Blower Speed too High?

Problems related to residential installations.

Blower Speed too High?

Postby Mr.Chips » Tue Jun 07, 2011 11:08 am

In both the AC and Heating modes the Blower speed is very loud, and the wife is always complaining about the noise. Does it need to be like this for proper operation? Give me the pros and cons of different blower speeds and the reason for running in a higher speed.
I recall seeing older units where you simply change the wiring connections between the Hi or Low speed positions, but this unit in the attic is completely sealed, and haven't seen an access panel in the blower area.
These units are 5 years old and In winter the electric furnace portion of the furnace uses the outside compressors as a heat exchangers so they must be heat pump type heating units.

Thanks
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- Blower Speed too High?

Postby cascadehvac » Thu Jun 09, 2011 5:55 pm

blower speed needs to match your heat pump. too little and the outsi9de unit will not run properly. not sure of you blower noise....just air noise?...*?...winding?...wistling or whining?...could be mny things. might be worth it to have an inspection done and ask the questions when someone is looking at it
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- Blower Speed too High?

Postby Mr.Chips » Thu Jun 09, 2011 7:25 pm

Anyone else???
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- Blower Speed too High?

Postby nomadpeo » Sat Jun 11, 2011 3:03 pm

all systems come with manufacturer specifications published on the blower. the static pressure needs to be measured before and after the blower to determine what speed it should be running. a technician will use a magnehelic and consult with the blower specs. he should also evaluate the duct system to determine if it is adequate. return and supply air ducts can be undersized and cause airflow issues such as noise and poor performance. discuss this with service managers over the phone before selecting a company.
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- Blower Speed too High?

Postby Freon » Mon Jun 20, 2011 1:22 pm

Be careful playing with the blower speed. If you slow it too much, you may end up with an iced indoor evaporator coil. Here is what I suggest. First I will assume the installer put together an heat/cool combination that's close in sizing. So if you go to the outdoor condenser unit and read the BTU rating you can determine what minimum flow rate of air you'll need. For every 12,000 Btu/hr (1 ton) of condenser cooling you'll need approximately 400 cubic feet per min (cfm) of air flow through the indoor coil. In the blower compartment of the air handler you should find the cfm for each of the available speeds. These cfm values will be according to static pressure. For now use the cfm values for 0.1

Now that you know if you can adjust your motor speed, that may be enough. However, if, as I suspect, the motor is already set to the proper speed (a good installation), then you go to Plan B. That involves mitigating all noise sources from the duct system. You have 3 usual sources. First is fast air flow into return registers or out of supply registers. This whistling noise is like wind blowing in an open car window. If that is the problem, make sure all return and supply registers are fully open. If they all are, then some duct modification may be your best alternative... increase the physical volume the air flows through (bigger/more/ducting.

The 2nd noise is from air handler vibration transmitted through the physical duct. If they are metal ducts and you can hear rattling or vibrations, then this may be the cause of your noise. Easiest way to fix that is insert a piece of flexduct at each supply and return connection at or close to the airhandler. This will stop the vibrations at the airhandler from propagating along the duct.

Last noise is the same vibrations but conducted by the air in the duct. Here, I suggest introducing a gentle bend (S curve) in the duct using flex duct. You want it gentle, no sharp 90 degree bends, that will restrict airflow.

Since the last 2 sources involve vibrations at the airhandler, I would start there first. Put your hand over the blower compartment when the blower is running. If you feel excessive vibrations it is possible your blower wheel may be out of balance. They can throw a balance weight as they age. Also consider shock absorbant pads under the airhandler. Any way to decrease the vibration at the airhandler will mean less noise for you.
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- Blower Speed too High?

Postby HVACnewbie11 » Mon Jun 20, 2011 4:08 pm

Those are very good instructions above! However, I would caution you when working on this to make sure that you understand what you are getting yourself into. There will always be some sort of noise from these units. Inside the unit there should be the specs that should dictate this speed. When you are doing yearly maintenance I would always check this speed and the balance of the fan! Let us know what you find out!
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