Furnace Plenum Question
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From: North East
Furnace Plenum Question
Hey all, I have an oil furnace that I got for the garage, it came out of my brother-in-laws house, it's all assymbled except for the plenum on top. Here's my problem, I am broke, I wanted to use the rigid fiberglass board that I have on my home furnace, but at 35.00 for a 4x8 sheet. Any other materials that you could think of that would work, but are cheap.
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From: Gainesville, FL
95,
If your duct is in the area to be heated, there is no need to insulate. This makes tin your cheapest option and most durable. Do you know how much air your moving? Standard rectangular tin can be bought at Home Depot but a tin shop might give you a better deal?
Good Luck,
KingFisher
PS Loose the rebel flag.
If your duct is in the area to be heated, there is no need to insulate. This makes tin your cheapest option and most durable. Do you know how much air your moving? Standard rectangular tin can be bought at Home Depot but a tin shop might give you a better deal?
Good Luck,
KingFisher
PS Loose the rebel flag.
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From: North East
Thank you for the suggestions, I believe I will go with the tin, the furnace is not in the same room as I will be heating, at least not this winter.
As for the flag, it's not meant to offend. I am southern originally and it means something to my family, was not put there for any other reason.
As for the flag, it's not meant to offend. I am southern originally and it means something to my family, was not put there for any other reason.
Posting Guru
Joined: Jul 2001
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From: Gainesville, FL
95,
You can choose to insulate your duct upto the point where the duct enters the area your heating, after that, insulation may not be required. Do you have any combustibles near the ductwork? I believe I've seen duct work get up to 225F degrees. Does anyone else know (have an opinion on) what duct surface temperatures can reach in indirect fired furnaces? If you need help sizing your ductwork, ask me, I do it for a living.
KingFisher
PS Thanks
You can choose to insulate your duct upto the point where the duct enters the area your heating, after that, insulation may not be required. Do you have any combustibles near the ductwork? I believe I've seen duct work get up to 225F degrees. Does anyone else know (have an opinion on) what duct surface temperatures can reach in indirect fired furnaces? If you need help sizing your ductwork, ask me, I do it for a living.
KingFisher
PS Thanks
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Well yes, I was thinking 2 8" ducts off of the plenum into the shop. These would be T'ed then reduced to 6" with vents every 10 feet or so. Just going to run duct down the left and right side of the shop. Eventually the room that houses the furnace (my rec room) will be ducted in, but that's some time down the road. For the time being, I will be feeding the furnace through a block duct from the shop, double filtered. Filter 1 to catch 90% of the crud that goes airborn in the shop, and the second to catch what the first doesn't. This will also be a visual cue on the first one when to change. This an acceptable idea?
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From: North East
Originally posted by dfisher1
95,
Whoa, Let's talk numbers?
How many BTUs/hr is this furnace?
90K BTU I think I have to check the sticker, but I am almost positive 90K.
What is the plenum size?
Hasn't been built yet, suggestions would be appreciated. The box is about 4' sq mount on top of the unit.
How many square feet are you heating?
currently about 750, but when the rec room is piped in, maybe by next year mor like 1850 or a hair more.
Is this a basement or 1st floor?
offset first floor. The basement per say is a 4 stall barn, the furnace is in the rec room and about 6 feet below the floor of the garage.
Kingfisher
95,
Whoa, Let's talk numbers?
How many BTUs/hr is this furnace?
90K BTU I think I have to check the sticker, but I am almost positive 90K.
What is the plenum size?
Hasn't been built yet, suggestions would be appreciated. The box is about 4' sq mount on top of the unit.
How many square feet are you heating?
currently about 750, but when the rec room is piped in, maybe by next year mor like 1850 or a hair more.
Is this a basement or 1st floor?
offset first floor. The basement per say is a 4 stall barn, the furnace is in the rec room and about 6 feet below the floor of the garage.
Kingfisher
Last edited by 95se5m; Oct 13, 2003 at 08:49 AM.
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95,
Size looks more than adequate.
At a forty degree rise (return air vs. supply air temp) you will have to move about 2000 cubic feet per minute (CFM). This will require a 2 ft. by 2 ft. plenum. This is more than generous. If that is a problem, a smaller plenum would suffice. No smaller than 16" X 16".
It sounds like you will have two major branches: Each branch will carry 1000 CFM. A 14" round duct will be required. A 12" duct would be pushing it, but might work. That's your gamble.
The following will be your general rule of thumb:
1. A 6" round duct can carry 150 CFM.
2. An 8" round duct can carry 250 CFM.
3. A 10" round duct can carry 500 CFM.
4. A 12" round duct can carry 850 CFM
5. a 14" round duct can carry 1300 CFM.
You should be able to design from here.
KingFisher
Size looks more than adequate.
At a forty degree rise (return air vs. supply air temp) you will have to move about 2000 cubic feet per minute (CFM). This will require a 2 ft. by 2 ft. plenum. This is more than generous. If that is a problem, a smaller plenum would suffice. No smaller than 16" X 16".
It sounds like you will have two major branches: Each branch will carry 1000 CFM. A 14" round duct will be required. A 12" duct would be pushing it, but might work. That's your gamble.
The following will be your general rule of thumb:
1. A 6" round duct can carry 150 CFM.
2. An 8" round duct can carry 250 CFM.
3. A 10" round duct can carry 500 CFM.
4. A 12" round duct can carry 850 CFM
5. a 14" round duct can carry 1300 CFM.
You should be able to design from here.
KingFisher
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Thanks alot for the information. It is quite helpfull. I will most likely be picking your brain again as I start assymbling the duct work. Now, is there a way to devide the plenum to zone the 2 areas? When I deside to heat both, I will need less in the shop and more in the rec room, can a baffle be placed in the plenum to devide it into like a 60/40 config? Or am I not looking at this correctly.
Posting Guru
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From: Gainesville, FL
95,
A 14" round will carry 60% of the heat.
Dampers can be placed in the duct to restrict flow.
Registers (air outlets) can be adjusted to regulate flow.
Don't screw with the plenum. Regulate at your outlets and insure ductwork is large enough to convey volume.
Kingfisher
A 14" round will carry 60% of the heat.
Dampers can be placed in the duct to restrict flow.
Registers (air outlets) can be adjusted to regulate flow.
Don't screw with the plenum. Regulate at your outlets and insure ductwork is large enough to convey volume.
Kingfisher
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