Smithers MINNEAPOLIS

I’m not scientifically inclined, but it is better to turn the thermostat down at night and when you leave for extended periods. I have a 97% efficient condensing furnace that is supposed to run steadily, but a setback thermostat kicks it back to 57° at night and 70° during the day. The insulation in your house mitigates the temperature between the inside and outside, so all you are heating is the space within the walls and you are just raising that 10-12 degrees.

This question requires more info than you’ve provided. I would talk to an home energy specialist (or something like that) - most power companies provide access to them for free (actually I think they are required to by state law).

THey will take into consideration your furnace and insulation.

Power fiction & facts

Fiction: It costs as much or more to heat a home back up after a setback. (Or to cool the house after a summer setup.)

Fact: The longer your house remains at the lower temperature, the more heat you save.

Fiction: The house will warm up faster the higher the thermostat is raised.

Fact: The thermostat isn’t like the gas pedal on a car. It’s either calling for heat or not, so setting the thermostat too high may cause you to overshoot the desired temperature.

Fiction: The kids will kick off the covers and get cold.

Fact: Children older than about two weeks can regulate their body temperature just like adults, so they don’t need any different temperature than adults. If they kick off the covers, try dressing them in two sets of pajamas with feet or using a sleeping bag.
The more you set back, the more you save

I have a buddy who sells heating and AC stuff and installed a furnace and AC unit in my Mpls house.

If your house is older like mine was, he said keep it at a constant temp. I was doing what you were doing and he said I was burning more energy then saving. Because older houses are not efficient in terms of heat loss, it takes a ton of energy to bring them up to a certain temp.

He said that if you lived in a new house that was super efficient then you could play the up and down game.

Your “97% efficient” means nothing for an older house.

57 degrees while I’m sleeping? Yeah, like I want to freeze my balls off going to the kitchen for my midnight snack.

Why don’t you just try one month one way and the next month the other? You’ve probably got start dates for each new cycle by your bill and it’s going to be a good 2-3 months before average temp’s start rising again.
Hoo-ray for science experiments!

When my mom started going through menopause, she kept the thermostat at 50 all winter long. My parents saved a shit ton on their winter heating bill for a few years.

how close are you to menopause smithers?

wah, does the it matter what constant temp? also, does it matter what type of heating - forced air vs. radiators?

and to everyone, is there a perfect temp that sits right at equilibrium between going up and down, and holding steady?

seems like if you could check how many minutes each day your furnace actively ran you’d be able to quickly (over two days, for instance) check which way used less energy.

according to this site the savings between running steady at 70° and going up and down from 63° day/night and 72° evening, comes out to $180 - 300 per year (on a 1400 sq ft, 40+ year old home)

Quick answer; heat flow is proportional to the difference in temperatures across a barrier (thermal diffusion), and is slightly higher with radiated heat. Translation; if you keep your house cooler at night, you will lose less heat to the outside, and your heating bill will go down.

When I installed thermostats that turn things down (65 to 60F) at night, it reduced heating bills about 10% to 20% each month vs. otherwise.

I don’t see how it could possibly be better to leave it at 1 temperature, unless there is some sort of furnace inefficiency or if air is poorly circulated. From a purely energetics perspective, it takes more energy to maintain a well mixed house at a constant temperature then it takes to warm and cool a house. But if a furnace is less efficient when on for long periods of time (seems like the inverse would be true) or if the house didn’t mix well, that is when trying to heat the house back up from a colder temp, part of the house would heat greater than the desired temp, while the thermostat still saw a colder temp, that would make cooling and rewarming less efficient.

It is simple math…turn down you heat and you save. PERIOD. Your energy use is an “area under the curve” equation. If you put a dip in the curve you will save money, no matter what the R value of your walls. There is no such thing as “Thermal Inertia”. Ask Mrs. Smithers, she will confirm.

where is Billy D. when we need him. ?!?!?!?

Funkster speaks the truth…..

While it’s the inverse example, a buddy of mine in Texas looked at the same situation - holding the AC constant during the day to keep the house cool vs. scheduling it off while no one was home and ramping it back right before people got home. The latter scenario cost far, far less.

The point Bubba makes about radiant heat flow being proportional to temperature gradient is especially apt for winter. Hardest to heat the house when it’s coldest (at night). And least necessary, since people are typically under blankets (or have one-sies with footies).

Funkster - while there is no such thing as “thermal inertia” there is this pesky thing called heat capacity (in units of energy/degree). If you happen to have objects in your house that have mass (interior walls, furniture, etc.) those contents of your house cool down. When blowing warm air into the volume of the house, energy from the air (even in the case of radiators, the air temperature is still what we’re talking about) might be lost through the insulation in the walls, but also goes into heating those things up too - which means needing more energy to warm the air - consuming more energy than heating “just” the air. Think of it like ice cubes in coffee (but without the phase change).

Why do you care? It’s not like you pay the bills around there, anyways.

Biscodo,
I understand that all objects in your house have mass (including the AIR) and have different rates of heat transfer. Where do you think the energy goes when your Flintstone type lazy boy cools by 10° F. It goes into slowing the rate at which your house cools. Now, when you ramp the heat back up, you need you need to refill that capacitance. You didn’t lose the energy from the chair, and then are forced to replace it. The chair is a zero-sum game.

I agree with Funkster — heating some mass of objects back up to temperature is certainly no more energy to maintain that temperature all day (in fact it must be less).

nerds

Funkster - I wasn’t disputing that the energy inputs/outputs to the system on the heating-cooling round-trip sum to zero. Just pointing out that “thermal inertia” might not be a phrase in a textbook anywhere, but the analogy does have merit even if the language is messy.

Cuban’s earlier comment about a poorly mixed volume has merit too - imagine a very lossy house with a badly placed thermostat. If you end up with a long-enough time constant, the warmup-ramp overshoot can waste plenty of energy. Depending on how long that ramp is and how short the cold interval is, the total energy expended before the thermostat stops heat input can be more than it was in the stable, smaller interior gradient (better mixed) example.

Whatever. checkbook seems to think it’s already damnable nerd territory, so I’ll just quit there so everyone can get back to their TV, beer, and porn.