Whole House Fan

mtnelect

HVAC Contractor
Location
Southern California
Occupation
Contractor
On a recent HVAC inspection for a Whole House Fan, What are you going to do when you run out of material ?
 

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Location
United kingdom
Occupation
Builder
1960s-70s whole house fan finally gave up the ghost. It was a 30x30 (or more) which was mounted vertically hanging in front of a large (36x36?) louvered vent from chains screwed into the roof sheathing. (Yes, not kidding).

Am getting a new 30x30 7000cfm rated fan, which are usually mounted horizontally above a vent in the hallway. Any reason not to replicate the vertical mounting (instead building a frame out of 2x4s and attached to the joists)?

Also, the old fan had canvas stapled from the fan frame to the louvered vent, I guess to ensure the exhaust went out the vent, but given typically these fans are just mounted horizontally and only push air into the attic, mounting horizontally without the canvas would be enough.

(I know 7000cfm might be oversized for a 1600 square foot raised ranch - the old fan used to create an actual wind when it was on, but I want to replicate the air changing power of the old fan, and I already bought it…)
 

mtnelect

HVAC Contractor
Location
Southern California
Occupation
Contractor
Gone are the days when the Building Inspector put on some coveralls and went "pioneering". I had my coveralls on to find these wiring violations. In California they now use Combination Inspectors for residential to inspect plumbing, electrical, mechanical and structural and everything else. Basically, a "rubber stamp" approval.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
1960s-70s whole house fan finally gave up the ghost. It was a 30x30 (or more) which was mounted vertically hanging in front of a large (36x36?) louvered vent from chains screwed into the roof sheathing. (Yes, not kidding).

Am getting a new 30x30 7000cfm rated fan, which are usually mounted horizontally above a vent in the hallway. Any reason not to replicate the vertical mounting (instead building a frame out of 2x4s and attached to the joists)?
Was the fan mounted with a vertical exhaust through the wall of that attic, effectively exhausting the attic? Or was it mounted at the end if a 90° chase that exhausted just the house, like a horizontal mounting would do?
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
1960s-70s whole house fan finally gave up the ghost. It was a 30x30 (or more) which was mounted vertically hanging in front of a large (36x36?) louvered vent from chains screwed into the roof sheathing. (Yes, not kidding).

Am getting a new 30x30 7000cfm rated fan, which are usually mounted horizontally above a vent in the hallway. Any reason not to replicate the vertical mounting (instead building a frame out of 2x4s and attached to the joists)?

Also, the old fan had canvas stapled from the fan frame to the louvered vent, I guess to ensure the exhaust went out the vent, but given typically these fans are just mounted horizontally and only push air into the attic, mounting horizontally without the canvas would be enough.

(I know 7000cfm might be oversized for a 1600 square foot raised ranch - the old fan used to create an actual wind when it was on, but I want to replicate the air changing power of the old fan, and I already bought it…)
So which is it, exhausting air or pushing air into the attic? Either way, the fan needs a ducted connection. Just having it hang out a couple of inches from the opening will be almost useless.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
So which is it, exhausting air or pushing air into the attic? Either way, the fan needs a ducted connection. Just having it hang out a couple of inches from the opening will be almost useless.
There are two different applications for fans in the attic.
The 1960's whole house fan was typically a horizontally mounted fan with an integral metal shroud that mounts on top of a framed opening in the ceiling. It draws air into the attic and leaves it for appropriate sized passive attic vents to give the air someplace to go. It would be turned on after the outside temperature had fallen in the evening to make sure that the house temperature tracked down with the outside temperature. As a side effect it would cool the attic during the night but do nothing to control the attic temperature during the day. There was no need for any additional seal between the fan and the ceiling framing, and either a gravity or powered vent louver kept hot air from drifting in during the day or hot air leaving in winter.

The other application is the attic fan. Typically mounted vertically against a louvered opening in a gable wall. No need for a closeable louver and its sole funtion is to draw air in through passive attic vents and exhaust it to the outside. All that I have seen are rigidly mounted to a framed opening, just as the whole house fan is, but with opposite airflow. It keeps the solar heating input from raising the attic temperature well above ambient and forcing heat through the ceiling insulation into the house. Adding a controlled louver vent in the ceiling would allow it to also function as an inefficient whole house fan, since the attic vents are in parallel with the ceiling vent. This sounds like what the OP is describing.

I have never seen either type of fan mounted other than rigidly (with vibration isolation integral to the fan assembly.) The chain mounting and canvas duct sound like an effort to use a high vibration fan for a purpose it was not really suited for.

P.S. An unducted fan can actually move quite a bit of air if the opening it is facing is larger than the fan and is relatively open with unrestricted airflow. And in fact it may entrain additional air into the airstream, so that more air exits the vent than passes through the fan itself.
 
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goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I got a "virus scan failure" when I tried to open the PDF's of the pictures. Why not just post a JPG or PNG?
Just a side-bar - not looking to pirate this thread. I had the same issue and I discovered that it had to do with settings in Mozilla-Firefox (my default browser). I was not able to open any PDF's (including my own in a Mike Holt forum post). You'll have to go into either your browser program or your virus program and set their parameters differently.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
There are two different applications for fans in the attic.
The 1960's whole house fan was typically a horizontally mounted fan with an integral metal shroud that mounts on top of a framed opening in the ceiling. It draws air into the attic and leaves it for appropriate sized passive attic vents to give the air someplace to go. It would be turned on after the outside temperature had fallen in the evening to make sure that the house temperature tracked down with the outside temperature. As a side effect it would cool the attic during the night but do nothing to control the attic temperature during the day. There was no need for any additional seal between the fan and the ceiling framing, and either a gravity or powered vent louver kept hot air from drifting in during the day or hot air leaving in winter.

The other application is the attic fan. Typically mounted vertically against a louvered opening in a gable wall. No need for a closeable louver and its sole funtion is to draw air in through passive attic vents and exhaust it to the outside. All that I have seen are rigidly mounted to a framed opening, just as the whole house fan is, but with opposite airflow. It keeps the solar heating input from raising the attic temperature well above ambient and forcing heat through the ceiling insulation into the house. Adding a controlled louver vent in the ceiling would allow it to also function as an inefficient whole house fan, since the attic vents are in parallel with the ceiling vent. This sounds like what the OP is describing.

I have never seen either type of fan mounted other than rigidly (with vibration isolation integral to the fan assembly.) The chain mounting and canvas duct sound like an effort to use a high vibration fan for a purpose it was not really suited for.

P.S. An unducted fan can actually move quite a bit of air if the opening it is facing is larger than the fan and is relatively open with unrestricted airflow. And in fact it may entrain additional air into the airstream, so that more air exits the vent than passes through the fan itself.
Checked mtnelect's link and now I see what's up. I thought it was a fan just hanging in the attic space, I didn't realize that the suction side was ducted. My bad.
 
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