What I'm Seeing Now

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Clogged Air Intake

Furnaces and even houses need to breath, and a clogged air intake does not help!

This house has a high-efficiency, condensing gas furnace. 

Installed the way it was initially designed, these furnaces have two plastic flues which extend through the house to the outside. 

One flue is bringing in fresh air and the other is blowing out the furnace exhaust.

The thermal image on the right shows one of these furnaces properly operating.  The cooler fresh air intake flue can be seen as the purple stripe above the unit.  It is working well.

The exhaust flue can be seen as the yellow stripe on the right side of the unit blowing the warm exhaust outside.  It is working well.

Somewhere along the way the local codes changed to allow the intake tube to draw air from inside the house.  This does not have the same benefits as one that brings in fresh air, but the change was made nonetheless.

But, in order for this to happen, a fresh air source needs to extend from the outside directly to the furnace room.

An example of one of those direct air intakes is on the left.

And, over time, it has clogged.

To me it looked like dust, dog hair and some white stuff I could not identify!

And the bees like it too.  It's a nice bee spot, for sure!

But, such a mess is very restrictive of air!

But this passage of this "fresh" air to the furnace room is totally passive.  There is no forced air. 

However, it is obvious that air is indeed flowing toward the indoors, even passively, as this clog is occurring from the outside in.

While not the same as air brought in by a vent fan, it is outside air.  But its ability to flow freely must be maintained.

My recommendation:  high-efficiency, condensing gas furnaces are very good units.  They are extremely efficient where most of a dollar spent on gas actually is converted into heat.  But their efficiency is aided by air and when the air source is passive, like the one above, it is essential to keep it maintained.  Nobody likes to choke!

 

 

 

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

www.jaymarinspect.com


Comment balloon 13 commentsJay Markanich • May 25 2012 04:25AM

Comments

It is like putting a potato in someone's exhaust pipe of their car. We all know what happened next.

Posted by Winston Heverly, GRI, ABR, SFR, CDPE, CIAS, PA (Winston Realty, Inc.) about 6 years ago

Pretty much Winston, except that the furnace room won't explode!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 6 years ago

As you well know, whatever the equipment has to work so much harder and is not as efficent with a clogged duct.

Posted by Joe Petrowsky, Your Mortgage Consultant for Life (Mortgage Consultant, Right Trac Financial Group, Inc. NMLS # 2709) about 6 years ago

So explained on the inspection Joe!  It can also contribute to a mix with air that can contribute to more carbon monoxide production than otherwise.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 6 years ago

In my area the source of combustion/dilution air is determined by the installer/manufacturer, not building codes. I see high efficiency furnaces (not condensing) installed all too frequently with out a source of outside air. Over all it makes them less efficient. In any case it's schmuck work. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) about 6 years ago

Agreed buddy o' mine!  I don't know when the change was made over the years and the indoor intake crept into the practice.  I just think it isn't best practice.  For all I know a 5th of something was passed around and somebody agreed to a "change..."

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 6 years ago

Good morning Jay,

Eeeeewwww, gross!

Posted by Lisa Von Domek, ....Experience Isn't Expensive.... It's Priceless! (Lisa Von Domek Team) about 6 years ago

Jay- That looks like it's been neglected for quite sometime. I'm surprised the owners didn't notice a difference in their air flow.

Posted by Amanda S. Davidson, Alexandria Virginia Homes For Sale (Amanda Davidson Real Estate Group) about 6 years ago

Jay -- this looks like one more thing that has to be added to the semi-yearly maintenance list.

Posted by Steven Cook (No Longer Processing Mortgages.) about 6 years ago

Jay, What is a gas furnace? I heard of them and I think they are an endagered species here ; ) Only flow we need is from the Power dam down some wires to the electric thingamajig and bingo you have heat ; ) So simple!

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) about 6 years ago

So you say Lisa...

Amanda - unless you actively look for such a decline you won't notice anything!

Steven - or even longer.  I doubt this clogs real fast, unless the dogs do lots of scratching under the deck!

Don - hmmm.  It's like electric, only different.  Hope that explains it.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 6 years ago

 An addition to the maintenance check list that few people would consider...they will now !

Posted by Sally K. & David L. Hanson, WI Realtors - Luxury - Divorce (EXP Realty 414-525-0563) about 6 years ago

This is a high deck too S&D and can easily be checked.  When the deck is low the maintenance check is a bit more difficult!  But necessary.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 6 years ago

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