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Discussion Starter #1
I live in NJ and have a forced-air gas furnace in the attic. Right now, the attic floor is insulated but the attic ceiling is not (even though i specifically asked the contractors to insulate the ceiling but that's a whole other bag of snakes).

I would like to insulate the attic ceiling to make the attic a semi-conditioned space because of the furnace. I see no problems with stapling the insulation on and also, i assume i should remove the insulation from the attic floor since the attic will become part of the thermal envelope, right?.

My questions are:

1. how do i go about making sure there is adequate ventilation to avoid moisture/mold issues.
2. Does the furnace itself need any additional venting or modifications?

On a related note, if i were to decide NOT to insulate the attic, of course my utility bills would be higher, but would there be any risk of damage to the furnace with the cold weather?

And before anyone asks, no there is no other place to put the furnace in the house. Every other square foot is taken up and i don't have a garage.
 

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retired framer
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Insulate the ducts.
Right now you should have soffet vents that let air in and ridge vents or box vents to let air out.
If you want to insulate the roof deck the rafters likely are not deep enough so adding to that maybe. the air chutes at the soffets have to be extended all the way to the peak. If you have box vents, they will have to be changed to a ridge vent.
The fire in the furnace will need outside air and you do not want it sucking dirty moist air from the house. So every hole between the house and attic need to be sealed, which should happen anyway.

Ail this to save the heat caused by the fire and is not used normally anyway. You would do much better by adding to the ceiling insulation, leaving the attic cold with whatever lost heat there is.
 

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Discussion Starter #3
So basically you're saying just increase the insulation on the attic floor? For all i know, it could be adequate now but i can check. If i do add to the insulation on the floor instead, is there anything i need to know about ventilation? In other words, does the floor need to "breathe" at all to avoid issues or am i free to seal it as much as possible?

Also, if i don't insulate the roof deck, the furnace itself will sometimes be subject to temperatures below freezing. Could this cause any issues? I don't it to stop working at the time i need it most!
 

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retired framer
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So basically you're saying just increase the insulation on the attic floor? For all i know, it could be adequate now but i can check. If i do add to the insulation on the floor instead, is there anything i need to know about ventilation? In other words, does the floor need to "breathe" at all to avoid issues or am i free to seal it as much as possible?

Also, if i don't insulate the roof deck, the furnace itself will sometimes be subject to temperatures below freezing. Could this cause any issues? I don't it to stop working at the time i need it most!
If you did seal the roof from the house and insulate the roof sheeting and have an air tight attic you would still need a vent for fire air.
We have furnaces in crawl space under the house all the time here with out a problem.
If it was a problem my first thought would be an insulated furnace room or box. The manufacturer has limits to how close things can be built to the furnace.

Just wait there will be a bunch of different opinions here soon.:vs_cool:
 

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Exterior Construction
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There is no "semi" conditioned about it. Its either insulated and sealed up (i.e. seal all the soffits and the ridge), foamed, and then treated as conditioned or it is not.

Unless you are going to use the space, I highly suggest you follow @Nealtw suggestion of air sealing the attic floor and blowing in additional insulation over the top.
 

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Discussion Starter #6
I am going to use some of the space for storage. Can i put insulation over the ducts and nail boards down on top to use as a floor?
 

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retired framer
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The bigger question is, is the structure enough to allow storage and floor.
If you have engineered trusses with a 2x4 bottom cord the usual answer is you should not.
If you have rafter and ceiling joists the joists are sized to carry the weight of the ceiling so maybe would be the answer.
 

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Discussion Starter #8
The bigger question is, is the structure enough to allow storage and floor.
If you have engineered trusses with a 2x4 bottom cord the usual answer is you should not.
If you have rafter and ceiling joists the joists are sized to carry the weight of the ceiling so maybe would be the answer.
Huh. How would i know? I'm looking at pictures i took of the house after it was framed. The boards that make up the 2nd floor ceiling/attic floor look to be about a 2x14 (hard to tell scale in the pictures though). Definitely much wider than 2x4s. And they're about 14.5 inches apart - in line with the wall studs on the 2nd floor walls.

