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Old 12-29-2011, 06:48 PM   #1
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Closing dampers too much?


I have a
Bryant 311JAV024045
Eff: 80.0%
BTU input/ouput: 44,000/ 35,000
CFM max/min at 0.5 ESP: 845/555
With 4, 6" supplies.

Each run has it's own damper.

I closed down one run so it doesn't dry out the holiday tree. I closed off another run to the spare bedroom. Now the other two runs are rather loud. I dampened those two runs so that the airflow is more pleasant. Now I'm wondering if there can be a problem by choking the system to much with the dampers?

Should there be a damper on the return duct to compensate for the reduced flow on the supply?

thanks


Last edited by fromscratch; 12-29-2011 at 09:04 PM. Reason: clarify furnace type
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Old 12-29-2011, 06:52 PM   #2
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Closing dampers too much?


yes you will cause the furnace to trip off on high limit.you can't cut that much heat flow out of unit ..when having only 4 runs to start with seem to small. should have more air flow over heat exchanger so you don't crack it..

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Old 12-29-2011, 06:54 PM   #3
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Closing dampers too much?


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I have a small 50K BTU furnace with 4 supply runs. Each run has it's own damper.

I closed down one run so it doesn't dry out the holiday tree. I closed off another run to the spare bedroom. Now the other two runs are rather loud. I dampened those two runs so that the airflow is more pleasant. Now I'm wondering if there can be a problem by choking the system to much with the dampers?

Should there be a damper on the return duct to compensate for the reduced flow on the supply?

thanks
no don't install any dampers on return air side....
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Old 12-29-2011, 06:55 PM   #4
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Closing dampers too much?


No pro but I think I've read here that to prevent overheating of the furnace that returns should not be dampened and it is best not to do so with supplies.
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Old 12-29-2011, 06:59 PM   #5
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Closing dampers too much?


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No pro but I think I've read here that to prevent overheating of the furnace that returns should not be dampened and it is best not to do so with supplies.
yes we put dampers on the feed lines to control and balance the heating system...but as you mentioned have to be careful so furnace don't overheat....I have never installed on cold air return...ben
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Old 12-29-2011, 08:00 PM   #6
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Closing dampers too much?


might want to relieve that discharge air with a duct looping back to the return right off the discharge with a damper if this is a seasonal happening
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Old 12-29-2011, 08:05 PM   #7
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Closing dampers too much?


A 50K furnace should be moving around 800 cfm. Four 8" supplies will be close to that. Much less then that and you'll ruin the limit and risk cracking the heat exchanger.
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Old 12-29-2011, 08:12 PM   #8
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Closing dampers too much?


First off, what is the ambient air temp and humidity of the house? Second, at what temp do you have your thermostat? If you do not keep the tree watered, and with the fact, that it is now the 29th of December and most cities are almost done with tree pickup, I would say it is time to take that puppy down, or switch to a fake tree next year.

Open the vents to do yourself a favor. If the system was designed with just two supplies and no return in the living area, it would have been done that way.
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Old 12-29-2011, 08:26 PM   #9
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Closing dampers too much?


Age/brand & model of the furnace would help. The indentification plate inside your furnace will list the recommended temp rise for the heat exchanger of your furnace. That is the difference in temp of the air entering the furnace compared to it's temp when leaving the furnace.
By placing a thermometer into a small hole in the plenum beyond the line of sight of the heat exchanger and subtracting that temp reading from the room temp, you will see if you are within the recommended furnace temp and if adjustments will need to be made. (like how much dampering of your ducts is possible)

We don't know here if your installed ducting was over or under sized for the furnace. We also don't know your real gas output or fan speed but the measured temp rise compared to the furnace listed temp rise will give us the best info to work with..
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Old 12-29-2011, 09:00 PM   #10
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Closing dampers too much?


Bryant 311JAV024045 (year 2003)
Eff: 80.0%
BTU input/ouput: 44,000/ 35,000
CFM max/min at 0.5 ESP: 845/555

There are 4, 6" supplies.

Last edited by fromscratch; 12-29-2011 at 09:29 PM.
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Old 12-29-2011, 09:21 PM   #11
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Closing dampers too much?


Not only should you not damper any runs,you might want to consider adfding 3 or 4 more supply runs,or like Marty says increase the 4 runs you have to 8"
These suggestions are for metal pipe sizes.If you have flex pipe all the sizes should be at least a size larger.
Now I have seen a lot of things with return airs.I have even seen a few that were not connected to the furnace,but I have never seen one with a damper in it.
Do not damper the return.As it is just going by the supply side,your return is already probably too small.
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Old 12-29-2011, 09:53 PM   #12
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Closing dampers too much?


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you might want to consider adfding 3 or 4 more supply runs,or like Marty says increase the 4 runs you have to 8".
The joys of buying a home, The projects never stop.
The return air goes through a 12" duct. Seems OK for the 4X6", But probably have to increase that as well if I add any more runs.

So in short, OPEN up those dampers. and #2, I probably need to consider expanding the supply side for the long term benefit of the furnace.
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Old 12-29-2011, 10:11 PM   #13
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Closing dampers too much?


Long term benefit of the a/c system and yourself moreso than the heating/furnace. With high static pressure, higher in cooling mode as the blower speed is high versus when in heating mode and running low or med-low, the air is being resisted over the evaporator, less evaporation, more chance of liquid returning to the compressor and taking it out, less system capacity so less and not as cool air being delivered to living space equating to system running longer (until compressor and blower motor burn out) which means higher electric bill and on the comfort side, less dehumidification so sticky cool air comparatively.
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Old 12-30-2011, 12:08 AM   #14
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Closing dampers too much?


No A/C, just a furnace.
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Old 12-30-2011, 12:19 AM   #15
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Closing dampers too much?


dang it.

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