Hey guys, thought I'd throw this question out and maybe catch a response or two. I live in an old trailer, with an old oil furnace, I believe it's an Intertherm Mac-1265. It's my understanding that all these oil gun type furnaces in a mobile home, are considered down draft furnaces. It's also my understanding that they either pull air down the 2 pipe chimney (air comes down to feed the burner, and exhaust also goes up and out), or through an air supply duct in the floor. Is there a precise method of determining if I need the air supply hole underneath? If it apparently pulls air in the chimney, why is there a hole letting cold air into the shack? It's not like 1970's mobile homes are air tight lol I replaced the furnace with a virtually identical used unit some years back, but if I remember right, the chimney is the 2 pipe (pipe within a pipe) kind. Just trying to deal with the draft that sneaks in below the furnace. Thoughts?
Mine pulls air from under the trailer, If you crawl under and look to where the furnace is, there should be an opening there that draws the air for the burner, do not block that off or your furnace won't run....I know what you mean by the cold air coming through....
So, they put a hole in the floor to let the furnace breath? No pipe/duct to feed it that could be sealed?
I ran a dryer vent from that intake to the outside to see if it made a difference in air being sucked in through the skirting but it didn't make any noticeable difference, my skirting is heavily insulated and I managed to block some air from migrating but you can still feel it...Like an OAK...
It's been a long time since I was under there and looked, but it's probably a 2"x 8" hole/vent type thing. I never worried about it, thinking that's just the way it works. Then I read more about downdraft oil burners and confuse myself. So I was wondering if my air supply was coming down the outer inside of the chimney, and letting in a whole bunch of chilly air with the hole in the floor.
Wow I didn't think there were any of those still kicking around! Its been a coons age since i tangled with one. That suckers got to be over 30 years old! You have it right though they are a pipe inside a pipe system. You shouldn't need make up air from under the furnace to run it.
It had been tinkered with/refurbished somewhat by the older fella I got it from, it's not bone stock from the 70's. If the hole in the floor is required, I'm guessing the stove would run like a 3 legged dog or worse if I plug the bottom air? CO2 concerns? I just wonder why the 2 pipe chimney if there's an extra air supply?
They came stock with the 2 pipe chimney. IIRC the combustion air comes from the outer pipe and exhaust is up the middle. If you have a good co2 detector you could try plugging the hole and see if it runs. Maybe try it in the morning on a day your going to be around to monitor. If it runs and the co2 detector doesn't go off your probably squared away. Any hvac monkey would be able to use his sniffer to tell you if products of combustion were leaking out of it. A good idea! IMO a hole under the furnace is a poor method to mitigate that particular problem as you have mentioned you have skirting around the trailer. Co2 and CO (carbon monoxide) can and will pool under your trailer and then stack into the trailer if the furnace ran enough. It would probably have to run a lot for that to become dangerous but you never know.
