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Keep the heating in a house all day on?

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There are several oppinions about how to manage the house heater.

1. Some think it is cheaper to keep the heater all day on.
2. Others think it is better to switch off the heater and heat the cold house every time you arrive.

In my opinion is always better the option 2. You can waste a lot of energy heating the cold house, but it's less than maintaining all the time the house hot.

What are your arguments about the question?

It depends:

If the house is very well insulated, there is not much difference, as even if one would turn of the heat, it would not cool down very much.
For the temperature felt, the surface temperatures are also part of the temperaure perception. So when the surfaces are still cold one may need a high air temperature to the same subjective feeling.
I may need less energy to get it warm only ehen you really need it, but it is also more complicated to regulate an one may overshoot to more than actually needed.

It also depends on the type of heating system. Some (like a wood oven) work better when at a relatively high power and than off for longer. Other work better at partial power. This can especially be the case for a heat pump / air conditioner in heating mode. Here the outside temperature also make a difference.

I have temperature logging on my house, and examining the slopes of the heating and cooling curves the results show that if the heat is off for roughly twice the normal thermal cycle of the heater, energy is saved.  My house is well insulated and have a modest output fuel burning heater which results in a roughly two hour thermal cycle (temperature varies by about 1.5 deg C).  I find these results are in line with Kleinstein's observations and confirm the choice of option 2 if you are gone from the house for a normal workday.    In my situation it makes no sense to turn the heater off for short times away from the house.  Your situation may be different.

You also have to understand your needs.  In my case the house is a few degrees below comfort temperature for a sizeable part of an hour upon return from a long off cycle (also in the morning after leaving off at night).  You can usually conquer this by appropriate use of a timer, but not everyone will find this approach adequate.


--- Quote from: Picuino on October 26, 2021, 03:48:51 pm ---There are several oppinions about how to manage the house heater.
1. (..) heater all day on.
2. (..) heat the cold house every time you arrive.
In my opinion is always better (..)

--- End quote ---
I think your question is poorly posed.
You compare two different situations with vastly different comfort levels.
With first scenario you do not need to bother about planning or changing settings, every time you want to enter the room/house, in every imaginable scenario, it is already cosy, no compromises. With second scenario it is all about planning and additionally it comes with the penalty when you sit and wait in cold house till it gets to temperature. You trade comfort for kWh in your question, IMHO.

Or did you intend to ask in #2: "(..)heat house up before you arrive."?

Insulate your house. Then you can utilize the thermal capacity of the structures to your benefit. I live in a 1952 house with some insulation added in 1982 and I can cut all heating for half a day with little effect in room temperature.

When this is the case, i.e., the RC time constant is long enough, you can't save anything by cutting power for half a day; the "RC circuit" smoothes the "voltage" and same amount of power is delivered into the system in either case. I.e., you need more power to catch up with the small temperature drop.

But for reducing temperature during long enough, so that the duration of reduction last for longer than a few RC time constants, then sure it helps. For a well insulated house with some thermal capacity, that could be the "holiday temperature reduction". For a poorly insulated house (high "conductance" or low thermal resistance of materials), or one with very lightweight materials (low "capacitance" I mean thermal capacity), it could make sense to drop the temperature for just a few hours.

Given linear heating cost (like with gas, oil, resistive electicity), basically the average temperature directly determines the heating cost. In a well insulated house, you can't change the average fast. In poorly insulated, you can and should.

This is also why such trickery is not used in really cold climates; we have to insulate our houses and then the trick doesn't work. Except for those longer "holiday reductions".


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