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Old 04-11-2020, 12:09 PM   #1
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Combination whole house/attic fan


We just broke ground on a new house. We have a whole-house fan at our current house and love having it. I am curious if it would be a good idea to make a combination attic & whole house fan. I'm pondering placing the fan in the gables, ducted down to a shutter inside the house. Then, have a motorized damper near the fan, that opens to the attic and closes off the duct. The fan could pull from the attic or the house interior, depending on the damper position.

I know enough about HVAC to be dangerous, I have research to do, but I’m planning a very involved home automation system, so I’ll have the smart relays and temperature (indoor and outside) and humidity sensors to bring this all together.

One missing piece of fully automating this is, I think, I need a motorized shutter that can be temporarily placed in a window opening in the basement. Alternatively, we’d permanently install it in the basement wall. This would allow the system to run the fan operation fully automated.

Thoughts?
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Old 04-11-2020, 12:41 PM   #2
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Re: Combination whole house/attic fan


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We just broke ground on a new house. We have a whole-house fan at our current house and love having it. I am curious if it would be a good idea to make a combination attic & whole house fan. I'm pondering placing the fan in the gables, ducted down to a shutter inside the house. Then, have a motorized damper near the fan, that opens to the attic and closes off the duct. The fan could pull from the attic or the house interior, depending on the damper position.

I know enough about HVAC to be dangerous, I have research to do, but Im planning a very involved home automation system, so Ill have the smart relays and temperature (indoor and outside) and humidity sensors to bring this all together.

One missing piece of fully automating this is, I think, I need a motorized shutter that can be temporarily placed in a window opening in the basement. Alternatively, wed permanently install it in the basement wall. This would allow the system to run the fan operation fully automated.

Thoughts?
I would vent the attic and let it do it's own thing and seal the house fan completely two different systems.
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Old 04-11-2020, 12:44 PM   #3
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Re: Combination whole house/attic fan


I think it's a good idea, but I think you will catch a lot of flack from people. Many people say they are dangerous, or don't work. I have one that actually is ducted into the attic with 3 large attic fans and I can run 1, 2, or 3 on a timer. As long as you keep some windows open then your fine, especially in a newer, more airtight home. I love it in the spring and fall when it's cooler outside at night, open the bedroom windows on the second floor and set the fan to run for a couple hours so it turns off before it gets too cold. Creates a very nice breeze on a still night.
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Old 04-11-2020, 01:12 PM   #4
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Re: Combination whole house/attic fan


They only work well in dry climates and when the outdoor temperature is low enough.

They can cause natural draft appliances to backdraft.

To fully automate, you would need some kind of economizer control monitoring enthalpy difference.

You can actually look into some kind of residential economizer with relief instead of using a whole house fan.

Attic ventilation should be separate. Putting the attic under enough of a negative pressure can allow conditioned air to leak into the attic from the house.
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Old 04-11-2020, 06:11 PM   #5
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Re: Combination whole house/attic fan


Invest the cost of that fan and motorized vane register into more insulation. Normal attic venting via roofing ridge vent and gable end vents is adequate and with little to no maintenance, noise or electric cost. Outside air can be loaded with pollen, humidity, smoke, odors, tiny gnats, virus, dust... ad infinitum.
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Old 04-11-2020, 06:49 PM   #6
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Re: Combination whole house/attic fan


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Outside air can be loaded with pollen, humidity, smoke, odors, tiny gnats, virus, dust... ad infinitum.
this is where a some sort of residential economizer would come into play - pass the air through a merv 12 media filter and use the duct system to distribute.

switch to a/c automatically when enthalpy outside is too high.

use a programmable stat and do most of the cooling at night.
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Old 04-11-2020, 08:10 PM   #7
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Re: Combination whole house/attic fan


Some building codes require whole house fans to be interlocked with a smoke detector so the fan will shutdown on detection of smoke. A fire in a house with a running whole house fan will rip through the house faster than Grant going through Richmond. I would do the smoke detector thing whether it is required or not. I would also be concerned about appliance exhaust backdraft as mentioned above.
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Old 04-12-2020, 11:40 AM   #8
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Re: Combination whole house/attic fan


Assume you have A/C, Whole House Fan is supplemental.
Assume you are talking about using a specific ducted WHF (like QuietCool or Tamarack), not trying to adapt a gable power attic vent.
Not sure what the damper in the basement is for.

I commend you for thinking outside the box, but you want to combine a WHF with a power attic vent. Think of them as separate systems. Not sure why you'd automate a WHF unless your windows and doors are automated as well (you can however have remote or wi-fi controls). If you need a power attic fan because passive venting isn't working or not possible, it will be automatically running at times when you do want/do not want the WHF running, so there is conflict in that. The WHF moves much more CFM than a power attic vent.
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Old 04-12-2020, 01:27 PM   #9
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Re: Combination whole house/attic fan


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We just broke ground on a new house. We have a whole-house fan at our current house and love having it.
We have a WHF vented directly to attic in in the central hallway of our 1600 sf ranch big enough for a Mall and we love it. When it's on, all the curtains blow straight in. Four bedrooms, Livingroom and kitchen all with 6ft sliders. In the summer it runs all night and if the temp gets down to 65 outside, it's the same inside when we get up. We then shut it off and close up the windows and curtains. At five in the after noon when it is 90 outside it's only 70-75 in the house. When the outside temp starts dropping in the evening and the inside outside match up, we open all the windows again and turn on the fan till morn. We have no AC of any kind and no cooling bills.

