HVAC advice - picking a whole house fan

[yoink 321]

*specifically, the high-velocity type used to suck cool air in through windows at night and vent out of the attic space, rather than the low-velocity always-on ones.

Any HVAC folks out there with recommendations on how to pick a whole house fan? Are the any better or worse brands, or things to avoid?

Is the sizing / airflow just based on the space of the house?


Any advice gratefully received!

[BillyVance 34]

Bill Eisele is the man to answer your question. He's on here from time to time. Hopefully somebody alerts him to this thread and you'll have your answer.

"Mediocre people don't like high achievers, and high achievers don't like mediocre people." - SIX TIME National Champion coach Nick Saban

[Calvin19 0]

problem solved.

-SPACE-

[billeisele 122]

interesting question, never "sized" one

let's figure this out: seems like you'd want air exchanges but not necessarily a huge breeze, it depends on the volume of the house, the number of windows you'll open, the ability of the attic vents to handle the flow and the hole in the ceiling for the air to pass thru

what I'm saying is that the attic vents will be the smallest (area) of these items and they can only pass a certain amount of air without significantly raises the air pressure in the attic, ie a 50 HP blower won't do more than a 10 hp blower

one that is too large will create a lot of noise with air whistling thru screens, etc., and you'll start sucking bugs and stuff to the screens clogging them up

I'd open a bunch of window to have low velocity, high volume at the windows

mine is an old industrial circulation blower, about a 30" wide fan, it sits on top of the attic access pull down stairs

luckily the internet solves everything, there are calculators to determine what size fan to use, the one I used sized the fan at 9-12 air changes per hour, that's how many times the volume of the house is changed per hour

air changes per hour = house volume / fan cfm = x, 60/x = air changes per hour

the minimum changes per hour is about 6, but again the critical factor is the square footage of "free space" attic ventilation, google this stuff and you can figure it out

Give one city to the thugs so they can all live together. I vote for Chicago where they have strict gun laws.

[TEB6363 0]

Great Info so far.. But too technical for me.. I have owned two houses with fans and installed a few more with friends.. So, looking at "what works"

Pick a fan you can get locally from a distributor or even just Home Depot..

Get a BELT DRIVEN Fan.. Usually they advertise direct drive fans with a lower CFM for small homes (I had one of those).. WAY Too Loud - Especially in a small home..

The belt-driven type generally turn a larger fan and more CFM..

Pick a fan that comes with Multi speeds and timer.. Some come as a package and some can be wired on a 2-speed switch.. This make it GREAT to adjust a lower CFM for night and letting it run and then you can crank up the power in the am for a couple hours..

Make sure you have a good/open space to install the fan. I had one in the small house hall - great flow, but way to loud.. This house has a fan upstairs, I had to move it into the laundry room (adjacent to the central hall), but is still central to the house and we keep that door open any way..

Lastly - VERY IMPORTANT.. Have enough Vents OUT of your attic to let the air pass!!! I'm choking the performance of my fan a bit because I went with the standard attic side vents and under the eve vets.. You need to have X?? Square feet of vents depending on your fan CFM... So, Add some vents if you need them.. I actually get a little draft blowing from some light switches with the fan on.. Not bad, but I should fix this if I ever want to get ambitious..

Hope this helps.. Not a lot of calculations, but has worked well for me and some friends..

Oh Yes. This is a Two person, sometimes three to get it done safe and easy..

I LOVE OUR FAN.. Ran it this morning and every day we have cool temps in the AM...

Once the plane takes off, you're gonna have to land - Might as well jump out!!

[yoink 321]

Thanks guys! Some really helpful stuff here!

[Croc 0]

If you have a gravity type vented gas water heater you may have problems with it when the fan is on. The fan creates a negative air condition inside the house. Under these circumstances the water heater will not vent. Used to be a fairly common plumbing call (CO alarm going off--utility tagged water heater) but those type of fans are rarely seen any more.

"Here's a good specimen of my own wisdom. Something is so, except when it isn't so."

Charles Fort, commenting on the many contradictions of astronomy