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Wall thickness drilled to reach outside

I have been toying with the idea of installing a vent fan to suck in outside cooler air at night instead of using a dedicated room air condition to cool the tank room. The room air condition runs at 14 Amps and a room vent fans typically run under 2 Amps depending on the model and size.

Typically in the north eastern US the nights are still fairly cool in the mid-60's to mid-70's. On the few hot nights the room AC can be used. The tank room has been in the mid-80's. I was already exhausting room air outside but that was not enough.

Various parts being assembled

Home Depot has a decent selection of fans for venting bathrooms ranging from 50 CFM (Cubic Feet per Minute) to over 300 CFM.

The main issue in this projects is that I don't want to blow air out of the room, I want to draw outside air into the room. I need the fan to suck and not exhaust. This requires rebuilding the unit and making some new parts.

Hole cut in new unit cover for pipe adapter

The main issue I had was how to make the unit draw in outside air instead of exhausting air to the outside. Instead of destroying the internal units and remounting the fan backwards I decided to simply install the unit upside down. I would build a new intake system and use the original 3x10 inch duct exhaust to blow the air into the room. Picture here is the new plate the to replace the original grill cover which will get a 4 inch duct hose adapted to it.

300 CFM Blower nearly complete

This is the fan assembly. It is a 300 CFM rated bathroom exhaust fan made by NuTone that uses a dual squirrel cage blower. The box is lined with foam to absorb the sound of the blower. It is rated at 2.5 Amps which is more than I wanted but is still much less than the 14 Amps the room air condition uses.

Completed fan assembly ready for testing

Pictured here is the completed fan assembly with new custom cover with 4 inch duct adapter (top). The two squirrel cage openings where air will enter the room are the lower square openings.

The new cover is drilled and screwed in place with seams sealed with duct tape.

Fan assembly test running before being installed to ceiling

This shows the fan assembly blowing air into the room. This is obviously just a temporary installation for testing to prove the concept. It will be mounted into the ceiling with a short duct pipe for final installation.

Initial tested was very positive. The room AC was not needed for 2 weeks after this was installed.

The tank room as well as the reef tank were able to stay 2 to 3 degrees cooler.