General Furnace Question

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I have a Trane furnace.
One of the heat registers in my livingroom is underneath my sofa. There are two registers in that room.
Is it safe to completely close off the register, or would it be better to leave it open a tad?
I am not sure if this could damage my unit, and thought I would get some expert advice here.
Many thanks.
Kate
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Properly designed, modern units can handle a 10-15% blockage of discharge air. So if that furnace has 10 total vents closing one is no big deal.
It might whistle a little if it is on the high flow side of the plenum. If it does you may want to reconsider.
If it is an older system or you experience any noticeable change you can open it back up. It isn't going to kill the system on a trial basis no matter what. The worst thing that can happen is the furnace will shut down via the high limit switch.
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On Mon, 2 Feb 2009 19:33:49 -0500, "Colbyt"

Ive been in the hvac business almost 30 yrs now colbyt. Could you please point me to where you read that: "modern units can handle a 10-15% blockage of discharge air." Im not arguing that you cant close one register. I want to know where you pulled that number from.

........and if its a newer system, you can split the heat exchanger with repeated limit switch shutdowns. Bubba

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wrote:

That would be a quote from a certified engineer who was working on redesigning some systems a few year back so "modern" is a relative term.
I do agree that excessive high limit shutdowns can cause problems with the modern tin heat exchangers.
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On Wed, 4 Feb 2009 19:12:59 -0500, "Colbyt"

Ahh, an EE. That pretty much explains it. Usually I call that "BS". Bubba

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wrote:

Bubba,
I would expect nothing else from you.
Colbyt
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On Fri, 6 Feb 2009 19:39:36 -0500, "Colbyt"

The feeling is mutual, sweetheart. Bubba
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Thank you very much for taking the time to help.
Kate
Colbyt wrote:

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Can you move the sofa?

Move the sofa, is cheaper?

What about the sofa?
Expert advice: cost more! <G>
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or put the sofa on small platform where legs are raising sofa ainch or two so air can still flow
older folks will love the higher sofa, easier to get up and down
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On Mon, 2 Feb 2009 18:00:13 -0800 (PST), " snipped-for-privacy@aol.com"

You can tell me! Are you having sex; at your age, on the sofa - don't answer, but you can explain.
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funny.
but for other elderly family members I put sofas and chairs, and a couple beds on platforms so the elderly could still stand up....
my high school buddy did this for his wife after she ..had knee surgery.
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Kate wrote:

Kate, you might consider getting a long deflector for the register under your sofa. For example:
http://www.improvementscatalog.com/home/improvements/792923067-heat-register-deflector.html
"Use the heat register deflector to channel the heat into your room and not into the bottom of the couch. Our PVC air register deflectors sit over the register and re-direct the cooled or heated air from under the furniture. Simply place air register deflectors over the register. The air register deflectors click securely onto the floor register and extend from 22" to 37" bringing the air out from under your chair, couch, bed, cabinet, curtains or end table. "The heat register deflector is a 2-piece unit 11-1/4" wide and 1-1/2" high to deflect air discretely. The air register deflectors come with one long clip to lock onto the register and two short clips to lock the desired length."
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I have some of these leftover. I had placed one under my sofa, but the skirt on the sofa looked funny then. But, someone else on this newsgroup suggested putting the sofa on blocks a bit. I will try this and then install the deflector. Many thanks.
Kate
Erma1ina wrote:

http://www.improvementscatalog.com/home/improvements/792923067-heat-register-deflector.html

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The real question here is what's the point to closing it off? The heat you get out of it eventually makes it's way into the room. If the room was too hot relative to other rooms, or the sofa is getting hot, then it would make sense to try to balance it. But if it's ok in that respect, then I don't see any issue with leaving it open.
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Mmmmm, sofa with heat register right under it . . . sounds like a nice nap sofa. -- H
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Why don't you just deflect it with an extent ion like this:
http://www.improvementscatalog.com/home/improvements/792923067-heat-register-deflector.html
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On Fri, 06 Feb 2009 22:51:46 -0500, snipped-for-privacy@mucks.net wrote:

