Interesting HVAC Configuration & a Couple Questions

[Chuck Evans]

Encountered this HVAC configuration in a 1956 3,700 sf home in Houston yesterday. Very atypical. Large 3-phase commercial condensing unit coupled with large evaporator coil in the garage. Heat and air handling is supplied by tandem residential type furnaces mounted side by side below the coil in the garage. There is a single thermostat and no zone controls. Both furnaces and air handlers are configured to run at the same time.

Question #1: The duct work is all metal as required for installation in a garage, however it is fitted with bellows type vibration isolators. Does anyone know if the isolators are listed for use in a garage environment?

Question #2: The tandem furnaces are both induced draft type units. They have been fitted with a "manifold" to combine the exhaust vents. Does anyone know if this is a listed device or whether it was an on-site creation (it was well made)?

There are other issues with this installation, but these are the only two items I had real questions about.

[Charley L. Bottger]

Other than being a energy hog I see no problems with the tandem flue exhaust as it does appear to be shop constructed not factory. We are allowed to use flex vibration absorbers in garage installs very common on large systems TX may have their own rules. Personally I see no problem with the flex as long as it does not leak air

[Chuck Evans]

Thanks Charley

[rjohnson11]

The only issue I see, other than the furnaces are old would be the safeties. Being operated in tandem that way with a common flue, there should be a cut out control to prevent operation if one of the draft motors fails.

I would strongly suggest that a license HVAC contractor inspect the system to ensure proper and safe operation.

[Chuck Evans]

Here is the verbiage that I used in the report regarding the shared vent. BTW: The left side furnace was not operational and the vent sections were disconnected in the attic.

Atypical configuration for two induced draft furnace units to share a common exhaust vent manifold and vent. Recommend consulting with a qualified, licensed HVAC contractor to determine if this configuration complies with manufacturer's specification and UL listing.