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Furnace in Attic Causing Problems


mpernice's Avatar
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02-03-05, 02:13 AM   #1  
Furnace in Attic Causing Problems

A couple of years ago, we had a new furnace put in our attic (crawl space). Obviously, the space is getting some heat. This is very visible seeing the snow get melted form the roof above the area. This in turn will cause ice dams.

Can I do some type of insulation? Maybe put rigid foam under the roof joists?

 
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michiganguy's Avatar
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02-03-05, 07:27 PM   #2  
attic furnace

The best place to put insulation is around the ductwork up there. Ice

problems on roofs come with the territory, when the furnace is up there.

A secondary insulation, under the rafters will likely cause more problems

than it will solve. If ice is a big problem, you would want to consider

putting ice melting grids above the roof eaves.

 
yura's Avatar
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12-08-05, 07:21 AM   #3  
yura
problems on roofs come with the territory, when the furnace is up there

I have furnace in the attic, and snow constantly melts on the roof causing all sorts of problems.
1. Is there way to address those problems 100% ?
2. If yes - how?
3. If no - what's the way to make it not as bad?

Thanks for helping

 
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12-08-05, 10:47 AM   #4  
First and foremost you must find out what is permitter by local building codes.

I would encase the furnace in an insulated utility room in the attic if I could. Not only would I make the ulitilty room large enough for proper furnace clearances, it would be big enough to make servicing the furnace easy.

You must provide combustion fresh air supply vents for the furnace, unless the system has a fresh air supply pipe. You can tell because there will be two plastic pipes going through the roof. One for exhaust and the other for fresh air. If there is a single metal flue pipe, you have to put vents on the a wall or door of the utility room. Because it takes 15 cubic feet of air to burn 1 cubic foot of gas completely.

The rule for combustion fresh air supply vents is 1 square inch for every 1,000 btu output, high and low. For example, if the furnace is rated at 75,000 btu's output, then you need two vents equal to or more than 75 square inches. One vent installed on the upper portion of the access door and the other on the lower portion of the access door. Or similar separation on one of the walls of the utility room.

 
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12-08-05, 12:15 PM   #5  
yura
I would encase the furnace in an insulated utility room in the attic

Thank you so much for responding.
This is exactly what I started thinking about, but was in doubt if it's appropriate way of doing it, because I couldn't find any reference.
Your fresh air intake comment is extremely important, since I haven't heard about that anywhere either.
I do have exauhst coming up through the roof, but there's no fresh air in one. I can see one more hole on the top of the furnace right next to the exhaust pipe one, and yet two more on the bottom right accross from the top ones. All of them except for the one with exhaust coming out are nicely plugged with what looks like manufacturer installed plugs. Could it be that my contractor was lazy and did not install fresh air intake pipe, while he had to? Here's a link to the picture where those plugged holes can be seen.

 
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12-08-05, 02:32 PM   #6  
If it were a fresh air supply port (hole) it would not be plugged.

 
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09-04-06, 05:12 AM   #7  
yura
Next step?

I followed your advice and built the mechanical room in the attic last year, and insulated it with regular in-house R-13. The "walls" consist of 2x4s and insulation - no plywood or sheetrock. We still had snow melting off the roof, frozen gutters and downspouts. Good thing we at least didn't have any seeping into the house and walls.

I checked all the ducting in the attic, and it looks like the contractor did not do a good job sealing the main duct seams. My intention now is to cut the R-6 insulation the main duct is wrapped in with a single cut along the duct, seal every seem with aluminum tape, and tape the insulation back.

1. Do I need to actually complete the walls of the mech room? If needed at all - is covering one side only sufficient? And is then plywood OK, or do I need sheetrock?
2. I hope fixing seems in the main duct will do, but if not - what else can I do? I hear about all those infra red tools that allow to find source of heat - is there way to get a hold of one? Rent? How do I find contractors that do that in my area? (mid-NJ).

 
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09-04-06, 05:45 PM   #8  
The mechanical room has to insulated and the walls and ceiling has to be covered with sheetrock. Insulation within a room that contains a combustion appliance must be covered with a fire retardant material. Plywood does not qualify.

Infar red cameras and blower door tests are good tools. The contractors that use these tools are HERS rated. If you google that you will see a list of certified HERS raters. Most of them do the quality assurance inspections on new Energy Star Homes.

