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Need to install some in-line duct booster fans

Melensdad

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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 :sad: 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.
 

Big Dog

Large Member
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I have diverting dampers that divert flow to where it needed, works very well!
 

muleman

Gone But Not Forgotten
GOLD Site Supporter
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.
 

300 H and H

Bronze Member
GOLD Site Supporter
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
 

Melensdad

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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.
 

Kane

New member
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.


fujitsu-mini-split-system.jpg
 

Melensdad

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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.


fujitsu-mini-split-system.jpg

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.
 

Kane

New member
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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bczoom

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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.
 

Kane

New member
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.
 

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
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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.

2ae04331.jpg
 

Kane

New member
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.
.
 

Melensdad

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1. Yes we have air returns in each room

3. No
 

Kane

New member
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?
 

Kane

New member
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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Melensdad

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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.
 

tiredretired

The Old Salt
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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.
 

Melensdad

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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.
 

tiredretired

The Old Salt
SUPER Site Supporter
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.
 

Kane

New member
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.
Sounds reasonable. But I guess that's my point. You'll never pressurize a room in a residential home by pushing air. Like the old saying, you cannot push a rope. But pulling a rope (negative pressure) always works. RA>SA.

By placing the fans near the supply register, you are effectively pulling more air thru the SA ductwork. And the many turns. So the number of turns is moot either way. But either way, a good thing.

BTW, where is the T-stat located. Means nothing to this exercise, just curious.
 
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Melensdad

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Yes. Just before the elbow where the duct turns to go up through the floor.

Great. In my case the runs are pretty much a straight shot directly across the attic. My plan is to put them a few feet back so we don't get any fan noise, but still close to the end of the run.
 

Av8r3400

Gone Flyin'
I've been investigating these too, Bob. I have an upstairs room (office) that has the same hot in the summer cold in the winter problem.

I've been told (by a good friend in the HVAC business) the only ones that are worth buying are the "Squirrel Cage" style fans. The "inline" ones are only good at turning electricity into noise.
 

Melensdad

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The squirrel cage type seem to be designed for rectangular ducts, the in line type for flex or rigid round duct.

My investigations have turned up very mixed success/failure rates. I figure it's a multi-thousand $$$$ project to put in a second HVAC unit or $250 for 2 in line, automatic fans. The $250 bet is worth a try.
 

Av8r3400

Gone Flyin'
There are the cage type available for round ducts (6" round?). It was suggessted to me to put them right where the trunk comes off the main plenum for the two runs into my problem room.

Example
 

Melensdad

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Just got out of the attic.

One of the two booster fans is now installed. I ordered 2, of course only 1 arrived. The other is still somewhere in transit.

But not wanting to wait I went ahead and installed the first duct booster fan. Installation could not have been easier. Fortunately I had a duplex outlet in the attic very near to where the fans are to be installed. The fan comes pre-wired, with an 8' (?) cord. The sensor switch is also pre-installed. So there was no need to buy a separate temperature or fan sensor switch or to worry about doing any sort of actual electrical wiring.

Install took about 10 minutes (longer than you want to be in a hot attic, but still not too bad).

Cut the flex duct, insert the fan, insuring the fan is aimed the correct direction, and simply DUCT TAPE the flex duct closed around the fan, insuring that there is no cold air escaping into the attic. Plug it in. Done.

The sensor detects when the furnace fan is operating and it automatically turns on the duct fan. When the furnace fan turns off, the duct fan turns off. This thing is pretty much idiot proof. The only way to really screw it up is to install it backwards!!!

After installing it I went into the room and put my hand over the duct to check the airflow. It was easy to compare with another duct because I have 2 ducts in the wall that are almost side by side. The duct with the booster fan has noticeably MORE AIRFLOW coming out of that vent!!! That was the goal. It was achieved. I'll be installing the next fan when it arrives.

