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JDale 07-18-2012 03:57 PM

Success - Comfort Up, A/C Bill Slashed
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First, thanks to everyone giving advice on here. Getting the knowledge before starting a project is so empowering to a new homeowner like me.

My South Louisiana home- built circa 1968- was unbearably hot during the summer months. It is about 1850 sq. ft., all one level, and completely unshaded. The roof has black asphalt shingles, had a 17 year old condenser unit (3.5 ton) and the inspector told me the attic Ďmightí need more insulation. It has two gable vents on the front part of the house and several ridge vents. When things started really heating up, I put a thermometer in the attic (read 138 deg. F on a hot July afternoon), and the ceiling over my bedroom read 106 deg. F with an infrared thermometer. With the A/C constantly running, it was impossible to cool the place below 83 deg. F. in the afternoon. I couldnít stand the discomfort and knowing that I was spending a fortune on electricity that wasnít doing any good.

Where to start? I knew that double-paned windows were very popular to reduce heat gain; so too were solar attic fans, radiant barriers, spray foam insulation, super high efficient HVACs, etc. It would be great to do all of these things, but I was on a tight budget with this new (to me) house and the problem was urgent.

When I read up a little on building science, I learned that heat gain in houses like mine and in my area occurs primarily through the roof, so that should be my starting point. Back in the day, my house probably had brown wooden shingles, some type of can vents and louvered soffit vents (in addition to the gable vents). Wooden shingles donít absorb as much heat as asphalt and 'breathe' more than asphalt to allow better heat escape. Asphalt is much less expensive and perfectly fine, provided the rest of the roof system is functioning. I found that my few-and-far-between soffit vents were partially covered over with vinyl siding, which prevented cool air flow into the attic and hot air out the ridge vents. The roof is 7 years young, thanks to Hurricane Katrina, so Iím lucky there is a roof at all and completely understand the oversight in light of the probably crushing workload of the roofers during that time. To address the ventilation problem, I:

- Expanded the soffit vents (more or less continuous) and replaced all the solid vinyl pieces with perforated ones. In the attic, I installed soffit baffles to ensure airflow (~ $300 for soffit pieces, staples and a saw)

- Installed a thermostatically-controlled powered attic vent (not too powerful, otherwise it would depressurize the house below and draw up air conditioned air). I decided against solar powered, since they shut off in the late afternoon/evening, just when you want to replace the superheated air with cooler outside air (~ $110)

I revisited the insulation problem and discovered that I only had about 3-4 inches blown fiberglass (R-12 at best) and my bedroom's ceiling (the hottest part of the house) had no insulation at all. I learned about air sealing and spent a majority of my time on this overall project sealing all the ceiling penetrations I could reach. It turns out it was easier to do this due to the sparse insulation. Itís also really important to see what youíre doing, so I installed several lamps throughout the attic. To insulate properly, I:

- Sealed all wall top plates, around the supply HVAC vents, electrical and plumbing holes, etc with cans of spray foam or calk. (~ $200 for materials)

- Sealed the ductwork that I could reach with foil tape and mastic, then replaced/repaired the duct insulation (~ 150 for materials)

- Sealed the chimney for now (damper was broken open when I bought the place). (~ $20 for materials)

- Installed radiant barrier by stapling under the rafters. The data looked promising on radiant barriers in Louisiana so thought Iíd give it a try. I didnít cover the entire roof area, but maybe 75-80% of it (~ $300 for materials)

- Finally, a friend helped to blow an additional 7 or 8 inches fiberglass insulation with a machine rented from the hardware store (up to about R-30). This was one of the easiest parts of the whole project. It was tempting to jump right to this step, but it was very important to fix the ventilation and air sealing problems first. (~ $600)

The last piece of the puzzle was probably the largest contributor to overall success and most expensive, yet the results wouldnít have been near as dramatic had I not completed all the steps above. I replaced the 17 year old condenser unit and evaporator coil (10 SEER to 13 SEER and 3.5 ton to 4.0 ton). Not top of the line in terms of efficiency these days, but the old unit developed a leak in the condenser and bit the dust completely. I also hooked up a programmable thermostat to go with the new equipment to save while Iím away. (~ $4000)

Ok, now that itís Summer again, I can really see the results of my ~ $5700.00 capital investment project. Most importantly, the house stays cool even on the hottest afternoons. I could keep the thermostat at 76 or 75 and the thing cycles on/off beautifully. I estimated the energy used by the HVAC system by subtracting the estimated kWh for everything else (since I have a gas furnace and the HVAC hardly runs during the winter down here, the winter months served as a benchmark for this; generally you donít use the HVAC when the average outdoor temperatures are about 65 deg. F). I back-calculated the data from the time I purchased the house in 2010 until today. Also, I plotted the average daily highs for each of those months vs. the HVAC energy consumed. Overall, Iím currently using about 40% of the electricity to run the HVAC compared with the last two years. The 60% savings amounts to about $52/month over the year and 5700 kWh per year. Thatís a 9 year payback period, but worth so much more in terms of comfort!

In the future I will look into completing the radiant barrier, new windows & doors, wall insulation, solar panels, etc., but for now I donít think I couldíve done better in terms of bang for the buck. If it hadnít been for all the great information on here and elsewhere online I would not have figured all this out. The knowhow for each step and the order of operations was critical. Thanks for reading this very long post Ė Iíll post some additional pictures of the project in another post. Hope it helps someone else!

