# Draw furnace return air through furnace closet



## Tim D (Oct 15, 2017)

Hi,

I have a Ducane forced air natural gas furnace with sealed combustion (PVC intake and exhaust pipes that vent directly to the roof), and the system was installed with a very undersized return duct, resulting in low airflow.  One option a contractor recommended to fix it is to remove the old return duct, cover the hole where the return air enters the machine with a filter, and cut a louver in the door of the furnace closet.  This would allow the system to draw air from the main living space of the unit, through the louver, into the closet, and directly into the return of the machine through the filter (no return ductwork).

I think this would solve the low airflow problem, but is there any issue with drawing return air through the furnace closet?  The combustion is sealed as I mentioned, but my concern is that if there ever were an exhaust leak, carbon monoxide could get sucked into the return and be spread throughout the house.

Would this setup be a code violation?  I'm in Massachusetts.

Thanks in advance,
-Tim


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## cda (Oct 15, 2017)

Welcome

Not a hvac person

Mine is not sealed unit but draws like your hvac person is suggesting

I thinking there are several reasons you can have co pumped into your house 

A good co alarm should be installed


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## cda (Oct 15, 2017)

Should have asked??

One story house or more??

Just make sure there is enough vent return opening, so your unit is not damaged 

I have to about 18 x 8 inch vents


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## Tim D (Oct 15, 2017)

Thanks very much for your response, cda.  I have a CO alarm outside the furnace closet, but it might not hurt to install one in the closet as well.  It's a two-unit condo building (building is basement plus three floors, my condo is the top two floors).  My HVAC guy said that the system requires 1,600 cfm, and the current return is 20"x8" with a few bottlenecks before it reaches the furnace (which results in about 650 cfm).  The plan would be to widen the hole where the return air enters the machine to 20"x20" or so and make sure that the louver in the door is at least that big.

Thanks again for the help and please let me know if you see any issues with this plan.  I saw this post on another site (https://www.nachi.org/bbsystem/viewtopic.php?t=17394), which explicitly says, "A furnace can not draw return air from the same room/closet that the furnace is installed," which is why I was concerned.


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## cda (Oct 15, 2017)

I guess my concern is if you are occupying two floors

How is it going to get good return from all portions of your unit?

I have one return in a bedroom and when that door is closed, you can hear the a/c struggle


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## Tim D (Oct 15, 2017)

Yes, drawing return air from all portions of the unit has been a challenge since we moved in.  The short story is that the developer clearly cut some corners on the HVAC system to save a few bucks.  The single return is not ideal, but the bigger issue so far has been the low volume of airflow.


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## cda (Oct 15, 2017)

How old is the hvac unit??


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## Tim D (Oct 16, 2017)

Installed in 2009.


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## cda (Oct 16, 2017)

Did they suggest ADD 

More return ducts??


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## Francis Vineyard (Oct 16, 2017)

Tim D said:


> Installed in 2009.


Is this a new unit or a replacement?

Also direct vent appliance it is not a violation to draw return air through a louvered door but is must be sized accordingly for the amount of air flow.

We are also assuming the original return air duct is undersized or is the appliance over-sized?


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## steveray (Oct 16, 2017)

Central return system sucks (pun intended) but it is the cheap way to do it, which makes it the common way (but so does a poorly designed duct system). You could try cutting a small return at the unit in the closet and in the door to get some more return air back...Are there gaps under the doors in all of the rooms? If there are supplies in all of the rooms but no returns, door undercut is important to keep from trying to "inflate" the room and allow the return to work....


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## Tim D (Oct 16, 2017)

cda said:


> Did they suggest ADD
> 
> More return ducts??


Hi cda.  Yes, the contractor looked into adding more return ducts but it won't be possible without ripping the whole condo apart (which I'm trying to avoid for cost reasons).  Given how tight the space is, options are very limited unfortunately.  They should have done it right the first time.


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## Tim D (Oct 16, 2017)

Francis Vineyard said:


> Is this a new unit or a replacement?
> 
> Also direct vent appliance it is not a violation to draw return air through a louvered door but is must be sized accordingly for the amount of air flow.
> 
> We are also assuming the original return air duct is undersized or is the appliance over-sized?



