Recently, we had a scare with our furnace .. luckily, part was under warranty and we got it back up and running. However, having lived without heat for 2-3 weeks, I was super curious about .. how heat dissipated.. I am now aware of some sizing problems and return problems in the house. Specifically, i wanted to know if I should leave the Fan On or Auto, and how effective that was at equalizing temperatures between upstairs and downstairs. Answer: Its very effective. I answered these questions with the use of Govee temperature loggers, which can export CSV, tied into Excel.
The following is an overview minus the outside temperature, we’ll zoom into sections of this around certain things. It has two days, the first day was (mostly) fan ON, thermostat at 68; the second day (11pm 11/3) was fan on Auto.
The Gray line is the temperature at the vent – it shows when the heater kicks on and turns off. You’ll note that both days, outside sun warmed up the house to the point where heat was no longer being applied. About 10am-Midnight, amazingly. This is where multi-stage if we had it would be handy.
Upstairs is the green line, its where 3/4 grandkids sleep and play. What i didn’t know is that there’s a window AC unit in there, set to 70, that was turned on. First day, temperature trended upwards slowly, the AC barely kicked on (sharp downward spike). Second day – even during the night – AC kicked on several times, and a lot during the day. There’s a LOT of heat that just travels upstairs when the whole house fan is not running.
The Yellow and Orange are the two ends of downstairs. The Orange end does not have any returns, so whatever the A/C is doing, tends to accumulate there, especially when the fan is on. On the second day (I think) I tried to set up a house fan to help the air move out of that wing back into general circulation. It might have helped. Downstairs1, Yellow, btw, is directly below Upstairs, Green as far as these sensors go.
I also did a test of: What happens if I leave the door open, fully open, for 20 minutes, while its cold out. At the time it was about 35 degrees outside. Here’s a zoom in:
The door was fully open for 20 minutes, from 9:10 to 9:30 on this graph. During that time, the thermostat-area dropped from 68 down to 66, and I can tell you that the floor of the room with the thermostat (also where the door was open) got down to 54. and the heat kicked on, HARD. The rest of the house actually warmed up from all this furnace activity – Upstairs went up the fastest. Once i shut the door, it took a good 40 minutes of heat before the thermostat was happy. It took maybe another 2 hours before all the extra heat worked its way through the house and things returned to normal. During this time, the Sun was out and was warming everything up, and so data gets a bit.. too many signals.
Just to be complete, here’s the full graph including the outside temperature.