Mutiple filters

[David C. Macy]

I noted that the system needs to be evaluated due to the multiple filters.
I believe this can restrict the airflow. I also wasnt able to remove the paper filter due to the fins being jammed.

Secondly there where some disconnected wires in the cabinet and It appeared they were not being used any more.

Lastly, the exterior chimney had excessive damage and flaking and it appeared they should of installed a metal liner. The furnace was manufactured in 98. The ducts appeared to be newer.

When or does code state that a liner is required?

Thanks

Dave

[eschwartz]

Well, since no one else is answering your questions, I'll give it a try:

I'm not a furnace expert, but that fat filter looks like a combination of parts from different systems. The thin filter looks almost ok. I like to see the filter slide all the way into the plenum with a door to shut it in tight.

The chimney needs to be repointed. This is more likely to do with the weather outside than the furnace exhaust. It looks like the chimney is lined with tile, if it is properly maintained it should be able to handle the exhaust from the furnace.

It looks like there are two sets of thermostat wires, both with brown insulation. One set with two wires is not being used, one set with at least 3 wires is being used.

Hope this helps,

Ed

[Jae Williams]

Pretty good guess, Ed.

The larger filter is/was a "static filter"--they were never worth a damn--
and the small filter should have a door to eliminate draw from so near the furnace.

The chimney should have a screened cap.

The chimney would need a liner if the furnace is a high-efficiency.

[JLilly]

The large filter is April air/Spaceguard and is all that is required. The extra filter is not needed. The large pleated filter is able to go six months to a year without changing. The extra t-stat wires are going to the condensing unit or maybe a humidifier.

[eschwartz]

Hey Jae,
I appreciate all your helpful posts.
Help me with my train of thought here:
I assume a high efficiency furnace would produce less exhaust heat than an old inefficient model. Some of these new furnaces vent horizontally w/2" PVC. What am I missing?
Ed

[Russel Ray]

I think Jae meant "unless the furnace is a high efficiency." However, if he didn't, then I have the same question as you, Ed.

[jclark1]

The return air plenum should not be using combustion air and if it's a natural draft furnace could be sending products of combustion into the supply air by creating a negative draft. That plenum should definitely be sealed. Right?

[Jae Williams]

Originally Posted by jwilliams4

Pretty good guess, Ed.

The larger filter is/was a "static filter"--they were never worth a damn--
and the small filter should have a door to eliminate draw from so near the furnace.

The chimney should have a screened cap.

The chimney would need a liner if the furnace is a high-efficiency.

High-efficiency furnaces today use up to 97% of the heat capacity of the fuel. Older furnaces were about 45% - 65% efficient and the flues were very hot with the exhaust fumes. By draining all the heat from the gases to heat the house, there is very little left in the inert gases that are exhaused outside. Thus PVC is more efficient in removing these gases than is metal.

Since the flue gases are not warm, they would not create a heat-induced updraft in a large flue, so the smaller PVC, usually vented outside, would have to have a liner that would make the chimney small enough to draw the gases out. The best way, however, is to vent immediately from the furnace to the outside through the wall.

"The return air plenum should not be using combustion air and if it's a natural draft furnace could be sending products of combustion into the supply air by creating a negative draft. That plenum should definitely be sealed. Right?"

Right!

[eschwartz]

Thanks Jae and James,
Big flue + small cold exhaust = backdraft. That makes sense.
That's what I was missing.
Ed

[Russel Ray]

Originally Posted by jwilliams4

Since the flue gases are not warm, they would not create a heat-induced updraft in a large flue, so the smaller PVC, usually vented outside, would have to have a liner that would make the chimney small enough to draw the gases out. The best way, however, is to vent immediately from the furnace to the outside through the wall.

I'm not finding myself agreeing with that.

First, if one is using the furnace, that probably means that it is cold outside. And I think that even the 3% of the heat that is not used is hotter than the cold air outside. And since heat rises, I think that 3% would naturally draft up the chimney, unless, possibly, there was a hurricane outside; that would definitely interfere with the draft of the chimney.

Second, all the high-efficiency furnaces I've inspected here definitely have warmer air coming out the plastic flue.

Third, considering how expensive it is to line a chimney, I think it would be more reasonable to simply run a piece of plastic up the chimney for a high-efficiency furnace.

Fourth, all this thinking has made me thirsty. And you know what that means, boys and girls? That's right. Margarita break.

[Jae Williams]

That is why the manufacturers require a liner in most cases.

[Jae Williams]

..of course, if margaritas were induced into the flue I would suppose
the flue would be much warmer...

[Russel Ray]

Originally Posted by jwilliams4

With a large flue capacity, a 3% of the flue temperature would not sufficiently heat the much larger volume of cold air in the chimney.
That is why the manufacturers require a liner in most cases.

I don't think one needs to heat the air in the chimney. Warm air will rise, so any amount of warm air will find a way to rise. Air that is only 5° warmer than all the air around it will try to rise above that air around it. And a chimney provides a natural way for that warm air to rise, especially if it is directed into the chimney to begin with.

[scosta]

I dont think the reason for the liner is the draft, I believe the high efficency furnaces produce more acid byproducts which break down the mortar in the chimney. This is why you will sometimes find sand particles in the furnace.

Steve

[Russel Ray]

Originally Posted by scosta

I dont think the reason for the liner is the draft, I believe the high efficency furnaces produce more acid byproducts which break down the mortar in the chimney. This is why you will sometimes find sand particles in the furnace.

Steve

I thought that was the purpose for the liner with old chimneys and wood. And I thought that the high-efficiency furnaces were better at removing those byproducts. After all, those byproducts come from inefficiency. If something were 100% efficient, what would we get? Less of everything, right?

And acid will eat away at anything, including plastic. So if the high efficiency units produced more acid, plastic would not be my first choice for flues on those high-efficiency units. Metals, such as aluminum, even glass, would be much better.