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-   -   Correct way to handle HVAC in attic? (http://www.houserepairtalk.com/f8/correct-way-handle-hvac-attic-5676/)

pjcampo 12-04-2008 02:55 PM

Correct way to handle HVAC in attic?
 
I am in Northern NJ and the previous owner put the HVAC (gas Trane XR80 heat and A/C) in the attic. I am trying to figure out what is the "proper" way to look at the attic now. I understand traditionally you would simply insulate the attic floors with as much insulation as possible and let the attic get hot or cold. BUT...

First of all we have a full walk up attic with regular staircase and door leading up to the attic, and a subfloor on the attic joists (not exposed joists).

Second of all, with the HVAC setup up there, don't we want to keep it as cool as possible in the summer, and as warm as possible in the winter? Duct work is insulated with standard R6 insulation (flex duct). I am not sure how feasible it would be insulate the duct worth further.

On the joists of the attic floor is very old insulation from 1950?, unknown R value. Again remember we have flooring in the attic, so this insulation is not accessible.

On the walls/raftes we've got R13 and R11 respectively.

We have an attic vent fan that goes on at 110F in the summer. I crack the windows on either side of the attic in the summer. Not sure if I should cover this attic ceiling vent holeup in the winter, and/or close the windows in the winter.

The issue is that the attic is sort of half conditioned, half not. With the HVAC up there, I would think it's important to keep the temperatures relatively close to living conditions otherwise the HVAC is going to be negatively affected?

Finally I do not want to do anything too drastic, as I'd like to keep the option of finishing the attic...

So should I focus on insulating the attic rafters/walls more, or???? Close the windows in the winter?

Someone suggested I should be concerned about moisture in the attic. This does not seem to be an issue that I can see at least. Is it possible that the furnace keeps it dry? What about leaving cracks for the 60k BTU burner to get oxygen?

woodchuck 12-04-2008 08:54 PM

These systems were designed to work with the hot and cold conditions found in the attic. The duct work insulation separates the two environments. The evaporator is located outside?? where it's unaffected by the attic temp. The condenser is probably located in the insulated ductwork or in closet in the house.Moisture does need a way to escape the attic to prevent it from freezing on surfaces and doing damage.

pjcampo 12-05-2008 05:47 AM

Even with only R6 on the duct work?

So I should crack the windows and keep the attic vent fan hole open all year?

ciera 12-05-2008 05:49 AM

Quote:

We have an attic vent fan that goes on at 110F in the summer. I crack the windows on either side of the attic in the summer. Not sure if I should cover this attic ceiling vent holeup in the winter, and/or close the windows in the winter.
We had a mold inspector tell us that our attic vent fan should go on at 85. We close the windows in winter to keep out the moisture, but the vent will be covered adequately.

inspectorD 12-05-2008 05:55 AM

My advice
 
Have an energy audit done. They will look at your specific situation and give you the best advice.
Sounds like a lot of heat loss to me with those conditions. I see it all the time.
There are heat loss companies out there, or local home inspectors with infrared cameras who do them. Call your local utilities companies, they also have lists and sometimes do them for free to save energy.
Tell us what you find out.:)

glennjanie 12-05-2008 10:03 PM

Hello PJ:
My first complaint would be the flex duct. I was around in the late 60s when it came out. The manufacturer recommended that 3' was the maximum length to use. My experience shows that, as the air rolls over each little wire in there it looses its velocity and pressure.
I would want to change the duct to metal pipe with sleeve insulation on it. That would give you the same insulation value you now have on the ducts and the smooth pipe would allow the air to flow, unrestricted.
Secondly, I would make sure of where the evaporator coil (the inside one) is located and make sure there is a drain pan under it with an outside drain. A running trap at the bottom of the drain will keep insects out so they won't stop it up.
If you want to develop the attic space, I would recommend the additional insulation. However, with it being a conditioned space I would close off the ventilation. A house from the 50s (I live in one) is not sealed too tight for the furnace to function properly. A 4" vent pipe next to the furnace extended down to the level of the burner would insure plenty of air. I would also open one register into the attic to keep it a little better conditioned.
Glenn

agatto2a 01-13-2009 05:52 AM

Quote:

Originally Posted by pjcampo (Post 25759)
I am in Northern NJ and the previous owner put the HVAC (gas Trane XR80 heat and A/C) in the attic. I am trying to figure out what is the "proper" way to look at the attic now. I understand traditionally you would simply insulate the attic floors with as much insulation as possible and let the attic get hot or cold. BUT...

First of all we have a full walk up attic with regular staircase and door leading up to the attic, and a subfloor on the attic joists (not exposed joists).

Second of all, with the HVAC setup up there, don't we want to keep it as cool as possible in the summer, and as warm as possible in the winter? Duct work is insulated with standard R6 insulation (flex duct). I am not sure how feasible it would be insulate the duct worth further.

Hay PJcampo

Insulating your attic better is always a great idea. You will need to keep in mind not to make it to tight. I recommend googling attic insulation in your climate, you should get a fairly good idea of what has to be done.

On the joists of the attic floor is very old insulation from 1950?, unknown R value. Again remember we have flooring in the attic, so this insulation is not accessible.

If you insulate your rafters properly you really should not have to worry much about that. Is nice to keep the heat below though

On the walls/raftes we've got R13 and R11 respectively.

Is there batts in the Rafters? Again Google insulating an attic

We have an attic vent fan that goes on at 110F in the summer. I crack the windows on either side of the attic in the summer. Not sure if I should cover this attic ceiling vent holeup in the winter, and/or close the windows in the winter.

Winter times are pretty dry in Jersey . Cover the hole in the roof and close the windows in winter, its just giving room for the hot air to be pushed out.

The issue is that the attic is sort of half conditioned, half not. With the HVAC up there, I would think it's important to keep the temperatures relatively close to living conditions otherwise the HVAC is going to be negatively affected?

Yes indeed

Finally I do not want to do anything too drastic, as I'd like to keep the option of finishing the attic...

So should I focus on insulating the attic rafters/walls more, or???? Close the windows in the winter?

Someone suggested I should be concerned about moisture in the attic. This does not seem to be an issue that I can see at least. Is it possible that the furnace keeps it dry? What about leaving cracks for the 60k BTU burner to get oxygen?

Again -- batts for the rafters and proper insulating should help you right out. The batts leave space in between the rafters and insulation, so air from your soffett can float on in.


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