Quick question. I have an older house remodel in which I am taking out
the old HVAC system from under the house to install a complete new
My options to reinstall would be either in the attic which would get
really hot. I redid the roof with ridge vents down the length of all
ridges to help with this.
I could install under the house-- however, the crawlspace is really
crampped-- (I wonder how they ever got the original system in unless it
was during new construction.) Yet, there is a tendancy to get a lot of
moisture under the house.
What is your advice in this matter? Attic?? Under house?? Eliminate
the moisture problem?? Ensure I have solved the hot attic problem??
Thanks for any help.
Soffit vents? If not, your ridge vents may be totally useless.
If it's "really hot" up there, I'd look into fan-assisted,
thermostatically-controlled ventilation. I did recently, as did a
friend, and it works great in terms of avoiding roasting shingles and
heating house from above. In your case, you may want the fan blowing in
with exhaust along ridges.
As to where to put unit, I'd ask the installer- you may need all new
ductwork. Furnace may enter discussion, too.
Moisture problem definitely should be addressed, with vapor barrier,
ventilation, exterior swamp drainage, whatever works. DAGS on this and
await a deluge of hits.
I've owned my own HVAC business for about 28 years and think I have a
pretty good idea of what you should do.
Fix the water/moisture problem under your house, then put some vapor
barrier (plastic, 4 mil) on the ground, then put your ductwork back
under the house, use metal trunk line with metal ATDR take-offs/taps,
either flex or metal for the lines and return, insulate ALL metal
with 2" foil backed ductwrap after you screw and tape all seams.
I've done thousands of systems in middle tenn, in both attic and under
floors, unless the house is on a concrete slab, or it's a two story, no
way would I put it in the attic.
Also, about attic ventilation, I would not live in or have a home
without POWERED ATTIC VENTILATION, I've had to work in attics when the
temp was 180, after several tests I have performed with attic
ventilation, Powered Fan Ventilation more than pays for the 1 to 3
cents per hour the the fans use compared to the 25 to 50 cents the a/c
A very good site to find out more info is
You don't tell us the critical question of where you live.
If you live in the snow country, under the house would be good, because you
gotta remember, an a/c system is basically a heat exchanger- throw off heat
The fan takes the heat from the refrigeant and transfers it away, by
blowing it away.
Under the house would simply mean that all the heat you took OUT of the
house, is now UNDER the house, and we all know heat rises....
In the attic is better, but the best is on the side of the house. Away
from the house. Shaded. With a clear open view up to the sky to let the
heat rise and go away.
Also in the attic, the moisture condensation that comes out of your house
gets deposited in you attic, and if your drip pan and pipe system ever
becomes clogged up, you'll have mold, legionair's disease, mosquitoes,
bugs, insects, rats, squirrels, termites, damp, rot and falling down sheet
Installing a ridge vent was very wise; bang for the buck. Make sure now
you have soffit/eave vents to help draw the cool air from below, up to the
ridge vents to force the hot air out.
Two eave louver vents vertical at each end of the house attic is good also.
Do NOT install any of those stupid electric fans...they waste more
electricity running them than you save.
Running some of that cheap 2' panels of styrofoam vents up the sides of
your roof would also do a lot to make your roof last another 20 years (heat
kills, not sun or weather, roofs) and lower your AC bills even further.
The best desiegned house is a giant Bernoulli vent....
I think he's talking about the ductwork ... but what would I know.
Either way ... if you've got a lot of moisture under the house, then
overhead may be better. If your crawlspace is limited, overhead is better.
You'll get a lot of latent heat from the attic, of course, so if you live in
sunny climates where AC is more important than heat, you might consider
crawlspace (you can install vapor barriers, fans, etc to remove the
Contact several A/C companies in your area for quotes, ask them where they'd
install it, and ask them why ... the answers may prove enlightening.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.