Will radiant heat affect drywall (i.e. make it brittle and crack)?

heatquestion

I live in a building that was built around 1950, the ceilings are plaster, and there is radiant heat in the ceiling, above the plaster. My apartment’s plaster ceiling is in horrible shape so I'd like to remove it and replace it with drywall.

I spoke with someone at USG (the drywall manufacturer) who said that drywall can withstand temperatures up to 125 degrees F. When drywall is exposed to higher temperatures, it can get very brittle and ultimately crack.

I'm wondering whether that could happen if I use drywall for the ceiling. The drywall would only be about an inch below the radiant heat fins. I’m not quite sure how hot the radiant heat gets in the middle of winter….but it's probably pretty hot given that the heat can be felt in the floor above (which is through a metal deck and concrete and about 16” above the radiant heat).

Also, when the temperature is below zero outside, the water leaves the boiler at around 200 degrees F. The temperature drops as it goes through the system, but I don't know by how many degrees. It's a high-rise, so the water definitely covers a lot of distance.

If you have any thoughts or insight, thank you in advance! Of course, replacing the plaster with drywall would require building approval, etc. but that's not the issue at the moment. Right now, I'm just curious if it's okay to install drywall so close to radiant heat.

heatquestion

Here's a photo of what the radiant heat looks like.

kcopp

Is it just that one convector? If so it would certainly benefit from some insulation behind it.... What is the heat upstairs?
Another option would be to do cement board and skim coat plaster.

heatquestion

kcopp, thanks for your reply.

There are maybe 3 or 4 "convectors" (that's a new word for me) in the 750 sqft apartment, if I had to guess. But I don't know for sure because the ceiling hasn't been removed yet. But I do know that the convectors/fin tubes are spaced pretty far apart.

Does the fact that there are not many fin tubes mean that the 3 or 4 that DO exist will be REALLY hot, because they have to heat a significant space?

You asked about the heat upstairs... The apartment upstairs relies on the heat in my ceiling (which is about 16" below their floor), and radiant heat baseboards, which run the entire length of all exterior walls.

Also, I've been wondering... Is the ceiling heated by just the fin tubes or is it heated by the combination of the fin tubes and also the pipes that carry the hot water?

Thank you again!

kcopp

Yes to both. That is not a lot off fin tube to "pull" the heat out of the piping. More tube would allow lower water temps.
Odd thing generally speaking is that they are convectors..... that means you need air flow to pull the heat off. There is definitely some conduction going on.
Where is this that that gives you enough heat in the winter.?

Gordy

Would this be a dual attempt to heat the floor above, and the ceiling for apartment below? If not intentional it certainly is performing that task by accident, or shall I say poor practice.

For ceiling radiant installs that are applied to dry wall temps should be no higher than 120*. Usually they never need to be that high with a proper design. Maybe 80's 90ish depending on the load.

It's to bad you did not get a chance to shoot the ceiling with an IR thermometer in the heating season before you took it down. While your supply temps may be 200* yowza. The actual ceiling temp could be far less depending on the distance from the fintube.

Without knowing the intent of the fintube whether it is suppose to heat your ceiling, or the floor above, or both its hard to direct.

ChrisJ

How far away from the drywall will that convector be?
I've never heard of anyone complaining about drywall having issues an inch or two behind a steam radiator running @ 212-215F.

I'd trust USG, but that air gap makes a huge difference especially with it being under the convector.

Perhaps use setting type mud on all joints near that area as well just for good measure.

heatquestion

kcopp: This is in Chicago! And the building has single pane glass, so plenty of cold comes through the windows. Unfortunately it would be impossible for the building to install new double pane windows. And it would be impossible for them to change the heat setup. What's interesting is that some apartments are WAY too hot (some people run their AC in the middle of winter) and other people FREEZE and get supplemental heat from window AC/heat units. It makes a big difference whether an apartment gets south sun, and also it matters how high the apartment is...because the top apartments get the hottest water (because the hot water goes all the up to the top, through the risers, and then works its way down). Unfortunately, I'm about 20 stories up (which is about the top third) so the water still hasn't cooled off as much as it would by the bottom floors. This definitely is not a good setup--the building engineer can never keep everyone happy so he tends to just crank the heat extra high.

