Issue with insulating PEX

I've got a new zone of heating providing forced hot water heat to a converted porch which is now in 4 season use. Plumber used PEX for 2 baseboard units, one about 18 inches for a small bathroom and another about 4 feet in length.

Because the porch is over a ventilated crawlspace, I've gone overboard insulating the pipes. I've got fiberglass in the floor joists, but I also installed a closed-cell foam wrap over the PEX for the feed and return. Today with the heat on, the foam melted to the PEX. It smelled a bit, but didn't smoke or anything. Before I box the insulation in with plywood, I'm wondering if I should remove it and go strictly with fiberglass?

3/4 PEX and I live in MA. I guess I need to call the plumber who installed it but wanted to ask here too.

 

Hi Chris,
Whatever you insulate it with should be capable of withstanding 180 or 190 degree temps. The plastic type foam insulation is not intended for those temps. There is another one that is, more of a rubber material. The salesman explaining the difference stated the plastic will melt and stick to the hot pipe, which sounds exactly like what you have.

HOWEVER, a pipe in the location you are dealing with should only be insulated on the cold side. Wrapping the pipe in insulation will separate it from it's heat source and allow the temp to go lower. The more insulation between the pipe and the heat, the colder it will get, even with insulation on the other side.

So, max insulation between the pipe and the cold, well air sealed, and no insulation between the pipe and the heat. That should keep the pipes safe.

The other difficulty is maintaining the heat to the floor above. If you turn off the heat, the pipes would still be closer to the outside than the floor above, so the floor might stay above freezing, but that might not be enough. Keep the room warm enough that the floors in the areas of concern can conduct some heat to protect the pipes. Of course the circulating hot water should do well if it is not off.

Bud

 

bud,

I understand that melting insulation is a bad thing and should be remedied, but how can too much insulation around hot water hydronic heating supply and return pipes be a bad thing? In Maine that furnace will be running pretty often during the heating season so his concern should be keeping the heat inside the PeX WHILE the furnace is firing and circulating water rather than worrying about how fast the heat will dissipate from the lines once the furnace turns off right?

 

Shane, I've seen many a pipe freeze, both water and heating, when they were isolated from the conditioned space. Being a floor where the heat above rises will be challenging enough. But relying upon the heat being "on" to keep it from freezing would just be waiting for the warm day, heat is off and it turns cold. The key is some real good insulation on the cold side, then any heat lost will go to the floor above which is a plus. If they can only get an inch of foam on the cold side, then something else would need to be done. But even in that case, insulating the warm side could isolate the pipe from the primary heat source.

This is also one of the issues that is coming up with better insulated homes. Some are so good, that the heat only cycles on a couple of times a day. So we tell people to super insulate their homes and pipes that never had a problem now freeze. It's all part of that "house as a system" thinking where you have to be careful what else may be affected by the work that is being done.

Besides, I'm always overly cautious .
Bud

 

I've used the brown and black closed cell stuff on heat pipes (copper) and it hasn't melted... but now, I have to go look again!

When I read the first post, I understood it to mean that there are not only heating pipes, but also domestic water piping extending below the insulation between the floor joists into unconditioned crawl space below... isn't that the right place to insulate the pipes?

 

I will be removing the foam tomorrow, as it is 70 degrees here in MA...good timing. Bud, nice call on the pipe being insulated FROM the heat source of the floor above.

I've got the PEX within the space between the floor and the vapor barrier(which faces the house), with 2 R-19 bats sealed with plywood. The insulation is a little compressed, but I added a 2X4 to the floor joists to give the insulation some room.

Thanks again.

 

You have seen hot water heating system piping freeze when wrapped in pipe insulation AND encased in fiberglass?

Wouldn't it take like many hours for the heat in PeX to to dissipate out through foam pipe insulation and a layer of R-19? I would think if it were cold enough out to dissipate that kind of heat in short order then the furnace would be running pretty often and overcoming the heat loss through all that insulation.

I guess I just never even thought that could be possible but if you've seen it I guess you would know better than I would.

 

Hi Shane, the first one that comes to mind is a friend, Mike who also heated with wood. The wood heat kept the house warm, but not the pipes, which were well protected along the perimeter of the foundation. So well protected, they froze and broke.

Another was a zone that was rarely used. Spill-over heat from the rest of the house kept the room above freezing, but couldn't protect the pipes. Then there is Roger's house, and so on. When you get to be my age, all of the lists become long.

Part of the problem is burying the pipes inside the walls or floors where no one can see them. 9 out of 10 times, everything will be fine, but someone adds a bunch or electric space heaters, or closes off a room to reduce the heating costs and suddenly a problem pops up. Attics above, side attics, exterior walls are all places where contractors sneak heat pipes to get from one area to another. My infrared camera picks them up all of the time. Owners always comment that they had no idea there was a pipe in that wall. Add a couple of inches of rigid over the inside wall and you increase the risk of freezing pipes.

Just one of those good rules to follow, super insulate the cold side and keep the pipe exposed to it's source of heat and air seal.

Bud

 

When I put heat in what was a seasonal house, now I live in it most ofthe time, but for the times I go away to get warm, I bit the bullit and installed Cryotek about 50 % so when we get that rare ice storm, or other clamity I will at least not loose my heating system.
Sid