What I'm Seeing Now


Direct-Vent Furnace - It's Not A Blow Out, But A Blow In?

Like great "Out of Business!" sales and old tires, a direct-vent furnace is supposed to BLOW OUT!

You know, blow-out sale, a tire blow out and furnace venting.  Blow out.

But what happens when, with a direct-vent furnace - it's not a blog out, but a blow in?

Observing that bell-shaped thing a home inspectors knows that it is the furnace vent.  The first things I do when I enter a house is turn on the dishwasher, and crank the HVAC up or down.

This house has a high-efficiency, condensing-gas furnace.  They are wonderfully efficient, in their fifth generation or so (the bugs have been worked out), and while expensive they are popular.

Most furnaces, like mine, send a huge portion of their heat up through a metal flue that exits the roof.  They take their oxygen to burn from inside the house.  By comparison to the condensing units they are not very efficient.

These condensing furnaces are set up to draw in fresh air from outdoors, so they aren't taking so much oxygen from the house for combustion.  Then they burn the exhaust more than once, so what blows out is cool enough you could blow-dry your hair with it.  You might not want to as the exhaust is full of CO, don'tcha know.

The associated tubing is PVC, which is not able to take much heat, so you know what blows out is pretty cool, about 105F.

The exhaust is supposed to blow away from the house, out through that round hole at the end of the bell (or Mercury space capsule, depending on your generation).  Because of that set up these vents are allowed closer than 4' to a window.

The intake air is supposed to be drawn in from the base of the bell, near the siding.

But look at this photo!  The siding is wet with condensation!  When I felt it I could feel the heat blowing against the siding.  And the end of the bell was drawing air in!


The house is heating, so my initial fear that it was plumbed incorrectly at the unit was quelled somewhat.  But I thought to check with a couple of other home inspectors to get their takes!  They are two that are familiar with this system, and both said it was probably arranged backwards near the exterior of the house. 

That is where the Y-shaped connection would be located, combining intake and exhaust for proper in and out.

Covered with drywall I could not see it. 

  • How the "HVAC professional" got that connection backwards is beyond me! 
  • Why they didn't notice this when the "HVAC professional" installed and "tested the system" is beyond me!
  • Why this was never noticed before by a home inspector is beyond me!  (Maybe the house was only inspected in the summer?)

So, I did the only thing I could do - suggested that the buyers have another "HVAC professional" look at it!  Only this time, get a real one!

My recommendation:  sometimes when a home inspector sees something he's not seen before it is easily diagnosed.  Sometimes a circumspect home inspector checks with others.  Doing this can be a Best Practice!  Either way, a home inspection is to test everything and see if it's operating correctly!  This system is not.  And was so identified.




Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

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


Comment balloon 20 commentsJay Markanich • December 21 2013 04:03AM


 Good morning, Jay. Good catch! Charlie is a very good home inspector and has a lot of knowledge. Good that you consulted with him.

Posted by TeamCHI - Complete Home Inspections, Inc., Home Inspectons - Nashville, TN area - 615.661.029 (Complete Home Inspections, Inc.) almost 7 years ago

We speak often Michael.  When I have questions I go to guys I think have experience with what I am seeing.

And I was surprised by this one!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Nice catch Jay. Have never seen that issue myself, either. Please update us (if you are kept in the loop) with what was found to be the problem.

Have a Merry Christmas!




Posted by Jeffrey Jonas- Minnesota Home Inspector (Critical Eye Property Inspections / JRJ Consultants) almost 7 years ago

Good morning Jay,

That is why I have an HVAC person as I don't know!

Make yourself a great day.

Posted by Raymond E. Camp, Licensed Real Estate Salesperson Greater Rochester (Howard Hanna Real Estate Services) almost 7 years ago

I would guess that as long as the thermal dynamics are satisfied and there is no danger to either the inhabitants or of the heat burning the house it would be okay. Different but okay

Posted by Ed Silva, Central CT Real Estate Broker Serving all equally (RE/MAX Professionals, CT 203-206-0754 ) almost 7 years ago

Hi Jay,

I had one of these last year when they had installed the vent straight up into the air. That's right it was standing up into the sky. Open for what ever wanted to drop into the vent. High efficiency furnaces are great. They just need to be installed correctly.

Have a Merry Christmas in Bristow.

Best, Clint McKie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) almost 7 years ago

As with any installation Jay, it needs to be done right. It sounds like the professional may not have followed through on the testing this time.

Posted by Tom Arstingstall, General Contractor, Dry Rot, Water Damage Sacramento, El Dorado County - (916) 765-5366, General Contractor, Dry Rot and Water Damage (Dry Rot and Water Damage www.tromlerconstruction.com Mobile - 916-765-5366) almost 7 years ago

Jay, I bet that it is not in the protocol of the installer to actually look at the exhaust at the exterior of the home when the unit is running.  In the summer you might not notice it at all unless the siding rattled

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 7 years ago

Hi Jay, I must be a little slow, because it took me awhile to figure out exaxctly what you were saying. Could it be that it was extremely warm when the installer put it in, and couldn't check the heating function?? More likely didn't bother...

Posted by Tom White, Franklin Homes Realty LLC, Franklin TN (Franklin Homes Realty LLC (615) 495-0752 or www.FranklinHomesRealty.com) almost 7 years ago

Jay, That was awesome. Such a simple mistake could have ramifications. The cooler weather was such a help with that.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) almost 7 years ago

Yep, it is always good to have other inspectors to discuss the weird stuff we find.

Mercury space capsule, I can see that. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 7 years ago

Thanks Jeffrey.  I am seldom contacted later, but will make an update if I can.  Same merry to you!

Raymond - best to have available what we are not!

Ed - blowing backwards, and CO back against the house can't be a good thing!

Clint - I see that on church roofs when they have multiple systems.

Tom - certainly no testing was done.  And should have been no matter the season.


Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Charlie - when we made radios in 7th grade shop class we didn't get a grade until we tested it! 

Maybe so Tom, but even in the summer you'd want to check to see if it was operating properly.

Don - when I first saw the condensation I did not realize what was happening.  I had to feel it!

It was good of you and Charlie to answer me, Jim!  I think they put the Y on backwards!  Mercury definitely - not Gemini or Apollo!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Although I haven't read all the comments but I'm sure someone has already made the comment.  How do you think they did that? 

Posted by James Dray, Exceptional Agents, Outstanding Results (Fathom Realty) almost 7 years ago

 Deferring to a REAL HVAC professional is a good take on this situation Jay from the school of knowing what you don't know.

Posted by Sally K. & David L. Hanson, WI Real Estate Agents - Luxury - Divorce (EXP Realty 414-525-0563) almost 7 years ago

The Y installation was probably made backwards James.

S&D - we can't see what we can't see.  They will have to remove drywall, and probably flip that Y connection.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Jay, pretty sure I have not seen this in any of my inspections either!

Posted by Joan Cox, Denver Real Estate - Selling One Home at a Time (House to Home, Inc. - Denver Real Estate - 720-231-6373) almost 7 years ago

It's an odd one Joan!  Glad I found it!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Going that extra effort to contact other professionals who might have more experience with this specific issue is a very smart practice.

Posted by Morgan Evans, LICENSED REAL ESTATE SALESPERSON (Douglas Elliman Real Estate) over 6 years ago

Thanks Morgan.  That would be the role for the inspector - get solid advice where/when needed.

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

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