Whole house fan - solution that does not require opening windows?

auroraborelisJune 4, 2012

Our local code requires us to install a whole house fan, which circulates air from outside to inside. This is a great idea as I expect when combined with a well insulated and well sealed house will drastically reduce both our heating and AC bills.

However, our builder was explaining about how you have to open the windows for the system to work. Does anyone know of a whole house fan solution that is automatic and doesn't require going around the house and opening/closing windows?

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where is it code to have a whole house fan?

it would be either to run the whole house
fan or to run the a/c. not both at the same time.

best of luck.

    Bookmark   June 4, 2012 at 5:12PM
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Califonria, San Francisco Bay area.

Do you mean you would need a seperate air intake for the whole house fan, and it wouldn't be possible to use the duct work for the rest of the HVAC?

    Bookmark   June 4, 2012 at 6:44PM
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It really isn't possible to use the rest of the duct work.

Code is going to dictate some things. Like does the fan blow out (most do). You would want an intake with a filter.

I was guessing your area by the requirement and your description of climate.

I would think the HVAC ductwork is too small and too fragmented by there maybe a solution. But what you probably need is a large duct - something on the order of 20 inch round - attached to a grill - again very large. There would be a damper that opened with the negative pressure created by turning the fan on. A more elegant but expensive solution would be a motorized damper that opens when the fan is on.

This fresh air intake could be attached to your HVAC but may not be a great idea. The way the HVAC is setup is that there are large intake ducts and then an air handler with a fan and then your output ducts. You don't want the HVAC fan to run and if it doesn't, it will be a significant obstruction to airflow. And you need massive airflow. Imagine the outside particles getting into your airhandler and all your ductwork. Now you could come up with some way of bypassing the airhandler with a motorized damper but you are getting complicated and expensive.

So simple and inexpensive requires an extra grill for outdoor air intake. But really simple involves opening a window. In the overall scheme of things, a motorized window that opened when the fan is on might be the most appealing both in cost and aesthetics. I found one for $600 which isn't cheap but start putting in a duct/grill/damper and your are getting close anyway.

I am wanting a similar thing mostly to filter the incoming air. We can open windows a lot of the time but a decent amount of time the pollen is a big problem.

    Bookmark   June 5, 2012 at 5:59AM
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Below is the new green building standards code for California. It took effect in 2011.

The document is not well written and somewhat confusing. The way I read it a whole house fan is not a mandatory requirement. If you do install a whole house fan, the louvers must have an insulation value of 4.2.

If you are going to have an central AC system, then I don't see the need for a whole house fan.

Here is a link that might be useful: California 2010 Green Building Standards Code

    Bookmark   June 5, 2012 at 9:26AM
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This was a cross post from the home building forum as it was suggested there to post here. The link is below for reference

david_cary - thanks for the explanation! It makes a lot of sense the way you explain it. We may just live with opening windows, but it seems so silly when nearly everything else is no automated!

Mike_home - thanks for the link! Our builder just told us it was required, I didn't look up the code (could our county have it's own requirement?) In either case, I do think the whole house fan is a great idea, it is practically free with the rebate. Regarding AC versus whole house fan, with our climate it is often cooler at the end of the day outside and warm insides so a whole house fan is a great solution. Hopefully things will be different in my new, well insulated house (my current home has no insulation in the walls at all) however I often wish there was a way to run an exterior fan to cool things down instead of AC (opening the windows takes much longer, and it lets in pollen and dust).

Here is a link that might be useful: Cross post on home building forum

    Bookmark   June 5, 2012 at 9:57AM
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We had a whole-house fan in my parents house. It was about 4' in diameter and was located in the attic. There were louvers at the opened to a central hallway. During the winter, we went up to the attic and placed insulation (foam) on the louvers. In the spring, we removed the insulation.

And yes, we had to open the windows.

    Bookmark   June 5, 2012 at 4:44PM
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The whole house fan would work well when the humidity is low and the temperature is dropping in the evening. When the humidity is high, it may become more unfortable to pull in warm humid air. Today's houses have more insulation, are much tighter, and AC units are more energy efficient. There will be some savings, but perhaps not as much as you think. You will have to experiment once you move in.

