It means your duct system is too restrictive for the amount of air you are trying to move. Can also happen with restrictive or plugged filter or dirty cooling coil. What do you have for a filter?

It is not 66% fire! It is an error message!

sneaky pete

It is a ECM motor RPM limit matter.DIRTY FILTER, DIRTY COIL, LACK OF RETURN AIR, DUCT IS WRONG SIZE, OR YOUR IN AN EXTREME ALTTITUDE WHICH REQUIRES THE FURNACE TO RUN RPM LIMIT. Lack of air flow is a common matter with new (variable speed) ECM motor furnace installations WHEN YOU HAVE A LACK OF RETURN AIR. The new ECM furnaces have great features. Consumer Reports rates the Rheem RGFD #1 in gas furnaces. Many Hvac contractors are still ignorant of the importance of air flow and duct sizing.

baldloonie and pearson21 - thank you for the posts. Sorry I was indisposed for a couple days and couldn't get online. Anyway, the filter was very clogged so I replaced it and still the 66. This is a brand new install, so am thinking the coil shouldn't be too dirty. Lack of return air - when I had the pre-drywall inspection done, the inspector thought the place was light on return air. I brought it up but was pretty much shut down. Now I might have something more concrete to go on. I'm having my doubts about this contractor. The humidifier wasn't working, so called him out to get it going. When I went to check on things, I find the humidifier cycling on and off even when the furnace is off! Called him and he's coming back out, but isn't sure when - he'll call me back.

About the RPM limit. The book says that the "66" means the motor is turning at or above the limit of 1200rpm. Well, when I look at the specs of this variable speed motor, the lowest speed is 1200 and it goes up to 2000. So I started thinking that maybe the error code is bogus - the blower will always be running at or above 1200 since that is its slowest speed. As far as extreme altitude, I'm in Denver, so 5,280', but the furnace was ordered with the high altitude kit as designated by the -278 at the end of the model number.

If any other ideas after this update, I'd love to hear 'em. I trust you guys more than my installer!

Thanks,
Pete

Is your furnace a 90,000 BTU input? If so, I believe you are confusing some numbers.

2000 (CFM, not RPM) refers to the highest output available for cooling. 1200 CFM is the heating output at 100% input. This is the maximum for heating. At 40% input, the CFM falls to 515 cfm. RPM will rise and fall with the heat input to maintain a proper temperature rise. If the air flow is inadequate, the blower mower will attempt to spin faster to deliver the required CFM. This is the cause of your error code.

As far as the high altitude situation, wait for the pro's to check in.

V

Pete,

I want to know if there was a load calc performed for this install, the inspector was skeptical of the duct sizing. That can raise up the contractor to prove his point about the duct being fine or too small. Pressure drop and static readings with a magnehelic gauge can show some causes. I have a link that might help

Here is a link that might be useful: ACCA AND ASHRAE CERTIFIED HEATING AND AIR CONDITIONING LOAD CALC WITH DUCT DESIGNS

Yes veesubotee you're absolutely right - I was confusing CFM with RPM. And yes, this is a 90,000 BTU input.

pearson21, I'll have to check if there was a load calc performed. That will come out when I challenge the installer on all of this. And thank you for the link - I feel like I have a resource now to fall back on if I need to. I'm already overpaying for this house (appraised at 20K less than the sales price!) so not looking to put out any more of my nickels right now if I can help it!

More questions about this install. Reading the installation manual re. vent piping. For a standard horizontal termination, it talks about:

1. a drain tee assembly and trap installed in the combustion air pipe - I don't have this - how important is it?

2. a specific location of the combustion air inlet with respect to the exhaust vent terminal - I don't comply with the Figure in the manual - how important is this?

3. a 2" PVC coupling with a wind deflector vane to the combustion air pipe as well as a 2" coupling a the wall (for the exhaust vent too) - I don't have these.

4. Condensate Drain - I have one, but it doesn't have a tee with a minimum 5.5" open end riser.

Any thoughts? Should I package these up with my other objections to this installation?

Thanks,
Pete

First off check to make sure that you have a modulating T-stat on your system. It should be the blue touch screen T-stat if its been installed within the last year. If it does not have a modulating t-stat on it and the installer did not take the time to go through all the dip switches the modulating motor will run at a rpm out of its limit and give you that code. Also if you have the correct modulating t-stat he still has to set it correctly.
I have ran into this problem a number of times being a service tech for our rheem dealing company. Some installers try to get by without the correct $150 t-stat for the modulating furnaces. Hope this helps you figure something out.

Thank you ryan161984 - I do have the blue touch screen modulating T-stat, and I see the dip switches you are talking about in the furnace install manual. I can check some of the basic ones like, "the dip switches on SW2 must be in the off position for modulating operation". I remember now this installer saying he would have to go to class to be able to install this furnace, so obviously this was his first RGFD and I wouldn't be surprised if the settings are wrong. So, sounds like I have two potential causes now, either not enough air flow, or wrong settings. Thanks again - I appreciate all you guys.

We don't do 1 and 3. Termination is important so the intake doesn't suck in any exhaust products. We don't put a 5" topper on the tee of the drain but always put the tee in.

Make sure you have a capitol H in the LED display when the furnace is burning. That indicates you are modulating.

OK, went and looked at the dip switches. For modulation, SW2 both switches should be off and they were. For airflow though, on SW3, it looked like he was trying to increase airflow at 100% fire because he had dip switch 2 ON, but dip switch 1 was OFF, which needs to be ON if you want to override the airflow, so I flipped it on. SW1 I don't understand what all that is - they were all off. The only one that looked like it should be on was dip switch 6 because I have a 16 SEER AC, so I turned it on.

Still the "66" code, but baldloonie you're onto something, because as the thing is firing up, it has a lowercase letter "h" not an uppercase "H" in the display, indicating the modulating signal is NOT present. Now what?

Thanks for the notes on venting. I'll focus on the exhaust termination. Book says it should be 12" and it is 2 1/2".

Well if he did not set up the modulating on the rheem t-stat then it will not be sending the modulating signal. You must manually set the rpm settings on the t-stat or the blower has no signal telling it at what rpm to run. If you have the t-stat manual it should be able to tell you what exactly needs to be done to set that up. I could not tell you off the top of my head since its been a couple months since I have set one. If that is correct though then you may be stuck with a duct problem, which my guess is the installer will not be willing to fix. Good luck :)
You can be possitive that it only has to do with air flow or your modulating signal. Nothing will have to do with you flue termination, the 12" is mainly so it does not blow humidity back on your house and cause ice to plug it, or if your intake is right there its to avoid mixture of exaust and intake.

There's nothing to set up on the stat to make it modulate, it just needs to be wired right. Obviously it isn't. Get the dealer back there and correct his problems. Right now you are in timed 3 stage mode.