Using a tankless to heat a house

Reinvent

It was suggested that a large modulating tankless water heater could be set up to provide heat to a house as well as domestic hot water needs.
The house I am working on is 2600sq ft, with three full baths, two stories, complete gut rehab. We are looking to put an HVAC in the basement for the first floor and a unit in the attic for the second floor. The HVAC contractor was openminded abought the idea but has never seen it done.
Any thoughts, pros and cons. Has anyone ever installed a system like this?

Jack_21

GPMXDelta TX500=BTU

On a Rinnai 2352FFU-C (lowest pressure drop unit), you will pump at most 5gpm with a 009. Figure a 20 temp drop and you have created a 50KBTU heating unit out of a max 180K burner. For small jobs these are okay. I prefer them for low temp heat (hydro-air and radiant). you can run up to about 100' of baseboard but run it at 160 max. The commercial unit will produce 180 but do not reicrc to it at that temp. The limits can come in to play.

kevin coppinger_4

i supposse it.....

it might work but do you really want to use something that really was not intended to do what your application is. there atre plenty of wall hung boilers outthere that will heat the house well....Suposse after a year it does not work as desired...do you want to take it out and explain to the customer,I messed up or I was using your house as an experiment...??? kpc

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DaveGateway

Just remember

that most instant hot water heaters are not rated for heating. That's a nice size house and you might need 2 wall hung combo boilers to feed the HW and heating load. For that price, why not just get one large modulating condensing boiler with an indirect HW tank. More efficent to run everything out of one larger modulating unit. I would only get the wall hungs if I need the floor space that bad or there were plans to rent a floor and I need seperate gas billing.

kevin_5

Look at all your options.

The commercial Rinnai is only about a hundred bucks more than the residential, and is warranted for space heating. It also has double the warranty, and a bit more power. My house is small, but I just replaced my two hot water heaters with one Rinnai,2 circs (one bronze), and a heat exchanger (to separate the heating and domestic water) to do both. So far so good. I'm not saying it is the best fit for your house, but there are some applications where it will work. Kevin

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Reinvent

Do you think it would make more sense to have one boiler in the basement suppling heat to the attic and basement HVACs via a hydo heat exchanger or let the attic unit generate its own heat?

Weezbo

Why? should be the next question after How.....

hr

Check with

the local code officials, some areas require all heating boilers have the ASME "H" stamp affixed.

As far as one or two heat sources.. what are the loads of the various floors (zones). Typically basement heat zones have much lower heat demands. Do a heatloss calc first then size the equipment accordingly.

If the upper and lower zones are wide in terms of heat load, I'd consider a modulation heat source. As the boiler will need to be sized to the combined load, but the basement maybe a fraction of that load. Dependong on controls and boiler type you may get some short cycling. A modulating boiler would alow the output to match the load exactly, perhaps.

hot rod

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Scott Gregg

Here is how I'm doing it

I am doing the same thing now with a Noritz N-069M (Like the Rennai) The only reasons I went with it in this application is cost of the BTU and the fact that I wanted it outside to free up space in a 100 year old farm house.

Noritz supplies a circulated loop to a Peerless Pavillion system. The domestic hot water line pulls off of that loop. In the cold water line feeding the tankless I have a M&M flowswitch in a 1" tee wired up to break the call for heat wire from the t-Stat on sensing flow. No cold water is flowing at this point.

It takes about 2 - 3 gpm to activate the switch. When the heat is on and the loop pump running and no domestic load all tankless capacity goes to the loop. If someone opens a faucet to wash their hands there is no change. If someone opens a shower or tub or the demand exceeds the flow switch the pump is disabled giving total capacity to the domestic side until that load stops.

True domestic hot water priority.

I like the Noritz over the Rennai. I get better support and I think their product is a bit better. If you need a commercial heater, they REALLY have one. The Rennai's is the same model with a higher price (To cover warranty?) and a different paint. All parts are the same. If you have a Rennai they are a good solid product. I can't really say that the above comments are negative, just different. Either will do what they say.