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Attic Fan - Ceiling Louvers?

nz Member Posts: 125
I know it's not heating but it's ventilation. Let me know if I'm barking up the wrong tree please.

Bought a house last year, it has two very large attic fans - one that blows out a dormer in the middle of the house, and another that blows out a gable at the far end of the house. House was built in 1950, but has since had three AC units retrofitted. I live in Michigan, so we really only need the AC for about two months of the year, as evenings and mornings can be cool enough in early June / late August - and so we like to run the attic fans whenever feasible as the fresh air is nice and it saves money.

Each bedroom on the second floor, and several hallway areas have opening with wood grates in the ceiling that were open to the attic (presumably) year-round, which enabled warm air to be pulled out of those rooms and fresh air to be pulled from the open windows.

When previous homeowners retrofitted the AC, they took these openings and either blocked them off (bad), left them open (also bad), or blocked off half and used the other half for return air for the AC.

The challenge I have is when I want to use the attic fans, i don't believe we are getting the full efficiency of the fans because all these openings are blocked off. As it is a slate roof, we succeed in cooling the attic, but not much else. The only way to get good cooling is to open the door to the walk-up stairs to the attic. My wife doesn't like this option due to the dogs as well as the previous presence of squirrels in the attic.

I have considered the following:

1) Re-opening the blocked half of the openings, but this will presumably suck hot, smelly attic air into the AC return lines.

2) Install louvers in the blocked-off portions of the original openings. However, I'm not sure if the suction from the attic fans will be enough to pull the louvers open...

3) Install electrically operated louvers in each room that are remotely controlled via a switch near the attic fan switch. Probably very expensive as there are 8 openings.

4) Install manually operated louvers in each opening.

5) Cut new openings and install manual or remotely-operating louvers.

Curious on your thoughts/feedback. Are there other options I should be considering?

I've looked at a few websites but the choices for louvers are a bit overwhelming but most of them seem to be placed next to the fan, not in a remote portion of the house.

I'm not sure where to find someone who is an expert in attic ventilation, every HVAC company basically laughs at me and tells me to just run my AC :)


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    What do you mean by "... blocked off half and used the other half for return air for the AC..."?
    Open returns in the attic for AC-bad.
    Whole house fan that de-pressurizes the house-bad, and potentially dangerous. If you have any fuel burning appliances that are not completely seal combustion, you risk de-pressureizing you home. Products of combustion will be pulled into the home. Those products of combustion would probably include deadly Carbon Monoxide. Specifically fuel-fired water heaters. But don't forget heating appliances that can run in the shoulder season while the attic is hot enough to turn on the attic fan. An interlock that only allows one or the other to run is something is a must in that situation.

    There was an error rendering this rich post.

  • Jamie Hall
    Jamie Hall Member Posts: 23,567
    I don't quite follow the blocked off half either... never mind how half of a former ceiling louver can possibly be a good return for the A/C. Clarify...

    And @STEVEusaPA has a very good caution: if you are blowing air out of the house, it has to be coming in somewhere else -- and if the somewhere else is somewhat restricted, you will get negative pressure in the house -- which you don't want.

    Now ideally with the original arrangement, those grilles would be nice and open, and so would windows here are there around the house. The fans would take air out, and that would be replaced by air coming in the open windows. Kind of low tech., but it works splendidly well.

    Now, however, if you throw air conditioning into the mix, the chances are very good that you are also keeping the windows closed -- it's hot out there, after all. In that scenario, you actually don't want to ne pulling air from the house (you've put in a good bit of effort to cool it, after all).

    So... those attic fans should get their air supply ideally from vents under the eaves of the house, which empty into the attic space. This may or may not be possible, but that the best option. So long as you are conditioning the interior air, the grilles from the upstairs rooms to the attic should be closed. When the A/C is off, they could be opened -- which suggests either manual louvers or electrically powered louvers, which close whenever the; A/C is on. It would be nice to have louvers which opened on the suction -- but you don't want that; that's wasting cool air if the A/C is also running. Besides, off hand I can't think of any which are sensitive enough for an ordinary attic fan -- we use them in the ag. business all the time, but there we are talking about 5 horsepower fans!

