Warm air system getting you smoked?

            Last month you should have learned that when I look at a system, I think like the system in order to ‘see” the possible problems that can arise.  This time you will be confronted with the infamous ‘Warm Air Heater” or as my friend Dan Holohan likes to refer to it as ‘Scorched Air.” 

You may have already received some of the usual complaints like, ‘When the furnace comes on, it gives off a funny odor” or ‘The fan seems to make more noise than it did last year.” Sound familiar? Trust me, you are not alone. Many of us get that complaint this time of the year and most of the time it is simply, the ‘odor” the customer smells is the normal heating of air. Normally, but not always.  

            There are some items that can cause the odor and all need to be checked out to insure the safety of our customers.  A cracked heat exchanger is one area that needs to be checked.  A clogged chimney base is another, and don’t overlook the possibility that an attic fan may still be operating in a hot attic.  Poor combustion or a smoky fire can also cause odors in the home.  I personally need to strike out, before I condemn the unit.

            Since the furnace has been off all summer, the customer is not used to the odor that may have been present last winter, so a check of the chimney base is first.  A visual inspection of the base is taken, and if clear or when cleared, I would use my draft gauge to check the chimney draft.  Then I would move onto the heat exchanger to check.

In order to do this easily, I normally use a draft gauge.  In this case I would use that good old fashioned big gauge, not a pocket gauge.  Set the gauge on a stable setting and ‘zero” it out.  Insert the probe into the ‘peep hole” and read the draft.  It should be negative, unless you have a pressurized unit, in that case you will not have an opening and a different set of rules apply. 

O.K., back to a non-pressurized unit’with the fire on you should have a negative reading. When the blower comes on, should there be a change on your draft gauge? Think about it for a moment, the fire side and the house side should have no interaction at all, so the gauge reading should not change.  If it does, you probably have a cracked heat exchanger.  Strike one!  

Next, I would remove the humidifier from the ductwork. With the fire on and ALL the lights off in the area, I would put my flame mirror in the plenum and look for any sign of light. If any light can be seen, it has to be coming from the fire chamber area, right?  Strike two!

 At this point I am fairly sure I have a crack in the heat exchanger, so I would move on to the final test.  This test would only be done as step 3.  I would drill a small ¼” test hole in the plenum area, put the fire into a smoke condition, and do a smoke test.  If I saw a trace of smoke on the test paper, strike three, it’s out!

            One of the most difficult things to convince the customer of is that their attic fan is causing the problem.  The only way that I could convince them was for them to ‘see” it for themselves.  How, you ask?  OK, I’ll show you. 

Look at the home and the weather.  Is it cool enough outside that all the windows and doors are closed?  Is the weather just cool enough but the sun shining? This is the best condition for you.  Or possibly is the air conditioning on and all windows and doors closed’ also good for you. 

To check this you must put the house into the same condition as when the odor was detected.  Close all the windows and doors, ensure the attic fan is on and running. Now you and your draft gauge are going to enter the boiler room (or closet in most cases) and insert the draft probe into the test hole in the flue pipe.  If the attic fan is the culprit, you will see a positive reading on the gauge.  Have someone turn the attic fan off and the gauge will miraculously return to the negative. 

Now you can do the same with the customer in the boiler room.  This will literally ‘show” them the problem. In this case you can tell them they need more ventilation in the attic because not only is it causing an odor problem, it is taking the air that they have paid to cool and they are trying to cool the neighborhood with it.  The cooled air is being drawn out of the house to the outside. When you are finished, the customer will be satisfied, but possibly not happy with your diagnosis of the system.

            Remember, as we start to get busier as the seasons get colder, continue to send your war stories to me at johngriffin@tampabay.rr.com I love to hear from you.