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hvac1000:
Why didn't you just say "I don't know". We're not addressing heat transfer gradients across the heating tubes, nor harmonic frequencies of blower wheel blades. This IS common sense.

I...

Actually there is no difference in air flow, all else being equal. Concave positions the hub closer to the motor. Convex positions the hub further from the motor.

That's it.

Thanks for your...

I do have a question for everybody between an old blower wheel and a new one: If the blower wheel diameter and width is the same, the number of blades the same, the rotation the same, and the motor...

The blower wheel is rated to 1750 rpm and the motor is running 1625. The 1625 rpm motor amp is 5.4. The 1075 rpm motor is 7.4 amps.

It was deliberate. The air was too hot at the register. I've replace the motor and it's now ranging between 100-120 F.

But I will have to see how it performs at the coldest day in January.
...

The blower wheel is the same width as the original, but the diameter is 1/2" larger. I couldn't find an exact universal fit.

My take is the replacement blower has less blower blade surface area and so it is not "paddling" as much CFM as the original.

Thanks anyway. I'm always open to ideas.

I would agree with you, except that the blower housing is symmetrical, typically u-shaped from the side view, but rectangular at the top interface with the inlet. So there are no indications from...

Missouri:
I bought a ccw wheel and was shipped a cw. I reversed the motor rotation.

If I understand you correctly, by reversing the motor rotation you're saying that I am going against the...

Its working. I was just thinking of preventive maintenance.

How can I tell if it is defective?

Do you think I should replace the limit switch with a universal replacement? Its 30 years old. The insertion length is 10-3/16"

Then, I think I'm done. Thanks again for your help. It's much appreciated.

The furnace is natural gas. The old one is still working as we speak undamaged. It appears too risky to guess at the orifice and flame characteristic even with a photo if I send one. Maybe I...

That's why I had to resort to a universal motor and blower: whatever I could find.

I found one universal Pilot Burner:
Pilot Burner for use with Thermocouples (Natural Gas or L.P.Gas)...

Tappan model #SGUF 140 D 48 E7
s/n 771 19739

Tappan model #SGUF 140 D 48 E
s/n 77119739

I've located that spec sheet for the valve. It's the correct one. How do I tell what type of pilot burner assembly I need to replace?
Right, left, center?

36c03-333

How do I tell what I have? My Control Valve is White-Rodgers Model 36303.

I've replaced the thermocouple. Is there a standard universal pilot burner assembly I can use?

Do you have any recommendations?

I've received and installed the higher RPM electric motor and the furnace is operating superbly. The register temperature is running between 100-120 degrees F.

Thanks for all your help.

hvac1000:
Of course there was no problem with the original design of the furnace or it wouldn't have lasted 30 yrs. You think I will burn out the new higher rpm motor. You're the one who is...

I have followed fan law #1:
CFM varies in direct proportion to change in RPM
RPM (new) CFM (new) = RPM (old) x CFM (old) .

Sometimes all theoretical calculations and planning efforts don't take...

hvac1000:
You are right about BTU's. You are also right about best speed for heating is the slowest. The faster the air moves across the heat exchanger, the less time it has to heat. Thus slower...

hvac1000:
You are right that blower speed has nothing to do with the temperature of the furnace. However it has everything do with the velocity of air and cfm produced. The difference will be in...

Hi MarkwithAK
Thanks for the suggestion. I will do that. I know the blower wheel is pumping out less air than the original. We can tell at the air vents. It's much less velocity than before with...

hvac1000:
I've ordered the 1625rpm electric motor that will give me a 50% boost in air velocity. I don't trust the air flow for the January deep freeze. It gets down to 10 below zero around here. ...

You are correct. However the new motor and wheel are running very quietly, so I don't think it will bother us. You should have heard the noise from the original blower and motor. It sounded like a...

I've rebalanced the ducts. The net result so far is I've lost some blowing power with the new blower wheel. It has 12.5% less blade surface area than the original. If I need more blower power I...

I reversed the rotation on the electric motor to coincide with the wrong wheel, and its working much better. The ducts feel hot as they get closer to the furnace, but they feel normal further away.

Hvac 1000:
You were right about something being backwards. I inspected the curvatures on the original blower wheel to the new. They were opposite. The supplier sent me a CW wheel instead of the...

hvac1000:
I wouldn't be surprised if the rear wheels on my car were running backwards, too. I'll see if the supplier shipped me a CW instead of a CCW blower wheel.

I have a 30yr old Tappan Gas Furnace. I replaced the blower motor and wheel. Furnace now keeps running and running to just make a few degrees difference in the house. Air ducts now feel too hot...