I built a whole house fan system using a old squirrel cage blower from the original 100000 btu furnace after replacing it with a 75000 carrier Infinity furnace. I'm guessing the old blower I used is around 1600 to 2000 cfm? I installed a 18" hart and cooley diffuser With 24" of 18" pipe above it. Then used 18" insulated flex duct to route the air to the blower mounted in a 16ga steel box.


After checking the amp draw on my old blower I see its pulling 6 amps and it's the wrong static pressure. I would like to replace the old blower with something like this.


http://www.atrendyhome.com/qcwhhofan...hannelid=FROOG



Since I have the grill and flex already installed all I need would be a fan and damper set up. Can anyone recommend where I could buy one? Or what specifications I should look for? My home living space is 1500 sq feet.

Thanks

What exactly is the problem with the system you created? Maybe it is working fine.

I'm gonna guess that the problem is the power draw well north of 500watts (typical for furnace blowers) that's the factor.

For that level of power consumption in a humid climate you'd do better to cool 1500' house with a tiny 500W air conditioner controlled with a humidistat, since the latent load (humidity) is generally several times the sensible load, and reducing the RH from 70% down to 45-50% has a bigger effect on comfort than dropping the temp from 80F to 76F. Whole house fans in humid climates suck in cooler but more humid air, which doesn't necessarily generate more more human comfort beyond the breeze against bare skin, which is more economically achieved with a ceiling fan. Whole house fans are better at providing COMFORT mostly when the sensible loads are primary (drier climates), &/or the outside air temp is significantly below the interior air temp (~10F or greater delta-Ts). When the outside dew points are well into the 60s it's usually better to stick with dehumidifying the conditioned space rather than sucking in the fog.

18" duct is far more restrictive than typical for a whole house fan - it can be done, but of course you pay the price in more watts to push lots of air through smaller openings. The CFM you are getting is also probably higher than you think.

I use all of these - table top fan, ceiling fans, whole house fan, dehumidifier (basement), individual room AC (bedroom mini split), whole house AC. Each one has its appropriate time and place.

Can an attic fan make a significant difference in cooling a home? I see they have solatube solar powered fans or I suppose a hard wire fan w/ a switch.

We had a whole house fan when we lived in Michigan and it was effective until it got really hot or humid.  My wife suffers from allergies so opening up the house was more of a problem than the temperature where we lived.  The louvers in the ceiling did not seal well and it made the hall where it was located cold in the winter.  I think ours was a prop fan, not a squirrel cage.  It was not very quiet although the acoustics were not really a problem for us.

I think about 6 air changes/hour is needed to be effective for cooling and these fans are designed to operate at low static pressure (i.e., no ducts).  They pull air through open windows and pressurize the attic, so sufficient attic vents are needed....at least that was how ours was set up.

I am skeptical that a blower from a furnace will move that amount of air.  When you say the SP was wrong, what did you measure?  What is the fan motor rated for in watts or amps?

Bruce

There's a large body of evidence from studies at the FSEC and at Texas A & M that attic fans have only VERY marginal effects on cooling power use, and may even be detrimental if if there isn't a very tight air seal between conditioned space and the attic (the fan sucks air-conditioned air up from the living space, cooling the attic, but heating the house via infiltration from outdoor air.)

That said, with a decent air barrier between attic & conditioned space you can sometimes save a handful of percent in cooling power cost with a solar-powered version.  See:

http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/

The amount of cooling you can achieve this way will be reduced by higher insulation values in the attic.  If you're at R30 or better it's unlikely that putting the money into a solar (or other) attic fan is a better deal or more effective than even a small boost in R-value.  The sited study above had R19 blown fiberglass in the attic,   which typical in the southern-US.  In mixed or heating dominated climates the insulation levels tend to be higher.

Thanks! Then it will be more cellulose in my attic this summer!

Just for clarity, we have two comingling threads here:

Whole house fans to cool the occupied area (pulls outside air through open windows in the occupied portion of the house and exhausts to the outside to and/or through the attic).

Attic ventilation fans to lower the attic temperature (pulls outside air into the attic through soffit or gable vents and usually exhausts through the roof).

Bruce

I open the windows, that uses less energy.

Dana, is it advisable to install an attic ventilation (roof) fan to limit the attic temperature depending on the amount of ceiling insulation? I my case, I have measured summer attic temperatures near 120F. With the ceiling insulated to ~R-50, is there any value in installing a thermostatically controlled attic fan to limit the attic temperature? That is, will the A/C cooling cost savings be greater than the cost for running the fan?

Purchase a Solar Powered one .

Never mind, Dana, I read your referenced paper. The only value, it seems, would be to protect those items stored in the attic that might be vulnerable to elevated temperatures.

Better late then never.  I apologize..

The problem with the old furnace blower is it was designed for a residential duct system with allot of restrictions unlike the single 18" flex duct I have used. I have not measured the static pressure but I am sure it is not correct.  I had to restrict the exhaust end of the system because the squirrel cage would literally spin very fast yet not move any air. I increased the static pressure with the restriction and the system moved air quite nicely.  What I didn't consider at the time was how many amps it pulled. 7 amps.. Almost 900 watts.  The airflow also becomes turbulent sometimes.  Its annoying when the quiet air flow turns to a roar and then back quiet again.  I only use this system when the nights drop down the lower 60's leaving it on all night.   But it still only decreases the inside temperature 8 degrees higher then the low outside temperature. Then I close the windows at 8 am until maybe 6 pm as I turn it on.