    I'd go with manual, and try to remember to pen them when the A/C has been turned off.

    Now on those returns... can you explain? What I'm envisioning is the A/C returns are through those overhead louvers and ducted back to the central air system? If so... frankly, a very poor arrangement for several reasons.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nz
    nz Member Posts: 125
    All good points/feedback, thank you. To clarify:

    1) I only run the AC OR the attic fans, never both at the same time.

    2) If the attic fans are on, the windows are open. I'm not insane, but still appreciate the caution re: backdraft. They are large fans (48" each) so caution is always good :)

    3) interlock is a good idea - thank you, not sure how to accomplish that but I will have to look into this. It might cause issues with the hot water and the wife lol. Perhaps would need to put the attic fans on a timer.

    4) See first photo below. Could I just cut in a louver where the rest of the old vent has been blocked off? I would have to obviously close the louver before I run the AC, but we only switch from Fan / AC / Fan a few times a year, so not a big deal. There are 96 windows in the house between the first and second floors, so it's a lot of work to do a switchover....so opening/closing a few louvers manually would not be a big deal to add to the process.

    I took some photos to help illustrate the return air and other things:

    Attic view of previous ceiling fan opening w/ return air:

    Ceiling view of the same opening from below. Prior to AC installation there was simply a drop-in screen above the grate.

    One of the attic fans inside/outside:

    How I get air into the attic now (wife does not like this):

  • mattmia2
    mattmia2 Member Posts: 9,850
    You could add some grates with motorized zone dampers in a couple places. They might seal tighter than most ceiling louvers.

    Did this start out life as an unheated summer house?
    EBEBRATT-Ed Member Posts: 15,767
    I would put in a couple of motorized dampers. Hook them to the same switch that starts the fan(s).

    so the fans start .when the dampers open you should only need a couple of motorized damper louvers. Control the airflow by opening windows in the rooms you want to ventilate.....not all the windows.

    The above cautions on Co and backdraft are for real and can cause major issues.
  • MikeAmann
    MikeAmann Member Posts: 998
    edited August 2022
    You can take what you want from my story.....
    A friend of mine has a giant drum fan (36" or even larger) and attached it to a board and put it over the opening to his attic.
    He opens the windows in the attic and it sucks outside air in through the house windows and blows it out the attic windows. It works great, but this is happening at about 6 - 8 pm.

    My work hours are 2 - 11:30 pm. I noticed that it gets the coldest outside between 2 -5 am.
    At that time, the air in my attic is cooler than the house.
    So in the summer, my house has heated up all day and the rooms are HOT when I get there after work.
    My attic has pull-down stairs in the hallway. And I set my 24" drum fan up the same way as my friend did.
    It worked but not as good as when I flipped the fan over to blow the cooler attic air into the rooms and out of the house windows. And depending on how many windows are open, that air will blow the draft regulator open. Depending on the temperature difference between inside and outside, I can drop the house temp by 10 degrees in an hour. Once the hot air is removed, then I can turn on the A/C if needed.

    You might want to experiment with reversing your fans.
  • hot_rod
    hot_rod Member Posts: 22,394
    When the AC is running those louvers would not be a very good insulation value between the hot attic and AC interior

    Whole house fans were common in Missouri mine had a spring loaded louder that the fan would pull open. We blocked  that opening with 2” foam in the winter. I think you can buy insulated lovers now, mine were 1960 vintage

    They work well in a few shoulder season months, they pull a tremendous amount of dust into the home, especially when we were haying the fields😗

    Great for when you burn toast also
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 9,850
    I don't think I would want to suck all the crap in the attic in to the house.

    There are attic fans with a hinged door that is heavily insulated, maybe there is a similar louver.
  • nz
    nz Member Posts: 125
    Thanks for all the feedback... House was originally and still heated with hot water/baseboard, built in 1950. AC was added in the 80s or 90s it seems.