Energy myth-busting: Is it cheaper to have heating on all day?

QrizB

The OP's point is predicated on the idea that a heat pump will increase its output temperature under cold start conditions to ensure that the house warms up quicker. By running at an increased output temperature the COP will fall, reducing the efficiency. Under some circumstances this fall in efficiency can be enough that you use more energy than simply leaving the heat pump running.

If you can convince your heat pump not to increase its output temperature under these circumstances, it will take longer (potentially *much* longer) to warm your house but the COP will remain high and the efficiency won't fall.

I don't have a heat pump so can't comment on how, or even whether, you can achieve this in practice but I would hope you can.

Astria

The first thing I would do is check the configuration of the heat pump, as some installers seem to like to turn off things that cause customers to ring up and complain because they don't understand how these things work, things like "weather compensation" which I think are absolutely vital for things like heat pumps. Then again, some installers also install them "on the cheap" without a proper survey, and then the customer complains again because they are having to run them 24/7 because the pipework and radiators really don't suit it (or the customer wants smaller sized radiators because "they look ugly" or some such)

I'd read up on exactly how your particular system works and how to run it optimally, taking the words of the installer with a pinch of salt...

Chrysalis

No its cheaper with it always off.

ariarnia

Chrysalis said:

No its cheaper with it always off.

and there's my reason for my first post on the thread

Reed_Richards

QrizB said:

The OP's point is predicated on the idea that a heat pump will increase its output temperature under cold start conditions to ensure that the house warms up quicker. By running at an increased output temperature the COP will fall, reducing the efficiency. Under some circumstances this fall in efficiency can be enough that you use more energy than simply leaving the heat pump running.

If you can convince your heat pump not to increase its output temperature under these circumstances, it will take longer (potentially *much* longer) to warm your house but the COP will remain high and the efficiency won't fall.

I don't have a heat pump so can't comment on how, or even whether, you can achieve this in practice but I would hope you can.

Increased output temperature under cold start conditions is one aspect of a control feature known as Load Compensation.  Gas boilers will do this wired to a controller with OpenTherm capability.  Some heat pumps can do this if the manufacturer's own controller is used but there is no equivalent to the OpenTherm standard for heat pumps.  So actually you are quite fortunate if you have the option to set your heat pump to a mode where it will automatically increase its output temperature in the event of a cold start.  I cannot do this with my heat pump and would have to intervene manually by turning off the Weather Compensation for a while.  

wild666

I would say it's cheaper to have it on only when needed. Years ago I left it on all day when it was cold and it used 8 units of gas (90.4 kWh) with the thermostat set at 19 degrees in one day. When I set it to on only at a set times it used only 3 units (34 kWh). 

Now I have altered all the boiler and thermostat settings it is only using 2.5 kWh per week with no heating 

Astria

wild666 said:

Now I have altered all the boiler and thermostat settings it is only using 2.5 kWh per week with no heating 

2.5 kWh for no heating seems very expensive to me

ariarnia

wild666 said:

I would say it's cheaper to have it on only when needed. Years ago I left it on all day when it was cold and it used 8 units of gas (90.4 kWh) with the thermostat set at 19 degrees in one day. When I set it to on only at a set times it used only 3 units (34 kWh). 

Now I have altered all the boiler and thermostat settings it is only using 2.5 kWh per week with no heating 

but that's where more detail is really needed to work it out.

so when you were turning it off and on how many hours of heating was that for and what was the average temp of the house when you were in it? (i mean are you actually comparing like for like) 

boilers use most of there gas when first turned on so that 34kw could be just 2 hours of heating.

depending on how quickly your house loses heat and how long you are home for in the day then your average temp when at home could be a lot lower than 19 (meaning you could have set your thermostat to less than 19 and used less gas if that's comfortable). or if you really were only home and awake 2 hours a day then turning it on and off to a schedule would make sense if you see what i mean? theres a point somewhere in the middle that means no savings from manually turning the boiler on and off.