digitalmaster wrote:

Ventilate when the outdoor vapor pressure P(Ta,RHa) is less than
the indoor vapor pressure P(Ti,RHi) in the table below, and try
to do this with warmer outdoor air when the house needs heat
and cooler outdoor air when it needs coolth.

50% 55 60 65 70 75 80%

50F .1836264 .201989 .2203516 .2387143 .2570769 .2754395 .3121648
52 .1976689 .2174358 .2372027 .2569696 .2767365 .2965033 .3360371
54 .2126632 .2339295 .2551959 .2764622 .2977285 .3189948 .3615275
56 .2286653 .2515319 .2743984 .2972649 .3201315 .342998 .3887311
58 .2457342 .2703076 .2948811 .3194544 .3440279 .3686013 .4177481
60 .2639307 .2903237 .3167168 .3431098 .3695029 .395896 .4486822
62 .2833194 .3116514 .3399833 .3683152 .3966472 .4249791 ..481643
64 .3039678 .3343646 .3647614 .3951581 .4255549 .4559517 .5167452
66 .3259469 .3585417 .3911363 .423731 .4563257 .4889204 .5541098
68 .3493307 .3842637 .4191968 .4541299 .4890629 .523996 .5938621
70 .3741957 .4116153 .4490348 .4864544 .523874 .5612935 .6361327
72 .4006234 .4406858 .4807481 .5208105 .5608728 .6009351 .6810598
74 .4286993 .4715692 .5144391 .5573091 .600179 .6430489 .7287888
76 .45851 .504361 .550212 .596063 .641914 .687765 .779467
78 .4901487 .5391635 .5881784 .6371932 .6862081 .735223 .8332528
80F .5237118 .576083 .6284541 .6808253 .7331965 .7855676 .89031 "Hg

We need a little computer to do this automatically, eg a Smart Vent!

It turns out there are now two Smart Vents, a floating flood gate and
a ventilation fan controlled by a vapor pressure difference...

That may work very well for your area..but is impractical for the deep
south(middle Georgia).

NREL says w0.0112 from October through May in Macon, on average...

Nick