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Is it possible that using a solar-powered attic fan would be appropriate in my situation?

Is it possible that using a solar-powered attic fan would be appropriate in my situation? Would using "Reflectix BP24025 24-Inch by 25-Feet Bubble Pack" be a good choice?

I am a southern Californian living in a home built in 1955 facing an AC and Ducting Nightmare.

I read MARTIN HOLLADAY article posted oct 26 2012.... Musings of an Energy Nerd
Title: "Fans in the Attic: Do They Help or Do They Hurt?"
"Homeowners in hot climates need to understand the difference between whole-house fans and powered attic ventilators"

When I bought my home in 1979 I never even considered that one day I would want central air conditioning. Up until that time the only air conditioning I had was a whole house fan which I used in the manner that you discused in your article. The home had a heater installed in the attic with the ducting running in the attic also.

In 2002 I decided that I was tired of being hot throughout the summer and fall. I contacted a contractor that specialized in Central air conditioning. The question of where to install it was never even considered. They installed the central air conditioning system where the heater used to be, in the attic.

Twelve years later I learned by reading Martin's article that the attic is no place for a central air conditioner.

There is not room in the house to install it in any other place.

A month ago I came home and found that the AC unit could not keep the house cool and concluded that I needed to check the unit and ducting out. What I found upon examination was that the installers did a horrible job sealing the ducting and air handler. The cold air was being blown out into the attic and was hidden from being seen because it was wrapped with fiberglass insulation.

I managed to seal the ducting connections with a high quality tape. I had to remove the fiberglass insulation around the air handler and found that it was bent. It had a 1/2" gap that the installers attempted to patch with tape and that tape had failed badly. Cold air was being blown out at an alarming rate. I managed to seal it with the same tape as I had used with the ducting connections.

My fear is that the tape will not hold up for very long and I still need to re​-​insulate everything but am unsure of what product to use.

I found a product called "Reflectix BP24025 24-Inch by 25-Feet Bubble Pack" I have been considering using it to insulate the air handler and ducting connections in place of the fiberglass insulation that was previously used.

Would this material be a good choice?

After reading the aforementioned article I learned that using any powered attic fan is not
advisable for several good reasons.

I am stuck and do not know what to do. It seems to me that using some means of keeping the attic cooler would be beneficial. Is it possible that using a solar powered attic fan would be appropriate in my situation? I do have plenty of vents in the attic roof and gables on both ends of the house. The roofing that is on the house has venting feature built into it also.

Asked by John Alberti
Posted Sep 4, 2014 6:27 AM ET
Edited Sep 4, 2014 9:20 AM ET


4 Answers

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The bubble wrap is not as good as duct insulation with R 4.2:

Answered by Kevin Dickson, MSME
Posted Sep 4, 2014 7:18 AM ET
Edited Sep 4, 2014 10:03 AM ET.


The usual solution to the problem you describe -- an air handler and ductwork in a vented, unconditioned attic -- is to install spray foam insulation on the underside of the roof sheathing, in order to transform the vented attic into sealed conditioned attic. For more information on this work, see Creating a Conditioned Attic.

If you read my article, "Fans in the Attic," you know all of the many reasons why a powered attic ventilator won't help you.

If you have sealed all of the leaks in your ductwork, that's good. If you want to install duct insulation, buy fiberglass duct insulation. (It comes with a vinyl jacket on one side.) Don't install bubble wrap, which is basically worthless. For more information, see Stay Away from Foil-Faced Bubble Wrap.

Answered by Martin Holladay
Posted Sep 4, 2014 8:35 AM ET
Edited Sep 4, 2014 10:51 AM ET.



We had to put our air conditioning ducts in the open crawlspace. The HVAC guys sealed it (but not to my standards) and wrapped it with fiberglass insulation. I went over and re-taped all of the fiberglass seams to my extreme standards and then we boxed the ducts with polyiso foam insulation to couple the ducts to the inside of the house. During our blower door test there were essentially no air leaks to the outside.

Encapsulating your attic ducts in polyiso or some form of foam board is essentially the same thing that as what we've done in the crawlspace. It isn't easy though.

This photo shows some of the process. Sealing the fiberglass insulation, foaming around the duct where it attaches to the subfloor and then attaching the polyiso foam around the edges. You can see the foam board behind the duct. All those foam board seams were religiously taped as well.

duct in process of enclosed w:polyiso.jpg
Answered by Lucy Foxworth
Posted Sep 4, 2014 10:46 AM ET
Edited Sep 4, 2014 10:47 AM ET.


Air sealing both the ducts and all of the electrical/plumbing/duct-boot penetrations to the ceiling/attic-floor plane is critical for system efficiency.

With air-sealed insulated ducts (and an insulated air handler) there is very little energy-use benefit to either radiant barriers or solar attic fans. With a radiant barrier the additional benefit of a solar fan might ~5% on energy use, with a comparable effect on peak load. See:


Purpose made FSK tapes can seal pretty well if it was all shiny when the tape was applied, but most other tapes will fail in short years in that application (duct mastic is more reliable if the surface isn't super-clean to start with.) There is no tape that can adequately seal the duct boot to the ceiling gypsum- use can-foam or acoustic caulk there, and use duct mastic on any duct boot seams.

Once you've fully sealed the ducts & ceiling (duct-blaster or blower door test verification is best, but expensive- it may be subsidized by the state/county/utility), insulating the ducts AND the attic to at least code min has a greater effect on energy use than radiant barriers. Study carefully the tables and charts on pages 5 & 6 of this document:


If there isn't sufficient clearance to bring duct & attic insulation fully up to code, a radiant barrier can still reduce the peak load by a significant fraction. Even though it has only a modest effect on total energy use it may be "worth it" (particularly as a DIY project) to tip the balance enough that the system can keep up.

But it's important to avoid radiant barriers that are also vapor barriers, since the latter can create moisture problems where non previously existed. The bubble-pack stuff is an extreme vapor barrier and not your best choice. Perforated aluminized polyester/polyolefin vapor barriers applied to the underside of the rafters would be much lower risk. There are multiple manufacturers & vendors out there- do a web search on "perforated radiant barrier"- you'll find it.

Roof/attic gains are only part of the cooling load, and after insulating & air sealing, you may get a bigger load reduction and better bang/buck out of reflective window-films or exterior shades, particularly on west facing windows, since overhangs won't shade them, and the solar gains occur late in the day when both the outdoor air temperature and walls/roof are already hot.

If adding attic insulation, use blown cellulose rather than fiberglass, since it is far more opaque to infra-red radiation coming off the roof than fiberglass. With fiberglass you would need to also add an IR-opaque top-side air-barrier to avoid loss of performance at peak roof temperatures, since the heat radiates 1-2" into the fiberglass before it is absorbed, putting 1-2" of insulation between that location and the attic air. The result is that the hottest layer in the insulation is several degrees hotter than the attic air, which means you are insulating against a higher temperature with 1-2" less insulation (!) Even 1" of cellulose overblow is sufficient to counteract this effect, but 3" is better for preserving the peformance of the fiberglass during the heating season.

Answered by Dana Dorsett
Posted Sep 4, 2014 10:55 AM ET

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