WMC36 Outside air intake

[odonlarr]

Hi Everyone. This is my first post here. I have had a Majestic WMC36 for about 4 years that gets fairly frequent use. It is connected by 4" duct to outside for combustion air. I recently had reason to remove some drywall from around the fireplace (lowering the mantle for installation of flatscreen tv above) and noticed that, although the chimney cooling air duct was cold to the touch, the combustion air intake was not, with its damper lever (on the lower left front corner) in either position. I spoke to a tech at CFM (the Canadian manufacturer) about this, because I was wondering if it was because of the 1/4" - plus gaps between each of the glass panes. He told me that those fireplaces are not airtight - which I knew - and that they should be operated with the doors open, which makes no sense to me as you have to open the flue damper much wider to prevent smoking and consequently have little control of the fire. Does anyone know if there should be such gaps around the glass, and whether there is some sort of knockout plate for the air intake that should have been removed during installation?
Larry

 

[SlyFerret]

I have the 42" version of that fireplace. The glass doors on mine also have the 1/4" gaps in them. I also use the outside air intake.

I found a PDF of the manual for the fireplace online. It says that the fireplace can be operated with the doors open or closed.

I have a propane start on my unit. When I run the propane start, I have to keep the doors open so that the flames will come directly up through the wood on the grate. If I close the door, the air circulation inside the fireplace changes and the propane flames blow back towards the back of the fireplace and they go behind the logs on the grate.

Once the logs have started to burn, I turn off the propane, open the screen and close the doors. When the logs are burning on their own, the air circulation in the stove with the doors closed seems to cause the air to come into the fireplace from below and blow up through the logs.

I have found that the fire actually burns better with the doors closed. I usually don't damper it down much even with the doors closed though.

My biggest gripe is that the grate that is installed is too shallow to be real useful. Unless I split the wood way down, I can't get the logs to stack well on the grate. They keep wanting to fall down behind it against the back of the fireplace. This usually is followed by some swearing as I try and get the log back onto the stack while trying not to get singed too badly.

-SF

 

[DiscoInferno]

I also have a WMC42, with outside air kit. Best I can tell, the OAK is pointless; as you've noted, the glass doors barely restrict the draft from the room and it's hard to believe much is pulled from the OAK. Is yours hot (indicating drafting the wrong way), or just room temp (indicating no airflow)?

I've somewhat recently discovered that I can get a whole lot more heat (and slightly extend burn times) by closing the damper most of the way with the doors closed after establishing the fire. (By "most of the way" I mean moving the slider most of the way to the left; the damper in mine never fully closes.) This lets me get the firebox much hotter, to the point where I burned off some paint above the doors. Is it safe? Good question. If it's only designed for the relatively cool temperatures that result from a wide-open flue, then no. But it seems to be a pretty well-built unit for a prefab.

 

[odonlarr]

Thanks for the replies. I think it's a pretty good design too. I am generally happy with it, but I just hate when something isn't working as well as I think it should. When the flue damper is wide open as when getting fired up with the doors closed, I get a cool air inflow from the HRV return, indicating that there is lots of air going up the chimney from inside the house, rather than drawing it from the OAK, which irritates me because, like you, I had the forethought to install one at the outset. The duct was at room temp, so there appears to be no flow in either direction. Most of the time, I too run the fire with the damper closed as far as possible without producing smoke in the house which extends burn time considerably for me, and of course controls heat output, although I find that the wider the damper, the more heat...

 

[velvetfoot]

I'm surprised you can use the fireplace with the tempered glass doors closed.

 

[SlyFerret]

Really? I run mine that way all the time.

-SF

 

[DiscoInferno]

Thanks for the replies. I think it's a pretty good design too. I am generally happy with it, but I just hate when something isn't working as well as I think it should. When the flue damper is wide open as when getting fired up with the doors closed, I get a cool air inflow from the HRV return, indicating that there is lots of air going up the chimney from inside the house, rather than drawing it from the OAK, which irritates me because, like you, I had the forethought to install one at the outset. The duct was at room temp, so there appears to be no flow in either direction. Most of the time, I too run the fire with the damper closed as far as possible without producing smoke in the house which extends burn time considerably for me, and of course controls heat output, although I find that the wider the damper, the more heat...

No forethought on my part, it came pre-installed in a modular home w/ OAK. I wish I would have read up on fireplaces back then and got an EPA one instead. But for the moment that fireplace gets minimal use anyway.

What I found was that an open damper let so much cool air rush through the firebox and up the chimney, taking heat with it, that closing off the damper raised the temperature considerably. The air coming out of the blower ducts, in particular. I do worry about the tempered glass doors shattering from the extra heat, but I keep the metal curtains pulled and that serves to reflect a lot of the heat back before the glass.