I just searched this forum for "Whole House Fan", but I didn't find much about them (except this and this).

I'm curious to hear what experiences you all may have with these simple and relatively inexpensive devices out in the real world.

Here are some pictures and a basic definition of the type of fans I'm talking about:

4.7.12 Alternative Systems - Ventilation Cooling (2013 CA Energy Efficiency Standards)

The CEC also maintains a list of models approved for sale in California. Does this list adequately represent the state of the art?

Or are there other emerging whole-house ventilation technologies that home professionals ought to know about?

For this discussion, let's try to not confuse an old school "Attic Fan" (which isn't designed to ventilate a conditioned space) with a "Whole House Fan" (which is).

Don't hold back!

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Roderick,

Your experience is a good one and you are right about finding the best system for each home's unique needs. 

Tamarack makes an excellent product but it is a bit costly on a dollar per CFM basis.

Their motorized and insulated damper was the only game in town until Invisco brought out their thermally broken dual damper that is available motorized but works will with gravity and costs less. 

Invisco also created the SmartSpeed(tm) - the world's first automatic speed control. Your customers can't find a more efficient system. 

WHFs are ideal for the bay Area and Sacramento valley because of the sudden temperature drop.

I used to install Tamaracks until the Airscape came along around 2004-5.

The customer service at that time was so bad at Tamarack that I never went back - they may be better now as they are still in business.

Have you installed any Airscapes? http://www.airscapefans.com/ - they have got the remote controls  working properly and have good multi speeds and other accessories as well as online tech. http://www.airscapefans.com/products/Shop/Natural-Cooling/Whole-Hou...

I haven't yet found anything that compares favourably to all the Airscapes - they are well made - strongly constructed. If you are not using an A/C much the energy savings on an A/C upgrade are minimal (as long as the unit and duct leaks are sealed) and the cost of a changeout high - plus solar is taking off here as California is the start up guinea pig for solar instal corporations trying to make it big so 25 watt fans at low speed becomes a sales point once people understand the low CFM principle for cooling the shell.

Making a set of customized closing insulated ceiling doors for closing after use would work with some of the others but there might be a lot of maintenance wear and tear and eventual leakage from improper usage

I am a whole house fan 'Fan'- though I have never had one of my own. I've been in houses that do have them and have always thought they were great. After reading 3 pages of comments I've decided: yes, I still like them for Midwestern Missouri homes as long as: Attic Sealed properly with Insulated Dampers with Plenty of exhaust area. I'm on the fence as to how much Value- "comfort and economics" per Dollar is achieved.

Thanks to everyone who gave their 2cents on the subject.

Scotty

My parents built a split-level house in the '60s that had a large, belt-driven whole house fan with louvers in the ceiling of the 2nd floor. It was right beside the pull-down attic stairs. In the '80s they had AC installed (in the attic) and one of the returns was in the same hallway ceiling as the stairs/WHF. They rarely used the WHF as there are few nights here that are cool enough (and dry enough) where the fan improved comfort. Their second floor was extremely uncomfortable in Winter (Mid-Atlantic state). A couple years ago my father and I removed the stairs (created an insulated/gasketed hatch panel) and created a R-36 foam box to cover the entire WHF. That and adding additional attic insulation, sealing some gross leaks and some duct sealing made the upstairs much more comfortable.

The take away for me is that WHFs are mainly dependent on climate (my brother/sister-in-law have one in the Bay area (no AC) and it works real well for them), proper attic ventilation to match the fan flow, and - a topic that has not been voiced here - neighborhood security. If you live in a home where the open windows are available to home invaders (and this is becoming a very likely scenario in all places, not just urban) then the reduction in cost of operation vs AC is much less valued than the security of using AC. If you are using a WHF to only cool off the upper-floor(s) at night (again, maybe for security reasons), then you probably need a much smaller fan capacity (to match the input area) vs the "whole house"; maybe a window fan exhausting air while opposite-room windows admit outside air will work just as well and be far less costly, invasive, and impacting to your pressure/thermal shell. It all depends...

