Fan efficiency due to "crud"

[plainjs]

It's only logical that a fan loses efficiency as it ages and airborne crap (technical term) accumulates on the insides of the fan. Are we talking 2%-5% loss of efficiency or are we possibly talking 10% (more?).
I have inherited a Trane Voyager that I'm having a static problem with, I am down about 15% from when the unit was first commissioned, duct work looks tight and i am tempted to re-sheave, just wondered if there was any insight from the group, before i do anything. The consensus among my Tech friends is that it would only have negligible affect, is there any reference material out there?

..john

[dandyme]

it's been a long time since I was informed of efficiency decline, but I'm thinking something along the line of 8-10 % reduction in air flow with the slightest film on blower vanes.

someone will correct me shortly

[boilerman856]

I was told by a manufacturers instructor at a course that if the blade is 5-10% filled it will decrease performance by up to 25%. Take an amp reading before and after cleaning each blade Ans you will see the differance.

[Cooked]

It will dramatically affect airflow, especially if it is a forward curved centrifugal wheel in a Archimedic scroll housing. It can be easily 25% or more depending on the amount of crud.

[synergy]

Check total static. Suction side negative pressure and compare to air balance report befour speeding up the fan. Return air grills may be dirty evap coil dirty stuff like that.

[seascott]

Ever since Carrier got the great idea of putting oversized ceramic fiber gaskets on their combustion blower housings I have been dealing with the effects of fouled fan wheels contributing to premature heat exchanger failure. If you put your hand in front of the combustion blower outlet before and after cleaning the wheel you will notice a huge difference in airflow. I would imagine that this translates to larger blowers as well. York had the same issue but they thought to put in a pressure switch rather than going with the centrifugal for air proving.

[pairman]

I've cleaned many a blower wheel (light commercial rooftop) and have had substantial improvement in airflow and comfort.

[marsmech]

I once had a system that the blower wheel was full of "crud" and had to go back for frozen up evap. coils. Checked the airflow and it seemed ok. After two service calls an answer surely had to be found. Removed the blower, cleaned the wheel and we have not had a problem since!! Note: this only happened after the unit was replaced with a new R410a split system.