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I am installing a new furnace in a old home built around the late 1800s. There is NO current cold air returns. The only heating ducts are on first floor. The upstairs stays warm enough without any vents upstairs, so I didn't intend to add any up there. My question is : How do I figure how many cold air returns are needed downstairs, what size and where to place them in relation to the hot air vents. It is a forced air system. There are 4 rooms and a hallway that have hot air vents. Also are wall mount cold air ducts better than putting them in the floor. The rooms are : 1- 14'x13', 1- 13'x16', 1-14'x12', 1- 9'x12', and hallway 8'x14'. Thanks !!!
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Return air intakes for a heating mode are best located on the floor or as low as possible if in the wall(just above baseboard trim).
A general rule of thumb is to HAVE AT LEAST the same amount of RETURN as there is supply. They can be a centrally located return or individual ones. Your choice. It depends on installation (roughing in) difficulty.
Without a more definite layout of your present duct and/or piping layout, it is difficult to give you exact sizings.
Post back with more info, such as size of main supply trunk, BTU of unit, , twin plenums? or Hi-boy (low return leg, filter size, etc.
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like Hube said INFO, INFO, INFO, helps. Whats the Btu of the furnace and just what size registers do you have in the rooms
ED
My mistakes dont define me they inform me.My mistakes dont define me they inform me.Comment
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What I have (had) is an old coal furnace converted to natural gas back in the day. They used 12" round heating ducts, and NO cold returns. I was not going to use the old duct work due to the enormous size. I was going to go with 6" with the new furnace which is 100,000 btu. The current registers are 10x14 which I was going to keep in 2 of the rooms due to new carpet which is only a month old. I know I should of thought ahead of time. LOL.... This is pretty much a start from scratch install. Because of the old OLD system. Do I need cold air returns in each room ? There is only one plenum (heat) the cold air on furnace is left side low 24"x14". It is a Winchester/York GF9. If you need more info to help let me know.
THANKS AGAIN !!!Comment
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With a single High plenum opening,this is what is called a 'hi-boy' A supply (heat) plenum is fitted on this opening and a main trunk is added to the plenum. Or you can add various 5" or" 6 " take-offs and run them to the registers.
You dont say what efficiency this unit is. Is it a 'mid =80 %
Also, is this 100,000 rating the input or the output?
What other supply registers are you considerin adding to other areas of this house, as for 4 rooms and a hallway this unit seems a way too large.
Even in the old days of coal fired 'Gravity' furnaces ,they installed Return air openings, usually on the floor and rather large in size.
Your best approach to installng a properly sized duct system is to submit a sketch to this forum showing a general layout of what you have and also showing any other areas in the home that you would like to heat.
Do you have any heat in your basement area?
A ball park guess with a mid (80 %) unit would be you could have perhaps 7-10 heating runs taken off it and 3 or 4 well place returns.A main trunk line size of approx 22x8 for the supply and a approx 24x8 return main with a 16x12 drop leg into the filter box area (24x 16 minimum)
But ,like I said, you need to send a sketch out because sizeing is most important for your comfort, units fuel consumption, and above all the most important, your safety.
Without an informative sketch it would be very foolish to give you any definte advice on this ductwork installation....HubeComment
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Hello, and thanks for the fast replies to my questions. The furnace is 100,000 btu input and 95,000 out. It is 92% eff. My rooms (sizes listed above) have registers/vents in the cielings that go up to the floor of the next level, to let hot air rise from 1st floor to second. The living room and dining room are next to each other with a 4' wide and 8' tall door way. Also attached to the living room on the other side is the hall/stair way to upstairs with a 36" wide doorway. The kitchen is attached to the dining room with a door way 4'x8' . The small room is the downstairs bath. which is closed by a door from the kitchen. The basement is not heated. I will try to get a scetch on here If I can figure out how to. Now that you mention running a supply trunk vs. 5 seperate ducts for heating which is a better way to go???? Is one more eff. than the other? Does one work the furnace harder than the other ? Which one is better for more balance ? I am placing the furnace in center of the house (basement). I don't know if it matters but the house is well insulated and all of the windows are newer 5years old tops.
Thanks Again, and I will try to place a scetch on here.Comment
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P.S.
You had mentioned that the old gravity flow furnaces had returns. Mine did not, I don't know if they were removed or ??? But there wasn't even cut outs on the old girl for them. All that came out of it was the hot air supply ducts which each were 12" round.Comment
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ALL the old gravity type furnaces had intake pipes of some kind.they were essential even in that day and age. These intakes were either a 14" or larger diam, usually 16" and normally there were 2 of them.
The old supply heat pipes were approx 8"-10" in diamand larger.
All furnaces, even the old gravity (octopus looking ) needed return air in order to get the hot air out (especially without a fan,like the old gravity furnaces).. Its called 'circulation.'
Ok, so much for the old one.
We will await some type of sketch in order to give any advice on any sizes.Also, what sizes are these existing heat registers,how many? What sq footage area is the house ? how many rooms upstairs?
Btw, do you want any heat and return in your basement area? It is always a good idea to have some in this area. HubeComment
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Still working on the scetch. Register sizes are 2-10"x14" and 2- 14"x20" the 2- 14x20s I was going to make 10x14 to match somewhat. And there is a 4x10 in bath. House is 644sq ft per floor. 2 Living floors and a basement and a full attic. As for heating the basement. What advantages does it have ? Would I just need to add one heat and one return down there? It is a unfinished basement. The rooms upstairs are same size as bottom floor (- 1 1/2ft each in length due to hallway).
Thanks Again.Comment
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Like Hube said you had to have a return on the furnace down there. Had a lot of them that had just a big hole cut in the bottom sheet metal outside casing and have a cold air grill in the floor in the 4 corners of the home. If you didnt you wouldnt have any air to come on up from the furnace. For a time we would take and add a blower to the furance at the bottom side of it. Then run the large cold air pipe to the blower.
Way back when there where a lot of setup's like you have. We would pull all the pipe and furnace out. Set the new gas or oil furnace. Then use all of the heat registers there on the inside walls as cold air returns. All the new heat registers run the pipe for them on out to just off the outside walls to new floor registers. it would work very good
Ed
My mistakes dont define me they inform me.My mistakes dont define me they inform me.Comment
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You must have xray vision or a camera in my house LOL !!!! All of the existing heat registers on the floor are on inside walls. It sounds like a decent idea to use them as the new cold air. And place new registers as heat. I have removed all the old duct work. Didn't have much head room in basement with 12" ducts running EVERYWHERE. So what you are saying is to put the new hot registers in the far 4 corners of the house (rooms) right?
Thanks Again
WillComment
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