Thermostat swing

[LVSteve]

This house came with fancy electronic thermostats where I can set how much slack or swing in temperature there is to turn the HVAC system on and off.

I typically use a 1°F swing in A/C mode, but I'm thinking 2°F works best with the heat. Right now the heat comes on for 25-35 minutes every 80-90 minutes. What say the HVAC experts, should I use 1°F for heat as well?

 

[Rustyt1953]

 

[LVSteve]

Oddly enough, 72°F seems to be a good winter number in this house since the insulation was redone.

 

[9mmPatriot]

My advice has always been to not mess with the differential setpoint. This allows for a more evenly heated/cooled space.

Thermostats only respond to the temperature changes at it's location. They don't care you, the dog,the kids,the gold fish....

What I do (strongly) recommend is running your fan anytime you're home.
This will
Eliminate stratification
Provide cleaner air
Allow the the thermostat to measure the mixed air temperature, thereby providing better control of the true space temperature.

Try it for 2 weeks, you'll be surprised at the results.

 

[NYlakesider]

I like a two degree swing in heat setting. I have propane forced hot air. By going to the bigger swing you get less on and offs of the system. The system does run longer and that puts it into a more efficient mode. I can see outside temperatures of -28F here at times and I base what I say on close to 20 years of rural living here at the upstate lake!

My thermostat is in a very good place in the middle of the house.

 

[TX-Dennis]

If I run the fan all the time in winter I have to raise the set temp. To me the moving air "feels" cooler, and I am rather cold natured. I keep mine set on 75 in winter, 78 in summer, In winter it runs rarely - once or twice a day for a few minutes - unless the outside temp is below 40 which is fairly uncommon except during January and February. In summer with temps in the upper 90s to low 100s it runs about 75% of the day. I really don't know much about temperature swing other than mine seems to come on when the temp at the stat is 2 degrees below the set point. That is not adjustable (as far as I know) on my fairly inexpensive programmable thermostat. I don't program it, though, it stays on the same setting day and night.

 

[jeffrefrig]

I can't remember but I think when I set up my T-stat I used 1.5 degree on both heat and A/C. There really is no "right" answer as far as rules of thumb or whatever; it's what you prefer. Just be sure the settings for Type of Heat, Elect. or Gas, 90% efficiency or whatever.
When all else fails, thou shalt proceed to Post #2!

 

[Heymatt]

Temperature swing, a very loaded question in the industry.
A lot factors into this: type of system for heat and cool, where the thermostat is located, home construction, number of levels in a home ( two story house one system). Personal comfort is a very subjective topic with men and women in the home. More often then not a battle ground!
In a northern climate I would agree with running the fan in the “on” position. Here in South Floida that is a problem! It drives the humidity back up by evaporating the moisture out of the drain pan that you just took out of the air.
I always start with the factory settings on the thermostat(all brands differ).
Then adjust to the HO comfort. Or show them how to adjust the swing if they are not technologically challenged
Some are ok at a swing of 1 in cooling, some 2, some .5 everyone is different! Same in heating!
It’s like buying a gun, what YOU like is not what the next person likes.
Hope it helps.
OP what type of thermostat do you have? That always helps with offering tips to help you dial it in.

 

[Engineer1911]

Our thermostat is 78° for a/c, 67° for heat. House attire is shorts and t-shirts in summer, sweatshirt and sweat pants in winter. House is brick veneer, built in 1952, and we insulated the house ceiling. The furnace is in the attic.

 

[Onomea]

In winter, I set ours at 67° degrees daytime and 58° nights. We typically wear fleece vests or sweaters. In summer, if we turn it on, we set it at 76° ~ 78°.

I have no idea how much slack or swing it takes to shut off/on. Does having a tighter range use more or less electricity?

Interesting point above about how running the fan constantly improves the air quality. My wife has asthma and when the heat bumps back up in the morning, it makes her cough. I'm gonna try running the fan 24/7 for a while and see if it makes a difference to her.

 

[stansdds]

Ours is 72 in winter, 76 in summer. With temperature swings greater than +/-1 degree from the set temperature, it becomes noticeable, which is likely a reason most thermostats are set up to activate/deactivate at 1 degree from the set temperature. Another thing to consider is how long the HVAC system runs. Typically, they don't run too long to make up that total of 2 degrees delta from the desired temperature, but if they have to make up 4 degrees, the system is going to have to run a lot longer. Lengthy run times generate more heat in the motors that run fans and compressors and heat kills electric motors. Just my two cents and I am not an HVAC technician.

 

[glowe]

This house came with fancy electronic thermostats where I can set how much slack or swing in temperature there is to turn the HVAC system on and off.

I typically use a 1°F swing in A/C mode, but I'm thinking 2°F works best with the heat. Right now the heat comes on for 25-35 minutes every 80-90 minutes. What say the HVAC experts, should I use 1°F for heat as well?

