PVC pipe heat and fire insulation

[Willvv]

Hi there,

I need to run a speaker cable through the flue of my fireplace.
I've drilled a whole through the mantelpiece (on each flank) and got a clear vinyl pipe via which I'll have the cable run, so I need to isolate that vinyl pipe from the fire that will be 5 inches or so below. I also need it to be heat insulated so that it doesn't melt.

I've looked for sleeves such as the Rockwool Pipe Insulation sleeve (for example here) but was told it wouldn't be suitable.

Would you have any suggestions as to how to go about that? The vinyl pipe may not be the best option, but I couldn't find any pre-insulated pipe to have the cable run through.

Note that the fire is a gas one, so fairly small flames and not extremely hot either.

Any suggestions would be most welcome,

Will

 

[muggles]

Some photos of what you're trying to achieve would be most helpful here

 

[magicmushroom666]

I doubt you can insulate a cable to be 5 inches above a fire, and stay cool for potentially hours of heat being applied, no matter what insulation you use, the heat will get through eventually.

 

[Madrab]

Yup, have to agree. Not the right place to have the pipe, even a copper pipe would heat up enough to potentially melt the cable's insulation.

Secondly, have you actually drilled through into the flue from the room side of the fireplace? If so you could have now created a path for carbon monoxide from the fire to permeate into the room.

 

[Willvv]

Thanks guys.

Actually it’s 20in from the base of the (artificial) coals and around 12in of where the flames would get to when the fire is on with maximum gas.

Heres a picture:

A1608592-9F87-4BA2-9206-090B88827125

• Willvv
• 16 Nov 2020

I was thinking of one fire resistant layer and then one heat insulated layer. So for instance a heat insulated sleeve inside a copper pipe (although I would rather avoid a rigid pipe because I’m going to struggle to get it through if both holes aren’t perfectly aligned...).

@Madrab Your second point obviously worries me because I’ve already drilled the holes. But why is that a problem; the fireplace is already open onto the living room, so why would holes in the side of the mantelpiece make things any worse?
Any incoming gas is in the pipes and when it comes out to be burnt, if there’s a monoxide carbon leak, it would get into the living room through the open fire wouldn’t it? Or am I missing your point?

 

[Madrab]

With an open flued gas appliance, you want all the burnt gases to head up the flue/chimney.

Under normal use and if the fire and chimney is working correctly, when the gas burns the heat creates an updraught in the chimney that then draws the air and all the products of combustion (POC's) through the fire front, up the chimney and out to the air, there will be no flue gases entering the room, only radiated heat from the fire.

When a gas fire is tested, one of the tests is called a spillage test, it's a smoke test performed under the front edge of the fire box that checks that all the air and POC's are heading in through the fire and up the chimney, if there is any spillage (smoke entering the room) it fails the test and the fire is shut down and disconnected until it is made safe.

If you drill holes into the flue space then gases (Carbon Monoxide) from the fire could find a path out of those holes and into the room. The risk is small but it is still a risk.

Those holes need mortar'd up IMO.

 

[bernardgreen]

As already mentioned heat insulation only slows the rise in temperature of the protected item, it does not prevent the protected item from eventually getting hot.

You could consider heat shield material such as THIS but the cost could be high

 

[Willvv]

Those holes need mortar'd up IMO

If I manage to solve the other problem, I suppose I could seal the pipe to the rest of the wall, with plaster or something, no?

@bernardgreen thanks for the suggestion - I’ll look into that.

The third option I can think of would be to try and drill at the back of the flue, but the mantelpiece is very large, so even with the 1 meter drill bit I have, I’d need to drill from both sides and manage to have them perfectly aligned - not sure I know how to pull that off.

 

[bernardgreen]

Could you go down to get under the floor and get round the fireplace before coming back up on the other side of the fire place. A lot of work but given the risks from going through the chimney I would say it is a better and safer route.

 

[Madrab]

I suppose I could seal the pipe to the rest of the wall,

And if the pipe ever burned through .... unfortunately not ..... there shouldn't be anything in the builders opening/catchment space that could, in the event of a failure, offer a route for POC's to get into the liveable space.

Of course this is only to keep you and your's safe.

 

[Willvv]

Thanks everyone. After trying to find multiple routes (under the fireplace, at the back), I finally settled for a sideway cut where the cable will run from the side of the mantelpiece to the front, then run outside the front of the mantelpiece (it’ll be hidden behind a large mirror) and then dive back into the mantelpiece to come out at the side. That way I don’t go through the flue.

Now I need to fill in the holes I made in the flue which is going to be a bit of challenge. I read the plaster of Paris is fireproof and quite good with heat, do you see any reason not to use that?

Thanks again for all your ideas and comments