While being certified and using diagnostic tools is good, a good contractor will be experienced. For example, these tools will not see the impact a bathroom exhaust has with ice dams. This has to do with the "Latent Energy of Vaporization". If your take a pound of water and raise the temperature one degree Fahrenheit from 210 degrees to 211 degrees, you only require one BTU of energy. This is because you are not changing the state of the water. However, if you raise the temperature of this same pound of water from 211 degrees to 212 degrees Fahrenheit (boiling temp), you require 970 BTU's. This is because for are changing the state of the water from a liquid to a vapor. Since you cannot create or destroy energy, all you can do is transform it, when the temperature of the vapor drops from 212 degrees to 211 degrees which causes the vapor to condense, it gives off 970 BTU's of heat.

If we apply this to a bathroom fan that discharges into an attic, you will realize that it is the large amount of heat, vapor gives off when it condenses that causes the ice dams. Rarely are these tools used when someone in the home is showering.

 
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09-04-06, 06:33 PM   #9  
If your duct work is that bad you could seal the metal then cover it with the ductboard insulation that we use to make duct for and attic.Also check on the furnace some where is a tag that will say how close you can put wood or walls to the furnace
With all the ice dams out on the roof. Id put in a snow and ice melting system for the roof and gutter. Check out Thermwire Melt its a heating cable.
Boy this post goes back

ED

 
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09-07-06, 09:37 AM   #10  
yura
As to the fire stuff - when my 2nd floor addition was finished - the fire inspector approved everything. The furnace sits on the plywood floor, and the roof over it was bare at the time. Perhaps I do need to put some sheetrock over the insulation I added on top of the furnace, but I don't understand the rest of it. I'll still look at putting sheetrock all around.

There are two bathroom fan exhausts in the attic, and they are both routed outside with the terminating vinyl caps. There's no sign of them leaking into the attic.

The second floor addition was done recently, so it does not look like there's a lot of leaks from inside the home.

I just tried to cut duct insulation in one spot, and used aluminum foil to seal one seam, and put duct insulation back with the special tape.

It might help to just go and do the same for all the duct seams (probably 2 or 3 more), but I'd rather do some HERS analysis to understand the full scope of the problem.

Thanks for advice.

 
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09-10-06, 07:36 PM   #11  
yura
I just found insulation with double foil with 1/4 in foam in the middle. It is rated R-14.5, is fireproof, and is cost effective, easy to install (staple on, etc.), easy to seal, and reflects back infra-red. Would it make sense for me to put it inside my mechanical room?

It should both - help make it better protected from fire, and provide more insulation...

If this does make sense - any tips on which one to buy? I found this one http://www.insulation4less.com/highr_FfmF.asp - anyone bought this type or from these guys?

 
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09-11-06, 12:20 PM   #12  
Any insulation helps. Dont forget dont close the furnace room up all the way . You need make up air for it. 1sq" for every 1000Btu of the furnace.

ED

 
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02-07-08, 09:58 AM   #13  
just wondering if anyone solved the ice dam problems caused by the furnace in the attic. did the radiant barrier from "insulation for less" work?

i'm thinking of using the same stuff.

thanks.

 
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02-10-08, 04:30 AM   #14  
I have the same situation with one exception,my heat source is a heat pump. How about ventilating your attic, It is of the utmost importance to have positive air-flo through your attic to remove heat build up, it doesn't matter. how well you are insulated you will have some heat build-up if you do not have attic ventillation

 
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02-10-14, 08:01 AM   #15  
Attic Furnace and ice dams

Wondering if anyone has solved this problem yet. I see many posts on the subject but no afterwards results. We added R 13 around on top of the R 6 on duct work and same in battons to floor of attic between beams as it was light there as well but this year ice dams still forming and maybe worse as before snow melted off roof completely in about 24 hours. Now taking 4-5 days [but of course colder weather this year as well.] I have water running down outside of house behind soffits and in a couple of windows.
Access to attic is only about 18" by 18" hatch in ceiling so limited as to what I can have someone take up there to use to insulate further.
Been thinking about solid gutter guards to just have water run off instead of getting collected in gutters but that would mean reinstalling each fall and might lead to too much water falling near house and possible water in basement.
This is 80 year old house. gas furnace added to attic to help mainly with heating/cooling upstairs so basement gas furnace can better handle main floor and finished basement. Really thinking about turning off the attic furnace when we have snow but boy it would make upstairs cold when it gets to negative temps. Thanks for any ideas

 
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02-10-14, 10:32 AM   #16  
I tried multiple ways to solve this and in the end
my solution was to remove the furnace from the attic.

other option was to build an insulated "room" around the unit in the attic.
(and condensate drain)

the problem is that if you keep the attic cold enough to prevent
ice dams the condensate will freeze in the furnace rendering it inoperable.

this is based on a 90% efficient unit.

 
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