Adjusting Tempstar blower speed

Old 08-11-17, 08:35 AM
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Adjusting Tempstar blower speed

New unit:
ICP / Tempstar N8MXL 1102120A with AC Condensor H4A436GKA

Furnace is so much more powerful than my old that it is too loud: the furnace unit itself, the vents and particularly up through the returns. I cover the return in my bedroom at night so as to not be awakened by the sound!

My installer looked at it and the wiring diagram, and said he did not see any means of reducing the motor speed.
From my notes: N8MXL1102120A (ArcoAire; Tempstar; Airquest): 80% x 110k BTU = 89k BTUH, 1 stage, X(-13) ECM Blower.

Can anyone else please please help in finding a solution?

Most grateful,

Carl Sampson voted this post useful.
Old 08-11-17, 08:50 AM
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Was the old system smaller than the new? Sounds like the duct work is to small for the new system.
Old 08-11-17, 11:27 AM
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Threaded moved to furnace forum.

Every furnace must have an adjustable blower. Your furnace shows that you have an ECM motor which is an electronically controlled motor. There should be low voltage speed taps on the main board for speed adjustments in cooling and heating.

Your installer should know how to change speeds if he set the furnace up properly.

This should be your manual....
Old 08-11-17, 08:40 PM
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It looks like you have a 5 ton furnace matched with a 3 ton condenser.

The factory grey speed tap should have been switched with yellow for the Cool terminal. If the refrigerant was charged using the 5 ton airflow setting it may need to be adjusted as well.

The heating speed tap should not be adjusted without measuring the heat rise but it should already be less than the grey cooling airflow.

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Old 08-12-17, 04:28 PM
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Furnaces come from the factory with the heating speed set to provide proper temperature rise if you have properly sized air ducts.

I calculated out needing 1600 cfm for your btu output at a normal temperature rise (120f air out, 70f air in).

The blue tap is likely correct.

So in all likelyhood, the furnace is too large for the air ducts and possibly the house. This is a large furnace that you have.

If you want to toy with fans speeds:

You have to check the temperature rise, supply temp off the plenum (in the main duct) minus return air temp and compare it to the rating plate.

You may only lower the heating speed if it's not already on the upper end of the range (check the nameplate, it will list something like 40 to 60f) and re-check the temperature rise after.

You adjust it by changing the taps on the board, moving the heating speed tap to spare and using another tap.

Before you make adjustments, you should clock the gas meter to ensure the fuel input is correct. Google how. If it's not, the temperature rise reading means little and you need to call a service tech to change the gas pressure before changing blower speeds.

It's absolutely pathetic that you've called out a service tech and he doesn't even know that you can change the speed or how - unless it's just an excuse.

When they install the furnace, they're supposed to commission it; setting the fuel input to match the rating plate (there's an acceptable gas pressure range, like 3.2" to 3.8" - allowing for some fine tuning - they can change orifices in high altitude and propane applications if needed) and setting fan speed for proper temperature rise. Every duct system is different, the fuel content of the gas varies depending on location so the factory settings are not always correct.

If he doesn't know to adjust the fan speed, he hasn't been commissioning furnaces properly and is short-changing customers.

The 80% afue rating only applies with the correct fuel to air mix and proper airflow; an out of tune furnace will operate below it's efficiency rating.

Ignore silly user name, trying to get it changed.

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