Need to install some in-line duct booster fans

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.
 
Last edited:

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
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

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
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

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD 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.
 

MrLovable

Well-known member
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

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
. . . 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

worn out farmer
GOLD Site Supporter
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....
 

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
Well I got home this afternoon from running some errands, its 95 and SUNNY. Walked into the master bedroom and was pleasantly surprised that it was MUCH MORE COMFORTABLE today than it would have been before I had installed the in-line duct booster fan. So my initial impression is that the fan is actually doing some good.

Of course UPS dropped off the other fan today. While my original plan was to do the install in the morning when the attic was cooler I knew I was going to hop into the swimming pool anyway so I got up into the attic, installed the fan (in record time), and then joined my lovely wife out at the swimming pool. My guess is that 2 fans will be all that are needed to resolve my problems.
 

muleman

worn out farmer
GOLD Site Supporter
Glad they are moving enough air to do the job. It ain't right that you could just plug them in. A real HVAC guy knows you have to fight with the wire nuts while the sweat is dripping off your nose and you can barely breathe!:yum:
 

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
. . . A real HVAC guy knows you have to fight with the wire nuts while the sweat is dripping off your nose and you can barely breathe!:yum:
I guess that proves that I am not a "real" HVAC guy :w00t2:
 
Top