A furnace model number looks like a random string of letters and numbers. It isn’t. On most Goodman furnaces, nearly every character tells you something useful: which way the air flows, how efficient it is, how big the burner is, how much air the blower can move and how wide the cabinet is.
Once you can read one, you can look at the furnace in your basement or attic and know most of what you need before you shop for a replacement. That’s what this guide is for.
First, find the data plate
The model and serial number are printed on a label inside the cabinet, usually called the rating plate or data plate. You’ll have to open a door to see it.
- Turn off power to the furnace at the switch or breaker.
- Remove the upper access door. On many furnaces it lifts off or is held by a couple of screws.
- Look for a sticker with “Model” and “Serial” printed on it.
On Goodman 80% furnaces, the model and serial label is inside the cabinet on the left side. On Goodman 90%-plus furnaces, check the inside of the lower access door. Other brands put it in similar spots, usually somewhere inside the blower or burner compartment.
Take a clear phone photo of the whole label. It will also list the input BTU, gas type and electrical info, and it’s handy to have when you call us or your installer.
Decoding a Goodman furnace, character by character
We’ll use GR9S800603AN as the example.
| Position | In the example | What it means |
|---|---|---|
| 1 | G | Brand: Goodman |
| 2 | R | Airflow direction. R = upflow/horizontal. D = downflow/horizontal. |
| 3 | 9 | Blower motor. 9 = multi-speed ECM with nine speed taps. V = variable-speed ECM on Goodman’s communicating models. |
| 4 | S | Gas valve. S = single-stage. T = two-stage. M = modulating. |
| 5-6 | 80 | AFUE, the efficiency rating, in percent. Common values are 80, 92, 96 and 97. |
| 7-9 | 060 | Heat input in thousands of BTU per hour. 060 = 60,000 BTU/h. |
| 10 | 3 | Maximum blower airflow. 3 = 1,200 CFM, 4 = 1,600 CFM, 5 = 2,000 CFM. |
| 11 | A | Cabinet width. A = 14 in, B = 17.5 in, C = 21 in, D = 24.5 in. |
| 12 | N | NOx emissions rating. N = standard. X = low NOx. U = ultra-low NOx. |
| After that | (A, B…) | Some model numbers end with one or two revision letters. A is the first release, B the next revision, and so on. |
So GR9S800603AN is a Goodman upflow/horizontal furnace with a nine-speed ECM blower, single-stage gas valve, 80% AFUE, 60,000 BTU/h input, a blower good for up to 1,200 CFM, in a 14 inch cabinet, standard NOx.
Two more examples
GD9S920604CN
D means this one is a downflow/horizontal furnace, so air leaves out the bottom. It’s single-stage, 92% AFUE, 60,000 BTU/h input, with a 1,600 CFM blower in a 21 inch cabinet.
GR9T960804CN
Upflow/horizontal again, but T means a two-stage gas valve. It’s 96% AFUE, 80,000 BTU/h input, 1,600 CFM blower, 21 inch cabinet.
What each part means when you’re replacing a furnace
Airflow direction has to match your house
An upflow furnace in a basement blows air up into ductwork above it. A downflow sits on a platform or over a floor duct and blows down. Upflow/horizontal units can also be laid on their side in an attic or crawlspace. Swapping one style for the other means the ductwork has to change, so most people replace like with like.
AFUE: 80% versus 90%-plus
An 80% furnace vents through a metal flue, often shared with a water heater. A 90%-plus condensing furnace usually vents through PVC pipe and needs a condensate drain. Going from 80% to 92% or 96% is common and often worth it in colder places, but your installer has to plan for the venting and drain. Going the other direction can be a problem if the old metal flue was removed.
The BTU digits are input, not output
060 means 60,000 BTU/h of gas going in. What comes out as heat depends on AFUE. A 60,000 BTU/h input furnace at 80% delivers roughly 48,000 BTU/h of heat. At 96%, roughly 57,600. Our page on what a BTU is explains this in more detail.
Don’t just assume your old furnace was sized right. Houses change. Windows get replaced, attics get insulated. The sizing tool is a good starting point, and a load calculation from your contractor is better.
The CFM digit matters for your air conditioner
The furnace blower also moves air for your AC or heat pump coil. A common rule of thumb is around 400 CFM per ton of cooling, so a 1,200 CFM blower lines up with roughly 3 tons, 1,600 CFM with about 4 tons, and 2,000 CFM with about 5 tons. If you’re replacing a furnace and keeping a 4 ton AC, a furnace with the 3 (1,200 CFM) blower is too small for it.
Cabinet width affects the coil and the fit
The indoor coil sits on top of (or under) the furnace, and its width should match. That’s why Goodman coils carry the same A, B, C and D width letters. A width mismatch can be adapted with a transition, but a matching width is cleaner. Also measure the closet or space where it goes.
Low NOx is a local thing
Most areas take the standard N version. Some local air districts require low or ultra-low NOx furnaces. If you’re not sure, ask your installer or local building department before you order.
Single-stage, two-stage and modulating
A single-stage furnace is either on full fire or off. A two-stage furnace runs on a lower fire most of the time and goes to high fire when it’s really cold, which usually means quieter operation and more even temperatures. A modulating furnace adjusts in small steps across a wide range. Each step up costs more, and the comfort difference is easiest to notice in colder climates and bigger homes.
What the model number doesn’t tell you
It won’t tell you the age. Age is in the serial number, and each brand encodes it differently. It also won’t tell you whether the unit is set up for natural gas or propane. The data plate usually lists the gas type, and many furnaces need a conversion kit for propane. If you have propane, tell us when you order.
Common questions
Where is the model number on my furnace?
On a label inside the cabinet, behind an access door. Turn the power off first. On Goodman 80% furnaces it’s on the left side inside the cabinet. On Goodman 90%-plus furnaces, look on the inside of the lower access door.
What does 0603 mean in a Goodman furnace model?
060 is the heat input, 60,000 BTU per hour. The 3 after it is the blower’s maximum airflow, 1,200 CFM. A 0804 would be 80,000 BTU/h input with a 1,600 CFM blower.
What is the difference between GR and GD furnaces?
GR models are upflow/horizontal. GD models are downflow/horizontal. Pick the one that matches how air leaves your current furnace.
Can I replace an 80% furnace with a 96% furnace?
Usually, yes, but a 90%-plus furnace needs different venting (often PVC) and a condensate drain. Have your installer look at the space first so there are no surprises on install day.
Send us a photo of your data plate or call (877) 843-4822 and we’ll help you match it. You can also browse our gas furnaces.