Marty S. 07-18-2012 05:15 PM

Very nice! Did much the same to our house and it helps a bunch. Hot as all get out this year with many days at or near 100 degrees and last months electric usage was 628 KW. Right now it's 99 and the air is cycling on and off at first stage(it's a 2 ton 2 stage)keeping the house at a comfy 75 degrees with 45% humidity. Got to love it!

ionized 07-18-2012 06:41 PM


JackDidley 07-18-2012 10:03 PM

Good job. :thumbsup:I replaced a 1.5 ton 10 seer with a 2 ton 13 seer last fall and started insulating my walls. Latest E bill was $18 less than the same period last year. Not much until you consider we had 10 days at 100*F last month compared to mostly low 90*s and no 100*s last year.

tima2381 07-19-2012 09:15 AM


Originally Posted by JDale (Post 968939)
I put a thermometer in the attic (read 138 deg. F on a hot July afternoon)...

- Expanded the soffit vents

- Installed a thermostatically-controlled powered attic vent

What did this do for attic temps?


- Installed radiant barrier by stapling under the rafters.

And this? (Especially this.)


I didnít cover the entire roof area, but maybe 75-80% of it

Is it hotter in the uncovered areas? Or is the attic pretty much a uniform temp?


The knowhow for each step and the order of operations was critical.
Did you reassess after each step? I'd be interested in those results, especially attic temps before and after the radiant barrier.

JDale 07-19-2012 01:51 PM


It's difficult to separate the effects of the added ventilation vs. the radiant barrier since I made all of the modifications during the cooler months between Fall 2011 and Spring 2012. It isn't practical now to seal all those holes to run the experiment. That said, the pitch of the roof over the hottest area in the bedroom/back of the house was too low to install the radiant barrier under the rafters and still have space to crawl around with the insulation blower hose. Consequently, I haven't placed any radiant barrier in that location (I plan to lay some out over top the insulation). So this area now has ventilation and insulation comparable with the rest of the house, yet still remains hotter. Also, the ceiling temperature is a couple degrees higher than the rest of the house, indicating that the radiant barrier is in fact helping to maintain lower ceiling/inside temperatures.

As far as the attic air temperatures - they reach 115-120 in the afternoon now, a drop of 15-20 degrees. I will do the experiment of placing the thermometer in different locations around the attic to see if the air temperatures are uniform whether or not it is under the radiant barrier. I will try to 'tent' the thermometer with aluminum foil to get an accurate air temperature reading, as the radiant heat may raise the thermometer independent of the air termperature. This is probably the main point of the radiant barrier though - to prevent the insulation temperature from greatly exceeding the air temperature (in the same way a black asphalt driveway gets hotter than the air temperature unless it is shaded).

tima2381 07-19-2012 02:12 PM

Thanks, I started a thread on radiant barriers a few days ago and am very interested in your results. I think we have pretty much the same situation, though I only have a couple of things left to try as I explained in my thread, with a radiant barrier having the potential to help the underinsulated R4.2 ductwork as well as reducing the heat load on the insulation. Sounds like you got a good overall improvement so congrats on that!

JDale 07-19-2012 03:49 PM

Thanks, yeah I just sort of threw every solution I could think of at the problem and hoped something would do the trick. The heat and high bills are enough to make a guy go crazy. Thank goodness you can at least keep the house pretty cool as it is while you tweak things. I'd opt for the radiant barrier if I were in your shoes. It would certainly reduce the attic air temperature a little, but most importantly the surfaces that are exposed to the radiant heat, including the duct and ceiling insulation. I'll let you know how my additional experiments go as soon as I'm able.

jpc 07-20-2012 02:48 PM

Hey Jdale, curious about which radiant barrier you went with? and from where? thanks

FrankL 07-22-2012 10:50 PM

Nice job. How about planting some shade trees? This could help too.

FrankL 07-22-2012 10:53 PM

The cost of R-22 and R-410
Dupe post. Sorry

ionized 07-23-2012 09:22 AM


Originally Posted by FrankL (Post 972166)
Nice job. How about planting some shade trees? This could help too.

Trees large enough to shade the sides of the house are great. Near the Gulf of Mexico, big trees hear the house are very scary.

JDale 07-23-2012 09:43 AM

jpc - I went with the 48"x125' rolls of Reflectix radiant barrier off of Amazon. I think that was the best cost per sq. ft. To make stapling easier, I cut pieces that were about 50-52" across so that I could staple the sheets to three rafters at a time (24" on center). Rolling large sheets out would have been much faster, but access wasn't the greatest, I had a lot of trusses/braces to work around and I was doing the whole project by myself.

Trees would be great! They are a fine long-term strategy that I will certainly look into. Not sure about the cost:benefit after factoring in storms. Living down here comes with its risks.

jpc 08-02-2012 12:20 AM

Hey thats for the info.sorry took so long for me to see it. BTW good job

FrankL 08-02-2012 01:09 AM


Originally Posted by ionized (Post 972349)
Trees large enough to shade the sides of the house are great. Near the Gulf of Mexico, big trees hear the house are very scary.

We are lucky in Florida because some of the plams hold up very well to storms and even hurricanes. I planted my own to act as a wind brake in the front of the house. A lady wrote a book about it.

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