Why Closing your Air Vents Will NOT Save you Money???

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wrote:

Of course you have to close the doors to those rooms, and I noticed a lot of coldness at the crack at the bottom of the door, so you probably should put a rolled up towel at the open crack.
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On 1/27/2016 6:48 PM, Micky wrote:

I monitor my furnace run-time and graph it in real time. I can tell from the graph when I turned on my computer and added another 200W of heat.
I don't remember the numbers, but I did the experiment and determined that closing off the vents and closing the doors made significant reduction in gas consumption.
BUT!!! My house is tight...tighter than the minimum standards for air changes/hour according to the guy with the blower door. If you've got leaks, it's hard to predict, but you can measure it.
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On Thursday, January 28, 2016 at 3:08:12 AM UTC-5, mike wrote:

If you have a house with more air leakage to the outside, closing off vents is going to work the same way. In fact, because you'd be burning more gas in a leaky house, the savings would be even more than in a very tight house.
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On Thursday, January 28, 2016 at 6:41:34 AM UTC-6, trader_4 wrote:

You're assuming some or all of the leaking to the outside is from the rooms shut-down...
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On Thursday, January 28, 2016 at 7:47:23 AM UTC-5, bob_villain wrote:

That's only necessary for the last part of what I said, ie that you'd save even more in a leaky house. And it's a reasonable assumption. But the assumption that the shut off room is leaky is only necessary for the *more savings* part. You'd still save energy by shutting it off, just not more than you would with a room that was not leaky.
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Arnie Goetchius wrote:

Thanks for all of your comments. It looks like the next step is to block off the returns in the unheated rooms. I found a "Magnetic Vent Cover" here that I will try:
http://www.lowes.com/pd_73204-34146-AMAGCOV815_1z0uatv__?productId260659&pl=1
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On Wednesday, January 27, 2016 at 10:52:15 AM UTC-5, Arnie Goetchius wrote:

I bought one of those and it was totally worthless. The magnet is so weak, the cover heavy, that it won't hold on.
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On Wednesday, January 27, 2016 at 10:52:15 AM UTC-5, Arnie Goetchius wrote:

Do you actually have returns in all rooms? I don't, I have one return in the hallway, and the room doors are undercut to allow air return.
If you do, where is your return filter?
At any rate, it doesn't really matter.
The heat loss in that room is less when the room is cold than when it is heated. So the return air you pull back has lost less heat with the supply ducts closed.
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On Wednesday, January 27, 2016 at 11:32:10 AM UTC-5, TimR wrote:

I have returns in all bedrooms, 2 in the living room and 1 in the family room.
The filter is "in" the furnace, right at the main return trunk where all returns meet.
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you have REGISTERS in each room.
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On Wednesday, January 27, 2016 at 12:34:09 PM UTC-5, taxed and spent wrote:

Not true.
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Actually, I suspect he really does have returns in each room. That's quite common[*]. I've lived in several houses that have a register and a return in each room, generally on the opposite side of the room with the register low and the return high on the wall.
[*] To ensure proper airflow when the door is closed.
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On Wednesday, January 27, 2016 at 12:50:02 PM UTC-5, Scott Lurndal wrote:

I don't know why you would suspect that. I already posted the list of specific rooms that have returns.
You don't typically see returns in bathrooms, kitchens or basements.
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I was responding, obviously from the quotes, to the soi disant "taxed and spent" who "corrected" you, incorrectly.

Typically? I've seen more than one house where the basement _was_ the return (the returns in the main floor were simply open to the basement).
Bathrooms have, by code, exhaust vents.
Kitchens seldom have doors.
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On Wednesday, January 27, 2016 at 2:23:53 PM UTC-5, Scott Lurndal wrote:

Typically, as in "generally or normally". Would you say you have seen more houses "where the basement _was_ the return" or more houses where the returns are part of a ducted system?
BTW...in my house, the first floor return "ducts" are the basement joist bays which are covered with sheet metal and taped along the edges. If I were remove the sheet metal, then my main floor ducts would indeed be open to the basement.
I wonder...was my house "upgraded" from open returns or were the "more than one house" that you have seen downgraded by having the sheet metal removed? Curious.

My comment was based on *your* comment "I suspect he does have returns in each room". "Each", at least to me, mean "all".
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On Wednesday, January 27, 2016 at 9:17:41 PM UTC-5, DerbyDad03 wrote:

All the houses I've seen around here have used ducted return systems, pulling return air from various points around the house, including the second story. I think a system that just pulls air from the basement is a half-assed, uneven, cheap way of doing it.

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On Wednesday, January 27, 2016 at 11:23:37 AM UTC-6, DerbyDad03 wrote:

Our house is the same as yours!
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"Arnie Goetchius" wrote in message
A local Plumbing contractor says the following:
“In the case of a central heating and air conditioning system, closing off vents has the same effect as a dirty air filter. It simply restricts airflow. Heating systems are designed to heat the whole home and are sized accordingly. Shutting off a section of airflow increases the air pressure in the system, in turn increasing the amount of duct work leakage."
"A more energy efficient way to control individual temperatures in unused rooms is by using a ductless heating and cooling mini split systems that are mounted on the wall and wired using a simple wiring process to an outdoor unit. No ducts are used so installation doesn’t take much time at all. Ductless heating and cooling mini split systems are a flexible solution.”
My question: Is closing the ducts to three unused bedrooms and an unused bathroom a bad idea and it won’t save any money on the gas bill?
The way that I look at is this way--Heating systems use a centrifugal fan (and when up to speed) runs at constant speed. It has a characteristic operating curve of delta P (pressure rise) vs air flow and as the air flow demand increases there is a slight drop (called Droop) in Delta P. The change in fan pressure usually is not very significant unless the flow demand is very high (very low system resistance). The duct work also has a system characteristic of Pressure Drop vs air flow. Plot the two operating systems (fan and ductwork) on the same curve and where they intersect is the system operating point--a fan pressure rise and flow.. Change the system resistance (close of some of the vents for example) and you will get a new operating point because the duct work characteristics have changed. Same fan speed but at a slightly different (higher) Delta P and at some reduced air flow. Unless the system changes are extreme, I don't see any significant operating or system problems. I don't think that closing off a few registers can be considered extreme. MLD
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On Wednesday, January 27, 2016 at 8:06:27 AM UTC-5, Arnie Goetchius wrote:

I didn't read this carefully enough the first time.
You have a furnace and gas heat. There might be places where a split syste m can heat for cheaper than gas, but not where I am nor any place I've live d.
I now see why you have more returns than I expected.
Yes, closing the ducts will save you money even if you don't block the retu rns. I'm assuming you close the door to those rooms. With no supply going into closed rooms, there's no pressure driving air into the returns. Ther e probably is slight vacuum in those return ducts but they're sucking on a closed room, and there are lots of other return ducts getting plenty of air . You could check this with a little smoke, I bet you'd find the returns i n the rooms you are using draw much more air.
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On 1/27/2016 8:06 AM, Arnie Goetchius wrote:

Less airflow across the heat exchanger means more heat goes up the chimney in the winter, not into the house, reducing the furnace's efficiency & the A-coil can freeze in the summer when running the air conditioning.
MikeB
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