Tankless water heater for space heating

Thinktwice

Anyone have design experience with Gas Tankless water heater supplying a air over water coil in a furnace? This would be a supplemental heating option for my pkg heat pump in extreme cold temps. looking at 12 x 12 coil that can produce 50,000-60,000 BTU with 160F water @ 6gpm, 700 cfm. Suggest Heat source?

Jamie Hall

Seems to me, if you need that much heat, you would be better served with a hot water boiler designed for the purpose -- there are a number in that size range. Water heaters -- even tankless ones -- are designed for intermittent duty, with very low duty cycles (percent of time running), rather than more or less continuous duty for space heating.

Leon82

I don't think you will get 160 out of a tankless heater unless it is a commercial dishwashing model. Also some have a max inlet temp

bob eck

If using a tankless gas water heater for a boiler I believe that type of job will void the warranty.
I would use a wall hung condensing boiler for heating. If you need heat and hot water look at a combi gas boiler.
Many good condensing boilers or combi boilers on the market.

pecmsg

700 CFM's is a 2 ton heat pump. Why 60,000 supplemental?

Rich_49

I would go with a combi also . Most of the tankless heat exchangers are very high head when used for space heating also .
http://www.htproducts.com/UFT-Combination.html

If it must be a tankless I would look at the HTP Crossover wall unit . You would require the optional circ shown and it would need to be stainless and have similar capabilities to the Taco 0013 . Like I said , high head . I have installed that in a Unicco system and 0013 was required . If you require 160* fluid though the Crossover will not get you there , I think max is 140*

DZoro

Sounds like you have a forced air system? Why not put a furnace in place of your air handler?

Jack

6gpm? 12x12 coil 60kbtu? I doubt you would get the delta t you need to do this on a 12x12 coil. The thing is, on todays tankless you do not get to choose the flow rate. The unit looks at incoming temp and set point and decides, modulating the flow to deliver the set point temp. I am generally against tankless for heating and as a rep, I have seen a lot, a lot, that had problems. I have also seen hundreds in open loops that worked well in 1 & 2 bedroom apts and were reliable. They all ran in the 120* range and provided dhw as well. Closed loop? Buy a boiler! Or, just buy a boiler and be happy. Absolutely the right tool for the job.

Rich_49

Did everyone miss the point about this being a backup and only being used when his heat pump lags behind ?

Ironman

There are packaged heat pumps available that have a gas furnace built in. Why try and re-invent the wheel when that's already available? Especially when you only need it for extreme cold.

If you already have the heat pump and it has electric backup that's insufficient, then I'd look at adding a larger heat pack.

At any rate, a tankless water heater is not the right tool for the job. As has been said, the heat exchanger has too much head; most will only give you 120* SWT; and it's not gonna last long because it's not designed for space heating.

SuperTech

I would rather have a hydro coil for auxiliary heat than electric strip heaters. Either way a tankless water heater isn't the right thing for the job. A condensing Combi boiler is a better option.

Ironman

SuperTech said:

I would rather have a hydro coil for auxiliary heat than electric strip heaters. Either way a tankless water heater isn't the right thing for the job. A condensing Combi boiler is a better option.

I would too, but is it worth the effort and expense if it's only gonna run for less than 10% of the season? You never see the ROI.

delta T

Why go to the expense of a condensing unit for 160* water? wouldn't a cheaper small low mass fin tube boiler fit the bill better? Especially as a backup....