Problems with 2 stage Rudd??

[duane7]

I have an earlier post about my new 2 stage Rudd 60,000 btu doing what almost seems like a short cycle. Outside temps are 30 degrees, no wind, R38 newly installed in attic. Furnace has been running an average of 6 mins on and then 12 mins off. Tsat is a White Rogers digital that has been set to a 1.5 difference (thats its max).

The contractor can find nothing wrong but this morning he tells me mine is the second one they are seeing this problem with. He is waiting for factory rep to call back.

Any one else running into this problem??

[BaldLoonie]

The furnace only does what the stat tells it to do. Have them try a Vision Pro instead and see what happens.

[duane7]

Thanks Bald....I talked to the supervisor and he is familiar with the Tsat but thinks he wants to try something else as far as Tsats go tomorrow.

I saw on a review of the Vision pro someone had posted a link to Honeywell that talked about the constant on/off not being detrimental to effiency but when I tried it the link was inaccurate so dont know what the white paper said..

Thanks....

[docholiday]

He's either miswired it or the supply register is blowing on the stat.

[duane7]

Thanks Doc..There is no supply register near it. The Tsat is located in a middle of the house hallway. I have checked for cold drafts that might be blowing on it and cant find anything.

[beenthere]

6 minutes on, and 12 off is 3 cycles per hour.

Did you look to see if the hole in the waal where the wires come through is sealed.

[duane7]

I haven't yet. They are supposed to come back out this morning and I will be home so that is one thing I want them to check also.

[docholiday]

Something tells me that the stat is miswired at the furnace and you are going into full 2nd stage heat right off the bat.

If it's a sigle stage stat, it should be wired to W2. When the furnace sees 24v at W2 without voltage at W it will operate on low fire for something like 12 minutes before going to high fire. If he wired it to W, then it would never go into high fire, if on the other hand he jumped W-W2 then it would never go into low fire.

[duane7]

Doc, it is a Tsat that has dual stage capability on it. It is only running on the first stage. When I bump it up over 3 degrees it then will go to high heat as the Tsat manual says it should but the rest of the time it only runs 5 or 6 mins in low fire.

[htrguy]

If it is cycling rapidly at an outdoor of 30 degrees and it maintains temperature in the house, I'd suspect oversized unit if all mechanical functions are correct. Was a heat load performed by the contractor prior to install?

[duane7]

I wasn't home when the salesperson was here. He did look at insulation in the attic so I am not sure if he did an actual load or if he "wagged" it. I do have a unfinsished basement that I shut some of the downstairs registers too but I don't think that would be short cycling it.

The house is 988 square feet built in 1976. Walls are insulated and I just had R38 put in the attic to see if that might stop the constant on/off but it didnt seem to help.

[BaldLoonie]

Where are you?

I have the same size house, R38 attic, R13 walls, good windows. I have a 80K 80% furnace, I just leave high turned off unless I do a warmup from being gone a few days. I knew I was way oversizing the furnace but at the time this mfr. didn't have anything smaller with a VS drive. I use a HP most of the time but on low fire, which on mine is 48,000 BTU input, I can keep the house toasty when it is below zero out.

So yes, I'd guess you are well oversized!

Definitely be sure you are wired for 2 stage operation then you won't be on high except for recovery from setback. But your operation doesn't sound that out of line. As been calculated, 3 cycles per hour where many are more than that!

[duane7]

Thanks Bald... I am in Eastern Iowa. Davenport to be exact. Spent 20 years in the Kokomo/Ft Wayne area. Five as a dispatcher/scheduler for J.O. Mory in northern Indiana