furnace filter - in vs out

[Stormin Mormon]

And, because different speeds and HP needed for heating versus cooling.

[mkirsch1]

More air flow is not better.

What you will notice is that instead of a steady flow of toasty warm air, you will be feeling a COLD DRAFT the entire time the furnace is running.

What happens is the air moves across the heat exchanger too quickly, and doesn't get warmed up.

The same thing happens if you open up all the dampers in the hot air ducts. Instead of warmer rooms, you get a cold draft because the airflow is too high.

[mkirsch1]

It's designed for that.

See my other response. Your thinking is absolutely opposite of reality.

[mkirsch1]

Block off the suction on your vacuum. What happens?

The motor runs FASTER.

you do the math

[Stormin Mormon]

Load decreases, amperage drops.

[greenpjs]

I think you misunderstood what he meant by supply side. The side that "supplies" the air is the same as your "return side".

[Stormin Mormon]

Only in the southern hemisphere. (ha-ha)

Between the furnace and the conditioned area is the duct that supplies the conditioned area with air. The low pressure duct that goes toward the furnace is the return air (returning from the conditioned area).

HVAC terminolgy is that the supply side goes from the unit to the conditioned area. When discussing furnace and AC, it's wise to use the terms properly.

[The Daring Dufas]

I've pealed layers of pet hair off evaporators that looked like a layer of felt. When I pulled it off, all the dirt came with it leaving a nice clean coil.

TDD

[Michael Dobony]

wear a sweater

[Bob F]

When I replaced my old heat pump, the heat exchanger was only slightly dirty on the air inlet side. I guess that electronic air cleaner really worked for the 25 years it was in use.

[Bob F]

I seriously doubt they have less air resistance than simple fiberglass filters. Those things have almost no real filtration - you can see through them.

[Bob F]

I have seen electronic filters that slide into the standard 1" space, with the power supply on a cable from it. I have no idea how good they were.

[trader4]

I would agree that at some point, with very severe restriction, that indeed happens. But I would think based on logic and science that this occurs do to a phenomena like cavitation. That is to say, at some point, the fan is no longer acting like a fan or moving any air at all, just spinning around. But this is a special condition and not a linear one.

Let's take a shop vacuum. Here's how I would expect power would change versus air flow. With the hose wide open, the power would be at minimum. As I start to slowly block off the hose opening in increments, the power will INCREASE. At some point, with the hose almost blocked or totally blocked, then the power may decrease again.

If it doesn't draw more power when air flow is choked off, why do circuit breakers trip on a circuit that shop vacs are on when they have a heavy load? For example, I've had my shop vac on a 15 amp circuit that had other various loads, so there was just enough left for the shop vac. I could let it sit running with the hose wide open all day and it won't trip. But if I hook up the wand and start vacuuming the floor, I can hear the motor starting to slow down, strain under load, and eventually the circuit breaker will trip.

[Twayne]

Just look at all the "experts" who climbed out of the walls here.

[Stormin Mormon]

I can easily believe that. Meow.

[mm]

My evaporator is totally surrounded by ductwork. Is that not the right way to do it? Should there be removable sides?

Is it usually the homeowner's obligation to cut into the ducts?

[The Daring Dufas]

I recently had to use a jigsaw to cut an access door into a metal duct in a commercial building to get to the evaporator to clean it. When my buddy and I install ductwork we usually go with fiberglass duct board which can be cut with a razor knife. There have been times when I would have to slide the A coil out of its housing to clean it. If the lines are long enough it's easy, otherwise the system has to be pumped down and the line set disconnected in order to remove the coil. If you replace your filters as recommended, your evaporator coil will never get dirty enough to require drastic measures to clean it. The "A" coil which is the most common evaporator in a typical residential HVAC system is usually in a factory made metal housing with one or more sides that are removable so the coil can be slid out for repair, replacement or cleaning.

TDD

[Stormin Mormon]

Ideally, the duct work comes apart one side, with a couple screws. Most home owners don't ever dissemble the evaporator part of the system. Some might pull the access panel off, and spray some cleaner on the coils. But, usually it's the HVAC guys who do evaporator cleaning.

[mm]

Well, at least it wasn't that I wanted to clean it. The condensate, instead of going out the tube and over to the sump in the basement floor, would overflow and run out through the base of the furnace! I had cut the plastic pipe off and looked down the pipe and run water through it and it was fine, and then reattached it and it worked no better. So I wanted to look closer, and I cut a 7x7 inch hole. Now I would make it a lot bigger, but I woudln't have found the problem.

The pipe went down an inch, two feet to the wall, and down 4 feet to the floor (then to the sump). Eventually I made it start by going down

13 inches, two feet to the wall, and down 3 feet to the floor, and after that it worked fine. (I assumed my neighbor's furnaces were all the same as mine and worked fine, but now I realize I should have looked at some of them. Now they've all been replaced.)

This must one of the few places they really economized on this house, so I shouldn't complain. Thanks, and thanks SMormon.

When I get a new furnace this year, I'll try to make sure that things are accessible.