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Old 07-06-2012, 03:11 PM
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Default Need to install some in-line duct booster fans

The HVAC set up in my house is not quite good enough. During weather extremes the master bedroom is either too hot (summer) or too cold (winter). The problem seems to be that the duct runs to the master bedroom end of the house are simply too long. Too far from the furnace fan and so we don't get enough airflow into the bedroom/bathroom.

The correct solution might be to add a second HVAC unit to the house. The problem with doing that is finding the space to install it that would shorten the duct runs.

Sooooo, as a last ditch effort I'm planning to install a couple automatic in-line duct booster fans. Of course nobody has them in stock placed 2 on order and should have them next week. That's actually good, I don't relish the idea of crawling around my attic when it's 105 outside, must be 40 degrees warmer in the attic. Hopefully the install will be pretty quick and hopefully it will cool off about 20 degrees for the morning I do the install.
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Old 07-06-2012, 03:24 PM
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Default Re: Need to install some in-line duct booster fans

I have diverting dampers that divert flow to where it needed, works very well!
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Old 07-06-2012, 03:35 PM
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Default Re: Need to install some in-line duct booster fans

Measure your return air grill size and be sure you are pulling enough back before you try boosting the supply. It is even more important for the cooling to work properly. Do you have flex duct or metal pipe? Twists and turns with flex really cut down volume.
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Old 07-06-2012, 03:37 PM
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Default Re: Need to install some in-line duct booster fans

Yes Bob you might try that.

In my two story home we have to leave the stair way doors shut, and I close a floor vent before I go to bed, in the dining room. This is enough to make a considerable difference, so much so if I forget I do it in the middle of the night....I also have dampners at the plenum above the A/C W frame to control all the runs in the house. I adjust them seasonaly in the basement. For what ever reason the floor register/vent is closeable in the dining room and it makes alot of difference in the second story for air flow. It's like plugging a leak sort of, as no one is in the dinning room to notice at night. Make the air go where it will do some good. Are your vent pipes in the attic insulated? If not you should consider this in cooler times later in the year.

Regards, Kirk
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Old 07-06-2012, 03:51 PM
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Default Re: Need to install some in-line duct booster fans

The ducts are in the attic.

They are the flex type (I bitched about that when the contractor put them in)! I think they are the insulated type.

I'm concerned about the return air back to the furnace too, but not sure how to handle that???

Seasonally we shut off some vents and open others, but when the temps are near zero in the winter or over 90 & sunny in the summer then things tend to get out of whack.
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Old 07-06-2012, 03:51 PM
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Default Re: Need to install some in-line duct booster fans

Or, you might consider a mini-split for the master bedroom. Wouldn't compromise the capacity of the main HVAC to get more air so far away.


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Old 07-06-2012, 03:58 PM
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Default Re: Need to install some in-line duct booster fans

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Originally Posted by Kane View Post
Or, you might consider a mini-split for the master bedroom. Wouldn't compromise the capacity of the main HVAC to get more air so far away.


Actually something like that may end up as a viable option. I use one of those to air condition my workshop. I'm trying the automatic duct booster fans first, it's worth the $250 to give it a try, and if it works (or even partially works) its a cheap fix. The automatic boosters I'm using have sensors that are built into them and will turn on the boosters every time the furnace fan kicks on. No need to run wires to the HVAC switch. Cost a bit more but dramatically simplifies the installation process.
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Old 07-06-2012, 04:06 PM
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Default Re: Need to install some in-line duct booster fans

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Originally Posted by Melensdad View Post

I'm concerned about the return air back to the furnace too, but not sure how to handle that???
Good point. Air will always find its way back to the RA grill, but without adequate return air, the boosters wouldn't even have enough "air" to boost. However [assuming air speed constant (i.e. no unacceptable drafts/noise)] the volume of your return air is already fixed by the sizing of the existing RA grill and ductwork.

hmmmm.
.
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Last edited by Kane; 07-06-2012 at 04:16 PM.
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Old 07-06-2012, 04:18 PM
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Default Re: Need to install some in-line duct booster fans

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Originally Posted by Melensdad View Post
I'm concerned about the return air back to the furnace too, but not sure how to handle that???
When your A/C (basically, your air handler fan) is running, close all the room doors. Starting with the basement door, if you leave it open an inch, does it try to close? Repeat for other doors. Each that tries to close means there's inadequate air return. You can also use a lighter or candle and see if the flame tries to draw past the door.

I leave my door to the basement level open just to make sure there's enough flow.
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Old 07-06-2012, 04:31 PM
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Default Re: Need to install some in-line duct booster fans

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Originally Posted by bczoom View Post
When your A/C (basically, your air handler fan) is running, close all the room doors. Starting with the basement door, if you leave it open an inch, does it try to close? Repeat for other doors. Each that tries to close means there's inadequate air return. You can also use a lighter or candle and see if the flame tries to draw past the door.

