Firing 3-4 minutes per cycle, 6 times an hour

[mike08054]

Thermostat is set at a constant temp (hold).

Outside temp is 35 degrees F.

Furnace firing 3-4 minutes per cycle, 6 times an hour.

If this was your house/furnace would this be ok?

[brassman]

you might want to have someone look at that

[beenthere]

Nope, I'd set the CPH to 3.
Thats too short of an on time.

[RyanHughes]

That's too often for too short of a time. What thermostat do you have? How many CPH is your thermostat set at (if applicable)? I set my relative's 80% AFUE York furnace to 3 cycles per hour this past Sunday, and I'm more comfortable with it being at that versus 5, which is what I had it at before.

[DavidInAustin]

hmmm Is the t-stat still calling or is it satisfied when the furnace goes off line?

[RyanHughes]

That's a good question to ask David. It's a good idea to see if this is a furnace problem versus a thermostat problem. What kind of furnace is it?

[mike08054]

Coleman Echelon 9.C Modulating (FC9C080B12UP11)
Honeywell VisionPro 8000 (TH8110U1003)

The default for the thermostat was 5 CPH. At lower settings the run times are longer but the blower seems to ramp up a lot by the end of the run cycle and is very loud.

I just set it back to 4 to see how it changes.

beenthere - sorry for posting the same question in two threads.

DavidInAustin - not sure how to tell. The t-stat calls exactly every ten minutes. (currently on the 3's: 9:03, 9:13, 9:23) I hear the click on, heat cycle runs, another click for off until the next call comes.

[RyanHughes]

I wasn't sure that the VisionPRO allows for the option of 4; I guess it does, or at least some models do.

[DavidInAustin]

I suppose there is no problem - Just finding a setting you are comfortable with. It seems to me to be just decisions about a thermostat setting. I dont think I would like that type of control. I assume it is keeping up with infiltration? If it is running every ten minutes for 4 minutes - it seems it would be running all the time! I know I wouldnt like that contraption...lol

[amd]

That furnace shouldn't be running short cycles unless it's grossly oversized.

The modulating is controlled by an internal algorithm which is based on duty cycle.

The service manual specifically says to set CPH to 5 or 6. It should start off at 40% capacity and slowly ramp up from there until the thermostat is satisfied. Operating at low capacity without a call for heat is also normal.

If noise is an issue, there could be a ducting issue or the blower speed is set incorrectly. (Assuming that it allows you to change the speed)

[mike08054]

I set the CPH back to 4. The first hour I saw 10-12 minute run times with about the same time off before the next heat cycle. Over time this gradually changed to a new cycle starting every 15 minutes. (8 heat and 7 off).

It seem that for any "x" CPH setting I get "x" calls for heat at 60/"x" minute intervals.

Is this how most thermostats function, should I ask for a replacement?

[beenthere]

It takes time for both the stat and the furnace to adjust.
Give it a couple days to learn the house.

[beenthere]

Operating at low capacity without a call for heat is also normal.



Continued burner run only happens when the burner meets or exceeds 54% of modulation.

The temp rise can be set to 10* higher, or lower then the factory 55* rise.

[mike08054]

I'll give it a few days to learn the house, should I do this at 3 or 4 CPH? Currently set to 4.

[beenthere]

Try it a couple days at the current 4 CPH.

[completehvac]

I believe the coleman mod needs to be set at 6cph for the ifc to run correctly.

[beenthere]

From my understanding, they UPG mods all use the same algorthm, so 3 and 4 CPH stat setting should work find on any of them.

[mike08054]

Still letting things run 4CPH at 67* (hold) to see if things even out but everything is pretty much the same. Started taking temperature measurements

Temperature of Supply Air = 102 degrees
Temperature of Return Air = 61 degrees
Difference = 41

Temperature at the vent = 93 (max temp measured during the 7 min heat cycle at the duct that is the shortest distance to the furnace)

The temp rise adjustment is still in the default setting.

[cn]

I think this has been discussed in this forum before re 6 cycles/hour:
http://hvac-talk.com/vbb/showthread.php?t=94155

I believe this is 'trademark' of Honeywell.

My "Honeywell CT3200" thermostat does the smae thing:
http://images.overstock.com/f/102/3117/8h/www.overstock.com/images/products/P918075.jpg

It typically runs 3-4 min per cycle; 6 cycles/hour, regardless of outside temp or tstat setting. House is nice and warm, no problems.

So it is Honeywell (and perhaps other brands) "trademark".

Google search "honeywell ct3200 6 cycles per hour" for yourself!

[completehvac]

ok you guys made me do it, just went and grabbed the training manual for the Echelon. It states that you should set it to 6 cph. setting it lower will cause short cycles ans setting it higher will cause the room temp. to exceed the set points.

[beenthere]

Fewer CPH doesn't make it short cycle, it runs longer.

[Airmechanical]

blower seems to ramp up a lot by the end of the run cycle and is very loud.


make sure all the vents in the house are open!



.

[mike08054]

yes that's what I'm seeing. 6CPH has the shortest cycles. Lowering the CPH leads to longer run times.

I'm still letting it run at 4CPH. I think this is day 3.

I do have one closed vent in the bathroom adjacent to the room where the blower sounds loudest. I'll open it when I get home.

