Question on adding radiant heating to existing boiler.


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Old 01-15-09, 09:30 AM
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Question on adding radiant heating to existing boiler.

You guys have been very helpful. I have another question. I am thinking of adding underfloor radiant heat (pex or similar) to my living room which is always 5 degrees cooler than the rest of the house. Can I tie the pex or whatever I use into the existing boiler 25 year old Burnham gas fired, and feed it off of that?

thanks again for the help
 
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Old 01-15-09, 09:42 AM
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It depends.

Read this:

http://journals.iranscience.net:800/...,62497,00.html

which is just about everything you need to know.

Beyond the mechanicals, a major consideration is the floor covering. If the room is carpeted, radiant output isn't very good. Compensating by raising the water temperature can sometimes lead to excessive drying and cracking (and creaking) of the subfloor, heating and degassing of the floor covering and accumulated crud (nothing like the smell of warm, old pet dander, eh?), etc.

There are also several flavors of underfloor heating. The transfer plate method is generally well-regarded for performance. There are other methods, however, such as suspended-tube.

The kind of approach Siegenthaler suggests can be had in an off-the-shelf solution, such as this:

http://www.roth-canada.com/caf/pdf/2...MiniShunts.pdf

Adding radiant can be quite expensive, even as a DIY job. Unless you have your heart set on it, I'd look first at adding to the existing radiation and/or reducing the heat loss of the room (add insulation if possible, do some air sealing around outside wall-mounted outlets, ducts, doors, etc., even putting in new windows if the existing are old and tired and the room would be reinvigorated by some better viewports...).
 
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Old 01-15-09, 11:32 AM
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Thanks, that gives me a lot to work with. Since I am dealing with hardwood floors and a crawlspace underneath, it does not look extremely difficult.
 
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Old 01-15-09, 11:52 AM
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For hardwood, you want to keep the floor temperature at 85F or below. Partly to keep the hardwood from drying out and shrinking, partly to keep the floor temp comfortable. You should figure out how much output you will get per square foot with that kind of temperature.
 
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Old 01-15-09, 08:21 PM
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I'm gonna add doing a heat loss calculation on the room to see where you stand with the current BTU output vs requirement, and whether or not you would be able to make up the deficit (if any) with radiant or not...

Keep in mind also that the PEX tubing you will be using is NOT nearly as flexible as it appears. If you are working in a crawlspace, trying to get that tubing in without kinking it... and then INSULATING below it, I can almost guarantee that you will be cursing the day you decided to tackle the job... it's NOT going to be "easy"...

you want to keep the floor temperature at 85F or below.
And to do that, you will need cooler water than the 180 that your current boiler is probably producing. That means that you will need a MIXING VALVE and another circulator PUMP...
 
 

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