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Spend on duct blaster or upgrading from R-8 to R-12 on ducts?

1910duplex | Posted in Mechanicals on

I asked the contractor I have chosen the questions that were listed here

He said that code is R-8 for the insulation on the ducts, and there would be a $600 upcharge for R-12. 

That seems like a lot of money, and I wonder if the payback would be there, especially since at least in the next ten years, I expect it will only be used for a/c (we have a natural gas boiler, and we have no minisplit system downstairs, but are trying to future proof if we want to get off natural gas some day).

He would charge $400 for duct blaster, which we were planning to do, but most recently he said:
 based on previous tests, if the system cannot meet the leakage test, we continue to seal until it does hold. Since we started doing duct blast tests, the first few failed miserably and we learned how to install to pass, and since then, no failures.

So do you think we should do the duct blaster instead of the extra insulation in zone 4a (code is R8 in 4, R12 in 5 and up)? Bite the bullet and do both? Skip the duct blaster since he says they’ve figured out how to install better and spend on the extra insulation?

The attic runs about 2 degrees hotter than the currently unairconditioned upstairs in the summer, as we have 2 inches closed cell foam against roof-deck/gable walls plus r-23 rockwool and 1.5 inch polyiso furring on rafters. (4a climate)

Sometimes it does get to 90 degrees upstairs, and therefore 92 or even 94 in attic.

We are not initially planning to use this system for heat, though we are buying the Daikin Aurora so it could more or less keep up with the need in the winter if we one day added minisplits to the downstairs and stopped using our natural gas boiler/radiator system.

In the winter, when it’s 32 degrees outside at 8 a.m., the attic is in the upper 50s as the second floor is 63 degrees.

So — how much difference would there be in our power draw be if we upgrade to R-12?  If we don’t pay them, is there a a diy solution to add r-4? 

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