Hi Francis.  Thanks for your response.  The condo was gutted and redone in 2009 (before I bought it), and I believe the furnace was installed new at that point.  The appliance is the right size (not oversized) -- my contractor confirmed this.  There is a 20"x20" return grille that feeds the system, but when you take it off, you can see that the actual return duct is only 20"x8".  When the duct reaches the furnace closet, it gets down to about 4" wide to fit the space (the closet is very tight).  My high-level research combined with my HVAC contractor's assessment indicate that this is way too small (like breathing through a straw).

My building was the first one the developer ever rebuilt, and I think the HVAC part was an after-thought that he didn't plan for appropriately.  Lesson learned for me.


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## Tim D (Oct 16, 2017)

steveray said:


> Central return system sucks (pun intended) but it is the cheap way to do it, which makes it the common way (but so does a poorly designed duct system). You could try cutting a small return at the unit in the closet and in the door to get some more return air back...Are there gaps under the doors in all of the rooms? If there are supplies in all of the rooms but no returns, door undercut is important to keep from trying to "inflate" the room and allow the return to work....



Hi steveray.  Thanks for your thoughts.  Yes, central systems are not great.  I got an Ecobee thermostat with remote sensors, which helps a bit, but it's still not ideal.  The plan is as you described -- cut in a return at the machine and put a louver in the closet door so the machine can draw air in from the living space.  This isn't great but probably the only option in my price range.

Yes, the space at the bottom of the bedroom doors combined with the low volume of airflow (due to the undersized return) make it so "inflation" is not much of a problem.  This may change once I make the modification to the return to get more airflow -- we'll see.


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## Pcinspector1 (Oct 16, 2017)

Coach didn't put me in the game till now. Could an additional return air duct be added going through the floors, maybe through some closets where it's not such an eyesore?


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## cda (Oct 16, 2017)

Tim D said:


> Hi cda.  Yes, the contractor looked into adding more return ducts but it won't be possible without ripping the whole condo apart (which I'm trying to avoid for cost reasons).  Given how tight the space is, options are very limited unfortunately.  They should have done it right the first time.


I am wondering if they could at least do a floor vent from some of the top floor into ceiling of the floor below.

Just free flow opening

At least there is some circulation


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## Tim D (Oct 16, 2017)

Pcinspector1 said:


> Coach didn't put me in the game till now. Could an additional return air duct be added going through the floors, maybe through some closets where it's not such an eyesore?



Glad coach put you in!  I had a similar thought about adding another return, but I don't think there is a good way to do it.  The unit backs up to the outside wall of the condo, so approaching from the back is out.  The floor below belongs to our neighbors downstairs, so approaching from the bottom is out.  The left side is where the current return enters (and the space is very tight).  Through the wall on the right side is a bathroom (not a good spot for a return).  The top is the supply plenum obviously.  That basically just leaves the front of the machine.

The only other option we considered is penetrating the wall on the left side (where the current return is) so that the machine draws from the shared common space of the condo building stairwell.  We could then put a transfer vent on the adjacent wall so that the machine pulls air from our living space, into the condo common space, and into the side of the furnace.  This would work, but noise would likely be an issue (people in the common space would hear us through the transfer vent and vice versa, and the return grill would be inches from the fan, making it very loud).


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## Pcinspector1 (Oct 16, 2017)

Poster sez, "Low volume of air flow"? May have duct dampers in the supply that are partly closed? Just thinking.


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## Tim D (Oct 16, 2017)

cda said:


> I am wondering if they could at least do a floor vent from some of the top floor into ceiling of the floor below.
> 
> Just free flow opening
> 
> At least there is some circulation



That's an option to consider.  Thanks cda.


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## Tim D (Oct 16, 2017)

Pcinspector1 said:


> Poster sez, "Low volume of air flow"? May have duct dampers in the supply that are partly closed? Just thinking.



Great call, Pcinspector1.  The supply side of the system was undersized as well (no dampers, just bad design).  My contractor fixed this as best he could, and improved air flow by more than 50% (we measured before and after).  That was a great start -- now time to fix the return 

It's incredible to me that they installed the system the way they did.  My contractor said that it was actually dangerous in his opinion.


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## Pcinspector1 (Oct 16, 2017)

The furnace manufacture may have a trouble shooter that might fine a solution.  It's worth
a shot to contact them IMO.


