Hi,
I just had radiant heat installed in my house, specifically, under the first floor. The radiant heating tubes (pex) were stapled up to the basement ceiling. At one end of the bay the tubes make a U turn. At the other end of the house the tubes drop down along and under each floor joist. The plumber said he did not drill holes in the joists because the code specifies that holes cannot be drilled within 3 feet from the end of the house … and that would compromise the strength of the joist. Is this true? I’ve read a little about radiant heat installation and it always looks like the holes where the pex tubing passes through is very close to the end of the bay. Also, the insulation company tells me I should insulate the pex tubing that drops down along and under each floor joist before the insulation is installed in the bays. The plumber says it’s not necessary as not much heat will be lost. Any advice is welcome!
Thanks.
Replies
Your plumber is probably wrong, they often are in matters like this. I would check with your local building inspector to be positive though, but that would be an extremely conservative standard.
I would want the tubing running through the joists otherwise it will interfere with installing sheetrock for the ceiling. If the tubes went through the joist then the insulation problem would be solved by having the fiberglass around the tubing.
I just looked up the specifications for drilling holes in wooden "I" beams used for floor joists and they specified that there should be no holes drilled in the beam within 6 inches of the centerline of the bearing surface. An "I" beam and a solid wood joist are similar enough in strength that there shouldn't be much difference in the rules for solid wood joists.
The "I" beam specs allowed for a 2 inch diameter hole a minimum of 7 inches in from the center of the bearing surface and additional holes at least 7 inches apart. In other words, if the beams were sitting on top of an 8 inch wide plate, the hole could be just three inches away from the inside edge of the plate, just about where you would want a hole for the tubing, close to the inside wall of the basement. This spec is for a hole located on the center line of the beam where the hole has the least effect on the beams strength.
Hope this helps, John W.
ckib-
It depends on the size of the hole. At the very end of a joist the main stress is shear, the force which would try to shear the member off vertically. As you go out towards the midspan, the force becomes one of bending moment where the top of the joist is in compression and the bottom in tension. The larger the hole at the bearing end the less material there is to resist the shear force. Thus if your plumber felt he/she had to bore 2 or 3" holes to pass the pex then he may be right. I question the need for such a big hole, though.
Radiant heat loss .... the conventional wisdom is that heat rises. While true, radiant heat 'radiates' in all directions. Except for the possible advantage of heating the basement as well as the main floor, I would opt for insulation under all the pex.
Just my opinion.
For a more in depth discussion post your question (if you haven't already) in the Breaktime forum. There have been numerous threads related to radiant heat installation problems there and lots of informative people.
From Beautiful Skagit Co. Wa.
Dennis
You can check the library for a copy of the code book or go to your town hall and ask the building inspector after all you pay a part of his salary most code books have charts and tables telling you were and how big you can make the holes.
generally you drill a 1 1/4" hole for the pex tubing and with out seeing your installation my thoughts are that he is not too experienced or just plain lazy to go below the joist.
Jack
That was my sense too. Thanks.
you should check the loop lengths a common problem is installers run the loops too long 1/2" should not be any longer than 300', 3/8" 250' you can check by looking at the tubing it has foot marks on it Jack
I have recently had the same deal installed in my home and I can assure you that they bored holes in the 2X10 joist. If you need any more info, just contact me, sincerely, bob
Bob,
It's too late now to get anything changed. I just wanted to confirm my suspicion that the plumber's claim that he couldn't drill the holes was untrue. I decided to follow the recommendation of the insulation contractor (they will be filling the bays with fiberglass insulation, with a 2" space between the insulation and the subfloor) and insulate the pex tubing that will be exposed with foam pipe insulation. See the photo attached. Does this look like a reasonable solution?
Thanks.
it will work just make sure that they insulate the rim joist first at least r19Jack
ckib,
It's not the way they do it on 'This Old House'. If I remember correctly, they lay the tubing in an aluminum bed that spreads the heat out from the tubing about 6-8". If you don't get proper heat transfer, you'll end up spending a lot more than necessary.
I'd check with the manufacturer of the tubing...talk to tech. My mother always hired tradesman like your plummer....headaches...
More like a migraine! Well, I've learned a big lesson ... educate myself before undertaking any home improvement project. It's frustrating to have spent so much money on a radiant system that I know is not installed well. Hopefully it will be efficient once the bays are insulated.
Thanks to all who have responded.
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