Newbie question regarding forced air furnace leak

[Socratic Monologue]

Hello all,

The last two or three months of perusing this forum has been very informative, and I'm always amazed by the friendly tone of everyone who posts here. I'm certain I'll have lots of questions throughout the coming season, but here's my first simple one: on our Hotblast 1300 (which was already installed in the house when we bought the house), there is a gap between the top plate of the unit (which is the top of the plenum chamber) and the front plate (which is the front of the firebox). Heated air flows out of this gap, heating the furnace room (which I don't really want to do).

I've tried loosening the screws that hold the plenum plates on, and shifting the alignment of the plates, but there is really no play in the screw holes. I'm thinking I should seal the gap with something like fiberglass gasket, in case I ever want to disassemble the unit. Furnace cement seems really permanent. Advice? Thanks in advance!

Edit: Not sure why I thought the furnace was model 1300 -- looking at the website of US Stove (who I emailed this question to three days ago with no response yet) it seems the stove is likely model 1557M. The question might make more sense now, since it doesn't look like the 1300 has the same sort of joint at the top front of the box.

 

[Gooserider]

Hello all,

The last two or three months of perusing this forum has been very informative, and I'm always amazed by the friendly tone of everyone who posts here. I'm certain I'll have lots of questions throughout the coming season, but here's my first simple one: on our Hotblast 1300 (which was already installed in the house when we bought the house), there is a gap between the top plate of the unit (which is the top of the plenum chamber) and the front plate (which is the front of the firebox). Heated air flows out of this gap, heating the furnace room (which I don't really want to do).

I've tried loosening the screws that hold the plenum plates on, and shifting the alignment of the plates, but there is really no play in the screw holes. I'm thinking I should seal the gap with something like fiberglass gasket, in case I ever want to disassemble the unit. Furnace cement seems really permanent. Advice? Thanks in advance!

Edit: Not sure why I thought the furnace was model 1300 -- looking at the website of US Stove (who I emailed this question to three days ago with no response yet) it seems the stove is likely model 1557M. The question might make more sense now, since it doesn't look like the 1300 has the same sort of joint at the top front of the box.

Welcome to the forums - I'm not familiar with that furnace, but I will try to help you out...

First off, the big safety question - is there any chance at all that the firebox might be leaking into the plenum chamber? If so, it needs emergency level repair, otherwise it's less of a concern. (I also assume that you have CO detectors in the house, which you should have regardless of what kind of fuel you are burning...)

Next - do you have the manual? And if so, is there a part list that shows whether or not there is any kind of part or gasket missing? - If there is, I'd try to get a replacement part, or something similar...

How big is the gap? What kind of edges are there on the plates? In order for fiberglass gasket to work, you really need to have some fairly wide flat surfaces for it to be compressed against, and preferably some sort of groove for it to fit into. I don't thing it would work if you had sheet metal edges as a contact surface... How hot does the area get? If it doesn't get very hot, and the gap is fairly small, I'd consider using high-temp silicone. If it was a gap that was to wide for silicone, I'd think about making a filler plate out of sheet metal (and seal it with silicone or furnace cement)

Furnace cement would also be a possible solution, though it might not work as well - unless it is trapped in a joint with no movement, it really isn't all that permanent, flex the joint at all and it will crumble and fall right out. High temp silicone will stick to the surfaces better, and have the flex to deal with any vibration or thermal movement in the parts.

Hope this gives you some ideas,

Gooserider

 

[Socratic Monologue]

Thanks for the welcome and the reply, Gooserider. I have no reason to think that the firebox is leaking -- no smoke smell, no leak when blowers are not running, and CO detectors in the house and the workshop adjacent to the furnace room are silent as church mice. The manual shows no gasket or the like for that location (and my email to US Stove has not been replied to after 5 business days...).

You're right about the fiberglass gasket being troublesome to install against the edge of sheet metal -- that's what I ended up doing, just because it was the easiest-to-undo option. The gasket (tape-type, not rope-type) was pretty challenging to install, but I finally got it sandwiched between the edge of the sheet metal that is the front face of the firebox, and the flat sheet that is the top of the plenum. Seems to have solved the leak problem about 95%, which I'm pretty happy with.

The reason I didn't want to cement the panels together is this: I was recently looking at a Caddy furnace, and noticed that the inside of the plenum is insulated with what appears to be foil-faced fiberglass. Can this (or something like it) be installed in the 1557? Or is there some essential difference between our simple-firebox-and-plenum furnace and the Caddy that makes this sort of retrofit a really bad idea?

 

[laynes69]

You don't want that insulation in a 1557 if the power goes out. Its an easy way to overheat that furnace, considering it has 2 8" openings. The Caddy has a large plenum opening to assist in the removal of heated air to help gravity feed in an outage. As far as the leaks are concerned, you can use foil tape, or furnace cement. You may want to periodically go around and tighten the screws up. Its a normal thing on those furnaces. If the leaks are minimal, I wouldn't worry about it.

 

[Gooserider]

Glad to help out... I agree that while you probably don't want to be putting the insulation in the HX box, it is important to be able to take it apart if needed... However silicone can always be cut out if need be, so that was why I was suggesting it...

Gooserider

 

[ikessky]

My first thought was foil tape, but then again, I'm not familiar with your furnace so I don't know how hot that area is getting.

BTW, where in WI are you located? It's finally getting cold enough in the northwoods that I can actually keep my furnace going!

 

[Socratic Monologue]

This location is actually the front plate of the firebox. The surface thermometer I stuck on there a couple days ago got up over 500 F when I loaded it up with wrist-sized sticks (still learning how to run this thing properly). I'm not sure foil tape would stand up to that.

We're about an hour north of Madison. We've had the furnace going constantly since Thanksgiving, but sometimes during the day I have to throttle it way back, and it still gets a bit warm in the house -- I like it in the low 60s, though my wife likes it about 10 deg warmer. Any way to have heating zones with a wood furnace?

 

[ikessky]

Not really, except for closing of registers and blowing heat to other portions of the house. I like it about 72 in our place, but running the furnace constantly gets it up to 76+. I'm going to put some ducts out to the garage so that we can close the registers in the house and then the heat will blow more into the garage. Otherwise, I end up sitting here with a window or door open until it cools down.

I'm about 3 hours north of Madison.

 

[mike1234]

How about using the gasket material used in wood stoves - the stuff that looks like rope. It comes in various sizes, and it would handle the heat, and you could stuff it in the openings and be able to remove it later if you wanted to.

 

[Socratic Monologue]

How about using the gasket material used in wood stoves - the stuff that looks like rope. It comes in various sizes, and it would handle the heat, and you could stuff it in the openings and be able to remove it later if you wanted to.

I'm assuming you are talking about the stuff that Gooserider and I are referring to as "fiberglass gasket". That's what I ended up using, and like you suggest, it seems to work pretty well. I found a size (5/8" flat) that fits well enough.