Joist heating

S Davis

Any one heard of problems with manufactured joists and joits bay heating?
I talked to a couple of joist manufactures(In Washington State) who were concerned about constant high temps effecting the glue used to hold the wood together causing it to get brittle and having joist failures occur.

S Davis

Mike T., Swampeast MO

From the isothermic data I've seen pertaining to joist-bay heating with extruded conduction plates the joists are NEVER subject to "constant high temps".

As to suspended products that essentially claim to be convective fins inside the joist bay and DO show rather high air temperatures produced???? I'd be wary of their long-term effect on manufactured joists as well...

John Felciano

Yet

Another good reason to use plates/track.

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Earthfire

Joist and heat

Has anybody checked the under sheating temps around roof rafters, especially in the southwest. The same manufacturer will tell you their product is suitable for that application. I feel that if a manufactured joist or any framing material can handle the heat of an attic space it can handle the heat exposure of a plated insulated radiant installation. If the Manufacturer states that their product can't handle the heat from a radiant floor install, that joist has no room in the frame of the building as there are too many cost effective framing materials and methods available today.

S Davis

I think using plates is ok because the temps are lower, but hanging tube in the joist bay and heating the air in the top of the bay could be a problem, I have seen some installs by other heating company's that needed 150-160 water temps.
I think the wood in the atic that would be exposed to these
temps are not supporting that much load anyway.

kevin coppinger_4

Have you picked....

up a bundle of asphalt shingles as of late? They have to be a minimum of 80# each. Plus throw in snow and ice load...we're talking some weight. kpc

hr

The best info

on LONG term exposure to elevated temperatures seems to come from the Wood Resources labs. Keep in mind roof temperatures from sunshine are not a 24/7 load like could be expected in a floor heating system operating at, or below design.

Sounds like many in the NE are currently seeing those loads:) Sorry about that.

Suspended and plates are different applications. The strongest transfer is conduction, by far, and I don't recommend high temperature transfer plate installs.

Can't imagine running a plate system above 150F supply to meet the load, or the design is off. Keep in mind with plastic tube the fluid supply and actual outer wall temperature will show a difference. Rubber more so.

I recall that 140 -150 temperature being the wiggle point for wood products that are glued together. Plywood OSB, etc.

I'm not sure how long in months, years, decades, before noticable breakdown could occur in the wood products. I suspect loading, humidity, temperatures, wood species, glue types, etc all play into the mix somehow.

I think the Wood Resources Lab is in Wisconsin, Madison perhaps. That may be the best source for up to date info.

Error on the safe side, work within the know, current, safe temperature range, and use supplemental heat if that wood temperature exceeds the "comfort" range would be the best approch.

hot rod

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Mark Wolff

I agree

In a properly designed staple up system, plate or tubing only, 150* temperatures are not only unnecessary, but inexcusable. If you heat the floor with more than 125* water your floor will become noticably hot, often to the point of being uncomfortable.

As for BCI's, TGI's etc. if the manufacturer ever puts a warning label on its products to not use them with staple up joist heating, you will see that company quickly lose most of its sales. No contractor wants to install something that APPEARS inferior. I have done many joist heat applications (never needed the plates, even once!) and bare tubing with a 2" minimum air space between the plywood and insulation is all that is needed. The actual temperature as Hot Rod stated is less at the outside of the tubing when compared to the fluid temperature inside it, and really, there is no reason your tubing should be under constant heat. If a zone of staple-up (or slab heat) has to run for more than 6 hours a day, you either have an underinsulated house or the doors are being left open a lot. Remember that a modern house up to temperature with doors and windows closed takes 24-48 hours (depends on wind and insulation) to cool down to freezing, even with freezing temperatures outside.