Home HVAC Question

[kbuhagiar]

Hello, folks,

I need some advice from an HVAC expert.

A little over a year ago I had a new heating unit installed in my house by a well-established local HVAC company (It's a Bryant, model 80 I think. Works really well.). There are two air intake filters, one at the fresh air intake in the main hallway of the house (20" x 16" x 1"), and another right on the heater (16" x 25" x 4"). During the estimate phase the contractor checked the existing ductwork and intake and confirmed that it was adequate to support the new unit. I have always replaced the unit in the hallway every six months.

Finally got around to replacing the air intake filter located on the heater (it's in the crawlspace - no fun) and I discovered that the installation techs placed a heating duct in a way that is slightly obstructing the filter access door, just enough so that it' s next to impossible to r & r the filter without destroying it.

I know I need to have that remedied - I will be in touch with the outfit that did the install first thing Monday morning - but shouldn't the other filter at the top of the intake run provide adequate filtration? This air intake setup is the same one that was with the house when I bought it 25 years ago, and with my old furnace (which lasted 35 years) it was the ONLY intake filter. The run from the front of the intake to the furnace is about 3 feet - 2 feet down to the crawlspace and 1 foot over to the heater.

Thanks in advance for your assistance!

 

[redsky49]

A certain amount of air sneaks around any filter. This is called the "bypass factor" and typically runs about 5-10% of the air, less for well fitting filters. Also, many residential filters have very poor arrestance and a lot of particles pass right through. Additionally, since your return air duct is under negative pressure (it is sucking the air back to the furnace), any duct leakage in the return air path will result in more unfiltered air entering the unit/final filter.

In practice, you should probably change the filter at the furnace once a year; the filters upstream (it sounds like you have a combination return grille/filter) every three to six months depending on usage.

If adventurous, take the side panel off the furnace and examine the fan blades for dirt and grime. If they are clean, you have no worries. If dirty, you should clean the fan and also examine the cooling coil.

The problem you are hoping to avoid is the use of the system when the contractor was sanding the drywall. This drywall dust hits the inner surfaces of the furnace and cooling coil and makes a mess. This stuff cannot be vacuumed off. It must be scraped off.

While you have things apart, clean and disinfect the condensate pan. Make certain that it slopes to drain. If you see a nice blue flame without a lot of yellow or orange (If this is a gas furnace), then you have just done 90% of the things a technician would charge you $100 for. Reattach the side panel and you are good until next year.

 

[rickairmedic]

Kbuh to make it simpler yes by all means yank the filter next to the furnace out until they retrofit the ductwork so it goes in and out easier . I would say after that if they are putting a 4" filter next to the furnace the one up in the house really isnt needed and will impede airfow . 4" filters should be changed every 6 - 12 months 1" pleated filters such as you have upstairs I recomend changing once a month durring the summer and every other month durring the winter . Leaving a dirty filter in durring the summer will cause your AC system to overwork itself and also could cause the freon not to change over to a gas which will allow liquid freon back to the compressor outside which will harm the compressor.


Rick

 

[redsky49]

Rick has a point. If there is actually a 4" deep filter in there, and not just a 4" deep filter holder (which was how I read it), you may not have enough fan horsepower to overcome the pressure drop across the filter, even when the filter is clean.
It would be interesting to see what the brand and type of filter is in there now.

 

[rickairmedic]

Well if its a true 4" that would mean either an Aprilaire or a Spacegaurd accordian type filter or it could be one of the Carrier/Bryant type box filters.

Rick

 

[kbuhagiar]

Well if its a true 4" that would mean either an Aprilaire or a Spacegaurd accordian type filter or it could be one of the Carrier/Bryant type box filters.

Rick

It's a Bryant.

 

[rickairmedic]

It's a Bryant.

Every once in a while I get to use all those years of training and tests . I still say pull the 4" filter till they get the issue fixed with the ductwork and also check homie desperate for the 4" filters that go in that box . I treat my customers pretty well on them but alot of companies try to fill the trucks gas tank by selling you a filter .

Rick

 

[hidollartoys]

I would expect that you do not need 2 filters unless you have 2 seperate air returns. This is also suspect because the filters should be placed in the return duct close to the air handler. This is done to assist air flow across the filter when it becomes dirty. This way the fan will more effeciently overcome the pressure drop across the filter. This being said, it may be more important to consider access and then the filter could be placed in the return duct where it is easier to change.