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Old 02-05-2015, 09:01 AM   #1
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Furance in insulated attic


Hello,

I have a high efficiency (97% dual stage, American standard gold series) that builder placed in the attic in an insulated room. It's finished with drywall and outside is covered with R19 batt. Please see picture below to get an idea of what it looks like.

I live in Chicago and and have been getting ice dam. There are no other heat sources in the attic other than this furnace. The room is running a good 10 degrees higher than 2nd floor conditioned space. And the ceiling where the supply duck is located is nearing 100F! I can't imagine anything else that may be melting snow on top of the roof...

Questions:

1. I am planning to hire HVAC specialist but do you guys think it's possible to move the top supply duct to lower such that it's not so close to the ceiling (roof)? I don't know if this unit can handle other variations.

2. Should this furance room be vented to 2nd floor conditioned space? It has no other appliances and I am not aware of any codes that require as such. I was wondering if some venting to the 2nd floor may reduce the temperature in this room?

3. The connections do not have mastic so there will be anther to do in this room.

Thanks!


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Old 02-05-2015, 09:16 AM   #2
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Furance in insulated attic


Heat rises so shortening the duct won't help. Insualting the exposed metal and case of the AC coil may help it radiate less heat. Not sure if there is any bldg code requirement for fire seperation that will not allow you to open it to the 2nd floor but once again heat rises so it will still be there. There are these stick on pins that stick to the sheet metal that Commercial tin guys use. The insulation stabs over the pin and there is a locking tab that goes over the pin/barb to hold it on. Use the same foil as on the round pipes.

Check with some qualified roofing companies if there are heat cables or some other method to prevent damming.

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Old 02-05-2015, 10:31 AM   #3
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Furance in insulated attic


Hi Yuri - thanks for the reply! Yes, got the heat cables installed and now may consider extending ice shield even higher to eliminate chances of water leak.

Great points above. I confirmed with builder that he put R38 on the ceiling so moving the supply duct 12" won't make much difference.

I presume mastic around the furnace is still a good idea?

I really like the insulation around the supply vent. Unfortunately I only have an 1" between ceiling and the unit at the top. I wouldn't want the insulation to touch the ceiling, correct?

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Old 02-05-2015, 11:46 AM   #4
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Furance in insulated attic


That foil insulation is 1" thick and IMO you can wrap the entire bonnet/plenum and top of the furnace and AC coil case with it. The plenum must be 1" from the ceiling in case of fire/code and to allow for expansion. Nothing in the code that I know of says you cannot insulate it to keep the heat and AC cold air in. It is soft so the furnace can expand up anyway.

You don't want to lose any heat or cooling in a dead room so insulating everything is good. I have seen insulated plenums and some need it or they sweat. The AC case coil is not that cold as the air has not passed thru it and got cold until it leaves it but it does get hot and radiate heat.

Mastic is a good idea. Check with your gas inspector if insulating the plenum is allowed or the AHJ. ( authority having jurisdiction - I just learned that term a few days ago, not one we use in The Great White North ).
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Old 02-05-2015, 12:03 PM   #5
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Yuri - you are amazing. Thank you! My hvac guy is saying no to plenum insulation although it sounds like a good move.
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Old 02-05-2015, 12:15 PM   #6
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Furance in insulated attic


Why is he saying no. Because he does not know how?

We used to insulate the inside of plenums for noise with Lennox Pulse furnaces and the top inside. Perfectly legal. I suspect he does not want to. Your furnace fan can move enough heat so it does not overheat and he should not be scared of that. If it is running hotter then he needs to speed it up. You may have a ECM variable speed fan which can move LOTS of air so that is not a problem. If you DIY he may get cranky and threaten to not warranty it but that is BS. Calmly ask him why he won't and convince him.

Durodyne makes these pins to attach it and any good HVAC supplier should know about them

http://www.durodyne.com/home.php
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Old 02-05-2015, 07:50 PM   #7
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Furance in insulated attic


I am definitely thinking about insulating the plenum with or without the contractor. The concern I have is only about 1" clearance between the plenum and ceiling.

