£65 Gas bill in less than 3 weeks in a cottage!

tyllwyd

But it is more subtle than heating on = bad / heating off = good.

Think about a period of time overnight. You have the house heated to 18 degrees until 12 am, when you go to bed, and you want the house to be at 18 degrees at 8am when you get up again.

Person one leaves the heating on and the thermostat set to 14 degrees. The boiler is not running constantly, but it comes on and off at intervals during the night to stop the temperature dropping below 14 degrees. At, say, 7 am the boiler comes on to heat the house so that it is back up to 18 degrees at 8 am.

Person two turns the heating off completely. The temperature drops to, say, 12 degrees. To heat the house back to 18 degrees, the boiler needs to come on at, say 6 am.

So you are comparing the total energy used over that 8 hour period - does it cost more to keep the temperature topped up at a steady 14 degrees overnight compared to the energy needed to heat the house from 12 degrees to 14 degrees at 6 am in the morning? (Unfortunately I don't know the answer, but I just wanted to explore the question in a bit more detail!)

Wywth

tyllwyd wrote: »

But it is more subtle than heating on = bad / heating off = good.

Think about a period of time overnight. You have the house heated to 18 degrees until 12 am, when you go to bed, and you want the house to be at 18 degrees at 8am when you get up again.

Person one leaves the heating on and the thermostat set to 14 degrees. The boiler is not running constantly, but it comes on and off at intervals during the night to stop the temperature dropping below 14 degrees. At, say, 7 am the boiler comes on to heat the house so that it is back up to 18 degrees at 8 am.

Person two turns the heating off completely. The temperature drops to, say, 12 degrees. To heat the house back to 18 degrees, the boiler needs to come on at, say 6 am.

So you are comparing the total energy used over that 8 hour period - does it cost more to keep the temperature topped up at a steady 14 degrees overnight compared to the energy needed to heat the house from 12 degrees to 14 degrees at 6 am in the morning? (Unfortunately I don't know the answer, but I just wanted to explore the question in a bit more detail!)

It really is as simple as:

Heating on = costing you money
Heating off = not costing you money

I know I have posted a link to this MSE article before in this thread, but I do think it is worth repeating it
http://www.moneysavingexpert.com/utilities/energy-saving-myths

tyllwyd

Wywth wrote: »

It really is as simple as:

Heating on = costing you money
Heating off = not costing you money

I know I have posted a link to this MSE article before in this thread, but I do think it is worth repeating it
http://www.moneysavingexpert.com/utilities/energy-saving-myths

That's not completely true though is it - it's more
boiler running = costing you money
boiler not running = not costing you money.

In the example I gave, the heating might be on all night but the boiler doesn't run for 8 hours. And at some point you have to pay to run the boiler to heat the house up to a comfortable temperature. Does it run for longer in total if it is coming on at intervals during the night, or if it is on for an extended period in the morning before you get up? [No need to answer that, I know you are going to say turn it off at night!]

Wywth

tyllwyd wrote: »

That's not completely true though is it

I believe it is

tyllwyd wrote: »

In the example I gave, the heating might be on all night but the boiler doesn't run for 8 hours

Lets not get into semantics, but in simple terms if the boiler hasn't come on for 8 hours I don't think the heating has come on

Fire_Fox

tyllwyd wrote: »

That's not completely true though is it - it's more
boiler running = costing you money
boiler not running = not costing you money.

In the example I gave, the heating might be on all night but the boiler doesn't run for 8 hours. And at some point you have to pay to run the boiler to heat the house up to a comfortable temperature. Does it run for longer in total if it is coming on at intervals during the night, or if it is on for an extended period in the morning before you get up? [No need to answer that, I know you are going to say turn it off at night!]

I understand what you are saying.

If both of the two hypothetical families living in identical houses are maintaining a temperature of 18C, one for sixteen hours a day and one for twenty four hours a day then the answer is clear cut: sixteen hours a day of heating costs less than 24 hours a day of heating. How much heat is lost dictates how much the boiler needs to top up, you are paying to heat the street if you are not home or asleep.

It's all about how fast the house loses heat, the higher the difference between the inside and outside temp the faster there will be heat loss. So the more the boiler needs to come on to top that up. If you maintain 18C all night the difference between inside and out is huge, so the heat loss will be maximal for that property. If you have very good insulation you might not spend too much topping up every hour but there is still maximal loss for that house, if you have terrible insulation you would spend an absolute fortune with the boiler being on more than off.

If you turn the heating off overnight there will be maximal heat loss for the period, then medium heat loss, then little to no heat loss by the end of the night. If you have very good insulation you might still have some heat left by morning so just be topping up from 14C to 18C, if you have terrible insulation you would lose much of the heat in the first hour but not be wasting much energy for the next seven hours.

You are wasting less so overall the boiler must be doing less. It costs less to heat the house from 4-8C compared with 14-18C because if the amount of heat lost, although you'd imagine the cost would be the same or more (since that seems very cold to us). I believe complicated modelling and calculations have been done and they support this.

If you are comparing a constant twenty four hour temperature of 14C to an intermittent temperature of 18C the answer is not so clear cut, depends on the insulation, number of hours heating is on and so on. But why would you want to live in a 14C house instead of an 18C house? It's much nicer having a warm house when you are there and a cold house when you are not than a tepid house all the time. If you can stand 14C you might as well have intermittent 14C and save even more money.

Don't know if that makes any sense because I am not that technical, I kind of 'get it' with images in my head which are difficult to put into words. It might not sound likely that a well insulated home would only drop down to 14C overnight but my flat maintains a remarkably constant temperature even tho I rarely heat it, I once measured 10C but that was in the depths of winter with the window open. That is down to having neighbours top and bottom, left and right plus a unheated internal corridor to the back, only the front is exposed to external temperatures.