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Old 01-01-2011, 12:55 PM   #1
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Rheem Mod Stat--minor annoyance


Have a Rheem RGFD furnace with 411 Mod stat, which I love. Using intelligent recovery (8 degree setback), after startup stat will reach setpoint in about an hour (O.K.).

About an hour later, with furnace running, the temperature will drop 1 - 2 degrees, and furnace ramps up slightly and coasts to setpoint. After reaching setpoint, it will maintain RT perfectly. Stat is set on fast staging.

The furnace was checked out by Rheem Distrib. technical specialist and all was well, but asked contractor to change stat, which he did. Second stat exhibits same behavior.

This is annoying to me as I am very sensitive to cold temperature (especially sudden drops), which is why I chose this furnace.

One thought I had was with regard to basement air coming up through the TS wire hole, but I checked it and the seals were intact.

Is this just an inherent problem with these W-R stats? I believe the 401 had the same problem. I looked in the manual at configuration changes, but nothing came to mind to change.

Any help appreciated.

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Old 01-01-2011, 04:28 PM   #2
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Rheem Mod Stat--minor annoyance


Its part of the draw back to setting the temp back at night. The furnace can heat the air up quickly, but not the walls and other objects.

Try a four degree set back, and see if ti does slightly better.
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Old 01-02-2011, 10:09 AM   #3
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Rheem Mod Stat--minor annoyance


BT, I understand the concept that in recovery, the air temperature will lose heat with the walls, furniture, etc., but in my situation, there are circumstances which lead me to believe that the stat is the culprit.

On most days, I awake and become active before the stat (depending on how much RT had dropped) would normally start the recovery. I will goose the setpoint maybe 2 or 3 degrees to take the chill off of the air. On average, this would cause the furnace to go to full recovery in about 40 minutes.

About 40 minutes or so, the stat will reach setpoint, and coast for a prolonged period. Strangely, about an hour later, the furnace will ramp up and the RT will very suddenly indicate an RT of 1 -2 degrees less.

The stat is set with an anticipation setting of 0.6 degrees, so even a 1 degree drop shouldn't happen. Interestingly, as far as I can tell, whether or not I wait for the stat to bring on recovery, or do my partial warmup, it behaves the same, and the 'behavior' always seems to occur at about the same time.

Regarding your suggestion, I plan to do some experimenting. Last night, the RT dropped only 3 degrees. At 5:15 AM, OD temp was 58 degrees. I allowed the stat to do its thing. I was not able to detect any abnormal behavior, checking the stat at 15 minute intervals.

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Old 01-02-2011, 01:09 PM   #4
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Rheem Mod Stat--minor annoyance


Its most likely the 8 degree set back temp. Use 4 and you won't have the problem.

If you want to use 8. Your probably going to have the problem.
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Old 01-02-2011, 02:32 PM   #5
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Rheem Mod Stat--minor annoyance


Quote:
Originally Posted by beenthere View Post
Its most likely the 8 degree set back temp. Use 4 and you won't have the problem.

If you want to use 8. Your probably going to have the problem.
Time will tell.

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