    Bookmark   June 5, 2012 at 6:24PM
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Low humidity and evening temp drops pretty much describe California climate. I've been thinking about installing a whole house fan here for a few years; am just surprised it is not more common given the high cost of electricity for A/C.

There were articles in the local papers just a few days ago that whole house fans will become mandatory in new construction in California in revised standards that will take effect in 2014. Other changes to the standards include hot water pipe insulation and solar-ready roofs.

    Bookmark   June 5, 2012 at 6:52PM
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Interesting... I wonder if it is currently required in my county now, my builder just said it was so we didn't double check. Though, required or not we would still install one as we are in the perfect climate for it.

As the above poster mentioned, low humidity and cool nights describe our summer whether perfectly. By 7pm every night it is much cooler outside than inside, and it is never humid! I know someone else who has a whole house fan in our area (and a well insulated house) and it can really replace a lot of AC use.

I was just concerned with pollen and dust, though I suppose we will just deal with it in exchange for the practically free cool air.

    Bookmark   June 5, 2012 at 7:42PM
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Annie Deighnaugh

A whole house fan is drawing air out of the house. The air has to be drawn in from somewhere to replace what's being taken out. We had one and decided to try to run it without opening a window thinking it would draw cooler air up from the basement. Next thing we knew the house started smelling like soot! The fan was actually drawing the air down through the chimney to replace the air drawn out.

We used to wait until the outside air to be cooler than inside and then we'd turn the fan on, opening windows in the rooms we were in and that room would start to cool immediately. If the fan is in an attic space then during the day when it is hot, you can open an attic window, shut the vent to the living space and let it vent the attic to keep the house cooler by keeping the attic cooler.

    Bookmark   June 5, 2012 at 8:03PM
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Thanks for the explanation Annie. I understand how they work, it just seemed to me that in this day of home automation someone may have come up with a whole house fan solution that doesn't require opening the windows and letting the pollen filled air into the house (and needing to be home to open the windows).

Some of the suggestions seem to point towards their being an option for some sort of Macguive'd solution, however, it would be unlikely to meet code requirements, and also add too much cost.

Oh well, it was just an idea.

On another note, I wish I had one in my house right now, it wasn't even that hot today and there is still a huge temperature difference between inside and outside right now, and putting a fan near a window doesn't work quite as well.

    Bookmark   June 5, 2012 at 9:35PM
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Laura - If you have the pollen issue, I would definitely try to put in a filtered entry point.

A/C energy use is interesting. If you cool the house while it is 75 degrees out and there is no humidity to deal with, you would be surprised at how little energy it uses - which is why whole house fans are actually an old house idea - ie before air conditioning.

Also with a modern house and some attention to window orientation, there is not much warm up during the day.

I am in NC. It was 83 yesterday but reasonably dry. A few open windows in the AM and the house cooled to 73. By the afternoon it was 77 with an Eastern facing wall of windows (and some West). No A/C necessary. If it is 90 and I have to run the a/c, it often adds $1-$2 a day to our bill.

While that $1 would be $3 in your area, your days of 90 are very limited. If you design the rest of the house right, your high tier use might not even be there much of the time.

A/C can be a total energy hog but with a tight house, low e windows, a reasonable shading of E/W windows, a modern high seer unit and low humidity - it really isn't.

CA is a little over the top with requirements and just because it is required does not make it a good idea. Many people would rather pay the $20 extra a month for electricity and stick with the pollen-less a/c use. I mean $20 a month for less dusting - compare that to the $400 we pay for house cleaning....

    Bookmark   June 6, 2012 at 5:45AM
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"Next thing we knew the house started smelling like soot! The fan was actually drawing the air down through the chimney to replace the air drawn out."

This is known as back drafting. This is dangerous situation if you have a gas fired hot water heater or furnace within the living space. You could be pulling carbon monoxide gases without realizing it.