Many duct insulation at local stores are showing 2" depth. I presume it's not good to put insulation that will touch the ceiling - thermal heat transfer? Even with the insulation touching the drywall, I presume I will see lower temperature with the insulation vs without...

Thus I am left with limited choices... Do you guys recommend any others?

Self stick 1/8" but no indicated R value...

http://www.homedepot.com/p/Frost-Kin...V516/100028603

or this:

http://www.menards.com/main/building...978-c-5778.htm

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Old 02-05-2015, 08:46 PM   #8
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Furance in insulated attic


The 1" clearance is to allow the furnace to expand and contract as it heats up and down. If it was tight against the ceiling it would creak or get damaged. In theory if the furnace caught on fire or got red hot then it would not touch the wood and ignite it. Maybe back in the dark ages with wood or coal burning units it may have happened but all modern furnaces have high temp limit controls to shut down the burner. I have never heard of a house fire because a furnace got too hot. Adding some non combustible insulation should not be a problem IMO. As long as the furnace has room to expand and it is soft then it should be OK.

I would not be worried about R value as you have no insulation now. The insulation and foil will make a huge difference. If it was in a regular cold attic or crawlspace under a house then the R value would be important. You just want to stop the radiation and any insulation should be good enough.

Your furnace has a supply temp of less than 140 deg F so it is not that hot and worrying about R value when the temp diff is not that great between the room temp and that is kinda a mute point IMO.
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Old 02-05-2015, 09:01 PM   #9
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Furance in insulated attic


Thanks so much Yuri! Really appreciate your help. I will report back with the results.
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Old 02-05-2015, 10:27 PM   #10
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Furance in insulated attic


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Old 02-06-2015, 12:49 PM   #11
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Furance in insulated attic


did a new post, did not want to hijack this thread
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Old 02-06-2015, 02:25 PM   #12
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Furance in insulated attic


Pictures worth thousand words, here's what my roof looked like that had the ice dam (see by the laddar). It's like a perfect storm with the ridges converging into a saddle. Plus I have bath vents, skylight... oh my. My roofer is planning to do 4-5ft of this valley with copper and add ice water shied up to 9ft to minimize or eliminate chance for water coming into the house.



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Old 02-06-2015, 03:24 PM   #13
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Furance in insulated attic


Yeah it is a problem waiting to happen. I am a meat and potatoes guy and stay away from houses with complex roof lines etc. Nice simple convetnional sloped roof and no valleys. The architects love to create these homes but have NO idea where to install the HVAC units or run the vents or vent it etc and just leave that to the poor HVAC guy who stuffs it where he can. Not the best way to design or build a house.
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Old 02-06-2015, 04:04 PM   #14
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Furance in insulated attic


Exactly right. Am not too happy that my architect/builder didn't warn me about this. To make matters worse, this is facing North! My next home will be a rectangle :D

Quote:
Originally Posted by yuri View Post
Yeah it is a problem waiting to happen. I am a meat and potatoes guy and stay away from houses with complex roof lines etc. Nice simple convetnional sloped roof and no valleys. The architects love to create these homes but have NO idea where to install the HVAC units or run the vents or vent it etc and just leave that to the poor HVAC guy who stuffs it where he can. Not the best way to design or build a house.
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Old 02-07-2015, 01:17 PM   #15
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Furance in insulated attic


That roof looks like a beautifully designed snow drift catcher!

Does any of that insulated ductwork that shows in your pictures go into that attic area? Whether they insulated the attic to R38 or R1000, if they ran minimally insulated ductwork through there the attic's insulation value doesn't mean much unless the ductwork is very carefully buried underneath it.

And please tell me that the two PVC vents that are showing in the picture of the roof are not the intake and exhaust vents for your furnace. If so, find the installation book for your furnaces and check the pictures and description on how they are supposed to be terminated.

Just as a curiosity note, what size is that furnace? Btu's/hr input. The size of the venting makes me think BIG. And I'm not seeing BIG ductwork on it's discharge. The sizes of the insulated supply ducts is?

Saw the other pictures of your house and the amount of ice coming from that valley, If you haven't already, I'd re-post in the builders area also and get some suggestions from the guys that build houses for a living. There are some serious issues that I think are caused by more than that furnace.

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