Conserve Energy: Can I Block basement vents? - http://www.hvacmechanic.com/ Forums
Original message
| ecofreako
 |  "Conserve Energy: Can I Block basement vents?"
, posted Thu 17 Nov 14:17:  
Greetings;
I have a gas furnace in the basement, (a Duomatic Olson HCS-70/60H) and have blocked the ducts that deliver to the basment, as I don't need to heat the house there. I've just discovered that on the actual furnace unit itself is a vent coming off the main duct trunk. Can I seal this off to allow less heat flowing to the basement and more on living floors?
---Good wishes to all, from Ec0 in northern BC
[this message was edited by ecofreako on Thu 17 Nov 14:20] |
| Replies:
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| Freon
|  "Re(1):Conserve Energy: Can I Block basement v"
, posted Thu 17 Nov 15:39:
DO NOT SEAL any vents! Your furnace is designed to safely run when there is a specified amount of air flowing through it. If you restrict the necessary air, the furnace will run hotter and will accelerate the death of the heat exchanger. Also running the heat exchanger hotter is less efficient with hotter combustion gas going up the flue. To balance your duct system you'll need to add a duct, either a return or supply, that's equivalent in air flow capacity as the duct (supply/return) you want to close off.
[this message was edited by Freon on Thu 17 Nov 15:42] |
| | ecofreako
|  "A Fine Balance?"
, posted Thu 17 Nov 17:44
Hmmm, thanks Freon for the reply. I certainly didn't guess the physics of the airflow was all that precise. I think I understand from what you're saying that I shouldn't close anything without opening somewhere else to keep everything at the same pressure...but not exately why that should be.
2 years ago, I taped up the duct supplies (at least 4) in the basement (in addition to the option of turning the switch that shifts a plate near the output that provides partial blockage). This noticibly increased the pressure, and probably temperature exiting the main floor supply registers. Discovering the vent I spoke of in the main output duct, that seems only to be venting hot air outward, I figured this would only be a fraction addition of the original bloackage I attempted to complete those 2 years ago.
Could you help me understand the implications of closing off supplies, better?
---Ec0
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| | Freon
| "Re(1):A Fine Balance?" , posted Thu 17 Nov 19:21
Your observations are correct. As you close off supply registers the static pressure in the duct system increases causing an increase in velocity at the registers. But with this increase in velocity comes an increase in the frictional effects of the duct walls. The net effect is total air flow volume will decrease even though velocity at the registers increases--it's not an equal trade-off. Picture a garden hose going into a straw. No matter the water pressure, there's a limit to the water volume flow through the straw. Now furnaces have a range specified on their data plate for temperature rise through the heat echanger so there is leeway. But before you go randomly closing vents you need to check this temperature rise to be sure it's within the manufacturer's specification otherwise your furnace may start intermittent gas burner shut-down on high limit safety. And realize the lower volume of ait flowing through the heat exchanger will result in less efficient heat transfer. Good luck with your project.
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| | ecofreako
|  "A fine Balance, then!"
, posted Fri 18 Nov 01:07
Oh, I see..thanks Freon! Yes, right...friction, so that return air wouldn't be as strong and therefor not 'exchange' the heat as efficiently. Well, I don't know if I'll seal up things as much as I originally wished, maybe I will...all those little angles and holes along the ducts themselves sure leak a lot, real duct tape I should try...but I'm on the 'wares now thanks to your guidance. I've even been using filters on the registers that I guess are messing with the flow as well...but the unit itself has been in great condition, especially for not being serviced in I'm guessing many years, maybe 20. Just trying to work with what I got, 'specially with the price of gas this winter. Cheers!--Ec0
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| | tomme44
| "Re(1):A Fine Balance?" , posted Thu 17 Nov 18:57
If you have a 2 zone system with dampers in the plenum to adjust the airflow or close it off to one zone then it is fine. This is assuming it is properly sized and installed correctly.
tomme
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| | ecofreako
|  "Unknown Zone:"
, posted Fri 18 Nov 01:15
Hi Tomme, I don't know if I have a two zone system...if those dampers are evidence of that, then i do. Things have been running well, I'll just hope that continues. Have a fun Winter! ---Ec0
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