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

molerat

I prefer a tank as in the worst case I can have the heating on full blast, use loads of hot water and if necessary flick the immersion switch. Maybe not completely MSE but it works, convenience v cost.

fredthefish

Fair enough. Could just be that they don't know how to use it properly...! Or perhaps their tank isn't large enough?

Molerat - exactly, I was about to point out that both households end up resorting to the immersion heater when they have guests round, not very economical.

Smiley_Dan

Maybe convenience and cost are not the only things to optimise for.

victor2

It's that time of the year again...

babbity

Cardew wrote: »

As you say the laws of physics are quite clear. It ALWAYS takes more energy to maintain a set temperature, than bring that body(i.e. property in this discussion) back up to that set temperature. Hence timed heating will be cheaper than constant heating.

Each year this subject is raised several times and from some posts on MSE people could be forgiven for thinking there are exceptions to that law - and there aint!

Heat pumps are no exception. The only reason they have to be run longer, or even 24/7, is that the low water temperature(typically 30C to 40C) is incapable of bringing a property back up to temperature quickly; not so with a gas/oil boiler that can heat water to 80C if required.

It is also pertinent that heat pumps are not cheaper to run than gas.

All I would like to add is that the laws of physics are one thing as stand alone laws, but each home building, each home system, each home contents and each person's lifestyle, perceptions or needs will affect the outcome.

I can go on my own trials over years, being in work all day, being retired, getting older, different winters and I can say, with absolute certainty that I use very little more gas to heat my home now I am retired, home most of the day, and feel the cold more, than when I was younger and at work all day.

It can take longer to heat a house that has been left without heating all day - and there is nothing whatsoever you can say that will change that because it's not just walls or air or the system that gets cold.

The whole fabric of the house and contents get cold too and even if the air temperature is heated to that set on the thermostat, as the air circulates and fluctuates the boiler will keep kicking in.

I did some tests and found that if the boiler was off all day whilst I was at work, it would then be on full blast trying to heat the house for much, much longer than if it was set to come on for short times during the day.

And this was the case for me with an old Potterton boiler over 20 years old and a combi boiler.

When I took advice to turn off my heating during the day, timed to come on about an hour before I got home from work, my gas usage was higher than if I had the boiler ticking over on a low temperature during below freezing days, or coming on at intervals during the day.

If someone works long hours and is away from the house for 12 hours or more as the norm, during a cold winter, turning the heating on an hour before they return will not save money. Other people have told me that by the time the house actually feels warm, it's time to go to bed, so they 've been cold all evening/night up to then.

I feel the only correct advice is to suggest that someone monitors their gas/electricity use over a period of time to see what works best for them, to try and reduce heat loss as much as possible, and to be prepared to adjust how they manage heating their homes according to outside temperatures and weather patterns, as well as their lifestyle.

naedanger

Cardew wrote: »

Heat pumps are no exception. The only reason they have to be run longer, or even 24/7, is that the low water temperature(typically 30C to 40C) is incapable of bringing a property back up to temperature quickly; not so with a gas/oil boiler that can heat water to 80C if required.

It is also pertinent that heat pumps are not cheaper to run than gas.

I obviously agree heat pumps are no exception to the laws of physics. However I thought they could, in some circumstances, be cheaper to run than gas because they were taking free energy (heat from outside) and transferring it inside. The economics of any installation depending on how easy it is to tap into a source of heat from outside.

PS Apologies if this has been covered already, I have only read a few of the recent comments on this thread.

lstar337

babbity wrote: »

When I took advice to turn off my heating during the day, timed to come on about an hour before I got home from work, my gas usage was higher than if I had the boiler ticking over on a low temperature during below freezing days, or coming on at intervals during the day.

I'm sorry but that is more or less meaningless, and the rest of the post is just waffle.

I expect you saw a higher gas usage because the external conditions were different. One degree temperature different, or 1mph wind speed increase, or maybe you opened a window for 5 minutes, who knows?

You cannot change the laws of physics, simple as that. Doesn't matter if you have a Coco Chanel furniture or you sit on old pallets, if your house is made from thermal foam or Swiss cheese, the physics remain unchanged.

lstar337

naedanger wrote: »

I obviously agree heat pumps are no exception to the laws of physics. However I thought they could, in some circumstances, be cheaper to run than gas because they were taking free energy (heat from outside) and transferring it inside. The economics of any installation depending on how easy it is to tap into a source of heat from outside.

PS Apologies if this has been covered already, I have only read a few of the recent comments on this thread.

Heat pumps have a coefficient of performance (COP). If the pump has a COP of 3 then for every 1kW of electric consumed you would get 3kW of heat out (in simplistic terms).

However, the COP changes depending on the circumstances at the time. The main culprit for effecting the COP will be the outside temperature. If the temp goes very low, the COP becomes very small as unit has to work so much harder. In addition to that, the unit may also have to work in reverse for a few minutes to melt ice that accumulates on the outside radiator.

Gas is roughly (depending on your deal) 3 times cheaper than electric, so (ignoring efficiencies) a heat pump must maintain a COP of at least 3 to compare with Gas. IIRC, a study a little while ago showed that heat pumps struggled to maintain the COP listed in the spec and actually did much worse than anybody was expecting.

This could be why Cardew says that heat pumps cannot compete with gas.

IMHO, they are the best option in an electric only household.

EDIT: Since you put "in some circumstances" I would have to agree, but majority of the time I believe gas would still win out.

naedanger

lstar337 wrote: »

Heat pumps have a coefficient of performance (COP). If the pump has a COP of 3 then for every 1kW of electric consumed you would get 3kW of heat out (in simplistic terms).

The main culprit for effecting the COP will be the outside temperature. If the temp goes very low, the COP becomes very small as unit has to work so much harder. In addition to that, the unit may also have to work in reverse for a few minutes to melt ice that accumulates on the outside radiator.

Gas is roughly (depending on your deal) 3 times cheaper than electric, so (ignoring efficiencies) a heat pump must maintain a COP of at least 3 to compare with Gas. IIRC, a study a little while ago showed that heat pumps struggled to maintain the COP listed in the spec and actually did much worse than anybody was expecting.

This could be why Cardew says that heat pumps cannot compete with gas.

IMHO, they are the best option in an electric only household.

EDIT: Since you put "in some circumstances" I would have to agree, but majority of the time I believe gas would still win out.

Thanks that's very clear. I had assumed it was the initial cost that was the main reason heat pumps were not more popular, I hadn't realised the running costs were so material.

Cardew

naedanger wrote: »

I obviously agree heat pumps are no exception to the laws of physics. However I thought they could, in some circumstances, be cheaper to run than gas because they were taking free energy (heat from outside) and transferring it inside. The economics of any installation depending on how easy it is to tap into a source of heat from outside.

PS Apologies if this has been covered already, I have only read a few of the recent comments on this thread.

There are several threads on heat pumps.This one for example.


https://forums.moneysavingexpert.com/discussion/2968958


The Energy Saving Trust carried out a 12month trial of heat pumps. The results were so poor that they ran another 12 month trial, with the manufacturers present and able to make modifications - including complete replacement of the ASHP.


The end result of the second phase was an average System COP of 2.45. see Istar337's post above.