The house was rebuilt after a fire and the attic had a solid floor before that. I'll be pretty ticked if the construction co didn't at least replace it with beams ready to take another floor. TBH, i'm still a little ticked that they didn't put a floor in the attic at all. Shows what i know. They said they were putting the furnace "in the attic", i didn't know that would mean using the entire attic for it.
 

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retired framer
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Huh. How would i know? I'm looking at pictures i took of the house after it was framed. The boards that make up the 2nd floor ceiling/attic floor look to be about a 2x14 (hard to tell scale in the pictures though). Definitely much wider than 2x4s. And they're about 14.5 inches apart - in line with the wall studs on the 2nd floor walls.

The house was rebuilt after a fire and the attic had a solid floor before that. I'll be pretty ticked if the construction co didn't at least replace it with beams ready to take another floor. TBH, i'm still a little ticked that they didn't put a floor in the attic at all. Shows what i know. They said they were putting the furnace "in the attic", i didn't know that would mean using the entire attic for it.
I would like to see the picture of those joists. I can't think of any normal joists that big.
 

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Discussion Starter #13 (Edited)
Heck yeah.

Park a car up there.

Still goes back to the how you are going to seal off that section that you want to condition is all.
Yep. so, if i make sure the ductwork that is between those joists is well-insulated, can i then nail boards over the joists to use as a makeshift floor. Since i'm just using it for storage and not living space, it doesn't have to be pretty. I just want to put something there so i can stack boxes and walk around without falling through.

My concern is ventilation. Will putting the boards over all those hoses cut them off from proper ventilation and lead to moisture problems or other issues?

Additionally, i noticed there is a pan underneath the furnace. Even though it's forced-air, i'm assuming the pan is there to collect some sort of moisture. If i follow your advice and insulate the ducts while leaving the main attic space (and the furnace itself) un-insulated, could the moisture that collects there freeze from time to time and would that give me problems?
 

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retired framer
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Yep. so, if i make sure the ductwork that is between those joists is well-insulated, can i then nail boards over the joists to use as a makeshift floor. Since i'm just using it for storage and not living space, it doesn't have to be pretty. I just want to put something there so i can stack boxes and walk around without falling through.

My concern is ventilation. Will putting the boards over all those hoses cut them off from proper ventilation and lead to moisture problems or other issues?

Additionally, i noticed there is a pan underneath the furnace. Even though it's forced-air, i'm assuming the pan is there to collect some sort of moisture. If i follow your advice and insulate the ducts while leaving the main attic space (and the furnace itself) un-insulated, could the moisture that collects there freeze from time to time and would that give me problems?
Yes you can cover that stuff. The ventilation to worry about is from soffet to peak next to the roof sheeting the rest will look after itself.
The pan under a furnace is fire protection, a pan under an AC unit catches water that is piped out.
 

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Discussion Starter #15 (Edited)
Oh, OK thanks.

Any advice on the best type of insulation to use for the ductwork? I noticed the hoses already have insulation around them but i assume it's minimal. Knowing the contractors, i'm sure they put on the minimum allowed by law.

A related question: How often does ductwork need to be repaired or replaced? If i do cover it up with boards, i'm thinking i might want to make them removable for access to the ducts if needed.
 

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retired framer
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Oh, OK thanks.

Any advice on the best type of insulation to use for the ductwork? I noticed the hoses already have insulation around them but i assume it's minimal. Knowing the contractors, i'm sure they put on the minimum allowed by law.

A related question: How often does ductwork need to be repaired or replaced? If i do cover it up with boards, i'm thinking i might want to make them removable for access to the ducts if needed.
Pipes, so it is an AC unit too?
 

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Discussion Starter #17
AC unit is outside. The ductwork in the attic is all huge "octopus-like" hoses with foil-covered insulation wrapped around them.
 

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retired framer
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AC unit is outside. The ductwork in the attic is all huge "octopus-like" hoses with foil-covered insulation wrapped around them.
It is an air handler. When the AC is running this is where the magic happens Air is cooled and water will condense in this unit and it drains out side, the pan is to catch anything that spills out when the drain is plugged. When the drain is plugged the unit can fill enough that the fan can send water down the duct work and then there is a mess to clean up.
 
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