Turn the unit off and the fan on see if it still makes the noise. Did you move the blwer motor shaft side to side checking for play in the bearings

 

Thank you all for your replies. I will try to answer them.



The furnace itself was never on during these test. I noticed the noise when the T-Stat was on refresh mode. I did not move it side to side to check, but I will.

Change your air filter

Air filter is recent. In any case, it's mostly useless as the furnace uses a single retaining bar in the middle and the filters always collapse over the bar, just letting air above and blow the filter. I have tried cheap thin filters and sturdier thicker filters. I even tried a reusable filter in a plastic housing to avoid the bend, that damn near got sucked into the blower -- waste of money.

do what both guy's above suggested. when was the last time it was professionally serviced? have you fed the squirrels? can it be oiled? I would try to oil it and call a pro if it doesn't help. they will be able to test it and may be able to save it and not replace it. they are not cheap.

The HVAC was looked at this summer when the AC died. There were no problems apparent or reported by the tech then. I have not fed the squirrels. My wife has a nut allergy (yes, it's funny) so we don't keep them around the house.

Sounds to me like blower surge. If you took the access panel off with the blower running, thereby taking the filter out of the picture, and the sound changed but continued, that to me appears like something is restrictive in the supply ducting.

Did you close any vents to get more air to go somewhere else?

I haven't vacuumed the return vents recently, and as a matter of fact I did close a handful of vents upstairs when we were using the heat a lot last week. The delivery system is very haphazard and will overheat 2 of the bedrooms upstairs. The smallest bedroom has two ducts, but the larger master only has one .

 

Change your air filter

 

do what both guy's above suggested. when was the last time it was professionally serviced? have you fed the squirrels? can it be oiled? I would try to oil it and call a pro if it doesn't help. they will be able to test it and may be able to save it and not replace it. they are not cheap.

 

Sounds to me like blower surge. If you took the access panel off with the blower running, thereby taking the filter out of the picture, and the sound changed but continued, that to me appears like something is restrictive in the supply ducting.

Did you close any vents to get more air to go somewhere else?

 

The reason you've been getting the filter "sucked" into the furnace is because you are using too restrictive of an air filter which is also causing the furnace to "woof" trying to get some air. Replace that pleated and restrictive filter with a standard fiberglass throw away and I'll bet the noise goes away. If filter does not affect it, then look at ductwork as something is causing a restriction. You don't have screen wire or filter material in registers do you?utergreet:utergreet:

 

I took the advice given. I full opened up all dampeners, temporarily removed the filter, and thoroughly inspected the blower. The noise did slow down considerably when I opened the dampeners, but stop. The sound is somehow positively coming from the motor itself. It seems like the blower responds to back pressure by significantly increasing it's RPM and air output. Under slow speeds with little restriction (say from having the A-coil housing opened to let air escape into the room) the blower slows down and it makes no noise. Restrict either the intake or the exhaust by closing the unit, the motor speeds up moments later and the noise begins.

Here are the things I'm absolutely sure it's not:

Noise in the ducts, furnace, or filter. -- Once opened and examined, I'm am 100% positive it's coming from the blower
Blower loose on motor shaft -- I used a mirror and a flashlight to observe the motor shaft while it was on. The blower is very firmly attached to the shaft.
Blower contacting the housing while operating -- The blow deflects a bit if you push on it, but it's not banging around like an unbalanced washing machine. It's spins pretty straight
Loose motor -- The motor itself does not appear to move at all during operation.

I checked the blower blades with my hand to feel if any were loose, they were all solid. This pretty much leaves the motor, which has little to no sideways play, but will move in and out a bit.

 

Did my last post asking about a new HVAC get split into a new thread?

 

Nevermind.

The cost of fully repairing our 18yr old existing unit is like 25% of the cost of a new unit, so we are just going to replace it.

We got a rep out from a local company that is, from what he says now a franchise of a larger company.

Had a very good and long talk with the salesman. He's a very nice guy, but he was also very light on details on what kind of system he would actually recommend. We talked about certain things I wanted done, like replacing and rerunning the A/C line set and the Furnace feed/exhaust vents so they can be hidden, and having the return and supply ducts inside the utility room remade so they properly clear the gas line, don't leak, and actually match up properly to the feed/return coming out of the wall.

We talked about certain problem areas of the house for keeping consistent temperatures, and that we needed semi-often to constant air circulation in the house to keep the rooms even temperatured, because the current design has very poor natural air circulation.

We talked about the importance of having a good clean install, and making some room with a different sized unit so we could install a new HWH that is a bit larger than the old one.

He didn't bring it up, so I asked him about doing a load calculation or 'manual J'. He said he does an abbreviated manual J, but would do a full one if I insisted (I didn't want to make a big deal out of it, so I didn't).

We took some measurements of the current furnace and return ducts. I had to ask specifically about what sized unit he wanted to install. I don't recall exactly what he said, but it didn't seem clear to me that he had something definite in mind. I also mentioned that I definitely wanted an air handler that had the capability use the existing ducts to max capacity in terms of air flow. I wanted a variable speed unit, but one with enough head room, that should the need arise, it could push enough air that the ducting system itself was the limiting factor and not the blower's output. He indicated he could install an oversized unit, but it would be pointless because it would just never run full speed and would waste money. I agreed and understood exactly what he meant, but just reiterated the point that I would prefer the new system to be able to clearly meet that max air flow capacity.

When he left, it was late, well after 6pm. He said he'd have to give me a price on Monday.

Did we miss anything? Was there something I should have asked about in particular, or made a focus of the visit on?

 

Sounds like your pushing him to over size the unit. not a good thing to do. As you can end up with a very noisy duct system.

 

I'm going to start a new thread to cover the new HVAC purchase. It's off-topic here and I fear less visible because of the title.