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## cda (Oct 16, 2017)

Tim D said:


> Great call, Pcinspector1.  The supply side of the system was undersized as well (no dampers, just bad design).  My contractor fixed this as best he could, and improved air flow by more than 50% (we measured before and after).  That was a great start -- now time to fix the return
> 
> It's incredible to me that they installed the system the way they did.  My contractor said that it was actually dangerous in his opinion.




Do you have any flex duct you can see in the attic area, if you have an attic


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## Tim D (Oct 16, 2017)

Pcinspector1 said:


> The furnace manufacture may have a trouble shooter that might fine a solution, it's worth a shot to contact them IMO.



Thanks Pcinspector1 -- I will give the manufacturer a try.  I appreciate your help on this.


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## Tim D (Oct 16, 2017)

cda said:


> Do you have any flex duct you can see in the attic area, if you have an attic



We don't have an attic unfortunately -- that's a big part of the challenge . All of the ductwork is behind drywall, so I would have to take down the ceiling to access it.  There is flex coming off the main supply trunk, but I can see through the registers that that there are no kinks, bends, etc.

Before making any changes to the ductwork, I got 424 CFM through the system (goal per my contractor is 1,600).  After fixing the supply-side issues, I got 653 CFM.  Now, when I run the machine with the front of the fan cage taken off (so that the system is pulling air directly through the front -- not through the undersized return), I get 1,087 CFM.  This is far less than 1,600, but a huge improvement.  I'm hoping that fixing the return will provide similar results.

Thanks again to everyone for providing their thoughts.  It has been super helpful and I really appreciate it.  If you have any other comments (particularly on potential safety hazards or code violations with my plan to fix the return), please let me know.


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## Paul Sweet (Oct 16, 2017)

20 x 20 grille and 20 x 8 duct is only good for 800 to 1000 CFM.


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## Tim D (Oct 16, 2017)

Paul Sweet said:


> 20 x 20 grille and 20 x 8 duct is only good for 800 to 1000 CFM.



Yup, way too small.  I wish the guy who installed it realized this .  Now I need to get creative to make the system work.


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## cda (Oct 16, 2017)

Is your unit on a platform where 

The return air moves from the floor,,  through the fillter,, into the unit??

Kind of like this::;


https://ixquick-proxy.com/do/spg/sh...06-15.JPG&sp=6a598fef253a5915a81e14a13fc87114


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## Tim D (Oct 16, 2017)

cda said:


> Is your unit on a platform where
> 
> The return air moves from the floor,,  through the fillter,, into the unit??
> 
> ...



No, the unit is not on a platform.  The challenge is that the unit is set back in the closet with storage space in front of it, so I don't think a platform would work well here.


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## cda (Oct 16, 2017)

Tim D said:


> No, the unit is not on a platform.  The challenge is that the unit is set back in the closet with storage space in front of it, so I don't think a platform would work well here.




Just wondering mine sets on a platform on the corner of a room/ hallway

Two sides have vents 
I can add one more


I wonder why yours necks down so much, once you get to the actual unit


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## Tim D (Oct 16, 2017)

cda said:


> Just wondering mine sets on a platform on the corner of a room/ hallway
> 
> Two sides have vents
> I can add one more
> ...



I tried to upload an image but looks like the site only accepts web links.  The short answer is there is just not enough space.  There are about 4 inches between the unit and the left wall of the closet -- this space is used for the return duct.  Through that left wall is the building common space, so no expansion options there.  There is no space at all to the right of the unit (it's up against the closet wall).  I'm guessing they built the closet too small by mistake, and by the time they realized this, it was too late/expensive to fix.


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## cda (Oct 16, 2017)

Tim D said:


> I tried to upload an image but looks like the site only accepts web links.  The short answer is there is just not enough space.  There are about 4 inches between the unit and the left wall of the closet -- this space is used for the return duct.  Through that left wall is the building common space, so no expansion options there.  There is no space at all to the right of the unit (it's up against the closet wall).  I'm guessing they built the closet too small by mistake, and by the time they realized this, it was too late/expensive to fix.




You have to be a paying sawhorse to post pictures direct.

But if you can make it into a link

You can post the link. That tech is also above  my kindergarten diploma.


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## Tim D (Oct 16, 2017)

cda said:


> You have to be a paying sawhorse to post pictures direct.
> 
> But if you can make it into a link
> 
> You can post the link. That tech is also above  my kindergarten diploma.