The fan on the link in my first post pulls only 3 amps and moves 2250 cfm.  I think that fan would move more air pulling less amps then my current furnace blower so I hope to find one.

I agree a undersized split AC system would also work Dana1.  I removed a 4 ton and replaced it with a 2.5 ton which pulls 12 amps including the furnace blower.  It drops the humidity level below 40% on hot days but may only drop the temperature down to 78 without cycling. Non stop. I use this AC when the nights get into the 70's. But a AC system which only removed humidity Dana1? A 500w AC system Im guessing would be very small like one ton or something? Not sure if that would achieve enough cooling even on cooler days. And I cant find a 1 ton system which has a coil for your furnace. 

Back to the Whole house fan.  I feel it would be a beneficial way to save on your cooling cost if it pulled only 3 amps.  And it also cools your attic prolonging the life of your shingles.  But my 7 amps is to much to justify.

It sounds like your 2.5 ton unit is now fairly "right-sized" for peak loads then- runs continuously and keeps it below 80F on the hottest days, but dries it out quite nicely.

For the same 7amp load as your whole house blower you could run a ~3/4-ton window-unit (or a coupla tiny ones for optimal efficiency at night.) Unlike a whole house fan, it'll handle the latent load as well as sensible loads, and the duty cycle may well be lower. For the same 3amps as the more-appropriate whole house fan you coud run a small dehumidifier(to deal with latent-loads only.) Which strategy makes the most sense really depends on what your nighttime cooling loads actually look like (latent/sensible). You may find this page of interest: http://www.udarrell.com/airconditioner_current_temperature_btuh_charting.html

Before I started retrofitting the insulation on my ~2500' ca. 1923 bungalow I'd run a single half-ton window unit in an upstairs room, keeping the interior doors to most rooms open. That was sufficient for comfort on all but the hottest days, using about the same amount of power as just the air-handler on my central AC(!). But the bulk of the AC loads here are latent, and the sensible loads light @ ~350 annual cooling degree days. (Right at this moment, it's in the low 70s outside right now, but the dewpoints are hitting the mid-60s. Opening the windows of my ~70-72F house right now would raise the RH to an unhealthy 80%+, a REAL latent load, at zero sensible load.)

Now that, sensible loads have been beaten back with higher R-values its mostly just the 500W room-dehumidifier in the basement keeping the whole house dry (rarely running over 50% duty cycle even on the muggiest of days). With sensible loads only reaching the uncomfortable range a handful of afternoons/year the tiny window AC unit is now on the floor in the attic, unplugged. (But since the house came with 2 tons of central AC I can crank it up for an hour in the afternoon and be done for the day when it's 95F+ & dew points in 70s.) Were I to resort to whole-house night-time cooling, most of the season the the dehumidifier would then have to run 100% duty cycle, and the power bill would go up. (I've both measured & calculated it.) In my location, at my shading-factor/insulation levels/air-tightness, in a typical year there are at most ~20 days where a whole-house fan/nighttime-ventilation cooling scheme would be optimal (and then, not by much over mechanical dehumidification + HRV on those very same nights.) On those nights I can just open a few windows. Clearly, YMMV.

From the net:
HEED demonstrated that fans were one of the most
important features for improving indoor comfort. It
also allowed the architects to demonstrate that whole
house fans introduced natural cooling at extremely
economical costs (it costs just $ 36 per year to run this
whole house fan). Using HEED’s graphic plots, the
architects were able to make a convincing argument
that more than any other feature, whole house fan
would help keep indoor air temperatures comfortable during the hottest months of the year

Clipped from http://www.energy-design-tools.aud.ucla.edu/papers/ASES-02-2.pdf , perhaps?

So, if you lived in that location (Los Angeles county CA), where the latent loads/dew points are very low, and the nighttime temps in summer are moderate, at the insulation & infiltration levels modeled in those affordable housing units, most of the time a nighttime ventilation scheme using whole house fans is quite beneficial.

So what would that have to do with the rest of the US, particularly the eastern half, where the latent loads are typically (and quite UN-like most of CA) several times the sensible load, and whole house fans will often raise the indoor humidity to unhealthful (even uncomfortable) levels, much of the time?  (not much, sez me)

It comes as no surprise that nighttime ventilation & whole house fans are a real cost savings with significant benefit in dry climates.  While coastal CA is nearly ideal for cooling with nighttime ventilation strategies, the same strategy would be a sticky moldy disaster on gulf coast, and not-so-great on much of the eastern seaboard, or even mid-latitude midwest.  What whole house fans are clearly not is a one-size-fits all solution independent of climate (particularly humidity.) 

The number of days/year they're ideal in my zip code makes them a less preferable option, not worth the up-front expense.  Clearly YMMV. 

If you're not sure, look at climate history (wunderground.com or similar) summer-month dew-points & nighttime lows to get a clue.  If the dew points tend to be in the 60s or higher on the higher temp days, whole house fans are likely to raise the latent load more than it lowers the sensible load for net degradation in indoor air quality due to high humidity, and the cost of removing the humidity will be several times what it costs to simply air-condition or dehumidify from the get-go, keeping the humidity at healthful, comfortable levels.

Prescribing general practices based on site-specific modeling clipped at random from the web just doesn't work.  The details count (sometimes they're everything.)

Both a whole house fan and powered attic ventilation pay for themselves (but not by much) in SE Michigan (humid, but quite limited by the fact that little AC is used anyway) according to HEED 3.0. But yes, it will vary; get the free HEED software and load in your own climate data and try different things.