Most furnaces will fire 1st stage and after a specified amount of time if the thermostat hasnt satisfied. It will fire on 2nd stage.

 

Only when the installer is too cheap or lazy to use a proper 2-stage stat.

Timers call for second stage when it's really not necessary. (After only 10 minutes for most furnaces)

 

If stage 1 is not able to satisfy the call for heat and the temperature is dropping still, stage 2 will fire. Or, if you raise the tstat to a higher setting it will call for stage 2 to help speed up the recovery. I don't know about the time thing, but the old mercury 2 stage tstats were not able to sense run time, electronic is possible. But you would have more comfort running continuous in stage one, rather then over firing.

 

Let's say you do not have an outdoor temp sensor for the tstat but have a DFHP (I have a York Affinity HP and VS NG furnace) and it's above the 35 F balance point, what determines when the HP locks out and transfers to the furnace? Would it typically be the tstat sensing a difference of greater than or equal to 2 F between it's setting and room temp? Or does the HP have to give its stage 2 a try and give up after some timed period say before signaling the furnace?

(Question rationale: I keep trying to figure out if my NG furnace or the HP should come on when the tstat setting goes from say the night time 68 F setting to the 70 F wake up setting - no tstat temp ramp up parameter setting involved.)

 

On yours, the temp must be below the balance point, for it to use the furnace.

 

If you don't have a outdoor stat, then I'd say your missing some vital stuff.

But, if your hp can't keep up, it'll kick to furnace. Or, if the stat knows to kick straight to furnace because of a massive change in what your setting your stat to (room is 65, you turn stat on and set to 75.)

 

I thought we were talking 2 stage furnaces, how did the HP come into the equation?

Personally, I have a HP, with OFHWBB it operates in 3 steps. (1st) the HP runs alone in mild temps, (2nd) gets stage 2 OFHWBB when it gets colder, (3rd) the HP gets shut down when it gets frigid out doors. I have a relay that makes the OFHWBB 1st stage during frigid weather.

 

On the TH8321. I believe its when the temp drops 2 degrees
Can't remember anymore. haven't installed one for a while.

 

Yes, 1 degree off set-point = stage 1, two degrees off set-point = second stage.

 

That won't happen. The stat senses temp in tenths of a degree.

 

The old mechanical stats used to have a mercury switch for each stage. (Differential between stages)

The good electronic models (honeywell, white rogers - not Lux/Hunter) stage based on rate of temperature change as opposed to using a fixed differential.

 

How petty/cheap is an installer who doesn't put in a proper 2 stage stat when he sells the guy a 2 stage furnace?? My old boss did that and just used the autostaging option which was basically a timed staging cycle similar to what has been described here previously..
Now that I have been on my own, I pop for the extra cash to buy the homeowner a decent stat (my last install job I actually used that same HWFP 6000 2 stager that you are talking about) The homeowner is happy, even if he has no idea that he has a 2 stage t stat, and I feel I did my job, and sleep better at night for it.

 

I'm informed by Heil, their 95% 2 stage funaces will run on first stage for 12 minutes with a single stage stat, when the dip switches are left at the factory settings.(Then it kicks into high fire) Otherwise the 2 stage stats depend on their swing temperatures, Usually 3 degrees.
RB

 

Is that what Carrier is ----is 10 minutes? Does the carrier cut in./H20 in half on first stage. I'm finding that almost none of the 2 stage manufacturers cut input by 2.
Wonder why?
OH,,,,,,,,,,tpa-fl----------what is Honeywells P+I?
Thanks
RB