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Old 01-25-2010, 12:19 PM   #1
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Register balancing - how to?


Hi, guys.

I am trying to balance the registers in our 2500 sf single-story home that we just bought. It has a finished upstairs room (part of the attic)but I don't want or need to heat the upstairs at this time, I've blanked off its outlet register.

I've cleaned the input filter, and am trying to balance the registers in the rest of the ground floor so that the family room gets more heat, and the bedrooms get less. The house is 10 years old, double-pane windows, furnace recently serviced (2 years or so).

Heating bills seem high, so I'm trying to tweak things to more efficiently heat the house.

I just wondered if there's a systematic way to go about this, short of calling the Utility out to do a heat-loss analysis.

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Old 01-25-2010, 12:48 PM   #2
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Register balancing - how to?


A short cut that has worked well for me was just moving the thermostat. I had a 988 sq. ft. home with a stat in the hallway between the three bedrooms and the single bath. Then I put on a monster
32x40 ft. living/great room/ kitchen eating area. The addition was always cool in the winter and hot in the summer (lots of windows). The rest of the house was cool to warm in the winter and warm to hot in the summer. I had put in a ton of insulation new windows and doors and lots of ventilation for the new roof. Finally after getting frost on "junior and the twins" for the first winter I decided to try the stat in the great room instead of the hallway. All my HVAC bills are back down to where they were before the addition and the whole house is comfortable at 66 deg. F in the winter and we only have to run the ac about 5-7 days during the entire summer. It's cheep and definitely worth a try.

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Old 01-25-2010, 01:02 PM   #3
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Yes, the single-zone thermostat IS in the hallway (coldest part of the house).

BTW, the house is slab construction with ceramic tile except for 3 of the 4 ground floor bedrooms.

Also, the Plenum has 1 un-dampered 8" diam. run (to the upstairs finished room), plus 2 dampered (appear to be 12" diam.) runs to the ground floors, with branches.
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Old 01-25-2010, 01:16 PM   #4
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Register balancing - how to?


Before getting a HVAC engineer salivating over all the math, just move the stat to the family room. It doesn't have to be permanently installed. Put a step ladder in the family room and hang the stat at about 5 feet off the floor; not by windows or doors to the outdoors. Then take a look at the wire from your stat in the hallway and get a piece from the local hardware store that at least has the same number of conductors in it and that will reach from the hallway to the stat in the familyroom. Hook it up and you should know within 48 hours whether you have to do anything more fancy.
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Old 01-25-2010, 03:12 PM   #5
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Register balancing - how to?


Have you tried just turning the dampers to all the bedrooms down a little for a couple of days to see if this works? No analysis will tell you how far to turn the supply or register dampers without some trial and error. Be careful not to close them off too far, or you will increase the backpressure in the system too much.
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Old 01-25-2010, 03:40 PM   #6
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Register balancing - how to?


I am a HVAV engineer, or was. I would start with the assumption that they are about the right size, most people get that right. but suffer from long duct runs. I would start wide open then check if they have about the same velocity. Doesn't have to be real accurate, just put your hand up. The ones near the fan coil will likely have more velocity. So choke them off a bit. This should reduce velocity to those registers and increase the others. Check all registers till they are about the same. Wait a day and from their just open slightly if cold and close slightly if warm, during heating season. It doesn't have to be fancy.
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Old 01-25-2010, 03:42 PM   #7
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Register balancing - how to?


Quote:
Originally Posted by sktn77a View Post
Have you tried just turning the dampers to all the bedrooms down a little for a couple of days to see if this works? No analysis will tell you how far to turn the supply or register dampers without some trial and error. Be careful not to close them off too far, or you will increase the backpressure in the system too much.
What will increased backpressure do?

(sorry if it's a wierd question - I'm new at this home HVAC stuff)
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Old 01-25-2010, 04:30 PM   #8
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Register balancing - how to?


