I was wondering how much trouble it would be to add an economizer to
my reidential HVAC. I live in the NC foothills and the temp in the
summer varies between the 90s in the day to the 60s at night. I
currently take advantage of this by closing off some of the internal
doors in the house to partition the the air return from the rest of
the house and open some windows. This draws in the cool air and chills
the house down nicely so the HVAC usally dosent come on again before 1
or 2PM. Basically I am looking for a way to automate the daily
procedure and elimenate the possibility of rain being blown in an
open window the way it did the other night. Could this be done as
simply as having a thermostat open a damper to the return air or would
I need a special controller to do this ? The controllers at work have
inputs for indoor and outdoor temps and humidity, hydrocarbon
detectors....hopefully I want need anything this complicated or
There is a pre packaged system for residences , but they normally
incorporate a 6" or 8" round damper tied to the return air duct and
ran to an outdoor air intake ; they are designed to bring in outside
air in very tight homes and/or to be used as makeup air for bathroom
fans, kitchen exhaust, fireplaces, etc... They arent designed to do
any measurable effective cooling because youd need to bring in alot
more air than what a 8" round duct can handle to cool your home off at
night. If you added, say, a 14" round duct for outside air, it
wouldnt work unless you had a way to relieve (exhaust) the same amount
of air from the house that you were bringing in from outdoors....
plus, youd need to close off the main return duct from the house so
youd pull only 100% outdoor air in . The simplest way and very
effective way, is to use a ceiling mounted exhaust fan which
discharges into the attic while pulling air in from outside via a
window thats open sufficiently ...and installing a hood (or simular)
over the outside of the window so rain doesnt get in ; the added
benefit is that you are exhausting all of the superheated attic air
that has accumulated during the day but you need to be sure you have
adequate openings from the attic to the outside in order to relieve
re: I currently take advantage of this by closing off some of the
internal doors in the house to partition the the air return from the
rest of the house and open some windows.
We often have the temperature swings where I live, so I'm interested
in your current process. Could you explain it a little further?
Are you leaving the AC on all night but just letting the outside air
"force" the t-stat to remain off?
I assume the fan is set to on, not Auto, to circulate the air
throughout the house, right?
Please explain what internal doors you close and how you are
partitioning the air return.
Sounds like you got it figured out, Know that I think about it most
houses may not allow you to isolate the return duct to the outside the
way I can. When I got my new HVAC unit a couple of years ago it was
suggested that I relocate my return as it would be a bad thing if the
return path became blocked. Unfortunately that change would have cost
me a couple of thousand dollars so I didnt do it. I got into this
situation when I closed off a window that was between a hallway where
the return is located and my great room. My wife didnt like this
window and neither did I, now I know it was placed there to keep the
return path from being obstructed if the hall door is closed.
You may have noticed a big light come on just now!
The key phrases were "the return duct" and "my return".
I'm guessing that you have one of those big return vents - and just
the one - unlike my house where I have a return (or multiple returns)
in every room.
What we do is simply shut down the AC when we open the windows but
leave the fan running for circulation to keep the house evenly cool.
Each bedroom has a window fan that we keep leaning up against the wall
under the window and if the occupant wants to draw in even more cool
air, popping it in is a "breeze".
I have often considered installing a filtered vent in the return duct
right at the furnace so the AC will draw the cool air from the
basement into the return for recirculation, but I don't know how that
will impact the "balance" of the system since I don't want to open an
offsetting outlet in the basement.
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