Crawl space ventilating fan
Hello, all —
I have a 625 square foot sealed crawl space that I need to ventilate. I can’t seem to find a ducted fan that will suit this application. I’m no internet moron, but maybe I am tonight? What do you all use? My local building code jibes with what Martin wrote about in his article “Building an Unvented Crawl Space.”
“a continuously operated mechanical exhaust ventilation at a rate equal to 1 cfm for each 50 square feet of crawl space floor area.”
By my calculations, I need a fan that can be operated continuously (and without too much of an energy penalty), very quietly, and at a rate of 12.5 cfm. Does this fan exist? Maybe I’m looking in the wrong areas? It seems that the smallest Panasonic moves 50 cfm.
Thanks.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Jeff,
Most Panasonic exhaust fans have controls that allow you to set the flow rate (as low as 30 cfm) as well as the number of minutes of operation per hour (for example, 25 minutes per hour, which would give you 12.5 cfm average air flow).
Here is a link to the installation instructions with an illustration of the controls:
http://lib.store.yahoo.net/lib/rewilliams/WhisperGreeninstallinstructions.pdf
David,
Thanks for the clarification; I stand corrected.
It still sounds possible to use a Panasonic fan, set on low speed (30 cfm), and control it with an external 24-hour timer -- right?
Yes, it is.
Martin, minor correction here, the Panasonic fans detailed in that instruction manual do not have internal control of how many minutes per hour they run. They have an adjustable low speed setting and a fixed high speed setting. They are designed to run more or less continuously at the low speed setting, going to high speed when more capacity is needed (such as when the shower is used). The internal timer controls how long the unit stays at high speed AFTER the occupant leaves and turns off the wall switch (or, the occupant sensor senses that they are gone).
If you want the unit to operate intermittently at low speed you need a separate timer control.
There are only a couple of them that go as low as 30CFM. The FV08VKS3 is the one I typically use in bathrooms (low is 30, max is 80, has no internal motion sensor).
Thanks, gents. Seems like Panasonic could stand to make a fan that's adjustable from 0 - 30 cfm, can be run continuously, and is nearly silent. Now I have to install a timer? Complicated for the homeowner...
Anyway, thanks D & M.
Jeff,
Here is a link to the Grasselin timer sold by EFI for $36:
http://www.energyfederation.org/consumer/default.php/cPath/39_766_133
Correct me if I'm wrong, but couldn't you use a dimmer to get a variable 0-30cfm? You wouldn't be able to know the exact cfm, but you could guesstimate.
Thanks for that, Martin. I might be looking into one a them!
I'm hardly even an amateur electrician, Nick. I have been known to play one from time to time as a GC (usually on my own house). Interesting idea. I'm sure someone smarter than me will tell us why it's a bad idea!
I would not try to slow a Panasonic fan unless the controller was approved by Panasonic. And there is no need to. Running the fan for less time does the same. And these fans are very quiet so if installed right they will not be heard. There are remote duct located fans too where the fan itself can be far from any vent location.
As to installation, call an electrician if you need such. We need work just like the rest of you on the planet.
aj