Furnace motor question.

[jantar]

I have a lennox OF23Q5 forced air furnace. I am trying to find out how many cfm of air does the blower move on Low/Medium/High setting.

We will be installing a HEPA filter in the return duct and we need to make sure that the hepa filter motor is going to be programmed for the same CFM as the furnace motor so they do not fight. Can anyone help to find out what the numbers are? ...

thx

[beenthere]

Your contractor will be able to determine that by use of a flow hood, or hot anometer, or by measuring esp if he has the blower chart.

[jantar]

Isn’t there a simpler solution available? I am surprised the lennox does not have this kind of documentation on their website.

[docholiday]

It's in their spec sheets but unless you know the resistnace your ductwork has and any additonal items (such as your big filter) you cannot figure it out.

Blowers have a curve, meaning that RPM, HP, and resistance all play into how much air a fan moves. Unless it is a constant CFM (ECM), you have to have the equipment and do the math to determine actual airflow.

[HeyBob]

You have an oil fired lowboy furnace. The Q5 means you have a 5 ton blower, max cfm is 2000.

[jantar]

What does usually a 5 ton furnace use for CFM during heating or cooling? I am going to have my furnace evaluated by I am just curious what the ballpark is.
thx

[turtle]

Originally posted by jantar
What does usually a 5 ton furnace use for CFM during heating or cooling? I am going to have my furnace evaluated by I am just curious what the ballpark is.
thx

This is Turtle.

400 cfm per ton of cooling and somewhat less for heating.

now there can be about 500 different veriation to change these figure if things change to the system.

TURTLE

[jantar]

400 CFM does not look like a lot.

[Special-K]

Originally posted by jantar
400 CFM does not look like a lot.

That's per ton,,,so a 5ton drive would be 5 x that or 2000 CFM. Now, that is a nominal figure, depending how your ductwork is designed it will in reality move less.