiant tankless and use the tankless as a water heater as it was intended. Put in a proper boiler for the radiant. You will be happier and so will the equipment. Generally, groans on start-up are fluid restriction, possible flow control valve problem, crapped up HX or gas valve problem due to inadequate gas size/pressure. Or maybe a vent issue.

Ironman

Nonsense?

If you'll check some other posts as well as the replies you've already gotten, I think you'll soon see that what the manufacturer told you is not nonsense.



This scenario comes up at least a couple of times each week on here. My response is usually the same: If a water heater could take the place of a boiler, there would be no need to make boilers. Common sense tells us that, not nonsense.

Jean-David Beyer

Reason for using tankless water heaters instead of real heating boilers?

I was wondering why, almost every week, someone uses a hot water heater instead of a real boiler. I began to wonder why. It seems to me that one reason may be because boiler manufacturers do not make small enough (in terms of heating capacity, not physical size) boilers.



For example, I have a relatively new mod-con. It is the smallest in the product line; 80,000 BTU/hour input.  My house needs only about 30,000 BTU/hour. My installing contractor handled only the one brand of boiler. If they had made a mod-con hot water heater rated for home heating, it would have made sense to use one. Maybe.

Gordan

That seems an unlikely reason

Tankless water heaters are usually in the 150000 - 199000+ BTU/hr range. Instant domestic water heating is a much more demanding application than space heating, typically, which is the cause for the often-heard lament "my heat loss is only X but I'm concerned that I size the boiler to it, then I won't be able to keep up with my DHW load."



I think it's much simpler than that. Tankless heaters are cheaper. MUCH cheaper.

Jean-David Beyer

So if I wanted a 35,000 BTU/hour mod-con, ...

... would I look for a tank type mod-con hot water heater with outdoor reset and an H stamp? I do not suppose there is such a thing, and if there were, it would cost like a mod-con boiler, right?

Gordan

I may have misunderstood you

My only point is that tankless DHW heaters typically have higher outputs than your boiler, not lower, so picking them for small loads wouldn't make sense on those grounds. If you were talking about a tank-type heater, we were at cross-purposes.



There are, however, smaller mod-cons than what you've got, and they're still mod-cons. Munchkin, Knight, Prestige Solo all come in the 50-60kBTU/hr range, and have for a long time. Nothing smaller than that, but my hunch is that it's a marketing decision. They couldn't be much (if any) cheaper than the big boys, and in this country we like "value"... which people usually interpret as "more is better, unless less is much cheaper."

Jean-David Beyer

You did not misunderstand me.

I was being unclear. This was really about tankless domestic hot water heaters being used for home heating.  You told me that tankless heaters have far more output than I imagined, and I believed you. Then I changed the subject without saying so, hence the confusion. I got my mod-con three years ago, and my contractor handled only one brand of boiler, so I got that brand's smallest mod-con. Since then I have noticed that there are smaller mod cons available, but they are not dramatically smaller.



So I wondered about using a hot water heater. But aside from the fact that they probably are not approved for home heating, they are missing things like outdoor reset, and probably do not modulate either. There are just too many problems using them for home heating.



The only time I saw what I thought was an intelligent use of an electric hot water heater was in a house designed to be heated with solar, using air as a medium and crushed rock as the storage (less problems with leaks and freezing). The architect calculated everything out, and used 4x as much rock as the weather records indicated would be needed. The AHJ did not trust solar heating there, and insisted he install a backup heating mechanism, so he put in baseboard and an electric hot water heater. Since it would not be used anyway, it was the cheapest way he could comply with the local code.

Jean-David Beyer

Nothing smaller than that

Just an afterthought..



I have an 80,000 BTU/hour mod-con and need about 30,000 BTU/hour output on a day 14F below design temperature. Obviously, I could get by with a boiler half the size of what I have. Even if it cost the same purchase price as the one I have, it seems to me I would have been better off with the hypothetical smaller boiler because it would be in the modulation range more of the time, and hence less short cycling.



It might be tough to sell a smaller boiler to a typical customer at the same price as the larger boiler, though. It is my experience that my former contractor did not really know how mod-cons worked either, and he should have known before selling them. He wanted to sell me the 105,000 BTU/hour one "to be on the safe side" and when I protested that the heat load (that he did not calculate, but I did) was far less, he said this one would modulate down to 16,000 BTU/hour (true) so it would be OK. That's nuts. One of my zones needs only 6500 BTU/hour when it is 14F below design temperature. I cannot modulate down to that in any case. The other zone needs only 24,000 BTU/hour on that very cold day.