People living in houses with no AC tend to keep the windows open throughout the summer. It was rare a whole house fan would be turned on with the windows closed. But in a house where there is AC, the windows will be closed when the AC is operating. There is a greater chance of turn on the fan without opening the windows.

For safety reasons I suggest the switch for the whole house fan be placed out of reach of children. I also think it is a good idea to use a timer switch in case the fan is left on and someone closes the windows.

    Bookmark   June 6, 2012 at 9:26AM
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Annie Deighnaugh

Good point. Fortunately it was summer and the chimney was only used for the furnace, which was off.

We used to keep our windows shut in the summer as by shutting them early in the morning, we'd actually keep the worst heat of the day outside. Then when it cooled off outside more than inside, we'd open the windows and turn the fan on.

But they do nothing for humidity, so we'd be damp and cool instead of damp and hot. Nothing like A/C!

    Bookmark   June 6, 2012 at 2:16PM
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I think what you're looking for is similar to a make-up air system for a kitchen exhaust fan. There are devices out there that are designed to take in outside air, filter it and deliver it where needed (kitchen in this case). I think what you would be doing is delivering it to your HVAC system (assuming you have one) so that the air would come through the AC vents already in place. The size of it (ductwork) would depend on the size (CFM) of the attic fan. You would also use an electric damper to open it when the attic fan was activated, and its own air filter.

    Bookmark   June 6, 2012 at 3:01PM
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weedmeister, in an ideal world, that is exactly how I would like the system to work!! Though, I'm assuming this isn't a typical setup?

    Bookmark   June 6, 2012 at 5:23PM
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Definitely not typical. Also a whole house fan will be several times larger (like 4000 CFMs vs 1200 CFMs) than a range vent fan. Otherwise you could just use your range vent as a whole house fan.

I suspect most of the make up air systems already in use will not be big enough.

Remember, there is nothing "typical" about a whole house fan in new construction. There just isn't that much of the country that benefits from such a setup.

    Bookmark   June 6, 2012 at 7:32PM
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We are quite a ways off from actually getting quotes from local HVAC dealers, at the moment we were just brainstorming ideas and we were curious about the options/process. We starting with google of course, but as it has been mentioned, it is just not that common a system to have much useful information out there.

On the cross post I had on the home building forum someone mentioned automatic windows, and that really might be the best solution, and I guess we can live without the filter :(

One a side note, after thinking more about this I realized how great it would be for my parents to install a whole house fan in their house (even though they have central AC) and they may go ahead and do it next month. It would drastically reduce the frequency with which they use their AC.

    Bookmark   June 7, 2012 at 7:16PM
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RE: Posted by mike_home on Wed, Jun 6, 12 at 9:26

Thanks for this! I think we just experienced "back drafting." Woke up this morning to our carbon monoxide alarm. The fire department detected very high levels of CO in our basement. However, all the appliances and boiler are running correctly. We think the problem might have been the whole house fan -- we had it on, but only the windows on the second floor were open. Apparently it got cool enough last night for our heat to turn on. We think that caused the fan to pull carbon monoxide back into the basement. Fortunately everyone is OK.

    Bookmark   June 16, 2013 at 9:51AM
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Tight house construction, central AC, and whole house fans are a bad combination in my opinion.

I am glad to hear your family is OK. If it were my house I would disconnect the whole house fan. The small energy savings are not worth the risks.

    Bookmark   June 16, 2013 at 9:59AM
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rmw621 - are you still using your whole house fan? Just curious if you have had any other issues?

I am still planning on installing one, actually quite excited about it due to how hot our current house is at 5pm and how cool it is outside by 5:30pm!

    Bookmark   June 25, 2013 at 6:28PM
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Automatic vents are sometimes used in conduction with evaporative coolers, but the air flows in the reverse direction. Sometimes people don't like to have their windows open because of the possibility of burglary or home invasions.

The National Weather Service and other forecasters may consider adding an element to their forecasts in some areas. That would be a prediction of whether it would be more economic for homeowners to open up and ventilate their homes in the evening low humidity, or it would be better to leave them closed up and run the mechanical cooling (low humidity).

    Bookmark   December 22, 2014 at 3:36PM
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