Well put David.  Horse and buggy used to be a primary transport.  The world has moved on.

Good point about security - there are ways to make windows secure as the openings are small if more than one windows is open.

Another is noise. WHFs need open windows so noise can be a problem.

However people in cities who live on main streets who open the front windows for ventilation may get better sleep if the air is drawn by a whole house fan from the back of the house where it is quiet outside.

Years ago I put a 1,000 cfm in a 2 story 4,000 sft Victorian with no attic insulation - the ground floor stayed cold all summer anyway because of tree shade but the second floor was hot and noisy - I told them I did not expect big results especially before the insulation was installed.

They had instant 'magic' results and a quiet nights sleep for the first time in ages.

Nice work with the box - do you have any photos?

Thank you, David! There are a lot of costs to whole house fans, and I've become less of a fan of them (no pun intended) as my Building Science knowledge has increased. Here are a few that come to mind for my climate in Cleveland:

  • Substantially increased stack effect in winter due to leakage
  • Loss of control of thermal envelope - brings in moisture at night, allergens, etc.
  • Possible IAQ issues - My house has a 'C'  OUTDOOR AQ rating from Air Advice, just south of me they have an 'F'. Is that the air you want to bring in?
  • Still running basement dehumidifier - an AC would tackle this task - what does this cost?
  • Moisture has to be removed the next day - if you turn the AC on the next day, all that moisture has to be removed - at what cost?
  • Mean radiant problems - the sun warms up the building materials in the walls and attic, will outside temps be low enough, soon enough to help bring down those temps?
  • Humidity concerns - what if it rains and jumps humidity, are you going to watch for that? What if dewpoint jumps to 70? Are you going to switch to AC? An AC can maintain a comfortable RH regardless of what's going on outside. No clammy feelings if it's right sized.
  • Security concerns - houses with AC have lower insurance costs because windows are closed and locked usually

WHFs were a good solution when we didn't have AC. We now have efficient ACs. Too cheap to buy an AC? Get a WHF, but accept the consequences. They are indeed a horse and buggy. Air seal the attic and use window fans, it works in my 1835 home (with no AC except a window unit in the bedroom) until outside temps go over 80. I still have some mean radiant issues then, though, the wall may be hot from the sun, which an AC would have helped with throughout the day.

A 'fixed' house with controlled air leakage and decent insulation and a small, right-sized AC running can keep humidity levels down in the entire house. How about we educate people and show them the way? I'm having nice initial success doing just that. 

BTW The YouTube video of the WHF cover is a box my crew built about 3 years ago when I was still contracting.

Finally, as I've learned in the past year or two, I've decided my house is too expensive to fix and I'm looking to move so I can fix my house in the same way I recommend to clients.

Thank you Nate Adams,

Thanks for taking the time to carefully write up the issues with Whole House fans from 

a building science perspective. with all the pros and cons.

Much appreciated.

Jan Gravemaker

Energy Auditor  Seattle

Stop Squeezing it, There's NO JUICE IN THAT ORANGE!

Funny tweet from Summer Camp:  "A system is fundamentally better if it's more Simple, Repeatable, Reliable, and Lasting" - J. Wells

  • Simple?  (teach psychrometrics, CO safety, open and close windows, deal with noise, dust, condensation and safety issues)
  • Repeatable?  (see simple..)
  • Reliable? (As reliable as the weather man)
  • Lasting?  (everything about this approach assumes we should make the outdoors in.  It is the opposite of what Building Science is all about, which is creating comfortable, healthy, durable shelters from the outdoors).  

“The great enemy of truth is very often not the lie--deliberate, contrived and dishonest--but the myth--persistent, persuasive and unrealistic. Too often we hold fast to the cliches of our forebears. We subject all facts to a prefabricated set of interpretations. We enjoy the comfort of opinion without the discomfort of thought."

