Zones With a Hot Air Furnace?

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I took it out today mcgiever when I rearranged the duct work.

Alright guys I'm missing something here! Outside went to 23 last night, house is 72 this morning per thermostat setting, but garage still 55, there's two 8" ducts, there divided equally now one goes to the house plenum, one goes to the garage, the house is twice the size of the garage, but I can't heat it with the furnace.. I have a cold air return for the upstairs, we all know my garage is off my
Basement, I put a vent in the door goin to the garage for a return, my basement is wide open, so there is no restriction from the vent in the door to the cold air return, about 18 feet away, so it should be circulating. I don't know why I can't warm the garage.

hotblast1357 wrote:Alright guys I'm missing something here! Outside went to 23 last night, house is 72 this morning per thermostat setting, but garage still 55, there's two 8" ducts, there divided equally now one goes to the house plenum, one goes to the garage, the house is twice the size of the garage, but I can't heat it with the furnace.. I have a cold air return for the upstairs, we all know my garage is off my
Basement, I put a vent in the door goin to the garage for a return, my basement is wide open, so there is no restriction from the vent in the door to the cold air return, about 18 feet away, so it should be circulating. I don't know why I can't warm the garage.

I have a 1000 sq ft basement with a box stove blowing hot air into my oil furnace return vents, my basement will only get to 60* - 62* because of cinder block walls and cement floor. When your air is moving it is also cooling itself, your furnace is in the basement so the garage is not getting any radiant heat like my basement.

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hotblast1357 wrote:Alright guys I'm missing something here! Outside went to 23 last night, house is 72 this morning per thermostat setting, but garage still 55, there's two 8" ducts, there divided equally now one goes to the house plenum, one goes to the garage, the house is twice the size of the garage, but I can't heat it with the furnace.. I have a cold air return for the upstairs, we all know my garage is off my
Basement, I put a vent in the door goin to the garage for a return, my basement is wide open, so there is no restriction from the vent in the door to the cold air return, about 18 feet away, so it should be circulating. I don't know why I can't warm the garage.

Maybe there is something else you've done that doesn't show in the pictures you've provided, but unless you have actually tied the return air from the garage into the cold air return on your furnace I don't think you will get air transfer.

How well insulated is the Garage? Could it be getting a lot of cold air infiltration?

MA- you are correct in that the basement does get a lot of radiant heat off the furnace that garage doesn't see. My basement stays 65-68.

Mcgiever-the cold air return from the garage is not directly hooked too the cold air return duct on my furnace, it is open to flow through the basement. There are 3 vents along my plenum that are for the basement but they are shut off, the radiant heat off my furnace usually can handle the basement. The return for the garage is not on the floor. It is about the same level as the heat goin in, and it is not piped directly to my return, which I think is hurting me. The garage has not had any heat all week an has stayed 45-50 degrees, it is currently 55.

Swpadon- the cold air return is not directly hooked to the cold air return on my furnace, it's flowing through the air kinda like your setup with the basement stairs.

Lightning- the garage is well insulated compared too the house, house is 2x4 walls and about 3 inches of insulation in the attic, garage is 2x6 walls with 5inches in the attic but it does have two garage doors, they are new but we all know they don't ever seal perfectly.

My main concern with hooking a return too the garage directly is that it will cool my air going to the house, because the return from the house is 70 the return from the garage would be around 50-55... But I guess eventually it will warm it up. I would think this furnace should handle the load, it is about 2900 sq ft TOTAL. And I have no problem heating the house. It took about 1.5 tons too heat the garage this winter with the baseburner my thought is that using a little more heat from the furnace I should be able to do it with only adding say .50-.75 tons too my house total.

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hotblast1357 wrote:the cold air return from the garage is not directly hooked too the cold air return duct on my furnace, it is open to flow through the basement. There are 3 vents along my plenum that are for the basement but they are shut off, the radiant heat off my furnace usually can handle the basement. The return for the garage is not on the floor. It is about the same level as the heat goin in, and it is not piped directly to my return, which I think is hurting me. The garage has not had any heat all week an has stayed 45-50 degrees, it is currently 55.

hotblast1357 wrote:the cold air return is not directly hooked to the cold air return on my furnace, it's flowing through the air kinda like your setup with the basement stairs.

hotblast1357 wrote: it does have two garage doors, they are new but we all know they don't ever seal perfectly.

Having the return set up the way you do, it will rely on a pressure difference between the garage and the basement. Since air is being pumped into the garage, it should create a slight positive pressure in there compared to the basement so air will naturally flow from the garage to the basement. This will work as long as the garage is well sealed. Otherwise some of that pumped in air will flow outside too.

On the other side of that scenario, the furnace (at the same time) is pumping air out of the house into the garage which will create a slight negative pressure in the house, urging air to come in whenever it can. Some will flow thru the basement door leading to the garage, some will come in as cold air infiltration at other points in your house.

Bottom line is, it will run more efficiently with a dedicated cold air return from the basement. So that you aren't loosing air to the outside thru the garage OR pulling in extra cold air infiltration in the house.

It is a concrete floor, and a two block high footer, then stick walls on three sides and obviously the basement wall on the fourth side. IR temps are, 60 degree slab by the entrance to the basement, and the farthest away is 54, ceiling temp, 10 foot ceilings, by the duct is 62, and same far spot on the ceiling is 60. I can't really measure air temp because I do not have a probe thermometer or anything. As far as BTU rating, wouldn't it POTENTIALLY be half of the furnace output? Seeing I am splitting the two 8" ducts? It's a 119,000 furnace, so it's actually probably 60,000 BTU, so right now would it be like 30,000 to the house, 30,000 to the garage?

Lightning I agree, right now there is positive pressure because I can feel the air coming from the garage too the basement with my hand in front of the door vent.

Also it is 8" coming off my furnace then goes too 6" going out to the garage, but my house is the same, it is 8" going too my plenum, then 6" off my plenum too each room, should I run the 8" inch the hole way too the garage? And roughly a 8" return? Piped down off the floor.

hotblast1357 wrote:As far as BTU rating, wouldn't it POTENTIALLY be half of the furnace output? Seeing I am splitting the two 8" ducts? It's a 119,000 furnace, so it's actually probably 60,000 BTU, so right now would it be like 30,000 to the house, 30,000 to the garage?

No, splitting the heat runs won't dictate distribution by half because of
#1 resistance differences of each run
#2 pressure differences that were pointed out in my post above

I'm betting its more a 70/30 split.

hotblast1357 wrote:Also it is 8" coming off my furnace then goes too 6" going out to the garage, but my house is the same, it is 8" going too my plenum, then 6" off my plenum too each room, should I run the 8" inch the hole way too the garage? And roughly a 8" return? Piped down off the floor.

Yeah, the choke down to 6 inch to the garage is limiting volume flow also. It doesn't work the same way for the house since there are many 6 inch runs instead of just one. I like the 8 inch return idea.

hotblast1357 wrote:My main concern with hooking a return too the garage directly is that it will cool my air going to the house, because the return from the house is 70 the return from the garage would be around 50-55... But I guess eventually it will warm it up. I would think this furnace should handle the load, it is about 2900 sq ft TOTAL. And I have no problem heating the house. It took about 1.5 tons too heat the garage this winter with the baseburner my thought is that using a little more heat from the furnace I should be able to do it with only adding say .50-.75 tons too my house total.

Both safety and insurance wise I would be careful about return air into the home from the garage. I understand what you want to do and I think I would run hot water and a Modine out there. just my 2 cents. be safe my friend.

MA's correct bout the safety...it's too late after the accident to say you "thought it'd never happen to you!!!"