Gordy: I don't know if the architect intended for the heat in the ceiling to heat both the apartments above and below... but it seems like that's how it works today, given how high the engineer runs the heat.
You mention 120 being an important number...that's what I'm worried about. It's good to know that typically radiant heat should only be 80-90 degrees. I hope that the radiant heat therefore won't be much hotter than 90 degrees.
On the coldest days, the water is 200 when it leaves the boiler but it does have a long way to travel (up about 28 floors, and then down 8 floors to me).

ChrisJ: The convector will only be about an inch above the drywall.
Can you tell me a little more about why the air gap (and the fact that it's under) makes a difference? I figured that I should be worried because the convector and the drywall will be so close...but clearly I'm a novice!

THANK YOU ALL for your help!!

ChrisJ

heatquestion said:

kcopp: This is in Chicago! And the building has single pane glass, so plenty of cold comes through the windows. Unfortunately it would be impossible for the building to install new double pane windows. And it would be impossible for them to change the heat setup. What's interesting is that some apartments are WAY too hot (some people run their AC in the middle of winter) and other people FREEZE and get supplemental heat from window AC/heat units. It makes a big difference whether an apartment gets south sun, and also it matters how high the apartment is...because the top apartments get the hottest water (because the hot water goes all the up to the top, through the risers, and then works its way down). Unfortunately, I'm about 20 stories up (which is about the top third) so the water still hasn't cooled off as much as it would by the bottom floors. This definitely is not a good setup--the building engineer can never keep everyone happy so he tends to just crank the heat extra high.

Gordy: I don't know if the architect intended for the heat in the ceiling to heat both the apartments above and below... but it seems like that's how it works today, given how high the engineer runs the heat.
You mention 120 being an important number...that's what I'm worried about. It's good to know that typically radiant heat should only be 80-90 degrees. I hope that the radiant heat therefore won't be much hotter than 90 degrees.
On the coldest days, the water is 200 when it leaves the boiler but it does have a long way to travel (up about 28 floors, and then down 8 floors to me).

ChrisJ: The convector will only be about an inch above the drywall.
Can you tell me a little more about why the air gap (and the fact that it's under) makes a difference? I figured that I should be worried because the convector and the drywall will be so close...but clearly I'm a novice!

THANK YOU ALL for your help!!

The air gap is essentially the same thing as insulation. I just don't know how big of a difference an inch makes, but it may be enough.

The fact the ceiling is under means less heat should get to it as heat rises meaning there should in theory, always be cool air being pulled between the convector and ceiling.

Canucker

The fact the ceiling is under means less heat should get to it as heat rises meaning there should in theory, always be cool air being pulled between the convector and ceiling.



Hot water, hot air rise. Heat doesn't rise, it flows to cold. I know, I'm nitpicking but it's true, otherwise radiant ceilings wouldn't work

ChrisJ

Canucker said:

The fact the ceiling is under means less heat should get to it as heat rises meaning there should in theory, always be cool air being pulled between the convector and ceiling.

Hot water, hot air rise. Heat doesn't rise, it flows to cold. I know, I'm nitpicking but it's true, otherwise radiant ceilings wouldn't work


Yeah,
You are nitpicking, I should've said warm air rises. Then again, does radiation "flow"? It's ok, I nitpick too and often it's important to have the correct details no matter how small.

But as I said cool air should be pulled between the convector and ceiling so even though IR will be heating the ceiling, that cool air flow should help keep it cool as well.

No?

4Johnpipe

WOW! That is not at the top of the line "radiant" system (using word loosely). You can be almost certain that the water temps required to heat the cavity above the ceiling would be in excess of 180 degrees....It seems they are trying to over heat the air space to allow some radiation to happen above and below.

Gordy

Radiant is best when conductive, anything else is convective. But once a convective emitter heats an object above ambient temperature it becomes a radiant surface. In this case it appears to be that effect.

What still is an unknown is the intent of the heating design initially.