Duct booster into 6" round metal vent

[matt_i]

Need help with a technique here... I want to put a booster fan in a 6" round metal vent tube to improve the velocity. However everything is finalized and I can't displace the ends or even flex the tube out in the center of the run due to Roxul insulation fitted all around it in a ceiling cavity.

Thinking after removing the appropriate length (equivalent to the inline fan tube), I could then cut two opposing flaps to allow the short fan tube to drop in , slide back to nest on one end and rely on the Carlisle foil grip to seal it all up after a couple of screws.

Is there any other good way to do this? Seems like if I had a wide solid band like a hose-clamp it could also work.

I feel like I'm not the first person to have this issue and there's either a special tool, technique or a fitting that would make life a lot easier!

Thanks for any help!

 

[pattenp]

Would a duct coupler work?
https://www.grainger.com/product/DU..._on_Your_Search-_-IDPPLARECS&cm_vc=IDPPLARECS

 

[matt_i]

YES! That's perfect. Thanks for the link. I also ordered a booster fan that can fit in a "hatch" cutout of the top and side of the ductwork. It has a rounded half-pipe that then seals the opening.

 

[bullnerd]

How would you wire something like this?

You would have to tap into the furnace blower motor wiring to have it come on with the furnace?

 

[matt_i]

I need to put a clamp meter on the existing furnace squirrel cage blower and see how much it draws. If its minimal as I expect it could be direct wired in parallel with that existing motor. If the draw was too much I could always drive a relay coil in parallel to the main motor (milliamp draw would be additional) and use a separate 120vac circuit for the booster fan(s) power.

However, a multi-zone setup is already in the works, I have a PLC control that's not yet fully wired. But when I get to that point, I will have the "Zone B" thermostat's call for heat to turn it on. I'll do a simple time delay to allow for the purge and the gas valve to open, heat exchanger to heat up, etc. Probably about 30-45 seconds. Could also do an off-delay timer to run after the tstat is satisfied.

So a couple options.

Even if the on

 

[Radix2]

I thought those just had a simple thermal switch in them - when the duct gets hot it runs, when it cools off it stops...?

probably something like a 110on/90off switch.

 

[bullnerd]

I thought those just had a simple thermal switch in them - when the duct gets hot it runs, when it cools off it stops...?

probably something like a 110on/90off switch.

That would be a lot easier! lol.

Sounds good op.

 

[Higgins]

look for A sail switch, vane switch or flow switch is a mechanical switch that is switched on or off in response to the flow or non-flow of a fluid such as air or water. A sail switch typically operates through the use of a paddle which gets displaced due to the force of fluid moving past it.

 

[brewchief]

Some furnaces will have an accessory terminal ( often for an electronic air cleaner) that you can power a duct booster from.
Don't wire it to the blower on a multi speed blower, if you do you can get power on that line when other speeds are running and it can be higher than normal, the motor can act like a generator.

Sent from my SM-G965U using Tapatalk

 

[LS6 Tommy]

I thought those just had a simple thermal switch in them - when the duct gets hot it runs, when it cools off it stops...?

probably something like a 110on/90off switch.

That would be a lot easier! lol.

Sounds good op.

That won't work if you have cooling.

Tommy

 

[75gmck25]

I used to have a whole house humidfier that turned on using one of those sail switches. It was very simple - just a lightweight paddle (plastic?) in the plenum, and when moving air pushed it out it turned on the circuit. For a booster fan it could work for both A/C and heat.

Bruce

 

[RoadBeater]

I just put one of the add on booster fans in. They make a pressure switch to turn it on. It works well to boost the air flow to my daughters room, which is the furthest from the furnace. It is noisy though.