JFK

Yet the unmeasured "savings" wives tale persists.  Dogmatic belief being tightly held on to.  Not a single case study to prove cost/benefit.

@ Tedd - Respectfully, sir, I see no indication here that anyone is intending to "lie" or perpetuate myths. Instead, I see colleagues from different parts of the country sharing their informed and HONEST opinions. Frankly, that's all I had hoped for.

Clearly Whole House Fans are not for everyone / everywhere. But as I, and others here have indicated, in some hot dry climates (especially the marine-influenced zones where most people in California live), the temperature can really cool off at night. For >25 years our family's been using a WH fan to take active advantage of this natural ventilation resource that's available to us.

Still, this exchange has given me plenty to think about beyond my own limited anecdotal experience with WH Fan technology.

We have no A/C, but in the summer friends often remark how cool our house feels, because we have a decent envelope, control our solar gains with triple-wall cellular shades, and charge our mass overnight by opening some strategic windows (thanks, stack effect). If the forecast high is going to be over 90F, we just run the WHF for ~20 minutes in the morning (to super-charge the floors and pre-chill the attic) and for ~30 minutes at night (maybe as much as two hours when we know it's going to be over 100F for >3 days). During heat waves, we've learned to pay closer attention to our timing, open the closet doors, and other tricks to ensure the mass is fully charged.

My wife is the self-appointed fan-master. She watches the weather report, the pollen count, and the indoor/outdoor thermometer, and runs her own proprietary algorithm accordingly. It might sound a little over-deliberate, but for us it's become as easy and routine as brushing our teeth. It also makes us feel more in touch with the seasons (which may sound strange coming from a Californian, but hey, it's all we've got).

We've never missed not having an A/C (not since we replaced 64sf of west-facing glass upstairs), except for maybe a few evening hours during the hottest week or two of the year. But for us, that's just a good reason to go out for a walk or drink a glass of wine on the deck until the fan can catch up.

And at ~$45/month peak electric (PG&E Tier 1 ~$0.147/kWh) if somebody forgets to close a window and we overheat, we can still afford to just take the whole family out to dinner!

Meanwhile, our neighbors live in a flop plan of ours (1986, 2-story, 2200sf), and sadly their A/C seems to run day & night, all summer long. For us, the noise of their A/C is probably a bigger "comfort" complaint than any we've ever have with our own indoor temperature or IAQ. (Funny what starts to matter as we age.)

I suspect that our adaptation to our mass radiant conditions (vs. air temperature) and our anticipation of the temperature swing are both key to our perceived high comfort with this admittedly low-tech cooling system. To this point, I recall Danny Parker remarking that his SF Bay Area friends operate their home similarly, which, when visiting from Florida, he finds uncomfortably TOO COLD for summer evenings. To each his/her/zir own.

I realize our climate and our behavior are atypical (everyone's is), but I'm curious where the cross-over point for this technology really belongs (particularly now that sealed, insulated, variable-speed, and sensor-controlled models are coming onto the market). The few formal technical assessments of these devices that I've seen to date strike me as a good start, but inadequate, and I suspect probably too conservative to estimate their true potential when installed and used properly. I'm encouraged that some others in other climate zones are curious about this too.

If anything, this discussion proves that we still have a long way to go before "home energy pros" are in consensus about what measures to recommend to a public even less informed than we are.

Thanks everybody for another spirited discussion!

Roderick,

Sorry - no photos. But it was similar to many other projects easily found. I used multiple, overlapping layers of 2" polyisocyanurate (2 on the sides, 3 on the top) glued together with urethane construction adhesive (I also used duct tape to hold the panels together so the adhesive could set up properly). Side panels were foamed/caulked/sealed to the existing ceiling joist areas around the fan base; top panel was partially inset into the side panels (the first 2 polyiso layers) and also had door weatherstrip at the joint of the uppermost polyiso layer and the side walls (just in case someone in the future wanted to re-use the fan). The box structure was large enough to contain the entire fan/motor/belt drive assembly.

Thanks  

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