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Whole House fans in garage

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I spoke with an A/C contractor recently about putting in a minisplit system in my 3 car garage. Needless to say the cost had me overheating!!(pun intended). His recomendation was to look into a whole house fan for the garage. The side effect would be lower energy usage throughout the entire home. I was confused how a whole home fan in a garage would help the electric bill and he stated that the pulling of the cooler air from the garage(cooler then the attic air) would push out the hot stale attic air and thus lower the energy load on the A/C system. Has anyone looked into these and would anyone have experience with them in actual use?

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My neighbors have one in the house and it does make a difference and allows the A/C to not work as hard. Although it has no effect on cooling the garage due to the type of roof design. They do draw the hot air in the house and out through the attic making the house cooler. Depending on whether your roof system is open from the garage through the house will determine its effectiveness in the garage. I have another friend who has one in his house and only uses the A/C in the extreme heat. They are cost efficient as they draw the hot air out and don't have a compressor to run. So your energy savings comes from not running the A/C as often. I've seen it be 90 degrees outside and feel like 75 in the house without the A/C being on.

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I had a whole shop fan system, which drew air up through a partially opened garage door and expelled it out through a vent in the roof. It worked great because I lived in San Mateo, CA at the time. No A/C. Draw backs? There were a few. When it is really hot outside, it turns the shop into a convection oven. So unless you live on the Pacific Coast, get ready to bake.

Second - dust that doesn't get thrown out the vent/cupola will fall back into your shop and settle down onto everything. So a whole house fan isn't a substitution for a well designed dust collection system. I don't know what the explosion exposure is, but I would not just exhaust dust filled air into your attic. I would only use a whole house fan if there was a sealed passage to the exhaust vent/cupola. I would be concerned that your ridge vent might get clogged with wood dust.

I'm in the process of installing a mini split system in my basement shop here in NC. Yes, it is expensive. It is probably over kill. But today is a heat index of 108+.

Another option is to get a professional disaster recovery fan that is used to dry out wet rugs or floors. I have a friend who uses one in his garage shop in Florida. This is the type of fan that draws air in from the side and shoots it along the floor. Don't get one of those cheap ones from the big box stores. You can rent one and try it out. He opens his garage door about a foot and sets the fan towards the rear of the garage, blowing across the floor. It draws air over the top of the open garage door, brings it down to the fan and shoots it out along the floor at great force. But again, the convection oven effect is real. If the heat index is high, break out the cookie dough. It will be hot enough to bake cookies.

Good Luck

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Air conditioners, especially the newer inverter models are extremely efficient. Mine uses 2.6 kilowatts of electricity and pumps out around 8 kilowatts of heating or cooling!

If you want comfort and a reasonably dry air, low humidity then buy an air conditioner.

I recently installed a 2.6 kilowatt split system in my lounge room which measures 11 x 7 metres, your language around 35 x 23 feet with a 12 feet high ceiling. It is brilliant. The unit is a samsung inverter aircon, cost me $1200 Australian, I bought the pipework to connect the inside unit with the outside unit for $190 ( I had to buy a 20 metre roll of twin copper insulated pipe, will sell the remaining 12 metres on ebay). I own a pipe flanging tool so installed the whole thing myself, not too hard. I hired an electrician to do the electricals, about $200. So for a total outlay of around $1600 I have an amazing machine that is relatively cheap to run for the amount of energy it is capable of converting to heat or cool. :rolleyes:

Of course, in Australia we are fully 240 volts so there was no upgrade, just runs on a 20 amp circuit.

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I'm an energy consultant and can tell you your HVAC guy doesn't have a clue. Here is an article for you to read that gets into the science behind why a whole house fan is a terrible idea. http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/38676/Don-t-Let-Your-Attic-Suck-Power-Attic-Ventilators-Are-a-Bad-Idea

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I have an powered vent that opens and closes on the west gable of my garage and a fan on the east gable, both which are on independent switches. As Vic posted in the link, I obviously don't turn them on when I'm heating or cooling as it will pull the heat or cool dehumidified air out and replace it with warm humid air from outside. I do however use them to suck the cool night air in and exhaust the heat, since even when it gets in the 70's for daytime temps without humidity it can get pretty stuffy and hot in the garage. Basically it's another option for cooling the garage and as soon as I kick on the air I leave them turned off. I have used it to exhaust fumes and pull in fresh air when doing finishing, ect., which is another advantage.

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I would not be installing the fan in the air conditioned house. My plan was to install the fan in the garage. We always leave the garage doo cracked slightly for the cat. I did attempt to take my large rolling shop fan and lay it flat in the attic access in the garage to pull some air up and out. It seemed to work but only slightly. I would imagine it's not as good as the larger whole house fans.

Also Thanks for the link to the article but it kind of wasn't the same thing. The article described attic vent fans which are installed on the roof. I'm talking about a whole house fan that installed on the rafters and would be pulling outside air from the garage. A quick read through the comments cleared things up for me.

I do however feel that it might be possible to have such a fan pressurizing the attic enough to push air into the house.

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One thing that really concerns me about this plan is that there should be a firewall between the garage and the house. Depending on the construction of the house it may be an actual vertical fire wall which continues up through the attic to separate the garage from the house or it may just be the drywall ceiling of the garage. If you penetrate the garage ceiling with an opening for a fan you also have created an ideal path for a fire in the garage to quickly spread to the house. It also would allow wood dust, solvent vapors, gas fumes, car exhaust, etc to be forced into the air space of the house. Overall I don't think it's a good idea.

It would be a fine idea if the fan output was ducted through the attic to a gable vent or out the garage side wall, but I don't think it's a good idea to just blow it into the shared attic space and hope the air will find its way out the ridge vent.

