On demand for hydronic backup?

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Old 09-05-14, 12:09 PM
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On demand for hydronic backup?

I heat my 30x 60 shop with an outdoor coal furnace,circulate water thru 4 radiators in various locations in the building.I would like to have a backup heat system that uses the plumbing I already have.I thought I could isolate the outdoor furnace with it's 45 gal reservoir from the building,then I could then heat the existing water( in the radiators and pipes) and radiate that water and have the same heat quality. A friend has a Tagaki on demand heater that I could buy from him, but I'm not sure how the on demand heater would work with the incoming(colder) water being only a few degrees cooler than the outgoing water.Are these heaters only designed to bring the temp up from 50 deg? I realize the loop would become closed with the furnace isolated so an expansion tank would need to be installed,anything else?Will an on demand heater suffer from having a glycol mixture going through it instead of water? Perhaps someone could chime in and let me know if this would even be a possibility.
 
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Old 09-06-14, 10:24 AM
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The first thing you have to determine is the heat loss of the building. Do you know it?

Do you know how much heat OUTPUT you get from your radiators in BTUs at various water temperatures?

I presume it's currently enough to heat the building with what I presume is HOT water coming from the coal stoker.

Do you know the specs on the heater your friend has?
 
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