Inline booster blower for 3rd floor heating vent


We have relatively new high efficiency gas furnaces that feed into 100 year old ductwork.
In particular, our 2 third floor bedrooms are fed off the same 9" riser that feed the 2nd floor bedrooms underneath it. As a result, there is much less heat reaching the third floor than the 2nd floor.
Even adjusting the dampers at the takeoffs to the bedrooms has only limited effect, since the airflow is just not powerful enough 3 floors up.
So, I am wondering whether someone makes a booster blower that would sit just below the 3rd floor vent grill and would not require ripping up the walls, ceilings, or floors to install.
Note I know they make inline fans that it into the duct itself, but that would seem to require breaking into the wall to access the duct. I want something that would sit right underneath the vent grill.
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is the vent into the third floor in the floow or on the sidewall. You could mount a fan in either location if you have a way to get electricity to the fan.
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Vent is in the floor approx 4x12"
I have power in the wall nearby but was hoping ideally for a low voltage solution so that I could run wiring under the carpeting and into the vent without safety/code issues.
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We always think first about boosting input, but flow requires that input to get back to the furnace. Any chance that too many closed doors might be part of the problem? Or blocked/inadequate returns?
Joe
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Poor returns are undoubtedly contributing since the only returns are in the open first floor hall (which is open to the 2nd floor though the stairway to the third floor is enclosed).
In the future when we renovate, we will need to add returns on the 2nd and 3rd floor (particularly since we want to add AC) but in the short term there is no easy way to fix that situation since there are no obvious open chases, stacked closets etc. going up to the 3rd floor.
So that together with the fact that the supply duct is shared with the 2nd floor makes me think that the best near-term solution would be to boost flow from the terminal end. But obviously I am open to other suggestions if they are easier/simpler...
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I have my original ducts in my 119 year old house. I have four floors and the only returns were on the first floor. I was able to bring a small return to the second floor. Of course this can't possible cool the top two floors, but my roof is flat and I put a packaged unit up there that cools those floors with a big return at the top of the stairs. A good idea, but only if you have a flat roof.
Don <www.donwiss.com> (e-mail link at home page bottom).
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blueman wrote:

Google heat vent booster.
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Thanks very helpful - I tried googling before but did not know what to call it.
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I haven't seen you around for a while. Nice to know you are still here.
What size is the boot or grill area? I imagine some field engineering can be done.
One of those hassock type fans sat over a floor register or a cheap box fan in front of a wall register might let you test the concept at minimal expense.
Colbyt
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Thanks!
Register is 4x12"

Part of the reason I asked here was to get ideas on "field engineering". Most of the solutions I saw on google involve replacing the register with a unit that contains a pair of fans, a knob to control temperature, and a DC input from a wall wart.
I was thinking that through "field engineering" I could get a better solution using high quality PC fans, a DC wall wart and a temperature probe plus a simple circuit to control fan speed and temperature response) that would be: 1. Quieter (both by using better quality fans and by placing the fans inside the vent and below the register) 2. Neater looking (everything would be hidden below the register) 3. Better temperature response (by locating probe deeper in the duct so it would respond as soon as hot air starts flowing)
On the other hand, buying one would certainly be easier but I worry mostly about the noise.
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writes:

My mind finally started working and I figured out the Google search term you need to use: booster +fan +boot +mount
Lots of hits and the first page shown has several models to choose from. Thought I would let you do your own reading. :)
--
Colbyt
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Ive seen ones that plug into 120v and come on with airflow that fit on top a register like you mention but I dont know if they do anything, before just closing off registers you need to know and monitor the temp of the exchanger, reducing airflow can run it hotter than the design temp, overheat it and kill its life. You just drill a hole above the exchanger and insert a probe Meat-cooking type of thermometer. Booster Fans can easily be installed in the basement ductwork
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I was hoping for something that would sit inside the register since the register is on the floor. Also, low voltage would be preferable since I wouldn't need to worry about properly routing line voltage but instead could use a low voltage wire running under the carpet.

My concern over adding the booster fan in the basement is that the ductwork for each side of the 3rd floor is shared with the same side of the 2nd floor. So, a push solution would probably end up boosting flow more to the 2nd floor (since the ducts feeding the 2nd floor rooms are not only closer but also much larger).
Again, the root of the problem is of course a system design issue but until we renovate, I am looking for an interim solution.
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blueman wrote:

It sounds like your best option might be some sort of portable electric heater for now.
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