ERD50
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
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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