hotwater baseboard heat from tankless water heater

Old 01-05-08, 09:21 AM
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Lightbulb hotwater baseboard heat from tankless water heater

I already have a rinnai water heater taking care of my domestic hot water needs and am curious why I couldn`t use another one to heat my baseboard heat.Seems logical to just heat the water in the baseboard instead of keeping a large boiler warm all the time. In the winter months I burn wood in a hot air furnace and it drives me crazy to hear the oil boiler come on every hour or so just to keep the water up to temperture.Why wouldn`t a tankless water heater work? The thermostat would call for heat,kick in the circulator,which would the tell the heater to fire...Possible or not???
Old 01-05-08, 09:35 AM
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Many local building or mechanical codes specifically prohibit the use of potable water heaters for space heating. Many (not all) manufacturers of tankless water heaters will not honor a warranty for use of their product in a space heating system.

Modern boilers do not hold a large amount of water although your boiler might.

As far as your boiler firing every hour or so to keep the boiler hot...that may be a good thing. Some boilers are rather picky about being left to go cold and then firing up only when space heat is required.

So many "ifs" to consider. If you want to post a few pictures along with the make and model of your boiler and controls we may be able to help you cut back on the firing cycles of your boiler.
Old 01-05-08, 09:56 AM
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Originally Posted by hartin4 View Post
Possible or not???
It's possible... but there are issues.

The heat exchanger is designed to use street pressure to force flow through it. It's very restrictive. In order to get flow through it when part of a heating circuit, you'll need some serious high head pumping power. These pumps are noisier, costlier and consume significantly more electricity.

Controls will most likely be another issue. The water heater controls are designed to match flow requirements, but you'll need to jury-rig that for t-stat duty. I don't know what's involved with that.

Then there's liability. Try and find out if heating your house with a non-approved heating device affects your coverage. Not saying it will, but due diligence would be key before going down the road.
Old 01-05-08, 10:01 AM
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Two more points to consider:

1) unless you live somewhere with ridiculously low electricity rates, the cost would likely be ridiculously high.

2) fin-tube baseboard is a "high temp" form of heating. Most tankless (like Rinnai) come preset to 120 or 140. Chances are unless you have a very tight building envelope, you would not satisfy your heat requirement. There are probably ways to control around that, and improve your building envelope to lower the water temps needed, but that's getting a bit complex.

There are plenty of cold start boilers out there, cast iron and modulating/condensing, that would serve the heating (and someday the DHW when/if the Rinnai quits) needs of the house.
Old 01-05-08, 10:39 AM
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Thanks for the replies, it sounds as though the idea might make sense but the appliance may not....Are there any kind of heating units designed for just heating the water in a closed system without doing domestic water,and would it comsume fuel,preferrably propane,only when the need for heat is called for?Am I asking for my cake and eat it too?
Old 01-06-08, 05:20 AM
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The biggest issue is most jusrisdictions require a heating boiler to carry the "H" stamp. Most water heaters (if any) carry the "H" stamp.

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