I just tried to add in the image -- let's see if it works.  The part circled in red is the current return.  As you can see, space is tight!


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## Tim D (Oct 16, 2017)

cda said:


> You have to be a paying sawhorse to post pictures direct.
> 
> But if you can make it into a link
> 
> You can post the link. That tech is also above  my kindergarten diploma.



Looks like the image didn't work.  Here is the link: https://ibb.co/cUEtd6


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## cda (Oct 16, 2017)

Sounds like sacrifice some space or find the best way to add more return

Hopefully your ac guy told you the unit can get damaged by the way it is now, at least that is what my guy said about restricted return


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## Tim D (Oct 16, 2017)

cda said:


> Sounds like sacrifice some space or find the best way to add more return
> 
> Hopefully your ac guy told you the unit can get damaged by the way it is now, at least that is what my guy said about restricted return



Yes, that's exactly what he said.  The low airflow doesn't move enough heat, and eventually the heat exchanger can get worn out.  I plan to have him implement a fix soon.  Thanks again!


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## cda (Oct 16, 2017)

Tim D said:


> Looks like the image didn't work.  Here is the link: https://ibb.co/cUEtd6





That picture works

Stick a jack under it

Cut some of the duct off on top

Make some room for more return on the bottom


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## tmurray (Oct 16, 2017)

steveray said:


> Central return system sucks (pun intended) but it is the cheap way to do it, which makes it the common way (but so does a poorly designed duct system). You could try cutting a small return at the unit in the closet and in the door to get some more return air back...Are there gaps under the doors in all of the rooms? If there are supplies in all of the rooms but no returns, door undercut is important to keep from trying to "inflate" the room and allow the return to work....



You will probably end up doing what Steveray posted from a cost standpoint. It's not ideal, but it does work.

Just to add to Steveray's post, another option is to add air transfer grilles between rooms and the hallway. Some people prefer this look to the undercut doors.


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## Tim D (Oct 16, 2017)

cda said:


> That picture works
> 
> Stick a jack under it
> 
> ...



Tough to see from the pic, but there is another bottleneck in the return duct where it enters the closet.  There is no room for expansion unfortunately.  So I can add more return close to the machine, but the duct will still be restricted.


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## Tim D (Oct 16, 2017)

tmurray said:


> You will probably end up doing what Steveray posted from a cost standpoint. It's not ideal, but it does work.
> 
> Just to add to Steveray's post, another option is to add air transfer grilles between rooms and the hallway. Some people prefer this look to the undercut doors.



Thanks tmurray.  I agree, that's probably the best option at this point.  I appreciate the help!


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## cda (Oct 16, 2017)

Tim D said:


> Hi,
> 
> I have a Ducane forced air natural gas furnace with sealed combustion (PVC intake and exhaust pipes that vent directly to the roof), and the system was installed with a very undersized return duct, resulting in low airflow.  One option a contractor recommended to fix it is to remove the old return duct, cover the hole where the return air enters the machine with a filter, and cut a louver in the door of the furnace closet.  This would allow the system to draw air from the main living space of the unit, through the louver, into the closet, and directly into the return of the machine through the filter (no return ductwork).
> 
> ...





Can you do this fix and also bring another return duct from upstairs??


Is your unit upstairs or downstairs ?


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## Tim D (Oct 16, 2017)

cda said:


> Can you do this fix and also bring another return duct from upstairs??
> 
> 
> Is your unit upstairs or downstairs ?



The unit is downstairs.  I'd love to bring in another return duct from upstairs but there is no room (without considerable expense).


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## cda (Oct 16, 2017)

Tim D said:


> The unit is downstairs.  I'd love to bring in another return duct from upstairs but there is no room (without considerable expense).




I was wondering about the idea of vents in closet door

Plus just an duct from upstairs that also dumps open, into the closet


Anyway you have your question answered

Plus some ideas

With your ac company get the best results you can 

Hate to say might be a little trial and errror


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## Tim D (Oct 16, 2017)

cda said:


> I was wondering about the idea of vents in closet door
> 
> Plus just an duct from upstairs that also dumps open, into the closet
> 
> ...



Yes, trial and error for sure.  We've already had some improvement, so that's encouraging.  Thanks again for all the help -- I really appreciate it.


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