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Got it, so that means RH of < 60% for 75F outside... Today the RH here is 9% :).

Thanks beenthere. I haven't considered the extra dirt loading on the filter and coil, that pretty much puts an end to this idea!

True, good point. But if I could (which I can't) supply the cooler outside air right to the return, wouldn't that be better than recirculating and cooling the 80F air that is in the house?

It...

I guess I look at it analogous to a car (maybe it's flawed). They say if you get into a hot car that's been sitting in the sun, to first run the AC with the windows open, to "push out" all the...

Thanks shophound!

My original question was not so much "use the AC or a wholehouse fan?", because the latter takes too long.

What I wanted to confirm was that under the conditions I listed...

Thanks guys, this all makes sense. Regarding running a mechanical fan, yes, I know it is more efficient. But it's a large house, and when it heats up to 80F, it takes like three of four hours to...

If it's 80F in the house when I come home from work, and 75F outside and low humidity (around 20%), is there a pro or con to keeping the windows open while I run the AC to cool the house off?
...

Bad, bad, Key1, generating his own data... But please do share it :).

Ah, OK, I see what you are getting at. The key (no pun intended) word here is primary - so you are saying that Key was trying to find the primary source of restriction, or conversely, to show that...

I think I see what you are getting at, and if so, then we are not disagreeing (I don't think :) ). All I was trying to say was that if you increased your return area, you would reduce your total...

Ha, I am not so sure - I think you take the "obsession" prize :).



Hmmm, I don't understand - when you simulated adding more return, your system static dropped from 0.98 to about 0.78 - isn't...

Key, you and I seem to have the same obsession (some might say we are pathetic :) ), but to answer your direct question above, my thoughts are that your test results do not confirm that your system...

Thanks Dash, that would explain it. My Manual D is a few years old.

You wouldn't happen to have a current flex duct friction loss chart handy, would you? :). I'd like to update the equations in...

I am finishing up my efforts to "model" my existing duct system, using values from Manual D, as a precursor to trying to find the most effective changes to make in order to reduce my static.

My...

0.22" static in the return duct (without a filter) seems like a lot of resistance. I also have a high static system (about 0.9"), of which 0.25" is in the return with the filter. It drops to 0.15"...

Dan,

I didn't see your e-mail address in the profile, but I posted my e-mail in a message to you, so if you get a chance, send it over! I spent a couple of hours last night setting up the basic...

I am looking for software where I can input my as-built system, and have it tell me what static pressure I can expect with the existing ductwork and system cfm. Then I'd like to try changing some...

I am just a homeowner, but like Key1, I try to learn as much as I can. So a couple of thoughts:

First, I have no doubt that Mr. Davis has measured some 90% furnaces to be running at 50%. But I...

I'm just a HO, but it sounds like what he measured was exactly what you asked him to measure - pressure drop in the ductwork. By measuring before the filter on the return side, he measured the...

Yup, we're birds of a feather then :). I'm putting my worries about my static on the backburner for the holidays, but I'll attack it head on in January.

Key1, are you still worrying about your 0.7" static? I thought that Trane told you in their lengthy one-word answer that the 0.5" limit is without a coil, and can be increased to 0.8" when a coil is...

I'm having a hard time picturing this. These numbers would suggest that you have twice the resistance on the return side as on the supply side; i.e. your return duct and filter have two times the...

They are reasonably tight; certainly not "stretched", but also not kinked or loosely placed like I saw on many other installations.



Yes, I appreciate this concern, shophound. My thinking was...

Well, don't take my numbers too literally :). I am still struggling with the bouncing Magnehelic needle (although I just received their pressure snubber that is supposed to fix that), so I made the...

Dash,

Thanks for the reply. I see what you mean about lower static downstream due to the vanes, but I am surprised by no change in the plenum static. Does this mean that my TESP will not reduce...