P.S. You must have attic venting equal to the cubic feet of air pushed by the fan to get the most out of it. We have lived here 26 years and only had a few summers when it got to hot in August for this to work very well. So you just put up with it..... A design day for this system is 70 at night and 90 during the day. Any thing lower for either temp is gravy.
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Old 04-12-2020, 08:35 PM   #10
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Re: Combination whole house/attic fan


Thanks, everyone! Lots of good info. It seems I need to do more research. I must admit ignorance of backdraft and enthalpy. But, and assuming I'm still interested in the benefits, and regarding modifying my plans, at least to the point of separating the two systems (attic vs. whole-house fans), what about:

a variable-speed fan in the gables, no ductwork, but motorized shutters on the top floor of the house. In the summer, run the fan on slow speed, activated by attic temperature. Fall and spring, open the shutters and run the fan at medium or high. I figure the shutters might just be gravity type pulled open by negative pressure, but by fully opening them, I'm reducing the problem with negative pressure drawing air through recessed lights and cracks and whatnot in the ceilings, right?

In attic-fan mode, would running the attic fan in reverse, drawing cooler air in, help in anyway? it would push hot air out the gable vents and eaves, correct? Since hot air rises, it wouldn't push it down into the house, would it?

I will have a very extensive home automation program running, on a Raspberry Pi, so I can utilize temperature, humidity, enthalpy(?), smoke sensors/detectors as inputs in the program sequences. By the way, I am also considering running the WHF upon carbon monoxide detection and possibly by the kitchen smoke detector activation (as we're getting a half-useless range fan).
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Old 04-13-2020, 10:34 AM   #11
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Re: Combination whole house/attic fan


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I will have a very extensive home automation program running, on a Raspberry Pi, so I can utilize temperature, humidity, enthalpy(?), smoke sensors/detectors as inputs in the program sequences.
Automation is cool with all the new tech and with new toys sometimes people like to find ways to maximize what the toy does.

But, think of a refrigerator door. You can hook that up to automatically open based on heat gain within 2' of the door (so when somebody is standing there). But why would you, there are so many other variables determining when you choose to open the door and for how long you stare into the abyss.

So think of a WHF as that. It requires human decisions, but the kicker is, the whole (pun intended) purpose of a WHF is to open the windows to bring in fresh/cooler air at a time the human chooses. From personal experience, I do not use the WHF when I smell a skunk has sprayed, nor when I smell leaves burning or the neighbor has a fire going, or when the town has fogged for mosquitoes. I also choose which window and height it's open based on security or visual access and adjust the fan speed based on how much air I can bring in (i.e. draw the blinds, leave only a sliver so no one sees any nekkidness, some rooms/floors closed depending where I'm at in the house). Some nights, however cool outside and how I currently feel about the humidity (i.e. one night 62% humidity may feel ok but another may feel sticky based on my clothes or what I'm doing), I'd just rather use A/C. So maybe I am missing something, but unless you have a separate wall damper in each room (and why would you do that?) I just don't see how an automated WHF can work. But again, as a nod to technology, you can hook up the WHF control to your wi-fi if you are too lazy to walk to the fan or reach for the manual control.

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By the way, I am also considering running the WHF upon carbon monoxide detection and possibly by the kitchen smoke detector activation (as we're getting a half-useless range fan).
Again, without windows open, a WHF is useless. Just guessing without air intake from the window openings, it may pull maybe a hundred or 2 CFM, and pull it from whereever it can make it up from, not necessarily the place you are trying to exhaust. Think of the fire dept coming for a CO call, they will open your windows. So unless your windows are automated too, this feature would be useless. Am I missing something?

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and regarding modifying my plans, at least to the point of separating the two systems (attic vs. whole-house fans), what about:

a variable-speed fan in the gables, no ductwork, but motorized shutters on the top floor of the house. In the summer, run the fan on slow speed, activated by attic temperature. Fall and spring, open the shutters and run the fan at medium or high.
You have two placements of attic WHFs. One is horizontal in the ceiling, so it directly pulls air from the interior. The other is a remote fan and ducted to the ceiling. If it is not ducted, but only has the ceiling damper, then it becomes just an oversized power attic vent. You cannot control how much air it is pulling from the ceiling, it will pull the easiest path, which will probably be from the roof venting.

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In attic-fan mode, would running the attic fan in reverse, drawing cooler air in, help in anyway? it would push hot air out the gable vents and eaves, correct? Since hot air rises, it wouldn't push it down into the house, would it?
AFAIK only certain styles of fans are reversible, they are lower CFM, need ducted, you should have a filter on it, and should pull air from the exterior wall not the general attic. A typical WHF has 4K-7K CFM (and disregarding that they will never meet the CFM based on attic venting or how much window is open) you do not want to push that much air into one point of the house without the equivalent and room-specific exhaust. Mechanical ventilation overpowers natural convection of hot air rising, but yes you would initially be pulling hotter air in from the attic in this situation.

