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Old 02-07-2011, 12:15 PM   #1
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Fire Sprinkler Freeze Fix


I'm in a bit of a jam and hoping someone here can help. I run a nonprofit school in a building that was built in the 20s, sprinklered in the 80s, renovated in 2000. It's a wet system in the Rocky Mountains.

The install has the riser right against an exterior masonry wall. A 1" pipe extends off the riser and runs above drywall, 18" parallel to a north exterior masonry wall (no insulation) through the floor joists of the 2nd floor (moderate insulation) in to a classroom to feed 3 heads. There is a wooden soffit outside between 1st & 2nd floor that is probably the main way cold infiltrates, but at sub-zero temps, nothing I can do to this historic landmark there can fix my issue.

About 5 years ago a T-junction froze, split in half, and exploded through the ceiling. Flooded the whole place and make Hurricane Katrina look like a spring rain. It was a miracle no one was killed. The repair tried to better insulate what they could but basically left the pipes in the same place.

A few times since then, including last week when there were two days of over night temps around -20, I've seen the same freeze symptoms of leaking heads in that same section. So I drain the system, wait for warmer temps, replace the heads, put compressed air in to it, and fix sections of pipe where appropriate. But this is getting old.

So with all that background, my question is, how do I fix this for good? I'm damned if I do/damned if I don't all the way around.

- First, I'm aware of the problems of draining the system - but I'm not going to risk killing a kid or a teacher, or a $400K water damage insurance claim b/c a mostly stone building *might* catch on fire at that particular time.

- Can't retrofit this building w/anti-freeze or a dry system. No room.

- By code you can't apply heat cable or pipe insulation.

I'm open for other suggestions. At this point I'm not too impressed with the code that allowed this setup in the first place though, and I'm leaning toward cutting sections out of the drywall ceiling, installing heat cable (is there such a thing a plenum rated heat cable?), hard wiring it in to a nearby electrical outlet, and replacing the cutouts w/access panels. Given the alternatives (or lack of), what's the lesser of all evils?




Last edited by golddog; 02-07-2011 at 02:32 PM.
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Old 02-07-2011, 01:29 PM   #2
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Fire Sprinkler Freeze Fix


Okay, I am by no means an expert in this but I will mention what jumps out at me: You seem to acknowledge that you really cannot keep the cold out of this area so you have to figure a way to keep it warm. You say this pipe is above drywall, is there also a drop ceiling or something else? You use the word "plenum" which I take to mean the path of the return air to the heater to be recirculated. If this pipe is in the plenum I would expect it to stay warm enough so I am just trying to picture what you got where you got it.

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Old 02-07-2011, 02:26 PM   #3
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Okay, I am by no means an expert in this but I will mention what jumps out at me: You seem to acknowledge that you really cannot keep the cold out of this area so you have to figure a way to keep it warm. You say this pipe is above drywall, is there also a drop ceiling or something else? You use the word "plenum" which I take to mean the path of the return air to the heater to be recirculated. If this pipe is in the plenum I would expect it to stay warm enough so I am just trying to picture what you got where you got it.
Thanks for the reply. I probably didn't use the word "plenum" in the strictly correctest sense of the word b/c it's (HVAC) non-circulating. So the layout is solid wood ceiling joists 16" OC w/insulation in the cavities. Hanging down from the bottom of those approx 8" is the grid to hold the drywall ceiling. In that 8" void, running perpendicular to the joists (w/90 degree off-shoots going to the heads), is the sprinkler pipe of concern. There is also Armored Cable conduit in there powering surface mounted light fixtures. Whether the fire dept would consider it plenum (for their purposes) given my issues, I'm gonna go out on a limb and say they'd default to the most conservative option and say yes.

From a fire sense, any fire that starts in that space *would* have a quite a run and probably the oxygen for the fire to move quickly within this 900 sq/ft room, although presumably fire blocking is in place on the perimeter. Certainly me cutting access panels in to it is going to make it plenum (again, not necessarily from an HVAC point of view, but from FD's).

I think the main problem is that the stone masonry wall, at sub-zero temps, just absorbs and radiates cold. The probing I've done hasn't revealed any horrible drafts I can seal up; although I've given thought to drilling small holes in the ceiling between the wall and the pipe and injecting expanding foam to try to cut that down. But I initially rejected the idea b/c it'd have to not only fill the 8" void but the joist space as well to be truly effective. Heat tape seems to be a more guaranteed solution.

Last edited by golddog; 02-07-2011 at 02:31 PM.
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Old 02-07-2011, 03:04 PM   #4
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Fire Sprinkler Freeze Fix


First, I would really like to hear an experts opinion as to whether this is a plenum. If it is not, I would cut in some grills in the drywall to let air ciculate. Do the surface mounted light fixtures generate heat? Could you leave them on? Could you replace a light fixture or two with ones that do get hot. Is that a dumb way to fix this by keeping lights on? Do I like to ask questions? ?????
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Old 02-07-2011, 05:10 PM   #5
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Fire Sprinkler Freeze Fix


1. Convert it to a compressed air filled system. If a sprinkler is triggered, the air is let out and the water comes through. Note that some brands of sprinker heads, although they hold water, do not hold air. (Doesn't an air filled system use the same pipes?)

