What is your heating/cooling cycle time?

[ArcReactorKC]

Currently we are in a rental and I feel like our heating cycles are short. Not short-cycling the furnace short but the temp rises quick and falls quick. Indicative of poor insulation, which I am 100% sure we have in the house.
This graph shows the temperature swings from 6pm to 9am you can see at the beginning of the graph as the outside temperature falls and the thermostat starts calling for heat it is a rapid up and down. House is electric heat no heat pump. Thermostat is set for 69 degrees, I'm not sure if it is a hysteresis issue or if we genuinely just lose the heat this rapidly.

IR scans show no leaks anywhere windows are dual-pane and door seals are good. The walls are poorly insulated at best.

 

[jlv03]

Is the graph a report from a thermometer or from the thermostat?

 

[ybnormal]

welllll, we just suffered thru another ice storm here in Austin and I can give you a comparison. I've done some recent remodels etc to the house we've been in for the last 27-1/2 yrs. Turns out we don't have a whole lot of wall insulation either but we are >85% brick with double pane windows on an elevated 2-story that faces east. Within a certain outdoor temp range our electric heatpump runs, reaches temp, and then after awhile runs again, etc. This is regardless of summer or winter, our "sweet spot" seems to be about 72-76 degrees where it does nothing. Somehow the temperature fluctuation factor of how fast the house loses or gains temps is right in that "sweet spot". go below or above that range by about 20F or more and it either loses heat too fast in the winter or gains heat too fast in the summer from the sun.

when temps are down in the 30s I've noticed our heat pump pretty much runs constantly. the same for when it gets above 100-105 outside.
with the freeze over the last 3-4 days, our heat pump pretty much runs all night even when set at 65F, and we use flannel sheets and 2 blankets. in the summer we set the tstat at about 78-80 overnight but if we have an extended heatwave it's definitely working overtime to cool down the attic which has blown insulation a foot thick.

 

[ArcReactorKC]

Is the graph a report from a thermometer or from the thermostat?

It's from the living room temp/humidity sensor. I have sensors in every room, they are used for different home automations. The Alexa thermostat sadly doesn't chart temperatures. I have creating my own thermostat using all my room sensors on the slate for the coming weeks but I want to be sure I don't have something weird happening before adding another variable.

 

[Yankeefarmer]

It looks like your temperature controller is very sensitive, allowing less than 1 degree of temperature variation. The typical thermostats in my house allow for a 2 degree swing: if your set point is 69, for example, it will call for heat at 68, and shut off at 70. My Emerson Sensi in my shop allows you to pick 3 levels of variation, and the “loosest” is tighter than the 2 degree swing I mentioned, but not as sensitive as yours.

Remember that heater “on” time is a function of heating system output; “off” time is a function of how rapidly the space loses heat.

 

[PoorUB]

My thermostat doesn't fluctuate in temperature at all, at least as far as I can tell. It is always at set point. It probably fluctuates a half degree on either side of the set point, but not far enough to show on the read out. I have back up the temp measurement with another thermometer. don't remember what range it showed but it agreed with my thermostat.

A two degree swing would make me and my wife crazy!

To the OP, do you have anyway to control the heat output? Less BTU output over a longer time would be more comfortable. Perfection would be to match the BTU of the heating equipment to the heat loss of the building so the equipment runs steady but maintains temp. It looks like you have two issues. Large heat loss and greatly oversized furnace.

 

[Yankeefarmer]

@PoorUB, the swing at our house may not be a full 2 degrees, since the tstats thankfully only display whole degrees, no decimals. So, when I’ve watched it come on at 68 and off at 70, it might be calling for heat at 68.4 and ending the call at 69.5. We don’t notice the temperature variation at all.

 

[ArcReactorKC]

It looks like your temperature controller is very sensitive, allowing less than 1 degree of temperature variation. The typical thermostats in my house allow for a 2 degree swing: if your set point is 69, for example, it will call for heat at 68, and shut off at 70. My Emerson Sensi in my shop allows you to pick 3 levels of variation, and the “loosest” is tighter than the 2 degree swing I mentioned, but not as sensitive as yours.

Remember that heater “on” time is a function of heating system output; “off” time is a function of how rapidly the space loses heat.

The Alexa thermostat is somewhat a piece of garbage in these respects. The hysteresis isn't adjustable. I'm hopeful that making my own will help with that portion.

My thermostat doesn't fluctuate in temperature at all, at least as far as I can tell. It is always at set point. It probably fluctuates a half degree on either side of the set point, but not far enough to show on the read out. I have back up the temp measurement with another thermometer. don't remember what range it showed but it agreed with my thermostat.

A two degree swing would make me and my wife crazy!

To the OP, do you have anyway to control the heat output? Less BTU output over a longer time would be more comfortable. Perfection would be to match the BTU of the heating equipment to the heat loss of the building so the equipment runs steady but maintains temp. It looks like you have two issues. Large heat loss and greatly oversized furnace.

The furnace is a cheap-o resistive strip heater. It doesn't have any adjustment per se but I haven't dug in very deep to see if I could separate the strip circuits so I have "low heat" and "high heat" modes. With my HA setup I could probably make these alternate on each heat cycle which would effectively reduce the exit air temperature and prolong the life of the strips, not that I'm very concerned with that since this is a rental.

