Hello,
This is my first post and hopefully not my last I bought my first house a few month ago in the province of quebec, Canada.

I did my first furnace checkup 3 week ago as the winter was coming. We found out with the technician that the fan had to be replaced due to its bad state... it was all dusty and unbalanced due to poor maintenance over the years and it was causing some vibration on whole furnace/vent setup and so we proceeded to change the fan.

But as soon as we changed the fan a new problem arose. Now the airflow isn't constant and so is the noise from air duct.

It does something like:

I brought the technician back and he didn't had much clue. His best bet was that I wasn't aware of this problem with the old fan because it was so used that the air pressure in the air duct seemed or was constant but now that we installed a fresh and way more efficient fan more pressure gets in the airduct thus causing this effect as the fan tries to do his job.
According to him I don't have to worry about damaging the fan.

But it's still annoying
What we tried:
-Lower the speed of the fan : didn't had much effect on the airflow issue
-remove all the airduct plate on the ceiling and from the walls to ensure minimal resistance : still didn't had much effect on the airflow issue

so here I am. I do not know what to do next and what to look for.

 

Does this furnace or air handler have a ecm motor?

If yes, I could see this happening if there's a problem with the module or control board.

If it has a regular psc motor, i don't have a clue.

 

not sure about this one but im pretty sure I have a psc module since I dont have direct access to the fan speed other by rewiring stuff on the fan module ( am I right?)

 

After some investigation I found out that I do have variable speed on my fan
but no matter which speed is going at I still get the noise issue.

the louder noise happens when the furnace kicks in rather than the heatpump. Opening the fan door significantly reduce the amount of variation (spikes) in the airflow.

I keep doing research but I do not know exactly what to search of what to look for :/

 

Post the model number of the furnace and maybe we can help. When you say he changed the fan, do you mean the fan motor?

 

I changed the squirrel cage of the fan sorry if I caused any misinterpretation.

Regarding the model of the furnace:I couldn't find the info it's an old dettson furnace dating from 1991 I think. Can't tell you more :/

thanks for your time

 

Did you just change the blower wheel or the wheel and motor ?

 

Only the blower wheel.
According to the technician that changed the blower wheel it( the airflow issue)has nothing to do with the engine. But if I place my hand on the furnace i can tell something isnt turning smoothly but according to that same technician that would be caused by the pressure in my air duct and having too much restrictions.

 

A problem with duct work isn't something we can give you much help with. The only thing I can think of is to do a static pressure test to confirm the issues.

I would also check for damper controls in the ductwork that may have closed or moved by themselves.

 

already checked the damper they're all open. About the static pressure. I doubt i'll get a good reading as the pressure keeps goings up and down every few seconds dropping more than an half of his airflow.