I am wondering if it's advisable to circulate the cool basement air
throughout the house, using the blower and ducting from the forced air
I would need to install an auxiliary air intake into the return duct
(small house - only one return), in its basement run and cover up the
original inlet on the first floor. I would also need to figure out how
to control the blower. I don't see any of this as a big technological
problem, the question is: is it worth it?
My biggest concern is the potential for some musty smells traveling
from the basement (the usual basement smell) throughout the house.
Aside from this, it seems to make sense - take the very cool and
comfortable temp air, even on very hot days, from the basement and
distribute it throughout the house, where each level (two floors +
basement) go up in temperature by what seems like 5-10 degrees.
The house does not have central air, nor a whole house fan. I know the
benefits of the latter - let's not discuss that again - but am
interested in your thoughts of circulating the basement-cooled air.
Least of your worries...
Basements, being typically more humid and dark, are breeding grounds for
molds you wont see....till they find a food source..:)
You can do what you want. This has been talked about many times.
Your basement will not act like a heat sink, in enough of a manner to make a
difference for more than about an hour, then, the basement temps will be the
same as your home....warm.
Geothermal systems, (basically what you are wanting to do) that use nothing
but buiried pipe to remove heat from the air, can have several hundred feet
of pipe buried deeper than your basement, and still require an evap and
compressor to remove, or control humidity.
Your basement does not have the capacity.
So, in effect the underground pipe can only replace the condenser?
Sounds like a small benefit...
Mold - yes, thank you for reminding me - and I take your point. Makes
sense not to introduce it to other levels of the house.
I didn't realize the cooling capacity of the basement "operates" on
such a limited efficiency (one hour or so?).
Basement Humidity - I do have that condition, but a dehumidifier is in
place and collects about 45 pints in 24 hrs. I am converting it,
today, actually, to discharge the condensate into a sink so it will
always be in the loop (it won't shut off when its tank fills up).
I guess the only hope I had was that the dehumidifier (or two) would
be capable of removing enough moisture from the basement to dry the
air sufficiently. One DH can now maintain 55% to 65% humidity level.
The grand plan was to install two dehumidifiers that would both drain
into a sink. With two of them running, my supposition was that enough
moisture could be removed to handle both, the natural basement
humidity, as well as the additional humidity introduced by the air
intake from the rest of the house (it's a small cape-style home, 26' x
30,' two living levels + basement).
Assuming the dehumidifiers can reduce the humidity well enough and
fast enough, we are still back to the natural cooling capacity of the
basement itself; only one hour? that's a disappointing
I look at it like this: an extra dehumidifier is only about $150. With
most of the rest of the hardware (ducting and fan) already in place
and the basement acting as the cooling apparatus, this sounds like it
could work - in theory.
I am not being argumentative - I respect the laws of physics - just
trying to see if something can be done within the "gray areas" on the
On Sun, 16 May 2004 10:46:25 -0400, "*CBHVAC*"
To prove your theory open the fan door on the unit and let it run for a few
hours. I unfortunately agree with CBHVAC. After a few hours you will be
equally warm threw the house and basement. If your don't want or for some
reason cant install AC try an attic fan.
Why not just apply the $150 to a window-rattler AC for the upstairs?
That way you would be directly cooling your living space with a machine
designed to do just that?
Best of luck to you with whatever you decide. Let us know how it works
Do you have duct work in the basement? If so open the dampers and turn the
fan to ON.
If you do not have dampers then your going to have to provide a return for
the air. Pretty big one like leave the basement door open. Low pressure air
does not find its way easily through small openings. It will work to a
point. The mustiness will probably go away because of the dryer air and the
fact your moving air all of the time. As long as the basement is the same
size or larger you will get some benefit. When I use my whole house
ventilator I usually get outside temp +5-8 degrees.
It really depends on a number of factors. However it should reduce the
humidity in the basement, and that should reduce any mold production.
Note: MOST mold is not harmful. However that kind that is is very
My underground 25x25 basement never gets above 72 even with a
dehumidifier and 90+ outside , I cut in returns as you are thinking
about. I have central air and it helps balance and circulate air a bit.
A sawsall, jigsaw a closeable vent and 15 minutes are all it takes.
If you need a new dehumidifier a 70 pt Sears is quiet and operates to
45f. I just bought one. The cooling benefit depends on your basement ,
location, ground temp, size of windows , type, amount underground
and air infiltration. For the effort and cost it is a good experiment.
Did you block the return intake on the first floor or did you add new
ones in the basement and let them contribute only in the summertime?
On Sun, 16 May 2004 10:51:12 -0500, firstname.lastname@example.org (m Ransley)
Before we got our air conditioning, I just turned on the furnace fan
during the summer. It helped as the cooler air in the basement was
distributed to the first and second floors, and there was a bit of a
breeze. We then added a window unit on the second floor, and kept the
furnace blower going, and that worked even better.
