Thick furnace filters?

Mine is. We use one like this as a pre-filter, which we change every month:

And a big pleated filter downwind of it, which we change two or three times a year, like this:

Specified by my husband when we installed the furnace. I'm sure he consulted the HVAC guy.

Cindy Hamilton

I wonder if a 5-inch thick filter lasts five times longer than an ordinary 1-inch filter?

Probably not. It will require signficantly more power from the air handler motor than a 1-inch filter, and as the filter efficiency degrades more power is needed to pass the same amount of air through the filter.

In other words, the air handler needs to be sized to the filter (and vice versa).

Same deal here

No but you can get up into the HEPA filter range with them instead of a screen that only catches dust bunnies. You do want a cheaper high flow pre filter to get the big stuff first so they don't plug up right away. I have a louvered door on the closet where my air handler is and I have a frame around the inside for a "cut to fit" woven filter that I can squirt with the hose. That keeps most of the dust out of that closet and makes my Space Guard last longer.

The delta through my space guard is 0.1" H2O when it is new. At around

True. And then there's the cost of premature failure of an ECM blower motor.  Ouch!

I call BS on that article. The only way restricted airflow is hard on the motor is due to lack of cooling air. A fan is not a positive displacement device, and the more air it MOVES the harder it works. Restricted flow, by definition. is less air moved = less work done, = less current draw and less heat produced. Try it some time. Block off the filter and measure current draw. On a PSC motor the fan woll "unlkoad" and speed up. The highest fan current draw possible is a freestanding furnace with no ductwork attached.

I suspect they are just covering up for a poorly designed blower card/motor combo. Blame it on the customer. I know I have already had to replace both on my Bryant but it was on warranty. I also had 2 go bad in the Trane TWE we had, one warranty, one not. The second time it got a regular motor.

That is still a design flaw.

In the A/C application the motor should be plenty cool, it is running in the cold air downstream from the evaporator. The heat strips are past the motor so it will be ambient air in the room going over the motor. The only issue I see is a heat pump where, in heat mode, the motor is running in the heated air.

I don't think my furnace is laid out that way. I think it's the blower, then the burner/heat exchanger, then the A coil for the AC. The blower gets the air from the return. We once found a dead mouse stretched around the squirrel cage; husband's hypothesis was that it came in through the return.

We had all that jazz open last winter. You'd think I'd remember. I suppose I could ask the hubs.

Cindy Hamilton

Furnace? I have not heard of this thing. It must be some northern deal ;-) We just have air handlers and A/C is the main application. Do you have a variable speed motor in your furnace?

In a furnace the squirrel cage is much bigger than that normally provided for a mouse. He probably wore himself out trying to turn it fast enough and died of exhaustion.

Heh.

In the Northeast, they use boilers instead. (IIRC you lived there once?) I don't understand how they can tolerate the stagnant air. Perhaps those liberal bastards don't fart.

Seems to be two-speed. I can hear it ramp up when the AC or furnace kicks on. We run the blower all the time, to push air through the filters.

Cindy Hamilton

We're thinking of writing a children's book entitled, "Mr. Mouse's Ferris Wheel Ride". Illustrated, of course.

Cindy Hamilton

I installed a 4 or 5" one when I put in a new furnace ten years ago. What kind of filtering options there are, what you want, is something competent installers should ask, but as I recall, I was the one that brought this up. And yes the filters catch finer particles, but they are considerably more expensive. I get a couple years out of a filter though, so it's not much of an issue.

You don't usually even hear a variable speed A/H come on. After a while it is just there. The motor starts out slow and speeds up as the heat or cool builds up in the system. It tapers off when it shuts down. It is supposed to give you some added efficiency but when I went with a modern high efficiency motor on my Trane TWE after the VS failed, I didn't see any big difference in my bills. It certainly wasn't anywhere near the parts cost of replacing the card and the motor with the original. ($1600 with me doing the work). They (authorized Trane techs) said they couldn't guarantee the old card wouldn't blow the new motor or vice versa so they replace both. The fancy tester they had gave ambiguous results.

I usually do mine in the spring after we turn on the A/C. I start seeing the gauge move about then.