Return air grate noisy at high CFM

[john-hvac-new]

The return air grate in our hall makes a lot of noise when the blower is at full CFM. If we remove the grate, the noise stops.

There is no filter behind the grate, just the return air plenum.

Are there grates that are designed to handle high CFM without making noise? Where would I get one?

[Big Unit]

Sounds like your return is undersized. A different grate may solve the whistling problem but if you could make your return bigger that would be a better solution. Tha air going into your return should not be fast enough to make any sound.

[drees]

Looks like you have a stamped register there. You could get a bar-style register which should improve airflow - not too expensive, either.

[john-hvac-new]

Sounds like your return is undersized. A different grate may solve the whistling problem but if you could make your return bigger that would be a better solution. Tha air going into your return should not be fast enough to make any sound.

Sounds like a bar style grille will be my first step.

If that doesn't get rid of all the noise, I could open a second hole in the return plenum and add a second grille. The back side of the return plenum is in the hall closet. That closet has louvered doors, so it should let plenty of air through.

[beenthere]

Its a code violation to use a closet as an open return chase.

[wahoo]

Get a size larger register. If you have a 6X03, then go to an 8X30 and the noise should go away. You are exceeding the rated air flow of the register. Of course you'll need to cut the hole 2 inches larger also!

[beenthere]

The pic he posted. Shows a grille about 24X24.

[john-hvac-new]

Its a code violation to use a closet as an open return chase.

Thanks. I won't do that.

[catmanacman]

is this a new problem a new system maybe

[john-hvac-new]

is this a new problem a new system maybe

No. When our system was installed, 3 years ago, we had a much louder sound coming from the return grate than with our old system.

Instead of suggesting a different grille (which didn't occur to me until a few days ago) the contractor changed the DIP switch settings on the variable speed furnace - reducing the max CFM - which quieted the noise almost completely.

Now, I'm thinking that the unusually high head pressure in our heat pump, in heating mode, might be due to insufficient max CFM.

So, if our new contractor recommends upping the max CFM, I will need a different grille to deal with the noise.

[ticotech cayman]

normally the dip switches have one for cool and other one for heat mode

[2old2rock]

You need a new contractor.

[jimj]

Instead of suggesting a different grille (which didn't occur to me until a few days ago) the contractor changed the DIP switch settings on the variable speed furnace - reducing the max CFM - which quieted the noise almost completely.



That's the nice thing about those VS motors, you can just keep lowering the speed until you get the proper noise level.:eek2:

Just kidding, get someone that knows what there doing and have your unit set to its proper cfm. Lowering the noise level from there can be accomplished several ways, ask your tech.

[john-hvac-new]

That's the nice thing about those VS motors, you can just keep lowering the speed until you get the proper noise level.:eek2:

Just kidding, get someone that knows what there doing and have your unit set to its proper cfm. Lowering the noise level from there can be accomplished several ways, ask your tech.

I think we have found a good contractor.

Since, as you say, lowering the noise level can be done several ways, I won't order a new grille unless he says that it's needed.

I'm so used to trying to figure out what to do myself because our original contractor has been so unhelpful, if not outright shifty.

I sure hope the new contractor works out (as I think he will) because, after asking lots of questions here, and getting lots of answers, I realize that I'm in way over my head. It will just be a great relief to have a professional (in every sense of that word) fix our system.

[jimj]

Sounds like your on the rite path. Good luck.

[air j]

you can also bend the louvers open more . This sometimes helps if sizing isn't too far off. Taped seamers is best for doing this so you don't scratch the finish.

[sktn77a]

A lot of speculation going on here without asking the obvious question - how big is your furnace/AC? If it's 3 ton/75000 BTU or smaller, your return is fine - just get a different (high flow) grill (or bend the louvers on your existing one). If it's larger than this, you may need a larger return but you should measure the static pressure and return velocity before doing major (and expensive) surgery on your return ducting.

