Whole house exhaust fan?

[cgallery]

I have a two-story house, with an attic. The attic is accessed from my bedroom via a 1/2" plywood panel in the ceiling that lifts out of place (if you stand on a ladder). I've thought, in the past, of making a summer-time replacement for this panel which has a fan that could pull fresh air through the house and push it into the attic. The attic does have vents to the outside.

I know that exhausting steamy bath air into the attic and not outside is a no-no, as it puts too much moisture into the attic space. But I don't think I'd be doing that. In fact, the temperature of the air I'd be pushing would probably be lower than the air otherwise in the attic, so I would think that it is possible that I could have a net increase in the lifetime of my roof. The fact that it would be running almost constantly might reduce any moisture that has formed in the attic from rain and stagnant air, too.

Anyone ever done anything like this? Am I crazy? I imagine it would allow me to cool the house w/o having to run the air conditioner so much. Any suggestions for where to find a good fan to do this with?

Thanks!
Phil

[mahfuz]

I do not have any suggestions, more questions.

I am not sure I understand your plan. Are you not taking away the fresh conditioned cool air (in the summer) from the inside of the house and sending it in the attic? Where would you get those air back? Would you have door and windows open? Would it not increase your air-condition bill?
Isn't the opposite happens in the winter? Both ways you have to bring in more ait fromthe outside somehow and condition it (cool it or heat it), which would cost you more money.

[billwmeyer]

If what you are talking about is an attic fan usually called whole house fans in the stores, I have never seen one installed that you could slip out of place and back in. The require a permanent installation. Try the Home depot website and search for whole house fan. The have one for about $170.

One of these worked great in my sisters old house. It did not replace the a/c, but it delayed her turning it one many times.
Bill


Bill

[Tom Miller]

I would think even the one that Bill refered to could be installed on a moveable panel, so that you'd still have attic access. I'd be inclined to test the functionality with something you already own, like a box fan. You could mount it to a board to get it to fit into the access hole. I would think you'd want to be able to close off the opening when the fan is not running, though.

Every time I ponder these possibilities, I usually end up putting a box fan in the window. Maybe someday....

Regards,
Tom

[LCHIEN]

You mention running an air conditioner.
If you run the air conditioner, then you willbe exhausting cool air from inside the house to the attic and drawing in outside air, which will be warmer and therefore making your Air conditioning run more, not less.

The correct way of venting you attic better than it is now would be to put a powered gable fan in or at least a thermostatically controlled roof fan in.

your attic will then be at a temperature lower than what it would be if the sun shone upon it with no ventialtion (running the temperature up) and reducing temperature loss thru the ceiling.

[Tom Miller]

I'm pretty sure he's talking about something that will help pull in fresh air (through open windows), on days that he'd otherwise have to run the A/C to be comfortable. Is that right, Phil?

This is a subject that resonates with me especially this time of year.

Regards,
Tom

[dlminehart]

The whole house fan is useful primarily in the evenings, when outdoor temperature has dropped below that of the air in the house. During the heat of the day, the outdoor air is usually hotter than that in the house, so you'd not want to exhaust (relatively) cooler indoor air and replace with hotter outdoor air.

An attic fan, which sits in attic wall or ceiling, ejects air from the attic rather than from the house. If your attic floor is well sealed, the replacement air comes from the vents in the attic itself rather than from your house. Keeping an attic well ventilated is a good idea, summer or winter, as it prevents excessive heat buildup in summer (which can shorten roof life and radiate down somewhat into the house) and prevents moisture buildup in winter (warm humid air rising up to lower surface of cold roof, condensing, and causing moisture damage to underside of roof, possibly dripping on attic insulation, etc.

Attic fans, however, require energy (i.e., we send more heroes to the Middle East). Better is to put proper vent holes in attic, soffets plus ridge line or wind-powered turbines near the ridge. Then, you can let the warm air rise to do its own work.

[uncle al]

Try this site for some ideas. http://www.atrendyhome.com/nequcowhhoat.html

This is a pricey install, but it will give you some ideas, perhaps.
I installed this in my home near the beach, and love it. I installed a single fan, the smallest one,, and it is plenty for a smallish 2 bedroom house (1700 sq.ft, three level). I don't have A/C since we are on the coast, but people with A/C who have this unit use this all the time in the evening ( with the A/C off).
The HD fans are pretty good, too. and cheaper. The problem with just a fan is some sort of damper to stop hot air from moving through the fan when the unit is off. This install has spring loaded louvres, and a very quiet air intake for install in a bedroom area.
The HD fan will be quite noisy, something to consider.

This unit has a soft rubber strap which it hangs from and "floats" which insulates it from the joist to stop vibration. There will be a lot of resonance if it is firmly attached to a joist or similarly

[cgallery]

Uncle Al and Tom Miller nailed it on the head. I wanna use this instead of having to turn the A/C on. I would leave some windows open so it could draw the cool air into the house during the evening. I live one mile from Lake Michigan, and the temps drop her starting at about six in the evening. So the days can hit 85F, but drop to 65-70F during the evenings. Uncle Als suggestion is pretty much right on target, but I was hoping to do something less expensively. Someone else suggested trying a box fan, and I think that makes tremendous sense. I'm going to pick on up and mount it to a piece of plywood and see how it works.

