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Old 07-27-2020, 11:16 AM   #1
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Big savings by sealing and re-insulating attic ducts


Long story short, last fall I had to remove old plenum insulation and old flex ducts in the attic and re-insulate the plenum and run new flex ducts.


While I was at it I sealed the plenum with mastic and foil tape, and used R8 to replace the old R6. Found lots of gaps and bad modifications so that all got sealed up as well. When running the flex ducts I was diligent about sealing them well where they terminate at both ends.



This is A/C only, so now that summer is in full swing I got my first electric bill for a full month of running the A/C. On the bill there is a chart showing average temperature this month, as well as average temperature the same month last year. Last year avg. temp for the month was 77, this year it was 75 so a very minor difference.



This month I ran the A/C more than last year because we were home a lot more due to COVID, and I also set the thermostat 2 degrees cooler than last year.


Even with keeping it cooler and more people spending more time in the house, I used 25% less electricity than the same month last year! Nothing else in the house or our lifestyle was changed. I was very pleasantly surprised that my efforts paid off more than I expected.
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Old 07-27-2020, 11:48 AM   #2
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Re: Big savings by sealing and re-insulating attic ducts


So that won't take long to pay you for your work.
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Old 07-27-2020, 11:58 AM   #3
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Re: Big savings by sealing and re-insulating attic ducts


Nice. This is why we preach the benefits of air sealing and insulation. Keep the air in the envelope and getting it to where it needs to go...is critically important and will yield massive results as you are seeing.
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Old 07-27-2020, 12:05 PM   #4
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Re: Big savings by sealing and re-insulating attic ducts


This was just on ductwork - not sealing or adding insulation to the attic itself although I have foamed a couple of big gaps around vent stacks since it was easy low-hanging fruit. I may attempt a proper airseal on the attic someday, but it's got a lot of flooring in place and I have other projects to do first.
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Old 07-27-2020, 12:10 PM   #5
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Re: Big savings by sealing and re-insulating attic ducts


Quote:
Originally Posted by Dan1973 View Post
This was just on ductwork - not sealing or adding insulation to the attic itself although I have foamed a couple of big gaps around vent stacks since it was easy low-hanging fruit. I may attempt a proper airseal on the attic someday, but it's got a lot of flooring in place and I have other projects to do first.

I realize that. Duct sealing of exposed sections is part of our standard attic air sealing and insulation protocols.
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Old 07-27-2020, 02:14 PM   #6
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Re: Big savings by sealing and re-insulating attic ducts


Hi Dan. Assuming your numbers are correct there is more good news. To get a better percentage savings number you need to remove all other electrical uses, called the baseline. Example.
If your bill was $100 last year and then $75 this year it would look like a 25% savings. But if your baseline use is $25 then last year would have been $75 (for ac only) and this year $50. That would be a 33% savings.

To estimate your baseline look at the months when no ac was used.

Good job and do consider more air sealing any place you have access. If you have access to a basement ceiling air sealing down there will work also.

Bud
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Old 07-27-2020, 02:24 PM   #7
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Re: Big savings by sealing and re-insulating attic ducts


I didn't calculate based on dollars - that would only work if electricity rates were exactly the same last year. In my area it fluctuates, and we have the ability to shop providers for better rates, which I do periodically. I used the actual kilowatt-hours on the bill to do the comparison.


I had a home energy audit done last year by the local utility. They provided recommendations and bid on doing the work - to have them airseal the attic and add insulation (blown-in) the return on investment was something like 27 years and that's after rebates! Not worth it, but if I attack it piecemeal on my own I'm sure I can make improvements and get a much faster ROI.
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Old 07-27-2020, 02:53 PM   #8
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Re: Big savings by sealing and re-insulating attic ducts


Using kilowatt is the same when estimating the actual ac consumption. Mine was just an example.

How much insulation do you currently have in the attic and what type. I'm a retired energy auditor and usually air sealing and more insulation has a much faster payback, unless their labor was way high.

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Old 07-27-2020, 07:15 PM   #9
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Re: Big savings by sealing and re-insulating attic ducts


There's about 6" of insulation up there now - one really old layer of something that is brown and crumbly and has foil on both sides, then on top of that is some unfaced fiberglass batting that might have been added later. Their estimated annual savings for air sealing is only $22 (yes, I asked to make sure these weren't monthly savings!) and to blow 10" of fiberglass would be annual savings of $117. Approx. attic square footage of 1700. I was incorrect about the ROI time - it's only 25.9 years (still way too long.) Their cost was about $9,000 to air seal and insulate.
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Old 07-27-2020, 08:15 PM   #10
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Re: Big savings by sealing and re-insulating attic ducts


LOL, $22 for air sealing, that is funny. Did they use a blower door, it is a huge fan that mounts in an outside door frame to depressurize the house and estimate the total air leakage. That is total leakage but it gives them a reference to judge how much the attic air sealing improves. If they did a blower door test did they give you the CFM leakage number?

If no blower door test then it wasn't a real energy audit, more of a sales pitch.

What should be done is, all of that questionable insulation removes and a good vacuum job. Then you have access to properly air seal. After that either you or a company could blow in new cellulose, much better than fiberglass.

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Old 07-28-2020, 01:57 AM   #11
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Re: Big savings by sealing and re-insulating attic ducts


Hi Dan, you may want to check with the energy audit folks again. Here in Mass I just had an energy audit and they are covering the cost 100% for another layer of insulation in the attic amd some air sealing and a few other things. It usually 70%ish covered but it's 100% and was a virtual audit. Good job with the sealing you did!


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Old 07-28-2020, 05:48 AM   #12
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Re: Big savings by sealing and re-insulating attic ducts


When I bought this house, I checked the ducts and patched all leakage. No way to figure how much I saved but I am sure it added up over the 5 years I used the system. What I did see was the duct work was a hack job, done by the lowest bidder.
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Old 07-28-2020, 07:11 AM   #13
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Re: Big savings by sealing and re-insulating attic ducts


They did the blower door test. I don't have the papers in front of me but can check later. The guy was pretty thorough.


If I ever do decide to properly airseal it'll be a real pain because about 60% of the attic has flooring that would have to be taken up to do it right.
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