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So I installed the fan last weekend and it's made a large difference in the attic temps as well as creating a cool breeze in the garage. I ended up placing it in the center of the room. I did indeed cut through the single layer of drywall on the ceiling. I don't have a barrier wall between the garage and the rest of the house(in the attic). I did look at the possibility of a fire path but after coming back to reality I realized it's about as likely as your dust collection system blowing up from the dust particles.

If there were to be a fire the flames would have to be 8' tall in the center of the room. They would have to cross a metal Louvre that closes when the fan turns off and then they would have to climb another 1- 1.5 feet through the metal fan housing. After that they would need to either build another 8-12' in height to get to the roof above or mushroom cloud out around the fan by 6-8 feet. I'm thinking by the time this happens all the wood, gasoline, and other flammable items in the garage would have gone up in smoke. Is it probable that if I ever have to sell my house I'll have to remove the fan and re-sheetrock the attic, yup, but nothing that I can't do in an afternoon.

The install wasn't to bad at all and the fan came with it's own switches for on/off and high/low. While i was installing the fan I put a thermometer up in the attic with me(1-3p.m) and it got to a temp of around 120-125. After the install I turned the fan on high and took a shower(15 minutes) after the shower I checked the thermometer and it was below 100 degrees. Not to shabby I say

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I did look at the possibility of a fire path but after coming back to reality I realized it's about as likely as your dust collection system blowing up from the dust particles.

I think you're underestimating the speed that fire spreads in an attic space. The issue isn't flame height; it's the superheated combustion gases that create a flashover condition which ignites the entire attic. It can turn a contained garage fire into a whole house fire in a few minutes. An intact firewall will provide at least 15 minutes of protection (some up to 1 hour) which allows enough time for the fire department to arrive and extinguish the garage fire before the whole house is engulfed. It is worth considering a ducted output on the exhaust fan to a gable or roof vent to make a much safer installation. Hope the worst never happens, but it's always good to be prepared if it does.

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Ben has it right. Most fire spread is by convection of fire gases, not by direct impingement of flames. The reason why attic fires are bad are really twofold. Not only are they hard to find and extinguish, but the void spaces allow travel across the whole underside of the roof, not just a single compartment. This leads to early failure of the roof due to exposure of the trusses to fire. Fire spreads in very predictable patterns. First vertically until it is blocked, then horizontally. The smoke has two effects, it preheats surfaces in advance of the fire, and contain byproducts of combustion that can ignite when the ceiling temp reaches a high enough temperature. When you cut a hole in your ceiling sheetrock in the garage, you lessened your fire protection. That said, there are a couple of things you can do to minimize but not eliminate your risk:

-Have a working fire alarm system with remote station alerting. Install a rate of rise or other kind of heat detector in the shop to allow early detection and dispatch of fire units. (Not a smoke detector, they falsely alarm when confronted with dust.)

-Have a fire extinguisher in the shop by an exit. Know how to use it, and when to use it.

-Keep your flammables isolated and readily combustible substances like shavings and dust picked up. Lay out oily rags flat on a non-combustible surface to let them dry.

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Ben has it right. Most fire spread is by convection of fire gases, not by direct impingement of flames. The reason why attic fires are bad are really twofold. Not only are they hard to find and extinguish, but the void spaces allow travel across the whole underside of the roof, not just a single compartment. This leads to early failure of the roof due to exposure of the trusses to fire. Fire spreads in very predictable patterns. First vertically until it is blocked, then horizontally. The smoke has two effects, it preheats surfaces in advance of the fire, and contain byproducts of combustion that can ignite when the ceiling temp reaches a high enough temperature. When you cut a hole in your ceiling sheetrock in the garage, you lessened your fire protection. That said, there are a couple of things you can do to minimize but not eliminate your risk:

-Have a working fire alarm system with remote station alerting. Install a rate of rise or other kind of heat detector in the shop to allow early detection and dispatch of fire units. (Not a smoke detector, they falsely alarm when confronted with dust.)

-Have a fire extinguisher in the shop by an exit. Know how to use it, and when to use it.

-Keep your flammables isolated and readily combustible substances like shavings and dust picked up. Lay out oily rags flat on a non-combustible surface to let them dry.

There are many reasons a whole house fan is a bad idea, as I already linked to. But, definitely in this scenario it is a dangerous solution. Btw, I actually ran it by my co-worker who is a fire commissioner, also.

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Guys I appreciate your advice and will look into installing a heat detector into my homes fire detection system. The other items discussed I've already got installed, fire extinguisher etc.

The temp in the garage didn't drop a whole lot maybe 2 degrees or so. What the fan did do for the garage is create a cooling airflow. Fans don't cool the air though they simply create a breeze to get the stale air moving around. I don't run the fan all day I will typically turn it on when I get home and kick the AC down for the evening, typically turning it off after about an hour.

I thought long and hard about the possible fire risks associated with the install of the fan. In the end I decided to do it for reasons I've already stated. Is it doing what I wanted it to do? yes it certainly is. I'm not sure if it will lower the Electricity bill next month but dropping the attic temps from 120+ to 100 or lower can't be hurting and the cool breeze created by it's drawing air into the garage certainly are nice.

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One thing about keeping your attic cool is that your shingles will last longer. I've experienced what happens when an attic doesn't breathe. 20 year shingles can be cooked in a matter of 10 years instead. It causes the shingles to bake, become brittle and start to flake.

Yes, speaking from experience. Having reshingled the roof, I had a ridge vent installed and it has brought the attic temps down and in winter I no longer have issues with ice damming.

Having said that, I agree that you can never overestimate a fire's capabilities and glad to hear you're looking into increased fire protection/prevention.

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