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Kelly haskin
Radiant floor heat

We are installing a 24'by 19' addition to our house. My question is our exsisting house heats with boiler system ? Can I use boiler water for radiant floor heat in the concrete of the new addition and what type of flooring can I use ? Thinking either carpet or laminated floor.


Re: Radiant floor heat


I assume you have a HOT WATER boiler (and not a steam boiler), and that you intend to hire a contractor to do this work, as opposed to it being a diy project.

The answer for a hot water boiler is yes, the procedure is very commonly done & requires that the plastic tubing (called PEX) be embedded in the concrete at the time it is poured.

There is also the issue as to if your present boiler has enough additional heating capacity (known as btu's per hour) to heat the new addition, as well as the rest of the house (most boilers are slightly oversized, so the present boiler can usually handle it).

However, make sure the contractor you hire to do the work does a HEAT LOSS CALCULATION to find out how many btu's/hour will be needed on the coldest days to heat the house PLUS the addition.

Assuming 8' ceilings, it usually takes approx. 30 btu/hr per square ft. to heat a house in the winter (depending on your location).

Thus an addition of 24' X 19' = 456 sq.ft. X 30 = 13,680 btu/hr to heat the addition.

You can do a rough calculation for the rest of the house & check the i.d. plate on the boiler to find its IBR or DOE rating to see if the boiler is big enough; the heating capacity of most modern boilers can be increased a few thousand btu's/hour simply by switching to a larger capacity fuel nozzle (this increases fuel consumption, so I always advise homeowners to add additional insulation to exterior walls & attics before changing nozzles).

The construction contractor doing the addition would have to have knowledge of radiant floor installations; they would also have to know about installing supply & return manifolds and other components associated with radiant heating, such as 3-way mixing valves and air-purging systems.

Laminate flooring is more compatible with radiant than is carpeting (the more plush the carpeting, the worse it is); but some non- plush carpeting has been sucessfully used with radiant.

Consult the Yellow Pages under "Heating Contractors" & read their display ads to find several who install radiant in your area; get several estimates, as the prices will vary widely.

The sites below have additional info on radiant heating.

Generally speaking, radiant reduces the water temp going thru the plastic tubes to ~100 degrees (instead of the 180 degrees of standard boiler/radiator/baseboard systems).

This lower water temp makes the slab act as a giant radiator, heats the room more efficiently & save lots of money on heating bills.

Another advantage of radiant is that the heating elements are completely hidden in the slab & thus don't interfere with furniture placement; but the alternative way to heat the addition would be with baseboard (probably ~25 ft. of baseboad for the addition), which would cost less in installation, since they use the same water temp as the rest of the house & don't require special valves, etc.

Whether you choose baseboard or radiant, the addition should be on a separate zone of its own with its own T-stat if it will have a specialized use, so the room temp can be adjusted separately, which is easily done with hot water systems.


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