A question for the clever scientists on the forum. Let's say you typically heat the house up to 20 degrees for 8.30am and again for 5pm. How much energy do you save if you have the heating turned off between those times ? If the heating is off say the house temperature drops to 15 degrees at a minimum. To get the house back to 20 degrees for 5pm will take a long run of continuous heating. How would that compare to the energy required to keep the heat close to 20 degrees across the day by putting the heat on occasionally during the day ? Is the extra energy usage simply because the house loses more heat/energy at 20 degrees than as it drops towards 15 degrees, otherwise the energy usage would be exactly the same ? If so, how much more heat and energy would the house really lose at 15 degrees vs 20 degrees - the differential to the outside temperature is still huge......this has always bugged me.... !!
[This isn't my area of expertise, so if anyone knows better do chip in, but this is my take on it.] The heat loss from the building is defined by this equation: q = (UxA) x delta t where: q = total heat lost U = overall coefficient of heat transmission (how well insulated the outer surfaces of the house are) A = total surface area of the building delta t = temperature difference between inside and outside So, given that you're not talking about altering the building in any way, the rate of heat loss depends only on the difference between inside and outside temperatures. Let's assume it is 5 degrees outside. For your 20 degree warm periods delta t = 20-5 =15 For your 15 degree cool periods delta t = 15-5 =10 So, in this case, when the house is warm, it loses heat 50% faster than when it is cool. Thus, minimising the time the house is set to be warm will conserve energy.
Yes though I guess if the house drops down to 15, it would be an average of 17.5 across the day so reducing the heat loss difference from 50% to 25%. I accept that the house loses heat more quickly when it is warmer but given it needs to be heated back to 20 degrees by 5pm, I'm not clear in my mind what the % energy/cost saving is by allowing it to drop to 15 and then heating all the way back to 20 vs keeping it close to 20 all day. The answer surely isn't 50% or 25% energy/cost, that would be the saving if you didnt have to heat the room back up to 20 wouldn't it ?????
First of all it might be worth setting the thermostat to 19 as opposed to 20, this will save you money. FWIW I have two thermostats, the one in the kitchen is because it has underfloor heating, as stone (concrete, screed & tiles) based floor it retains heat like a storage heater and it is constantly on and set to 18, this prevents the floor from cooling down as it takes a lot of energy to warm up again. Usually I switch it on in late October and switch it off in mid-March. As for the rest of the house the thermostat is set to warm to 19 during certain times, 90 minutes in the morning and evening but set to 16 outside of those times so the house wouldn't drop below 16 at any time, given how mild it has been recently I doubt it's dropped that low for a while anyway. In the autumn I added more insulation in the loft, ultimately how well insulated your home is will affect the energy usage.
23? You could almost fry an egg on your radiators! My missus is Peruvian, although she's lived here for just over 20 years, she still hasn't got used to our climate. But she's OK with the thermostat given the size of the bills.
Yes she doesn't want 23 degrees. It's just the flawed logic that somehow a cold house get warm quicker if it's turned up to 23 than if it's just turned up to 21. During the week when I'm working from home, and she's at work, I'm in the study at end of the house which is always colder. I have the c heating off but a separate heater in that room set to 18. Sitting still 90% of the day I really notice the cold below that. That's where my original query came from, just how much you save by letting the house temp drop to 14/15 if it's heated back up to 20 by 5pm anyway....
I have just checked, the air temperature in our Edwardian house. In the north facing front of the house, it has dropped from 20C at 08:30 to 17C at 14:30. The heating operates 6 hours a day, there are three thermostat zones. We do have decent insulation, under floor and some external wall, the windows are double glazed, but there is still some air leakage. The south facing rear rooms with today’s bright sunshine have maintained the 20C. In fact a reading (not in the direct sunshine) shows 24C right now. The loft is 5C. Outside in the shade it’s -2C. I tend to keep all the main room doors open so that the warmer air flows a bit around the house. I have no idea if that makes any difference. But the solar gain at the back of the house, makes me question why I have an office at the front - well until the summer that is! I guess the main answer to the question on how to maintain the desired air temperature in the house is that there are very many variables. You need to fact in why does your house lose so much heat in eight hours; how efficient your heating is to gain 5C in a short time; etc.
Yes I have a massive difference between shady front and sunny back but luckily work in the back. I therefore close doors between back and front to keep the heat in the side of the house that I work in given I'm alone in the house during the day. House needs far less heating in sunny freezing weather, than in cloudy warmer but cold weather.
To decide whether or not to keep the heating on all day, I would suggest getting some energy consumption data. I am assuming your heating is by gas central heating boiler. Take a gas meter reading, then set your heating to one of the heating patterns for a week. Take a second gas meter reading. Set your heating to the other heating pattern for a second week. Take a third meter reading. You will now know how much gas was used in each case. The trouble is the accuracy of the comparison will depend on the outside temperature being consistent between the two weeks. Also, if you cook by gas and/or have a gas fire, that will affect the results, so don't use the gas fire and don't cook. Let us know how you get on.