Now only time will tell if these 2 fans do enough to actually help with the issue I have, but its clear that I got some added airflow from this first fan. Not sure if its enough, but it can't hurt and it will obviously help.

FWIW, I did look at the booster fans that are at the hardware store that DO NOT have the automatic sensor in them, they are cheaper. Add the non-auto fan + the cost of the sensor together and the price is still cheaper. However, in comparing the install instructions it appears that FOR ME and MY LEVEL of HVAC skills, paying a bit more and buying the auto-sensor fan was the right choice.

As I said, time will tell if this little fan does what I hope it will do, but it clearly boosted the airflow out of vent so it passes the initial test.
 

tiredretired

The Old Salt
SUPER Site Supporter
Just got out of the attic.

One of the two booster fans is now installed. I ordered 2, of course only 1 arrived. The other is still somewhere in transit.

But not wanting to wait I went ahead and installed the first duct booster fan. Installation could not have been easier. Fortunately I had a duplex outlet in the attic very near to where the fans are to be installed. The fan comes pre-wired, with an 8' (?) cord. The sensor switch is also pre-installed. So there was no need to buy a separate temperature or fan sensor switch or to worry about doing any sort of actual electrical wiring.

Install took about 10 minutes (longer than you want to be in a hot attic, but still not too bad).

Cut the flex duct, insert the fan, insuring the fan is aimed the correct direction, and simply DUCT TAPE the flex duct closed around the fan, insuring that there is no cold air escaping into the attic. Plug it in. Done.

The sensor detects when the furnace fan is operating and it automatically turns on the duct fan. When the furnace fan turns off, the duct fan turns off. This thing is pretty much idiot proof. The only way to really screw it up is to install it backwards!!!

After installing it I went into the room and put my hand over the duct to check the airflow. It was easy to compare with another duct because I have 2 ducts in the wall that are almost side by side. The duct with the booster fan has noticeably MORE AIRFLOW coming out of that vent!!! That was the goal. It was achieved. I'll be installing the next fan when it arrives.

Now only time will tell if these 2 fans do enough to actually help with the issue I have, but its clear that I got some added airflow from this first fan. Not sure if its enough, but it can't hurt and it will obviously help.

FWIW, I did look at the booster fans that are at the hardware store that DO NOT have the automatic sensor in them, they are cheaper. Add the non-auto fan + the cost of the sensor together and the price is still cheaper. However, in comparing the install instructions it appears that FOR ME and MY LEVEL of HVAC skills, paying a bit more and buying the auto-sensor fan was the right choice.

As I said, time will tell if this little fan does what I hope it will do, but it clearly boosted the airflow out of vent so it passes the initial test.

I knew it would help. It did for me. FWIW I purchased the regular type. I did not even know you could buy one with a sensor. It must be some sort of a sail switch that detects air movement. Anyhoo I wired mine back to the controller and installed a relay that closes only when the blower fan for AC is running. The sensor type would not work for me as I want it to run on AC only, not in heat mode. Works great. You should notice a nice difference.
 

Melensdad

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. . . You should notice a nice difference.

That is certainly the hope. However, I think when the next one arrives I'll wait until the following morning to install it. Its about 85 and sunny today, must have been every bit of 120 in the attic when I was doing the install this afternoon. Sort of stupid of me to go up there but I had it pretty well planned out so it really took very little time up there in the heat; just glad I wasn't up there any longer!
 

muleman

Gone But Not Forgotten
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Ten minutes is a long time in a hot attic. That heat can overwhelm you quick. Our boss tried to always schedule attic jobs real early for that reason.
 

BRGTold

Bronze Member
SUPER Site Supporter
Your Air Handler/Furnace has a blower fan not a sucker..If you fill-up the envolope with Air..where does it have to go..except to the RA....might be under doors and such..if no returns in each room..But it's better to put out more supplyed air ..than return...Some might disagree..?..If you have more R/A than supply..then you have a Blower that is free spinning..shorted life....
 
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