1a. Charge the pipes with antifreeze instead of water, although plain water comes up shortly after a sprinker is triggered.

2. Put heating tape around the pipes running their full length.

3. Heat the spaces where the pipes run.

Simply putting foam around the pipes will not protect them from prolonged freezing temperatures.
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Last edited by AllanJ; 02-09-2011 at 08:09 AM.
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Old 02-07-2011, 10:57 PM   #6
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First, I would really like to hear an experts opinion as to whether this is a plenum. If it is not, I would cut in some grills in the drywall to let air ciculate. Do the surface mounted light fixtures generate heat? Could you leave them on? Could you replace a light fixture or two with ones that do get hot. Is that a dumb way to fix this by keeping lights on? Do I like to ask questions? ?????
Me too (a plenum determination). Part of the problem is I can't call the FD for an opinion b/c they'll know who I am and flag the issue for review for all eternity. So I'll take all the questions I can get :-)

I've thought of cutting grills in to the ceiling to allow warm air to rise up (which will also allow the cold to fall but I'll bump the thermostat to compensate I guess). This is also the same way I'd aim to get the pipe wrap on w/minimum destruction. I found a product at Grainger (3V or 6V, dry or wet/dry, variable temp control, up to 2" diameter) that I could hard wire in to a GFCI circuit. An NFPA knowledgeable guy brought up the point though that this solution relies on the electricity being on. Really. But the power is pretty reliable and it's still better than nothing.

To answer your other questions, the surface mounted fixtures are 4' florescents - and far from the pipe - so no heat to speak of. You might be on to something though...I suppose I *could* wire up a couple of things (at the risk of this needing to move this post to the electric forum):

- Some kind of infrared heat lamps that mount in the void and point at the pipe, or,
- Recessed cans that throw off alot of heat, although I don't know that it'd be enough.
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Old 02-07-2011, 11:21 PM   #7
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Fire Sprinkler Freeze Fix


You say that the bottom of the joists are not sheet rocked so I'm going to make the assumption that you have a fire rated dropped ceiling. if thats true, I don't believe you can put grills in it as that would compromise the fire rating. Can you get some sort of heat up in the cavity such as a supply duct?
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Old 02-08-2011, 12:51 AM   #8
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got a picture?
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Old 02-08-2011, 01:50 AM   #9
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You say that the bottom of the joists are not sheet rocked so I'm going to make the assumption that you have a fire rated dropped ceiling. if thats true, I don't believe you can put grills in it as that would compromise the fire rating. Can you get some sort of heat up in the cavity such as a supply duct?
Unfortunately no. The building is so old that what ducts do exist in that area come up from the basement. The 2nd floor above it, the ducts come in from units on the roof added just recently.
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Old 02-08-2011, 02:00 AM   #10
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got a picture?
This is from after the last major freeze/rupture. The camera is looking from the problem pipe in to the room. The black sprinkler pipe you see is one of the 90 degree lines to a head in the room. It's a bit messy from the water but gives you the idea.
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Old 02-08-2011, 02:23 AM   #11
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well if its a fire rated ceiling and you cant add a return air grill to allow heat to find its way in id insulate the hell out of the joist space,especially the ends where it butts up to the outside wall
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Old 02-08-2011, 08:19 AM   #12
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Fire Sprinkler Freeze Fix


Is the living space heated?

1. Use standard as opposed to insulated suspended ceiling panels.
2. Do not put insulation between the pipes and the living space.
3. Do put insulation against the stone walls inside but not encircling the pipes.
4. Have a thermostat in the attic space so the room heat does not set back at night all the time.
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Old 02-08-2011, 10:26 AM   #13
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Fire Sprinkler Freeze Fix


Is the building heated with hot water or steam? I am only assuming it is heated one of these ways as it seems to be the preferred way of heating for commercial buildings. If this is the case, is it possible to install loops of fin radiation in this ceiling space that will be controlled by a thermostat installed in this space? I have installed piping like this for the same problem you are having, and since the best solution for your problem is to get some heat to this cold space, this may be a solution. This may seem like quite a bit of work, but it would be easier than replacing ceilings and other damaged items every time this occurs.
This would also have no issues with fire barriers with the ceiling space if you use steel or copper piping through the firestop.
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Old 02-08-2011, 10:48 AM   #14
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I agree with the compressed air/ dry system, does not take up more room from what i have seen. dont believe that's a fire rated ceiling, probably not called for with sprinklers or they would have heads above ceiling
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Old 02-08-2011, 03:01 PM   #15
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Fire Sprinkler Freeze Fix


Thanks for all the suggestions.

@Anti-freeze/Dry systems: I've asked our fire systems contractor if either of these are possible and they say no. Both would require retrofits that the current riser could not accommodate, and the current riser is not feasible to replace, but that was for the entire system. We have a meeting this week and I am going to double check the feasibility of making just that length dry. There are currently heads in an outside patio exposed to way harsher temps than what's in this space. When I asked why those aren't a problem I was told they were "dry" in that section, yet there is no compressor. Does anyone know the mechanism that allows this to work? Some kind of special one-way pressure clapper?

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