Old Lennox, what size is it ?

[98slvrcx]

Don't have model info, just a picture. 1980's - probably 88-89 . How many BTUs 60? 80?

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[rundawg]

Don't have model info, just a picture. 1980's - probably 88-89 . How many BTUs 60? 80?

That is the G12 series, and the 3 burners makes it about a 60-65,000 btuh output, depending on the full model number.

[98slvrcx]

That is the G12 series, and the 3 burners makes it about a 60-65,000 btuh output, depending on the full model number.

Output ?

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Output ? Model number would drive efficiency rating thus giving input ?

[rider77]

Is this because you want to replace the furnace and don’t know what size to buy?

[rundawg]

Output ?

Output ? Model number would drive efficiency rating thus giving input ?

Yes, Output.

I have the service manual for this model right in front of me, and this 3 burner model is showing 82,000 btuh input and 65,600 btuh output.

[98slvrcx]

Yes, Output.

I have the service manual for this model right in front of me, and this 3 burner model is showing 82,000 btuh input and 65,600 btuh output.

Were the 55k models using 2 burners or were they on 3 with some other differences ?

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[rundawg]

Were the 55k models using 2 burners or were they on 3 with some other differences ?

There were two other 3 burner models:

75,000 input and 59,000 output
60,000 input and 48,000 output (I didn't see this one at first glance through the manual.)

The 55,000 input units were 2 burners.

[98slvrcx]

There were two other 3 burner models:

75,000 input and 59,000 output
60,000 input and 48,000 output (I didn't see this one at first glance through the manual.)

The 55,000 input units were 2 burners.

Think I found the manual as well. Looking at the details and considering it was paired with a 2 ton unit it puts it at a G12D/Q 2/3 E-82

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[rundawg]

Think I found the manual as well. Looking at the details and considering it was paired with a 2 ton unit it puts it at a G12D/Q 2/3 E-82

That looks to be the most logical assumption.

Now the question remains: Are you trying to size a new furnace based on the size of the old one?

[98slvrcx]

That looks to be the most logical assumption.

Now the question remains: Are you trying to size a new furnace based on the size of the old one?

My parents furnace from a couple years ago and we were wondering what size it was before it got replaced because no one could remember, went from that 82 to 80/80% all good. Thanks for your help !

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[rider77]

My parents furnace from a couple years ago and we were wondering what size it was before it got replaced because no one could remember, went from that 82 to 80/80% all good. Thanks for your help !

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Doesn’t matter much what size you have, make sure the installer does a heat loss calculation to determine what size furnace you need.
It wasn’t necessary the right size back then, plus a lot has likely changed with the house since that furnace was new.