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It seems I need to do more research. I must admit ignorance of backdraft and enthalpy. But, and assuming I'm still interested in the benefits
WHFs accomplish their intended goals. You can do one, but keep it separate from venting the attic. If this is a new build, the roof should be designed for adequate passive venting first and foremost. Only if you have a hip with little ridge space or some shape of roof that does not allow high venting, should you then go to a power attic vent. So why are you intent on putting a power attic vent in from the get-go?
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Old 04-13-2020, 11:10 AM   #12
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Re: Combination whole house/attic fan


@threeonthetree excellent info and I am a little wiser for reading it. The attic fan, I figure, was a good green home investment. Keeping the attic from getting too hot in the summer should reduce cooling costs, right? Attic fans are not that expensive, so if it's saving us on the electric bills for A/C usage, its gonna pay for itself and save a lot of money over time, I figure.

This might be something I need to invent, but I thought I have seen shutters that you could place in an open window (in my case in the basement), to allow for an automated WHF operation. Also, I plan to have window sensors in my automation program, so maybe if the system sees no windows open it would not run.

But I do figure we'd see activation of the system more likely to be manually started, but I definitely want stopping it to be automated. I can't tell you how many times we wake up freezing because the fan is still running in the morning.

I'm planning out systems, and the wiring, and I am intentionally thinking about being future-proof, and maybe a goodly ways outside the box, and this attic/WHF concept is no exception. I will rein it in a little bit, but I still want the whole house fan.
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Old 04-13-2020, 12:16 PM   #13
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Re: Combination whole house/attic fan


In the right climate, with smoke detector shutdown it is a good idea. It would be complex for us because my wife has allergies. If we sucked in a lot of outdoor air she would be symptomatic. I would have to install a makeup air fan with a good filtration system.
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Old 04-13-2020, 12:33 PM   #14
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Re: Combination whole house/attic fan


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Keeping the attic from getting too hot in the summer should reduce cooling costs, right? Attic fans are not that expensive, so if it's saving us on the electric bills for A/C usage, its gonna pay for itself and save a lot of money over time, I figure.
A power attic vent can help, but it can also not provide what you intended it to do:
- If your roof has low vents (soffit) + high vents (either ridge, box, or gable), an additional power attic vent would then pull in air from the closer high vents, minimizing the low vents and leaving a lot of air at the ceiling joists in the middle of the attic outside of the flow.
- If you only have low vents it is better, but not from the standpoint of constant airflow. Only if you cannot have high vents should you rely on a power attic vent.
- If you have no vents it will just pull from any air leakage thru the ceiling and roof and not meet CFM.

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This might be something I need to invent, but I thought I have seen shutters that you could place in an open window (in my case in the basement), to allow for an automated WHF operation. Also, I plan to have window sensors in my automation program, so maybe if the system sees no windows open it would not run.
You can buy dampers and adapt to any type of system you want. So you can rig it to open when the fan is on, which will eliminate you walking down there and opening a window. In the basement you are then limited to whether the stair door is open or not. But that doesn't solve any other floor in the house where you don't want to see that damper, and must manually open the window. Having an open/close sensor on a window is fine, but what if you only want 3 out of 20 windows open and a low speed, it won't turn on? Unless it can open windows itself and determine how much to open it, then you are stuck with manual humanoid operation. If this were an industrial setting with constant known requirements, that's one thing. In a house, with different needs for people and rooms, aesthetics and security, many many variables (party going on, allergies, light rain?), it's a bit too complicated IMO to automate a WHF, not to mention the window thing. But surely give it a try if you want.

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But I do figure we'd see activation of the system more likely to be manually started, but I definitely want stopping it to be automated. I can't tell you how many times we wake up freezing because the fan is still running in the morning.
Timers are the simple fix, you can surely rig up more than that. But the windows will still be open if that effects your equation.

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I'm planning out systems, and the wiring, and I am intentionally thinking about being future-proof, and maybe a goodly ways outside the box, and this attic/WHF concept is no exception. I will rein it in a little bit, but I still want the whole house fan.
Hopefully you have the same zeal for attic venting and air sealing/insulation in your new house, which you will see more direct results in energy efficiency regardless of how you cool the interior. No disagreement here on having a WHF, just don't combine it with a power attic vent and think thru what part of it's use lends to automation.
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Old 04-13-2020, 01:01 PM   #15
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Re: Combination whole house/attic fan


If you're doing a ducted WHF, here's a good product line to compare others to:
https://quietcoolsystems.com/products/
Here's a good product line for stepping up a single blade ceiling-mount WHF:
https://www.tamtech.com/product-cate...le-house-fans/
Power attic vents are more generalized though across the board. Just make sure you differentiate between WHF and power attic vent, as sometimes it is not clearly stated.
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