When we moved in there was a dial thermostat on the wall as if the 1960's had yet to end. This house was built in 2021 so I find some of these design choices shameful. We were in a different rental temporarily while this one was being built. We made the decision to rent here based on the monthly price and square footage for the time being. Had I known some of these other things prior we definitely would have looked elsewhere but the builders assured me it would have good R-value walls and windows, they only lied about the walls.

 

[jlv03]

How many breakers are on the air handler? Can you shut down the one that runs heat strips only to see if the system performs better (note that the air will be colder out the vents)?

 

[ArcReactorKC]

How many breakers are on the air handler? Can you shut down the one that runs heat strips only to see if the system performs better (note that the air will be colder out the vents)?

Two breakers, one for the resistive heat, the other for the blower. Shutting off the resistive heat breaker would mean no heat at all.

 

[jlv03]

Interesting, sometimes you see two 2-pole breakers at a sufficient size (20A all the way up to 40A). Do you have a circuit diagram, installation instructions, or even an air handler model number?

 

[bonneyman]

We've been having a cold snap locally, and the dang furnace seems to be cycling constantly. (Just swapped out the old stat of 10 years for a NOS one I had). Eight minutes on, 10 minutes off. Annoying. I went into the stat programming and reset the differential to 2 degrees instead of the normal 1 factory setting. Seems to be more like 12 minutes on, 12 minutes off now. Better.

 

[Bert_]

Two breakers, one for the resistive heat, the other for the blower. Shutting off the resistive heat breaker would mean no heat at all.

I've never seen one that way although it could be possible.

Typically it's one breaker for the fan and any heat strip up to 10kw. Larger heat kits would have multiple breakers for the heat elements one would also include the fan

 

[fitter30]

Brand and complete model of thermostat.

 

[ArcReactorKC]

Brand and complete model of thermostat.

https://www.amazon.com/gp/product/B08J4C8871/?tag=atomicindus08-20

Amazon/Alexa thermostat, not hysteresis setting available, I requested the addition when I first bought it, as well as a bunch of other people. Apparently big Bezos doesn't care.

I'll be replacing it as I get some time in the next month with an ESP32 and hopefully by widening the hysteresis and having zone temp sensors I can get the "swing" out of the system.

 

[fitter30]

Thermostats that work on temp alone don't work very well. Thermostat needs anticipation based on the type of heat and heat emitters. This can be done with cycle rate, amp setting from a burner control or input of the mass. With looking at your temp chart and how many cycles per hour look at stat placement and would check to see if there is air infiltrating from back of thermostat or why is the air temp falling so fast.

 

[sundirect_heater]

It depends on particular system. Cycling Time of heating & cooling is around 10 to 15 minutes.

 

[My Old Tools]

With our new Waterfurnace geothermal system, 1/2 degree temp swing is programmed in. The system runs pretty much continuously as it is fully variable speed on blower, compressor, and water pumps. On a day when the outside temp matches the inside all day it will go to standby, but generally just throttles up and down as needed.

 

[justinjoyal]

Looks like 7-8 cph with a 0.75 to 1 *F swing each time. Not a huge swing. The system probably works on temperature alone, may be oversized and can only run the whole thing at once so yeah, that's what you get.

As you mentionned, see if you could get it to work on multiple stages. That would allow for a more precise temperature control (provided the thermostat allows it.)

 

[ArcReactorKC]

Looks like 7-8 cph with a 0.75 to 1 *F swing each time. Not a huge swing. The system probably works on temperature alone, may be oversized and can only run the whole thing at once so yeah, that's what you get.

As you mentionned, see if you could get it to work on multiple stages. That would allow for a more precise temperature control (provided the thermostat allows it.)

So Saturday I carved out some time for my HomeAssistant/ESP32 thermostat project. While I was inside the furnace I found a model number on the circuit board (there are not numbers or name on the outside of the furnace) using that info I found the blower is multispeed. I dropped speed by 1/3 and that has slowed the swings. The home is more "heat saturated" so it takes longer to lose the heat. My understanding is when you warm a space to quickly only the air is warm and not the actual environment. Now the heat cycle is longer but the space stays warmer longer as well.

I have two duct valves on the way as well to be controlled through home assistant so the only "uncontrolled zone" is the living room. The zone control I think is going to be a great quality of life upgrade. As well as the "geo fencing" from Home assistant.

 

[jlv03]

Did you follow the air flow chart to make sure you didn't slow down the speed too much? I'd be afraid of getting those coils too hot.

 

[ArcReactorKC]

Did you follow the air flow chart to make sure you didn't slow down the speed too much? I'd be afraid of getting those coils too hot.

Yes I did, I am one setting above the minimum.

 

[justinjoyal]

Do you have A/C ? Not enough airflow would cause problem.

 

[ArcReactorKC]

Do you have A/C ? Not enough airflow would cause problem.

Yes, according to the chart I should be fine. But I do have airflow meters on both sides of the A-Coil so if there is a freezing issue the system should react and correct it. I don't think it will be a problem but it was an excuse to put more gizmo's in.