Its not quite that simple. If you close the registers too much the furnace will overheat and cycle on the limit control and stress the heat exchanger and shorten its life. You need to check the temp rise thru the furnace after you have closed dampers to make sure it is within the manufacturers specs. Check the supply temp a foot downstream from the main bonnet on a horizontal section and subtract the return temp. Poke a hole in the ducts and use a meat thermometer. The temp rise specs are on the sticker inside the unit with the model #.
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Old 01-26-2010, 08:39 PM   #9
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Register balancing - how to?


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What will increased backpressure do?
That's why I said "turn them down a little". Otherwise, as Yuri says, the back presseure will reduce the airflow to the point your temperature rise is too high and that can damage the heat exchanger and other components. I wouldn't worry too much for a short time though; once you've figured out the problem, you're in a better position to fix it.
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Old 01-26-2010, 09:07 PM   #10
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Register balancing - how to?


I would get a energy audit done on your house with a blower door test. This will show you where the problems in your thermal envelope are and when these are sealed up you will save on energy.

Most people think that windows and doors are the problem when it is usually someplace else that is causing the problems. You would be much better off spending your money in this manner to save big.
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Old 01-27-2010, 10:35 AM   #11
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Register balancing - how to?


The acceptable system heat loss in our area is supposed to be 15% or less. I inspected all the duct runs for leaks/whistles, cleaned the cleanable air inlet filter, made sure the fireplace damper was shut (messed up on that the first month - my fault).

For a 10 y/o home, the utility bill just seems high for a somewhat temperate climate. I grew up in Philadelphia, Ohio and Indiana, so I know what cold is (save for you folks in Minnesota,UP Michigan and the Dakotas). I have double-pane windows throughout.

We have 2 problems here - the overall bill, and the fact that the Family Room is always 2 degrees cooler than the rest of the house. The temperature differential is why I'm trying to suss out the register balancing, in hopes of directing more heat to this room, and less in the bedrooms.
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Old 01-27-2010, 11:02 AM   #12
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Register balancing - how to?


Turn your fan to the on position and go around to the returns with a piece of paper and hold it to the return. If the ducts were properly sized and installed, the paper should draw to the return, though the farther you get from the furnace, the less it will seem to draw in. If you have one or two that don't seem to pull much at all, you need to address that by checking all the return ducts to be sure there is no blockage. No amount of forcing air into a room will help if it has no way to get back out of the room. Another thing you can do is to close all the internal doors with the fan on. If you have a leak somewhere in the returns, you may be able to trace which duct run is the problem by determining which room has air screaming out under the door. That's the run that isn't pulling its' share of the load. As sktn77 said, you only want to close the registers "a little" or you risk creating more of an imbalance.
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Old 01-27-2010, 11:37 AM   #13
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Register balancing - how to?


I feel stupid, but, where are the returns? All rooms have a register, but I don't recall individual rooms having returns. The only one I recall was the Main Inlet, where the filter is.
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Old 01-27-2010, 12:03 PM   #14
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Register balancing - how to?


I just want to throw this in since Yuri and the others did a masterful job fielding the other issues.

The OP stated he "Blanked Off" his up stairs registers. This means to me he sealed them with plastic or something like that ( feel free to correct me SixStrRzr) BUT EITHER WAY IT IS NOT GOOD TO COMPLETELY CLOSE OFF UPPER LEVEL REGISTERS BECAUSE THE WILL REUIN THE FURNACE AND EVEN MORE SO THE AC UNIT IF LEFT IN PLACE FOR THE SUMMER.
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Old 01-27-2010, 12:23 PM   #15
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Register balancing - how to?


Thanks for kicking in, hvaclover....

The upstairs room has 2 registers - one for the main room, and one for the upstairs bathroom. I blanked off the main one only, with foil, left the (smaller) bath un-blanked and fully open. This upstairs room is fed off the furnace plenum by a non-dampered dedicated 6" run, while the rest of the house is fed off two larger, dampered (at the plenum) main ducts, with finger ducts supplying the registers.

Yes, I'll un-blank the upstairs for a/c in the summer - but for now I'm not using the room,and see no reason to fully heat it in the winter.

How will this ruin the furnace?

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