Heatilator Mark 123 3138

**Jon Boettger** · 11-16-2019, 08:08 PM

Moved into my first house a year and a half ago and I'm having fun playing around with the old fireplace from 1979. One of the problems I have is the the house is 1959 vintage and it's a bit breezy, no matter how much of a blaze I get going my back side will still be cold and it can only slightly warm up the room. Does anyone here have a unit with the outside air kit hooked up and can tell me if it will make a difference? I assume it would have to do something to prevent sucking all the cold air into the house from every crack and seam.

I'm looking for an outside air kit Cat No 3140 AK. Does anyone have any knowledge of the kit and what it is all comprised of?

My fireplace does list on the operating tag than I can run it with the doors closed, and I do when I want a slow burn. The glass seems more than just tempered. Thoughts on putting a thin seal around the door frame?

Oh and after much digging and stumbling upon it by almost accident, I found the install PDF but I can't post the link
Google search fireplace outside air kit mark 123
And it will be the first one

**hearthman** · 11-17-2019, 07:42 PM

An outside air kit isn't going to warm you. If it is located in a negative pressure zone, it can suck heated air out of the fireplace into the flex duct.
Are your doors labelled "Heatilator"? If aftermarket, remove them at once or you'll burn your house down. Open hearth fireplaces can suck 400-600 cfm up the chimney.

Whatever you do, do NOT modify this fireplace with unlisted parts. Use only listed OEM parts.

**Jon Boettger** · 11-17-2019, 11:36 PM

My thinking is based on what heatilator themselves state on their website about using outside air for combustion. I hope to achieve 30% efficiency at least, currently I'm close to 0. That being it's a zero clearance style fireplace with hot air recirculation ducts.

The doors are original. Wish I could post some pics.

I really need some knowledge from any of the people that originally installed these units back in the mid 60's to mid 80's. I would love to find some new old stock of this out side air kit. From reading the install manual, it notes the connection for it can be on either side, back, or bottom. There is also a rough picture of the kit in the manual, just hard to make out what is what. It does appear there is two doors with some sealing material in them. Possiblity to regulate the flow of outside air...

Anyone it there have one of these old units with the outside air kit installed, and can provide some more info of operation?

**kdean1** · 11-18-2019, 07:30 AM

Joe,
Heathman is an expert on the topic. You should follow precisely any advice he gives.

**Jon Boettger** · 11-18-2019, 12:03 PM

I fully intend to follow good advice with proper safety in mind.

First, don't locate outside air vent in a low pressure area.

Second, doors are OEM Heatilator.

Third, need OEM Heatilator outside air kit 3140 AK.... If I can get it

**hearthman** · 11-19-2019, 08:09 PM

Don't hold your breath on that 30%. Outside air is cold. It slows combustion. These kits were a seemingly good idea on paper but not in practice. The open hearth will draw its combustion air from the room. If the room is depressurized a crummy 4" duct flowing 14 cfm on a good day won't touch the 400-600 CFM being sucked up the chimney. ASHRAE conducted a study on makeup air and concluded passive MUA is wholly unreliable and can hinder things.

I'd save my money and put it into air sealing the top of the thermal envelope while ensuring sufficient infiltration below the neutral pressure plane.

Good luck!