Our furnace runs about 75% of time on a cold winter day at 10-20 degrees daytime and under 10 degree early morning, with about 10 minute break between firings. The run duration totally depends on the outside temperature so we need to know what the outside temp is when your furnace runs at those times?

 

[Krogen]

Golly! This reminds me why I don't care much for forced air heat. I found hydronic heat in the mid 80's. It was a primitive system at that time - a 1940 house with cast iron radiators and a large boiler. Hot water, not steam. With all that thermal mass, one didn't mess with the thermostat. Tried to set back the temperature at night and quickly found the troubles. It took a long time to heat back up. By the time the thermostat shut off the boiler there was so much heat in the system the temperature would rocket well above the setpoint and take a long time to float back down. So a constant setpoint was the only answer.

In this house, the system is considerably more high tech. It has a Buderus boiler and Runtal radiators. It's a constant flow system where the pump shuts off only during warmer weather or during night setback. With the low mass radiators, setback works in this system unlike that old house with cast iron radiators. In addition to a room thermostat, there's an outdoor thermal sensor too. The system adjusts water temperature and flow rate so you don't even realize it's working. You can't hear it and you don't feel any moving air. Ostensibly, hydronic heat is more efficient than forced air. Of course I can't vouch for that short of installing a forced air system to compare apples to apples. I will say that the gas bills are less than comparable homes.

So back to the OP's question: In my opinion, the lower the differential the better provided the furnace doesn't cycle too much. With a lower differential, you can probably tolerate lower average temperature in winter and let it go higher in summer. That would save energy overall and you wouldn't suffer the chills or sweats.

 

[chief38]

Mine is set for a 1º swing and is set at 70ºF. Truthfully I have natural gas fired - copper baseboard heating and I don't really know when it's running and when it's not since it's pretty much silent - unless I am in the Boiler room. That works for me but the most important factor is where you and your wife are comfortable at.

With a 2º swing your heat will run less often but twice as long - so no real savings there. IMHO you will NOT be as comfortable either as the swing is twice as much.

 

[glowe]

. . . In this house, the system is considerably more high tech. It has a Buderus boiler and Runtal radiators. It's a constant flow system where the pump shuts off only during warmer weather or during night setback. With the low mass radiators, setback works in this system unlike that old house with cast iron radiators. In addition to a room thermostat, there's an outdoor thermal sensor too. . .

. . . I will say that the gas bills are less than comparable homes . . .

. . . unless you have to add air conditioning.

Water systems have no duct work to carry cooled air, thus the installation of A/C is very high and usually creates a dramatic difference in temperature in various parts of the home in hot weather. We are fortunate here to have an artesian well that circulated 45 degree water through coils in our furnace to give us very cheap cooling for the summertime.

 

[SMSgt]

I'd run ceiling/floor/room fans before I ran the HVAC fan full time. The former fans are inexpensive to replace, the HVAC fan not so much. All will circulate the air just fine. As for the temp swing, go with what makes you feel most comfortable and check the utility usage down the road. You may be more comfortable with the temp but not the bill that may result. Trial and error.

 

[Krogen]

. . . unless you have to add air conditioning.

Water systems have no duct work to carry cooled air, thus the installation of A/C is very high and usually creates a dramatic difference in temperature in various parts of the home in hot weather. We are fortunate here to have an artesian well that circulated 45 degree water through coils in our furnace to give us very cheap cooling for the summertime.

Right you are! A/C would be a problem, either requiring a separate ducted system or installation of a mini-split. In this area we only get a few days; maybe a week of exceedingly hot summer days. About the time we say "time to install A/C" the heat wave is over. Last summer it cracked 100F for a couple days which is way above the norm.

Well water cooling is (I'm gonna say it) pretty cool! I've never heard of that approach. Do you have any issues with condensation and associated corrosion?

 

[glowe]

. . . Well water cooling is (I'm gonna say it) pretty cool! I've never heard of that approach. Do you have any issues with condensation and associated corrosion?

The furnace plenum is set up just like an A/C system with a drain pan under the coils, draining to the floor drain in the basement. Humidity does collect on the coils, just like with standard compressor driven systems, but isolated from the furnace below.

A small submersible well pump is all that is needed to feed the cold water into the house and it is returned to a pond after use. Average inlet temp is 40 to 45 degrees and exits at around 60 degrees.

 

[Rustyt1953]

You folks are lucky. I'm not allowed to touch it.

 

[mtgianni]

The American Gas Association tests gas furnaces for efficiency after 1 hour of run time. They state that most home furnaces should have at least 2 minutes of burner on time, not fan time, for efficiency reasons. I get that best with a 2 degree swing in thermostat settings. The fan should run as long as possible. While 90 F air is cool on your skin, it is usually 18-20 degrees warmer than the house.