HVAC ducting questions. What is this?

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DIY_Dutch

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Bought a 1979 build in the suburbs of Chicago this past year. Lots of new things for me to fix/figure out but this one has me confused.

Furnace & AC are carrier units from 2016. Seem to function well with the typical low airflow to the second floor issues. In the basement the mechanicals are installed in an oversized “closet” that is approximately 8’ x 40’. My question concerns some really big ductwork. There is a 13” duct with damper with an exposed end in the closet. The route from the exposed end is up into the chimney chase (home has a wood framed chimney chase), across the back of the chase, down back into the basement closet, five feet horizontally, and then ties into the cold air return.

I don’t understand the point of this duct. Local HVAC company allegedly told the previous owner it was for “make up air” for original furnace. Newer furnace is a 98% model with pvc intake and exhaust piping. Make up air from the same closet doesn’t make sense to me. Reconnecting this ductwork to a new cold air return (from when the furnace/AC was replaced) doesn’t make sense to me.

Two issues I’d like to resolve;
1) The area around this duct has a number of gaps leading to cold air pouring into the basement from either the chimney chase or the outside. If not needed, my work sealing up these leaks would be much easier with the duct removed and out the way.
2) Could this duct be minimizing the cold air returns for the first and second floor? There are cold air returns in the basement plus this oversized monstrosity hidden away in a closet.

I’m aware of which contractor issued the original opinion and am searching for a reputable second opinion but have learned a great deal over the years from reading this website regarding my last house and thought some of you might have some thoughts.

Thanks in advance,
Dutch

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wwhitney

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Not quite following your description of the duct routing--is it just going into the chimney chase the minimal amount necessary to get from point a to point b horizontally? Or is there a tall one or two story vertical loop within the chimney chase?

And you mention basement returns, are there open intake grilles in the basement, or just first floor grilles with ducting in the basement? Are there supply registers in the basement?

Cheers, Wayne
 

DIY_Dutch

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There are two supply registers and two return grills in the finished area of the basement.

I wasn’t sure about your question about the possibility of a tall loop in the chase so I shoved my phone up there on the end of a broom and took a picture. The duct is about 48” straight with a 90 degree turn. The attached picture seems to show nothing attached to the other side of the 90 degree fitting. The metal structure you see is the backside of the fireplace insert. Could they have plumbed it this way to try and capture heat from the fireplace and use the air handler to distribute the heat to the rest of the house? First home I’ve ever owned with a fireplace but my inspector, realtor, and previous owners HVAC guys all were perplexed by this duct.

Sorry for the image tilt, upper left corner is up.

Dutch
 

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Fitter30

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Fireplace takes house air to burn. Does it make any sense take the fresh air duct is make up air for the fireplace to burn and not pulling air from around windows and doors. Fireplaces in that era are energy hogs. A house i owned built in 1976 had a fp unless it had a roaring fire the house would get cold. Sheetmetal supplier in your town, internet, or hvac supply house can get u round caps. Might need crimpers for sizing them. As for as low air flow try turning fan switch to on at thermostat. If that air flow is enough the furnace just needs a simple wiring change.
 

DIY_Dutch

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Fireplace takes house air to burn. Does it make any sense take the fresh air duct is make up air for the fireplace to burn and not pulling air from around windows and doors. Fireplaces in that era are energy hogs. A house i owned built in 1976 had a fp unless it had a roaring fire the house would get cold. Sheetmetal supplier in your town, internet, or hvac supply house can get u round caps. Might need crimpers for sizing them.

I’ll look into capping it. The only reason I don’t think it’s make up air for the fireplace is the matching duct on the opposite side that is connected to the cold air return on the furnace. That seems like a good way to introduce carbon monoxide into the house.

As for as low air flow try turning fan switch to on at thermostat. If that air flow is enough the furnace just needs a simple wiring change.

Even during the cooling season with higher fan speeds the airflow upstairs is anemic in all but the primary bedroom. Since it seems to be an open wound on the return system I’m wondering if the furthest returns are really functioning when there is a much easier place for the system to grab air from i.e. the giant duct that doesn’t seal up completely.
 

jadnashua

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Do you actually have return ducts in all rooms? Without them, especially if you close bedroom doors, it's like trying to blow up a balloon...doesn't move much air through. Do things change if the doors are open?

What amount and type of insulation is in the attic?
 

DIY_Dutch

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Do you actually have return ducts in all rooms? Without them, especially if you close bedroom doors, it's like trying to blow up a balloon...doesn't move much air through. Do things change if the doors are open?

The only rooms without returns are the bathrooms. Bedrooms all have two return grills in a hi low configuration. No change to performance with doors open or closed.

What amount and type of insulation is in the attic?

Batt type fiberglass, R30. On the list of things to address. It’s installed poorly and nothing is air sealed up there.
 
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