SPAMBLOCK NOTICE! To reply to me, delete the h from apkh.net, if it is
Probably. Altho those furnace blowers are inefficient (300 W for 400 cfm?)
You might prefer Grainger's $73 4TM66 5850 cfm 90 W window fan mounted in
a basement stairwell.
Or open a plenum and stairway door?
You might want it on when the house is warm (eg 75 F) and the basement is
cool (eg 70 F) and off if the basement temp Tb is ever less than the house
air dew point temp Td, to avoid condensation on basement walls. Air at temp
T has Td = (T+460)/(1-(T+460)ln(R)/9621)-460, where R = RH/100. For example,
if the basement walls are 70 F and the house air temp is 75 F with 80% RH,
Td = 535/(1-535ln(0.8)/9621)-460 = 68 F, so it's OK to turn on the blower.
(You can also measure the dewpoint by stirring a glass of warm iced tea
with a thermometer and reading it when you see dew on the glass.)
You might keep the basement clean and dry, eg less than 60% RH.
stephen@ email@example.com wrote:
Exactly one hour? :-) Basements have lots of thermal mass, and the soil
surrounding them is cooler than summer air, and basements can be cooled
with outdoor air at night.
Basements can cool without compressors...
Stephen@screweduponpurpose is sometimes wrong about HVAC. For instance,
he's posted that there are no rules of thumb to calculate AC loads and
that evaporative cooling is mostly worthless.
Wow. Where does all that water come from? Maybe you need some poly film
on the floor and walls. Dehumidifiers generate sensible and latent heat.
Better to use an AC in summertime.
Even more reasonable, with a low indoor airflow (a dirty filter?)
so it mainly acts as a dehumidifier, dumping the heat outdoors...
If your 32'x32'x8' tall house has R32 (8" SIP) walls and 96 ft^2 of R4
windows and 0.5 ACH of air infiltration and a 300 kWh/mo electric bill,
its conductance from indoor to outdoor air is 96ft^2/R4 = 24 Btu/h-F
for the windows plus (1024-96)/R32 = 29 for the walls plus 1024/32 = 32
for the ceiling plus about 0.5x32x32x8/60 = 68 for 68 cfm of air leakage,
a total of 153 Btu/h-F. With 2048 of masonry surface, the basement might
have 10K Btu/F of thermal capacitance in series with a 3K Btu/h-F air film
conductance. The house might have 5K Btu/F of capacitance in series with
another 3K Btu/F of conductance. We might add these to make 15K Btu/F
in series with a 6K Btu/h-F conductor, approximately.
NREL says an average July day in Phila has an 86 F daily max and a 67 F
min, with humidity ratio w = 0.0133 pounds of water per pound of dry air,
which corresponds to an ambient vapor pressure Pa = 29.921/(1+0.62198/w)
= 0.626 "Hg. The 1992 ASHRAE-55 comfort zone has a 68 F wet bulb temp
upper limit, and 68 F air at 100% RH has Pw = e^(17.863-9621/(460+68))
= 0.699 "Hg, approximately. At the dry bulb temp T, Bowen (1926) said
100(Pw-Pa)/(Tw-T) = (69.9-62.6)/(68-T) = -1, so T = 75.3 should be comfy.
If it were 86 F for 12 hours per day and 67 for 12 hours at night in
a simplified weather world, we'd have an equivalent circuit like this
during the day (viewed in a fixed font):
86 F ---www-------- 75.3 F
|--|-->|---| Ie is the internal heat gain from
--- | electrical use... 300 kWh per month
Ie w is 10 kWh or 34120 Btu/day, or
w 1/(6K Btu/F) 2483 Btu/h, if all use happens
w over the 12-hour day.
--- 15K Btu/F
Here's a (Thevenin) equivalent daytime circuit:
Tt ---www-------- 75.3 F Tt = 86+2483/153 = 104.6 F.
w If I = (104.6-75.3)153 = 4480 Btu/h
w 1/(6K Btu/F) at the end of the day,
w Tb = 75.3-4480/6K = 74.6, max.
--- 15K Btu/F
During the day, RC = (1/153+1/6K)15K = 101 hours.
If 74.6 = 104.6+(Tbmin-104.6)e^(-12/101), Tbmin = 70.6 F.
At night, we have (approximately):
67 F ---www-----
| 70.6 = 67+(70.6-67)e^(-12/RCn)
w 1/(6K Btu/F) makes RCn = 16.6 hours
w = 15KR, so R = 0.00111
|- Tb and R-1/6K= 0.000907, so cfm = 1102.
--- 15K Btu/F
We could make this more precise with a simple TMY2 simulation...
Tired of Iraq? Do something about it. Learn to halve your energy use
while having fun with math and science.
Join solar guru Steve Baer and PE Drew Gillett and PhD Rich Komp and
me for an all-day workshop on solar house heating and natural cooling
strategies ("HVAC Nonsense") on July 9 in Portland, OR--see page 25 of
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.