Carrier Infinity furnace/AC 10-year runtime report stats

Messages
580
Location
MN
I was playing around with our thermostat’s installer menu when I happened upon the cycle and hour counts for the lifetime of the system, which I thought were quite interesting. Although it's not car-related, it is mechanical and something I could see BITOG maybe being interested in.

We have a Carrier Infinity gas furnace (95%, 3 stage, 100k btu) paired with a Carrier Performance AC (15 seer, 1 stage, 3 ton) that were installed in April of 2010. They’re controlled by the Infinity controller which has tons of functionality, diagnostic tools, and lots of hidden features. One small ac repair early on (capacitor, as I remember) comes to mind but otherwise the system has been excellent. The AC is very quiet (the materials said 66 db) and the furnace is imperceptibly quiet on low stage.

We run the fan pretty much all the time for circulation and to even the temps out in the house, as it’s a 4-level split (it has a selectable 3-speed fan). You can’t hear it running on low, and the temps are greatly evened out from upper floors to lower ones.

I particularly like the 3-stage furnace. It runs on low most of the time, and gives a gentler sort of heat. We usually use settings of 64 night/68 day (winter) and 74 day/72 evenings (summer). We never let the house warm up much above 75 - if it gets warm indoors, the AC goes on. Cost to run either the furnace or AC seems around $100ish per month in the more extreme months, January and July, less in the spring and fall, for a ~3200 square foot home in southern MN (built in 1980 but added blown-in ceiling insulation insulation and newer windows).

The AC runtime was 2733 hours, so about 260 hours a year. This sounds about right as it primarily only runs in the late afternoon/evening. We will open windows if it’s pleasant but the AC is on for most of the summer months. Our summer highs typically run in the high 70s - low to mid 80s, but 90 is pretty hot for our area, so we don’t tax the AC too much. Interior humidity runs around 48ish% in the summer.

The furnace runtime was 11,392 (low), 5094 (medium), 2243 (high), for 18,734 hours in total, or about 1900 hours a year. Low takes care of most of the heating needs, except for overcoming setback sometimes. We get comparatively rather cold (it’s not unusual to be sub-zero or in the negative teens; we rarely see temps above 40 in the winter). (Google says a January average high of 23 and low of 5.) For those without multistage furnaces, the idea is for it to run on low much of the time, potentially most of the time, on cold days. which improves comfort by decreasing temp swings. Of course, the runtime is much higher than it would be with a single-stage system - consider that it’s heating at about 1/3 capacity for much of the time. It seems to me the runtime if it ran only on high stage would be around 750 or 800 hours a year. It does work quite well, and has logic that uses lots of info including the outside temp and historical data to determine how long to run on each heating stage. If we’d coupled a Honeywell or something to the same furnace, it would kick up stages strictly as a function of time, so the more expensive stat does offer more control and does provide value.

And the blower has run a total of 82,122 hours, or an average of about 22 hours a day (we might turn the fan to auto if we’re on a longer vacation or something, but it pretty much stays on low all the time; it uses in the neighborhood of 100 watts but does wonders to even temps out). My calculations say that it costs about $75 a year to run the fan in this way, and likely saves a chunk of that back by reducing summer cooling needs (pulling cool basement air up).

Anyway, I thought this was pretty interesting. It shows the seasonal impacts of each system and how much more we use heat than AC up here. Plus it’s a neat way to see how much it’s actually been used and how well it’s held up over the years. The multi-stage furnace may sound gimmicky, but I would say it’s definitely worth the added cost.
 
Messages
1,231
Location
canada
Excellent post !
The break down of runtime is very interesting, wish my stat could do this.
the blower motor held up well almost ten years of constant run time....
 
Messages
4,298
Location
N.C.
Only 260 ac run hours in a year? I realize you’re in MN but geez! My 26 year old Trane runs more hours than that in 2 weeks during summer months. (y)
 
Messages
16,431
Location
Silicon Valley
Yes, running low continuously is definitely better than cycling on and off on high. I was doing the same all summer long on fan and ac (my AC is slightly undersized). Winter for us is a problem with moderate climate (between high 40s and low 60s) and a 100k BTU single stage 80% furnace in a 1500 sqft house.
 

TmanP

Thread starter
Messages
580
Location
MN
Only 260 ac run hours in a year? I realize you’re in MN but geez! My 26 year old Trane runs more hours than that in 2 weeks during summer months. (y)

Yup! I'd guess that we use our ac more liberally than most people in the neighborhood, too. We don't usually play games with opening and closing windows, etc. unless it's nice out, and we don't set it above 74 (72 in evenings). Some houses around town don't have AC, and the high school I went to didn't have it either. Although we are in the warmest part of MN (oxymoron, maybe, ha?) we still don't get too warm. 90 is definitely hot for us; the AC is usually not trying to maintain more than a 15-degree differential.
 
Your fan running and "pulling cool basement air up" doesn't really cool the house. Yes, it will help mix the cool air from the basement with the warmer air from above but I don't agree with it running 22 hours a day.

Here's what the fan running without the AC on does in the summer and, more importantly, in humid conditions does - it INCREASES RH in the space. When the compressor shuts off, you now have air moving across a warm coil and that warm coil will cause the air moving across it to pick up moisture. Is it ok for the fan to run 30-60 seconds after the compressor shuts down? Yes. But for several minutes/hours? No. In the winter, it's fine.

It does seem like the humidity is mot much of a problem in MN, but I'd keep an eye on it. I can tell the difference between 50% RH at 72 degrees and 58% RH at 72 degrees.
 
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