There are two registers in my bedroom BECAUSE the dresser is over one. You guys saying it being blocked is going to damage my furnace?
All closing one or two registers is going to do is make the rooms with the closed registers cold and make the other registers in the house provide a little more air. By blocking one 4" pipe out of ten you are NOT reducing the flow by ten percent. Not likely even by two percent. The pressure in the plenum will possibly go up .1 of an inch of water The blowers are generally rated at 1200-1700cfm at .3 inches water column pressure. Doubling the static pressure reduced the efficiency of the blower by half. - not the delivery, but the efficiency in CFM/watt. The average furnace fan is 10-15% efficient, and produces something like 2 cfm/watt. Actual airflow dropped by one third when plenum pressure was doubled from .6" to 1.3" In a study of furnace installations, plenum pressures were in the range of .25 to 1.9". That same test shows that a brushless PM blower motor is SIX times as efficient as an AC split cap motor at low speeds (used in constant flow systems extensively here in Canada). This amounts to a 74% savings in electricity used by the furnace - and as much as 25% of whole house use. The loss of heat output from the inefficient fan motor increases the gas consumption by 14%. (I guess that's why I didn't see ANY gas savings when I put in the new Medium efficiency (80+%) furnace but saw a huge difference in electrical consumption!!!
If you doubt what I'm reporting you can read the report yourself at http://repositories.cdlib.org/cgi/viewcontent.cgi?article527&context=lbnl
The test was done under the auspices of the Ernest Orlando Lawrence Berkeley National Laboratory at the University of California by Ian Walker and Jim Lutz. for the California Energy Commission and the US Department of energy.
VERY interesting reading if you are into that type of thing.
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snipped-for-privacy@snyder.on.ca wrote:

>http://www.improvementscatalog.com/home/improvements/792923067-heat-register-deflector.html
Apparently YOU did NOT READ this research draft.
I suggest you DO READ page 13 wherein the TEST SETUP is described. Here's an excerpt pertinent to the issue of whether a furnace can be damaged by blocking heat registers:
"The burners did not operate during the test and no gas was hooked up. No cooling coils or filters were installed. In real field installations the cooling coils and filters will act as additional flow resistance leading to increased pressures across the blowers."
In other words, ONLY the air-handling characteristics of the furnace BLOWERS were being examined in the test reported in this study, NOT the heat characteristics of the furnace and their effects.
Blocking supply registers can result in damage to a furnace by decreasing the heat dissipation from the heat exchanger and its environs.
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wrote:

I did read it, and I did understand it. And what's more I can test the static pressure in my system if I want to. I know how and caould make the required test equipment very quick;y and cheaply.

Fully understood.

And the airflow change (which can be tetermined by the pressure change) is all we need to know to know if there will be a problem. Accorsing to the information shown in the graphs included, it is obvious it is not going to cause a problem unless there are fewer than something like 5 outlets and you block one. In my house there are mo less than 12. For most of the time I have owned the house (26 years - 20 with the original (at that time 8 yr old) furnace) at least 2 of those registers were completely closed, one has been under/behind a couch, and 2 are shut off about half the time when 2 bedrooms are not needed (daughters not home).
Add to that the FACT that many homes have balancing dampers installed in the branch runners - my house has at least 3 (exposed in the finished basement) Two of them are set to about 2/3 flow (on the six inch pipes heading to the upstairs of the 2 story) to restrict the flow to the upstairs so enough heat gets into the main floor.
This was all checked when the new furnace was installed about 7 years ago, and the plenum pressure/airflow was all well within the specified parameters. Both the pressure difference across the exchanger, the heat rize across the exchanger, as well as the pressure in the plenum was checked, and all were well within limits. I don't have the pressure numbers but IIRC both pressure readings were well under an inch of water.with the fan speed adjusted for the desired heat rize. The installer did say the ducting was "generous".

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