[sskzekeman]

QUOTE=mike08054;1690728]I set the CPH back to 4. The first hour I saw 10-12 minute run times with about the same time off before the next heat cycle. Over time this gradually changed to a new cycle starting every 15 minutes. (8 heat and 7 off).

It seem that for any "x" CPH setting I get "x" calls for heat at 60/"x" minute intervals.

Is this how most thermostats function, should I ask for a replacement?[/QUOTE]

That is the definition of CPH. vs the cycle time.;one is the reciprocal of the other in hours. The 60 converts hours to minutes. Nothing to do with the tstat.
If this is a modulting furnace, then I wonder why you need such a high cycle rate (4) , especia;lly at 1/2 design load which is the case at 35 deg OT. I would lower the CPH to the minimum and see how it performs in terms of overshoot and blower speeds. If you also have outdoor reset, then the 4CPH is absurdly high. Or if you cant reduce this then I would change the tstat ( different model if possible). The cycle rate should be as low as possible noting that temperature overshoot inccreases as the cycle rate goes down; if your house is very well insulated you should be able to get away with a very low rate and vice versa.. Honeywell tries to appeal to a large number of applications and yours may not be within their assumed norm.

[beenthere]

I wouldn't set the CPH any lower then 3.

If you do, it will just cause both the burner to increase input, and blower to increase CFM giving you more noise.

Also, it will meet the 54% input quicker and go into a continued run (after stat stops calling for heat ) sooner then it should, and give you temp over shoot

[mike08054]

Holding steady at 4CPH.

Can you explain 54% input and continued run a little more. Not sure if I understand.

Also, I'm assuming that the furnace control board determines the blower speed. Is it directly linked to the firing rate or is there more to it.

[beenthere]

When it exceeds 54% of max input, it will go into an extended burner run after the stat stops calling for heat. This helps to prevent short cycling(especially on stats set to 6 CPH) during colder OD temps. It runs at a reduced input when it does this. Adds a lot to the comfort of the house when its 10* degreed outside.

The blower speed is determined by setting of the temp risesetting on the board, the temp temp the discharge air sensor is registering, and the input rate the board is sending the gas valve.

As the furnace runs longer, it increases the modulation of the burner, then shortly after that, it increases the blower if the temp rise has increased.
If the rise has not increased, it will increase the burner input until it does. Then it will increase the blower.

You will notice it more as it gets closer to OD design temp.

[jerrick]

try to clean up the nozzle because some rust from the gas pipe block the gas from spaying out. It is similar your car fuel injection

[mike08054]

Set the temp rise to 10* higher.

From the manual: ADJUSTMENT OF TEMPERATURE RISE: If less air is desired (higher temperature rise), move the jumper to the +10 position

On the first few cycles after restarting:
Temperature of Supply Air = 105 degrees
Temperature of Return Air = 61 degrees

But the blower isn't as loud as before. The next morning I listened to the cycles for a couple hours and it's about the same as before

Heat for 6 minutes, +2 minutes blower = 8 minutes heat followed by 7 minutes off before the next cycle. On+Off=15 minutes, 4 cycles every hour.

It seems almost like the stat is adjusting to enforce 4CPH. Or is this normal/acceptable? Thinking of moving down to 3CPH to see what happens.

[beenthere]

It seems almost like the stat is adjusting to enforce 4CPH. Or is this normal/acceptable?

Thats what the CPH setting does.

[mike08054]

But if the thermostat is adjusting to meet its setting does that interfere with the York/Colman logic? I thought the CPH was a maximum setting but it seems to be forced by the stat.

I'll move down to 3CPH. I did this initially but that resulted in the blower ramping up to full speed all the time. But now that the temp rise is set to +10 I'll see what happens at 3CPH. My guess is that I'll see 3 cycles 20 minutes total with 10 min heat and 10 min off.

I still feel like I don't now what qualifies for normal operation. 6-8 minutes of heat 4 times an hour, 18-20 minutes 2 times an hour?

[beenthere]

The board will learn the house weather you set teh stat for 3, 4 or 6 CPH.

At 3 CPH the furnace will go to a higher modulation, and teh blower will speed up some.
You have to give it a couple days for the stat and furnace to learn the house, after each setting.

[beenthere]

Also, as it gets colder outside, the burner on time will increase, and the off time will decrease.

It will at some point get to a 15 minute burner on, and 5 minute off time with a 3 CPH setting.

[mike08054]

Thanks! I think I get it now. I'm still at 4 CPH. I might try 3 but there's no rush. Seems like adjusting the temp rise (+10) had the most effect (improvement).

I may still have some duct issues and it seems that the inducer motor whines a lot. If I have questions about these issues but I'll start a new post.

[mike08054]

Would the york/coleman mod run better with a thermostat that didn't do CPH?

If you used a mechanical thermostat how would it affect the run times?

[beenthere]

Haven't used a mechanical stat on one yet.
Don't plan to either. :)

Your too worried abouot your CPH at the moment. You don't need to switch to a mech stat. You would probaly end up with the simular cycle rates, except when it got colder out side.

Let the stat and furnace do their jobs for a week or so without timing them. You might find you like it the way it is.