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Question DetailsAsked on 9/30/2015

Can a 95% efficient furnace pull air intake from a confined closet space with a vent on the door, but no ductwork?

I had a Trane XR95 furnace installed in an older home. The furnace was placed in a small hall closet where the old furnace used to be. There are 2 PVC pipes (outside air and vent) installed on the unit that run up through an old duct hole in the ceiling and out the roof. There is no duct work installed on top of the furnace connecting the air flow, instead the furnace is flashed along the top sides, sealing the top portion of the closet off. An air flow/return vent was installed above this in the doorway. Therefore, the furnace is pulling air from the top potion of the closet, which in a sense is acting as ductwork, but it is also pulling air from the hall through the vent. My concern is this is not an efficient set up. Shouldn't duct work connect the air flow directly to the return vent? Or is this set up ok, where we have all this extra space in the upper portion of the closet that the furnace is pulling air from? The manual says the filter should be right above the air flow and isnt

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1 Answer


Hopefully BayAreaAC will jump in on this one - sounds like he could have fun with it, as an HVAC contractor.

Sounds Mickey Mouse (or maybe more Wylie Coyote or Rube Goldberg) to me - unless this is a tiny house/apartment, without ducting to the individual rooms it is going to be pretty inefficient and result in very uneven air distribution at best - and sounds more like it acts as a single point source heater like is used in some small trailer homes. Also I would guess likely to be far less than 95% efficient.

Without seeing the details, sounds EXTREMELY likely to be VERY contrary to fire code too (because this is fuel fired and not electric), as well as to building codes, not to mention probably in total violation of manufacturer installation instructions.

Also, in many (probably most) jurisdictions using building spaces or walls as ducts is illegal.

On the filter - ALL the conditioned (ventilation) air passing through the furnace should pass through the filter - both the fresh incoming air and the flow from return ducts/openings - to be filtered BEFORE it passes by the fan and heat exhanger and into the house from there as hot air.

Your unit is available in different configurations - upflow, downflow, or side discharge, so it sounds to me like your unit is likely downflow (through ducting below the unit) or sideflow (out the side), so I consider it likely the flashed off upper portion is the air intake part, getting air from the outside through the PVC pipe (for combustion and maybe through the old duct for ventilation makeup air) plus indoor return air through the return vent in the doorway (which may be a code-required fresh air makeup vent for the older unit to ensure it got adequate combustion air - your unit should be able to get all its air from the PVC pipe if installed correctly), which air should be passing through the filter before it goes through the heat exchanger to be heated. The heated outflow would then be through ducting from the bottom or side of the furnace to the house, or if installed as a point source perhaps directly through louvers in the closet door ? In which case, it might be very marginally legal, but still hokey as blazes if not in a trailer home which does not have ducting at all.

If uncertain, I would send a printout of this question and some photos and maybe a simple sketch showing the flashing and ducting/piping to Trane for their opinion - I am guessing it will result in either a scream of terror or rolling on the floor in stitches - neigther of which should be taken as an expression of approval. Of course, if you do that, you clearly have to get it corrected (original installer should do it free, if you trust him to do it at all) because otherwise Trane may well void your warranty knowing what they will know.

Or get another well-rated HVAC contractor's most experienced man to come take a look at it - though that will probably cost you about $100-150 for the visit.

Answered 3 years ago by LCD

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