One thing I didn't take into account is noise. I suppose Uncle Al's suggestion is pretty quiet.

Thanks for all the input! My biggest concern was pushing air into the attic (on its way out of the house through the attic vents). Sounds like that isn't an issue?

Thanks,
Phil

[LarryG]

quote:Originally posted by cgallery

My biggest concern was pushing air into the attic (on its way out of the house through the attic vents). Sounds like that isn't an issue?

I wouldn't go so far as to say that, and will second David's remarks about making sure the attic has adequate ventilation. Most don't. Some nice big vents at or near the ridge line would be best.

(You're a woodworker, right? Maybe build some cupolas, if they'll fit the style of the house? That's how hot air was exhausted in the days before a/c, when whole-house fans were commonplace.)

Eave vents alone are okay for cross-ventilation to ward off moisture problems, but if you don't give the hot air a place to escape up high, where it naturally wants to go on its own, your fan will sit there and labor inefficiently as it tries to cram still more hot air into a place where no more wants to go.

If vents near the ridge won't work, vents in the gable ends (assuming there are gable ends) can work too, especially if the house is aligned with the prevailing breezes.

[JimD]

Phil,

In our house in Pittsburgh, Pa, I had a removable whole house fan on the attic stairs. I put the stairs in a box and added a hinged door on the top of the box to help with insulation. There was a 2x2 foot removable panel that was insulation in the winter and a fan in the spring and fall. I put a thermostadt on the fan with a relay to turn to fan off at the temperature the thermostat was set at. The fan plugged into an outlet right at the top of the stairs and there was an electrical switch in the stair box to turn the fan on or off. Worked fine. It helped to avoid turning on the AC for a month or six weeks. I wouldn't worry too much about the noise. It isn't terribly quiet but it's also a white noise that we adjusted to pretty quickly (but then the fan wasn't in our bedroom either, it was in the guest room).

In our Kansas house, we had a whole house fan but it was the typical in the hall louvered arrangement. That one had a timer so you could set the fan to run for a couple hours after you turned it on. In Omaha, it was a fan in the hall with a flat panel door you could shut and the timer to control the fan was on the back side of the door (so you couldn't turn the fan on without opening the door).

In the right climate, I would have one now. Unfortunately the climate in SC does not lend itself to whole house fans but in many parts of the US they are a good idea. I like a thermostat rather than a timer but I would definitely put one or the other on. In the spring and fall it's easy to wake yourself up because it's gotten too cool in the house if you just let it run all night.

Jim

[cgallery]

Okay Larry, I'll make sure I have enough vents. And Jim, you describe exactly what I'm going to do. I just need to find the right fan now.

Thanks!
Phil

[BillW]

In response to JimD's post. I would not recommend letting it run all night. In fact, many whole house fan manufacturers warn against this. The fan creates a big draw throughout the house with fresh air circulating to every part of the house including the attic. If a fire were to start it would spread much more quickly with the assist. With the fan running in the evenings while you are awake and would be aware of a fire quickly not a problem, but one would not want to be asleep and have this happen.

I've thought of putting one in myself, had one growing up, and just haven't made the move yet. Think it's a great idea.

[uncle al]

cgallery
If i were doing it over again, I think I could duplicate the installation of the web site I posted earlier by buying an HD fan, and attaching it IN THE ATTIC (not in the access space)with some sort of floating, flexible strap strap that isolates the unit--something like weatherstripping or the like that is strong but flexible. Then put the unit near the roof vent way out of the way and attach flexible A/C ducting (10" is what worked with mine and fit perfectly on the fan shroud and I think it would on the hd unit, too). Then all you have to do is cut a hole in whatever access vcent area you want,connect the ductwork (10 or 20 feet should do it) and presto, it is done.
The cost of doing that, as i recall, was about $40-$80 for the fan, depending on capacity/size, about $30-$40 for the A/C ducting, and a few bucks for the suspension stap and vent cover. Probably $200 would do it easily, and be veryclose to the unit I bought for twice that amount.
But mine was good, so it is simply a choice of simplicity vs cost.
Mine is VERY quiet, but the "home made" unit ought to be pretty good, too.
Good Luck.

[JimD]

I saw a tip one time where they recommended isolating the box the fan is mounted on using the foam insulation they sell to insulate water pipes. They stapled this to the underside of the box the fan was in so that the foam was between the fan and the house framing. It might make things more quiet but, as I said earlier, my experience has been that the fan noise did not bother anybody since it is pretty low pitched and constant. Suspending the fan off the roof rafters is another idea - I wish my heat pump in the attic was suspended this way - but you would need really large HVAC duct to make this work. You need AT LEAST a 24 inch fan to move enough air to cool the house by bed time and a 36 inch fan is better. Using a big enough fan lets it run on lower speed where it makes less noise. I don't remember seeing 36 inch ducting but I haven't really looked either.


Jim