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HVAC Supply & Fireplaces ?


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Inspector friend of mine in East Texas sent me the image below and related questions/concerns.

Tenant of home (rental) used the wood-burning only fireplace (BTW - only once) as when it got stoked up and running the house was filled with smoke that was coming through all the HVAC air supply vents. Damper for chimney flue was open.

When my friend got to the attic he found the additional vent pipes coming out of the chase around the chimney pipe, but was not able to see down the flue.

The vent pipes coming out of the chase were routed over to the HVAC system "supply plenum". The HVAC system is a vertical mount in a closet on the first floor. Supply plenum and distribution pipes in the attic and the return air plenum is the typical space below the vertical furnace/EVAP coil at floor level.

I am "guessing" that the vent pipes may be attached to a heat jacket (my crude terminology) around the fireplace as an effort to route the "heated air" into the HVAC air distribution system.

And ... obviously ... something has gone terribly wrong or was done really jack-legged back when.

If it were possible to remove the drywall around the chimney chase I'm sure a lot could be learned.

No identifying labels on the fireplace pre-fab type system.

Just tossing this out for some 'food for thought'.

My friend wrote a nice, clear, concise comment about having the HVAC and Fireplace representatives review and resolve as it is not a safe condition.

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You never know what you will find in East Texas, but that may be a "Heatilator" system that was popular in the 80's that had ducted warm air and blower. Seems like there was a sticker/prohibition against connecting them to the HVAC ductwork if memory serves me, so that is likely violating the listing if there ever was one. He made a good call.

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Curious, is that insulated chimney vent or tri-wall? Because if it's tri-wall, leaks in the return air duct might result in a suction at the top of the pre-fabbed fireplace appliance via the chase, which may then be carried by the outer portion of the tri-wall to the top of the flue where flue gases are released.

Marc

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The fireplace probably has a passive heat circulating jacket around the firebox. I suspect that someone tried to tap into the outer jacket to force hot air out, rather than keeping it merely a passive design. In this case, I would guess that the additional ducting is somehow "pushing" smoke out of the firebox when the furnace blower is on. Not sure how this is happening, but it's possible that the combustion air inlet in the side of the firebox and/or the hole where the gas starter line enters the firebox are allowing pressurized air to enter the firebox, blowing out the smoky air. If so, that would make for a pretty active fire -- what with blast furnace style forced air and all!

I'd love to hear what the problem really is when someone dissects it.

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