I leave my door to the basement level open just to make sure there's enough flow.
Good way to test, but this assumes the house has ducted RA from each room. Doubtful. I imagine Mel has one big-ass RA grill near the thermostat, which means, when doors are closed, the RA is rather limited to the hallways by the undercut of the door to the room. Alas, that's residential construction.

Quite honestly, if Mel wants more AC to the master bedroom he should simply leave the door open. Or put a louver in it.
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Old 07-06-2012, 04:44 PM
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Default Re: Need to install some in-line duct booster fans

Quote:
Originally Posted by bczoom View Post
When your A/C (basically, your air handler fan) is running, close all the room doors. Starting with the basement door, if you leave it open an inch, does it try to close? Repeat for other doors. Each that tries to close means there's inadequate air return. You can also use a lighter or candle and see if the flame tries to draw past the door.

I leave my door to the basement level open just to make sure there's enough flow.
Well see that is sort of a problem, our home is pretty wide open from basement to top floor.

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Old 07-06-2012, 04:49 PM
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Default Re: Need to install some in-line duct booster fans

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Originally Posted by Melensdad View Post
Well see that is sort of a problem, our home is pretty wide open from basement to top floor.
Time out, Mel.

First, answer a few questions.

1. Does your house have ducted returns from each room?

2. If not, is the whole-house RA grill near the whole-house thermostat?

3. Are you familiar with Boyle's Law pV=k?

Then we can talk intelligently.






beautiful staircase, btw.
.
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Old 07-06-2012, 04:58 PM
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Default Re: Need to install some in-line duct booster fans

1. Yes we have air returns in each room

3. No
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Old 07-06-2012, 05:09 PM
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Default Re: Need to install some in-line duct booster fans

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1. Yes we have air returns in each room

3. No
Your SA is surely ducted, but before we go on, are you saying that each room has RA ducted all the way back to the air handler? You have two grilles, a supply and a return, in each room?
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Old 07-06-2012, 05:12 PM
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Default Re: Need to install some in-line duct booster fans

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?..are you saying that each room has RA ducted all the way back to the air handler?
yes, every room except the kitchen, bathrooms and the foyer.
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Old 07-06-2012, 05:29 PM
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Default Re: Need to install some in-line duct booster fans

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Originally Posted by Melensdad View Post
yes, every room except the kitchen, bathrooms and the foyer.
OK. That's wonderful. A very expensive (but very correct) way to first build. That means you have two grilles in each room - a supply and a much larger return.

Bolyle's Law simply says that the pressure and volume of air moving thru your master bedroom is a constant. Hence, the only way to get more heat/cool in the room is to increase the volume of air into/thru the room. Hence the booster.

But without adequate/additional return air (which may be a problem in the first place), the booster you propose for the SA would just be trying to increase (fruitlessly) the pressure in the room, particularly with the door closed. So, you would be best served to increase the return air volume, thereby creating negative pressure and pulling more heated/cooled supply air thru the room. And since you cannot effectively increase the sizing of each room's RA grille and ductwork, you might want to consider installing the booster near the AH in the RA ductwork, particularly if your keep the door closed. Think closed system.

You could try the booster in the SA, but there's simply no messin' with Boyle's Law. Me? I'd go with the mini-split. Mama would be sooo happy.





Just a question, tho, where is the T-stat located? Multi-level houses are a bitch with one AH.
.
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Last edited by Kane; 07-06-2012 at 06:00 PM.
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Old 07-06-2012, 05:36 PM
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Default Re: Need to install some in-line duct booster fans

Well opening the master bedroom door should eliminate a positive pressure problem, and that door is open almost all the time. So I should be able to 'push' more air into the room and whatever won't get 'pulled' out by the air return should simply go out the door and be sucked into an air return somewhere else??? It makes sense, following Boyles law, simply because the whole house must be of a constant pressure so if one room is 'over-pressurized' then it should push that air out the door and into the remaining house.

I did think about installing a duct booster in the return air vent.

But I think installing the duct boosters in the 2 vents on the wall is a better option simply becuase of the contortions those ducts go through to reach that wall, if each 90-degree bend is equivalent to 10' of drag, then that air is travelling something like 100' to 110' from the furnace to the bedroom wall.
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Old 07-06-2012, 05:45 PM
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Default Re: Need to install some in-line duct booster fans

I installed two six inch booster fans in branch off the main ductwork to move more A/C at the furthest end of the house. Wired off a relay in the controller. Works so good I am going to install another in an effort to push a little more air upstairs.
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Old 07-06-2012, 05:50 PM
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Default Re: Need to install some in-line duct booster fans

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I installed two six inch booster fans in branch off the main ductwork to move more A/C at the furthest end of the house. Wired off a relay in the controller. Works so good I am going to install another in an effort to push a little more air upstairs.
Did you install them near the end of the run? From what I can find out it appears the best place to install these is within 6 to 10 feet of the wall vents.
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Old 07-06-2012, 06:07 PM
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Default Re: Need to install some in-line duct booster fans

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Did you install them near the end of the run? From what I can find out it appears the best place to install these is within 6 to 10 feet of the wall vents.
Yes. Just before the elbow where the duct turns to go up through the floor.
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