3 ms·

Yeah, I understand all that, but now you're having to waste energy to condition all that volume, instead of just wasting energy overcoming the heat coming throu

Yeah, I understand all that, but now you're having to waste energy to condition all that volume, instead of just wasting energy overcoming the heat coming through the duct insulation. So I'm questioning which approach actually wastes more energy. Also, there are other options: you could install a fan to ventilate the attic, so that the temperature isn't higher than ambient outside temperature.

philwelch 2y ago
I think you’re underestimating the efficiency you get from having a well insulated conditioned space. You also mentioned mini-split systems as possibly being more efficient because they don’t “waste energy cooling all the rooms”, but that doesn’t really work because if you only cool some of the rooms in your house you just end up with those AC’s fighting a constant temperature gradient as the heat from the rest of the house rushes into the conditioned room. And if you stop fighting that temperature gradient it’s only ever because you’ve cooled the whole house anyway. Likewise, if you have an insulated and conditioned attic, keeping it at whatever temperature you’re cooling it to doesn’t have to take a ton of energy. Ultimately what this basically comes down to is that you can insulate the ceiling of your attic to a much higher R value than your ducts are going to be insulated. > Also, there are other options: you could install a fan to ventilate the attic, so that the temperature isn't higher than ambient outside temperature. I guess you could do that, but now you’re spending energy running that fan to cool the attic from maybe 120 degrees to 100 degrees, and hoping that your central AC saves enough energy from that to make up for running the fan? I dunno, it sounds pretty marginal to me, especially in terms of whether or not the fan is even going to pay for itself.

philwelch 2y ago

I think you’re underestimating the efficiency you get from having a well insulated conditioned space. You also mentioned mini-split systems as possibly being more efficient because they don’t “waste energy cooling all the rooms”, but that doesn’t really work because if you only cool some of the rooms in your house you just end up with those AC’s fighting a constant temperature gradient as the heat from the rest of the house rushes into the conditioned room. And if you stop fighting that temperature gradient it’s only ever because you’ve cooled the whole house anyway. Likewise, if you have an insulated and conditioned attic, keeping it at whatever temperature you’re cooling it to doesn’t have to take a ton of energy. Ultimately what this basically comes down to is that you can insulate the ceiling of your attic to a much higher R value than your ducts are going to be insulated. > Also, there are other options: you could install a fan to ventilate the attic, so that the temperature isn't higher than ambient outside temperature. I guess you could do that, but now you’re spending energy running that fan to cool the attic from maybe 120 degrees to 100 degrees, and hoping that your central AC saves enough energy from that to make up for running the fan? I dunno, it sounds pretty marginal to me, especially in terms of whether or not the fan is even going to pay for itself.