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Old 03-23-11, 10:30 PM   #1
MN Renovator
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Default Home energy audit timing and my knee wall

I was going to get an energy audit done and aim for it to be sometime in the middle of January or February when we had very low temperatures but my house has been a mess and I never got it cleaned up well enough to where I could get things away from the walls, windows, etc for a good thermal imaging without a bunch of barricading items in the house.

...but now its almost the beginning of April and the energy audit has a lead time of 4-6 weeks. If it turns out to be a month out, I'm wondering if the end of April might be too warm to get good thermal imaging results. We normally have 50-60 degree highs at the end of April so the inside and outside temperatures might not vary much, especially for the sides of the house that are exposed to the sun during the audit.

My question is, should I do the cellulose insulation that I was planning to do now and then do the audit during the summer when I'm expecting it to be 90 degrees outside? ...or should I risk a 60 degree sunny day at the end of April so that way I can get advice before taking action?

I'm having a hard time deciding because I'd like to know if there are voids that need to be filled on a knee wall and would also like to know if I can add another layer of fiberglass stacked against the current insulation on the knee wall. For insulation, the only walls that I can add insulation to without tearing out drywall and adding thicker studs and shrinking rooms(some of which are already too small) would be the attic knee wall. It has 3.5" studs with 15" centers but then has studs on the outside of that which measure 23" on center and it looks like me that I could stack extra insulation on top of what is already there, it looks like I can buy either R19 that is 23" wide or go up to 12" thick R38 stacked over the original 3.5". I'm thinking that 15.5" of insulation is probably overkill and probably difficult to install since the R38 comes in packages of 8 batts that are 48" long and 24" wide. I figure the insulation won't mind being compressed an inch of width but I'd have to build a structure of some kind to hold that stuff against the wall and I'd have to cut batts in the middle to get the extra 10 inches for each width of the insulation. It seems much easier to buy two rolls of R19 that is 23" wide that is 39 feet long. If I'm doing my math right I think two would be enough.

The knee wall is 32 feet wide, I'm excluding the section where there is a vaulted ceiling area which is hard to get to in the attic but also has two layers of fiberglass(looks like 7 inches of fiberglass) stacked on top of the vaulted section. So 32 feet of width are left that I can improve on and that section is 4' 10" high. I've got about 16 widths of 23" insulation to put in(figuring the stud is roughly an inch wide for the sake of easy math) and at 4' 10" that means I'd need about 77 feet of insulation roll. It turns out that R19 comes in 39'2" rolls on sale for $19.88 right now. So $40 of insulation and a little bit of work and I'm creating a decent barrier against the hot attic during the summer. Would this work out? I'd need to be sure that I'm not creating an air gap between the original insulation and the stuff I'm adding but are there any other things I need to look out for or does this sound good? Should I be springing for the R38 or would R19 and R11(or R13?) be enough for this section? 9.75 inches of insulation should be just short of R30. I'm planning on living in this house for 30+ years or basically until I have a reason to move and I'd like to put this insulation in before I put the cellulose in so that way I'm not packing down the cellulose by walking on it after I blow it in. I'm looking to blow cellulose to R60 and will probably have a little extra up there to account for settling and to make sure any uneven application still has the R60 thickness in the low spots.

Based on my highest summer electric bill last year of $66 in the summer and just under $70 for the highest month in January, I'd like to add more insulation so that I can heat and cool the house to a more comfortable temperature while maintaining the previous energy costs. The house is 2200 sq ft of conditioned space. At the current energy costs, I can't justify upgrading the 29 year old 76% efficient furnace and the 25 year old air conditioner(probably 10 SEER) until one of the systems breaks down, at that point I'll replace both. At least once I have a blower door test, I could have an accurate heating/cooling load calculation done and that way I can have a properly sized system in the house. Based on my runtimes in the winter, it seems that even the smallest 40k input BTU/h 95+% furnaces will be enough to heat my house to 70 degrees(21c) at -20(-29c) outside with the current insulation and levels of air sealing I've done so far but I'd like to do better. I'd probably aim for a Bryant 355AAV/Carrier 58MVB since it uses less electricity in its blower than anything else out there, is a 2-stage with the lower stage of 25k BTU/hr output and is 96.6% and to make my life even better, I now personally know someone who installs Bryant equipment so that should help with the cost. The problem is that he is the type that doesn't do load testing but I'm confident that I really don't need it for anything but air conditioning but my current 2 ton seems to do the job and 16 SEER units don't seem to come in 1.5 ton sizes from most manufacturers so I might be slightly oversized with the insulation finished but humidity levels remained low last summer and 2 tons was not oversized then as the temperature during the hottest few weeks slowly creeped up while the unit ran constantly, which is what I want as it stays comfortable while keeping the humidity down.

Thoughts on my energy audit timing and insulation plans?

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