Thermostat fan setting (auto vs circ)?

[ERD50]

...
My system (Carrier) is the same age as the home, built in 2007. I checked the labeling on the outdoor unit and found no AFUE rating but rather a “thermal efficiency” of 80.6%. It seems that would be considered a “mid-efficiency” rating. . ...

The old gas furnaces (pre ~ 1990) were ~ 50% eff. Then the ~ 80% efficiency became common, they are the ones with the draft inducer, which was required to push the hot combustion gasses through the more labyrinth heat exchanger which pulled more heat out. These still require a chimney, but when replacing a 50% unit, they might put in a chimney liner to get a good enough draft with the cooler exhaust (more heat went into the house).

The high efficiency (>90%) are the ones with the sealed combustion and a condensate drip line. The exhaust gets cooled so much that the water condenses out. These also have a draft inducer fan and have a PVC pipe for exhaust, as the exhaust is now just warm.

Going from 50% to 80% is a big savings. Going from 80% to 90%, not so much. But those 90% are often set up with a PVC pipe to bring in outside air for combustion. I kinda question if this really improves efficiency, but I think it can provide more comfort, as it could lessen drafts in the house from outside air needing to "leak" in to feed the furnace air.

... The Honeywell thermostat is set for high efficiency by default so I changed it to standard. Apparently the effect is to change the cycles per hour from 3 (high efficiency) to 5 (standard).

Now to see how it goes but I’m hoping to have a smoother heating season ahead.

I had that "cycles per hour" setting on the high eff furnace/thermostat I left behind in the previous house. I found it to be quite interesting. Rather than just turning on/off at a specific temperature delta, it attempts to match the "cycles per hour" setting by either increasing or decreasing the temperature set points. So if it was warm outside (furnace OFF cycle normally longer), the set points would be narrow, the furnace would run for shorter cycle, but still cycle X times per hour, to keep the air circulated I guess. If very cold out (furnace OFF cycle normally shorter), the set points would be wider, so the OFF time and the ON time would be longer.

I never noticed the difference comfort wise, the delta wasn't all that great I guess. Also not sure how much it helps efficiency. But it is an interesting approach.

-ERD50

 

[steelyman]

This is very interesting, thanks for commenting.

I’ve been steeling myself (no pun intended) to prepare to replace the whole system but am now thinking it may be worth it (both in time and money) to hang on for a while. I know the recent repair/part replacement history (last 4 years) and quite a bit has been done. It helps to live in a more moderate climate than my prior midwestern home

The old gas furnaces (pre ~ 1990) were ~ 50% eff. Then the ~ 80% efficiency became common, they are the ones with the draft inducer, which was required to push the hot combustion gasses through the more labyrinth heat exchanger which pulled more heat out. These still require a chimney, but when replacing a 50% unit, they might put in a chimney liner to get a good enough draft with the cooler exhaust (more heat went into the house).



The high efficiency (>90%) are the ones with the sealed combustion and a condensate drip line. The exhaust gets cooled so much that the water condenses out. These also have a draft inducer fan and have a PVC pipe for exhaust, as the exhaust is now just warm.



Going from 50% to 80% is a big savings. Going from 80% to 90%, not so much. But those 90% are often set up with a PVC pipe to bring in outside air for combustion. I kinda question if this really improves efficiency, but I think it can provide more comfort, as it could lessen drafts in the house from outside air needing to "leak" in to feed the furnace air.


I had that "cycles per hour" setting on the high eff furnace/thermostat I left behind in the previous house. I found it to be quite interesting. Rather than just turning on/off at a specific temperature delta, it attempts to match the "cycles per hour" setting by either increasing or decreasing the temperature set points. So if it was warm outside (furnace OFF cycle normally longer), the set points would be narrow, the furnace would run for shorter cycle, but still cycle X times per hour, to keep the air circulated I guess. If very cold out (furnace OFF cycle normally shorter), the set points would be wider, so the OFF time and the ON time would be longer.

I never noticed the difference comfort wise, the delta wasn't all that great I guess. Also not sure how much it helps efficiency. But it is an interesting approach.

-ERD50

 

[sengsational]

I have the AprilAire humidifier set to humidify even when there's no call for heat. So it flips the fan on every so often to get a reading. Then, if too dry, it runs fan only with the water on. The whole house humidifier is something I'd tell my younger self to implement...so many dry and scratchy winters could have been avoided. But I don't have a fancy thermostat, though. Another comfort thing is the few square feet of electric resistance under the kitchen table I put in last fall. I find it much easier to linger at meal time if my feet aren't cold.

 

[Yoheadden]

Retired HVAC Engineer here. Circ is the recommended setting for two story houses to help even out temperature variations between 1st and 2nd floors. I have a nest thermostat and I run circ for 1/3 each hour plus I installed an extra temp sensor upstairs to control in the evening thru morning.

Is the extra temp sensor on a wireless system with the thermostat?
I have a first floor bedroom that was converted from a formal living room. It is right above the furnace, so by the time the temp reaches the first floor thermostat, which is in the middle of the house, it is usually extra cold or hot.

 

[Al in Ohio]

The Nest brand thermostat can be controlled by one or several remote temperature sensors that can be chosen by the Nest app to be the controlling temperature sensor for either the morning,afternoon, evening, or night time period, or any / all of those periods. Several sensors located around the home may be installed and selected for different time periods. They look like small 1.5 “ diameter white hockey pucks. You can even take an average control temperature of all of them. They are best installed at chest to head height on the wall. It’s the ultimate control at an economical cost. You can have up to four sensors. They are all wireless. Just put a little screw in the wall and hang it up! Very easy.