Relationship of WC and CFM?

[Wade Lippman]

After 5 years my radon fan failed. I replaced it with a similar unit that is supposed to be quieter.
The old one showed 0.5" on the manometer; the new one shows 0.7".
Does that mean the new one is moving more air?

It is a little confusing because the graphs show lower CFM for higher WC, but presumably that means for a more restricted air flow on a particular fan. If a different fan develops higher WC on the same system, I would think that means higher CFM. But I could easily be confused.

The new one is much quieter; hopefully that is despite being more powerful, rather than because it is less powerful.

[Lee Schierer]

I believe it shows that the new fan is developing more static vacuum than the previous fan, not necessarily moving more air, which should be good for radon removal. It is possible that your old fan originally produced the same reading and over the years the fan efficiency dropped off due to bearing wear. You could check with your original installer to insure that it is okay.

[Wade Lippman]

It is possible that your old fan originally produced the same reading and over the years the fan efficiency dropped off due to bearing wear.

The old one read 1" for 2 days, and then dropped to 0.5" for the next 5 years. Installer said that was normal. I never quite believed that, but it got the radon down to an acceptable level. Too early to know what the new one is doing; meter takes 6 hours for the first reading after being reset.

In the week with no fan (between the old one breaking and the new one arriving) the fanless system worked just fine when the wind was blowing, but failed completely with no wind. It didn't show anything on the manometer, but did on the radon meter. I don't understand that either.

[Lee Schierer]

The manometer is showing the amount of pressure reduction (suction) in you radon removal piping. If you have no reading on the manometer (no suction) then the radon is able to escape into your room and will cause the reading on your meter.

[Larry Frank]

You have a fan with a different performance curve. What is the cfm rating on the two fans? Please show us the fan curves you mentioned.

[Rod Sheridan]

If you have a lower pressure in the same system, it's moving more air.

Regards, Rod.

[Bill Dufour]

I would expect the bearings to seat in and reduce amp draw in a few days. I do not see how that would change WC or cfm unless it allowed fan to move out of position in venturi.
Bill

[Tom Bender]

After 5 years my radon fan failed. I replaced it with a similar unit that is supposed to be quieter.
The old one showed 0.5" on the manometer; the new one shows 0.7".
Does that mean the new one is moving more air?

It is a little confusing because the graphs show lower CFM for higher WC, but presumably that means for a more restricted air flow on a particular fan. If a different fan develops higher WC on the same system, I would think that means higher CFM. But I could easily be confused.
.

You are not confused, if the new fan develops more WC (pressure) it is moving more air thru the same system than the old fan was.

[Wade Lippman]

I finally got a radon level. It is 0.72, which is half of what it was with the old fan. It is less than half the noise of the old fan, so I am a happy camper. The sump is a few feet from the fan; when I took the top off the sump with the old fan, the WC dropped almost to 0. With the new fan, the WC doesn't change. That seems odd to me.

The two fans have similar fan curves. 0.5" is the best they can do, and is pretty much an open pipe. I am thinking the old fan was malfunctioning, which accounted for the low WC and the noise. The guy who installed it was a jerk who was unwilling to acknowledge it was defective. Well, live and learn.