# 2 vents off of one duct



## phantasm72 (Jul 19, 2010)

Im installing a bathroom in the basement. In the ceiling space, I have a duct supplying heat to the living room above. I was thinking, to get heat into the new bathroom, just cutting into the duct and adding a diffuser (or whatever you call them) to blow into the bathroom.
Obviously I can do this, but is it wise? Will adding a second vent mid-duct mean that all the hot air will exit the first vent (to the bathroom), and basically leave little for the second vent (going upstairs to the living room). OR will both rooms get about equal amounts of heated air?


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## beenthere (Oct 11, 2008)

How bad do you want your living room to smell?


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## AllanJ (Nov 24, 2007)

If the new register (diffuser) for the bathroom is closer to the furnace than the existing registers, it could drain off a disproportionate share of the warm air from the duct. If you put in an adjustable louvered register, then you could balance the flow.

There are formulas for choosing the size (square inches) of a register cut right in the main duct versus a register at the end of a (lateral) smaller duct extending from the main duct. I don't know these formulas.


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## hvac122 (Dec 10, 2007)

The heat run for the living room was sized for that area only. It is not a good idea to change that. I would add another vent off of the main trunk line.


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## phantasm72 (Jul 19, 2010)

beenthere said:


> How bad do you want your living room to smell?


 ?? this just a joke about 'bathroom' smells wafting up the vents or are you making reference to some serious potential moisture/mould issue?


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## phantasm72 (Jul 19, 2010)

hvac122 said:


> The heat run for the living room was sized for that area only. It is not a good idea to change that. I would add another vent off of the main trunk line.


 Yeah, I looked at that, but just the way the joists and existing duct work are, its not really possible without significant rearranging of stuff (more than it would be worth). There is another heat vent in the livingroom, and two in the dining room, which is open to the living room. Im not worried about _some_ of the heat being diverted, just not _all_ of it. But I suppose as the above poster mentioned, having an adjustable louvers would limit the air diversion. The bathroom itself I dont expect to be too cold anyways. The basement is well heated and insulated, and the bathroom is going to be pretty much in the middle. I could probably do without, but I thought it would be wise to have heated air going in on days that the shower is used, just to help circulate and remove any moist air and prevent any sort of dampness issues.


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## Jackofall1 (Dec 5, 2010)

Other than the possible drifts of odor from the bathroom the livingroom via the ducting there is nothing wrong with the idea, especially if you add a means of balancing the two amounts of air. If you wanted to keep the volume to the living room you could increase the line size upstream of the new branch, say if it was 6" make it 7" and then add a reducer after the new duct tap.


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## beenthere (Oct 11, 2008)

phantasm72 said:


> ?? this just a joke about 'bathroom' smells wafting up the vents or are you making reference to some serious potential moisture/mould issue?


When the heating system isn't on. those bathroom smells will rise to your living room.


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## Jackofall1 (Dec 5, 2010)

This is true, drifting odor, unless you have an exhaust fan running.


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## sktn77a (May 11, 2009)

AllanJ said:


> If the new register (diffuser) for the bathroom is closer to the furnace than the existing registers, it could drain off a disproportionate share of the warm air from the duct. If you put in an adjustable louvered register, then you could balance the flow.


If you put a damper where you take off from the living room duct, you can adjust the airflow so that you still get adequate air to the living room and some to the bathroom. The advantage of the damper on the takeoff over an adjustable register is that it will be quieter and the air velocity will be lower.


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## hvac122 (Dec 10, 2007)

phantasm72 said:


> Yeah, I looked at that, but just the way the joists and existing duct work are, its not really possible without significant rearranging of stuff (more than it would be worth). There is another heat vent in the livingroom, and two in the dining room, which is open to the living room. Im not worried about some of the heat being diverted, just not all of it. But I suppose as the above poster mentioned, having an adjustable louvers would limit the air diversion. The bathroom itself I dont expect to be too cold anyways. The basement is well heated and insulated, and the bathroom is going to be pretty much in the middle. I could probably do without, but I thought it would be wise to have heated air going in on days that the shower is used, just to help circulate and remove any moist air and prevent any sort of dampness issues.


Your bathroom exaust fan will remove the moisture and such to the outside. Not sure how heated air will help with moisture. 

Usually a basement bath will require a very small btu's to heat so if your not worried about living room then it should be okay.


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## beenthere (Oct 11, 2008)

And his living room will still smell like his bathroom.


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## hvac122 (Dec 10, 2007)

beenthere said:


> And his living room will still smell like his bathroom.


Agreed


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