[james broadrick]

The return is way to small if it makes that much noise. To small return = to high of a velocity. Proof is when the cfm was lowered high head pressure on the heatpump. Check out lowairflow.com Great read for airflow

[john-hvac-new]

A lot of speculation going on here without asking the obvious question - how big is your furnace/AC? If it's 3 ton/75000 BTU or smaller, your return is fine - just get a different (high flow) grill (or bend the louvers on your existing one). If it's larger than this, you may need a larger return but you should measure the static pressure and return velocity before doing major (and expensive) surgery on your return ducting.

The original indoor coil was CHPF3642D6. The condenser is GSH130421. According to the Goodman product spec sheet, the nominal cooling BTU/h is 40,000 and nominal heating BTU/h is 39,000 for the condenser. The indoor coil/air handler has a total BTU/h of 40,000. The new indoor coil is CHPF3642C6CA. From that number, I'm guessing its very similar in BTU/h to the original coil.

So, the heat pump is 40,000 / 12,000 = 3.3 tons?

The furnace is GMV950704CXA two stage gas fired, which has a BTU/h spec of 69,000/48,000 and variable speed blower with cooling capacity of 1.5 to 4 tons.

[RoBoTeq]

Its a code violation to use a closet as an open return chase.
Only for furnaces.

Ahh, I see it is a furnace.

Ya know, this should be changed for two pipe systems that don't have venting open to the area.

[wahoo]

Sorry, didn't look at picture first! Yeah, you need a different type of register. I hope this is an air handler using that closet as a RA chase. If it is a gas furnace, or has a gas hot water heater also in closet, you not only have a code violation, you have an un-safe installation! But, as I said earlier you seem to be exceeding the rated air flow of the register, just get a RA grill rated for the higher cfm.

[john-hvac-new]

Sorry, didn't look at picture first! Yeah, you need a different type of register. I hope this is an air handler using that closet as a RA chase. If it is a gas furnace, or has a gas hot water heater also in closet, you not only have a code violation, you have an un-safe installation! But, as I said earlier you seem to be exceeding the rated air flow of the register, just get a RA grill rated for the higher cfm.

Behind the grill is an open box that extends down through the floor into the crawl space. A large diameter, flexible duct connects from there over to the HVAC equipment. That duct travels at least fifteen feet before getting to the first part (the filter end) of the equipment.

[tinmam5959]

whare is the furnace looks like thare useing the wall space for the return turning down the blower speed will only hurt the performance of the furnace if it was sized right:tussor::bsing:

[sktn77a]

The original indoor coil was CHPF3642D6. The condenser is GSH130421. According to the Goodman product spec sheet, the nominal cooling BTU/h is 40,000 and nominal heating BTU/h is 39,000 for the condenser. The indoor coil/air handler has a total BTU/h of 40,000. The new indoor coil is CHPF3642C6CA. From that number, I'm guessing its very similar in BTU/h to the original coil.

So, the heat pump is 40,000 / 12,000 = 3.3 tons?

The furnace is GMV950704CXA two stage gas fired, which has a BTU/h spec of 69,000/48,000 and variable speed blower with cooling capacity of 1.5 to 4 tons.

Well, the 24x24 should be OK if the return ducting itself isn't undersized. I'd try a different grill first. Those stamped grills can sing/drone/howl if the airflow/resonant frequency is just right. does the noise go away if you push your flat hand on the middle of the grill?

[john-hvac-new]

Well, the 24x24 should be OK if the return ducting itself isn't undersized. I'd try a different grill first. Those stamped grills can sing/drone/howl if the airflow/resonant frequency is just right. does the noise go away if you push your flat hand on the middle of the grill?

No. At low CFM, it reduces the singing. At high CFM, you have to remove the grill to make much difference. When the grill is removed, there is no sound at all.

[beenthere]

While we have no idea how much air your system is really moving.

Good chance, a bar grille will not make noise.

Or a grille with wider openings.

[sktn77a]

No. At low CFM, it reduces the singing. At high CFM, you have to remove the grill to make much difference. When the grill is removed, there is no sound at all.

OK, then it's not primarily a resonance issue - try a high flow grill.