Re: O/T Positioning of Home

Posted by doug stockman on January 29, 2005 at 02:15:16 from (67.139.200.85):

In Reply to: Re: O/T Positioning of Home posted by Slofr8 on January 28, 2005 at 17:29:03:

Dan:

We also have radiant floor heating. It works well. Do not worry about overheating from radiant floor heat if used by itself. You will have multiple thermstat-controlled zones.

If you will also use passive solar, then you will overhead if you have 1. too much southern glass exposure or 2. not enough thermal mass that is hit by the sun. If you have at least 4-5 inches of concrete then you can have glass area up to about 12% of floor area. That is assuming the floor area does not have significant furniture or throw rugs on them. If not so much available thermal mass, then keep Southern window exposure down to no more than 8% of floor areas (e.g. 1000 sft main floor area x 0.08 = 80 sft window surface area). Make sure you have insulated shades on the windows. This reduces heat loss at night and you can close a few of the shades if the house starts overheating.

Windows are hard to calculate. If your area does not have much sun in the winter, it is easy to lose more heat out the windows during cloudy days than you gain during the occassional sunny day. Our walls are about R-40, but our windows are R2 on the southern side and R3 on the other sides of the house. Low-E windows block sunlight too much so we put double panes on the south and low-E on the rest of the house. Still, the heat loss through an R-3 window compared to an R-40 wall is huge. We keep triple honeycomb shades on our windows when there is no sun that add about an R-3. Windows have another measure that tells how well it allows light to pass through it. For the southern windows you want much light to get through. I cannot remember the measure - maybe transmittance value.

Make sure your southern overhang is adequate. If not, too much sun comes in during warmer weather. In Rochester, NY we have about a 1 ft overhang. During May, June, July, we have at most about 6-8 inches of sun getting into the house. We often close our insulated shades on hot days in the summer to keep the heat out. We then open the windows at night to cool our thermal mass down.

You can put wood over radiant heat. It will decrease efficiency some. Make sure you insulate well under the radiant that is under the wood. That forces the heat to go through the wood instead of through the underside of the gypcrete or concrete. You have to keep the radiant heating temperature down under the wood or the wood will crack. On our second floor we use carpet and the radiant heat works well if you use a special open pore pad under the carpet.

Consider using Gypcrete instead of concrete on top of your plywood or OSB decking. Gypcrete expands and contracts less than concrete.

I hope this makes sense and helps.

Doug

Follow Ups:

• Re: O/T Positioning of Home Slofr8 08:45:54 01/29/05 (3)
  • Re: O/T Positioning of Home doug stockman 02:34:35 01/30/05 (2)
    • Re: O/T Positioning of Home Slofr8 06:38:49 01/30/05 (1)
      • Re: O/T Positioning of Home doug stockman 02:14:59 01/31/05 (0)

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