Leaving the heating on

[selmanj]

Does leaving my gas central heating (worcester combi boiler) on low all day use the same amount of gas as having it on high for just the evening?

I suppose this could apply to any appliance - less for longer or more for shorter? Or are they the same? I dont' want to be burning more fuel than i need to (and getting higher gas bills in the process!).

 

[Diyisfun]

What it will give you is a warmer house in the evening. THe chances are if you have it off during the day, when you come home & put it on, it will take a few hours to warm the house. So you are cold whilst waiting, then by the time the house is heated you are going to bed.
When its cold as currently I would leave heat on low. I have just changed my t/stat so the temperature increase at a preset time. It is working well.

 

[baxpoti]

To start with.
A heat loss calculation would be required to ascertain how well your property retains the heat.

 

[RigidRaider]

As above I guess it depends on how well you are insulated. I have often pondered this question too. We tried it one winter and the gas bill was higher, but then the weather could have got colder.

 

[davelx]

The rate of heat loss is proportional to the temperature difference between outside and inside. So, all other things being equal, keeping the house at a high temperature all day will lose more heat, and thus use more gas, than letting it cool during the day and heating it up again late afternoon.

Just time the heating to come on early enough to get the temperature where you want it when you get home - the longer you have to maintain that temperature the more gas it will use.

 

[Agile]

For the few people who are obsessed by saving the last few pounds the bigest saving is to be obtained by turning the heating off about an hour before going to bed.

The best control is a programmable thermostst but do take into account the thermal inertia of the house and turn off ( or down ) early.

Its easy to measure the temperature fall rate by turning off the heating at say 1030 and recording the temperature every 10 minutes for the next hour or so.

If you run it at say 21°C then turn off the heating at the appropriate early time so it has gone down to about 16 or 17 when you are ready to go to bed. You will notice the slight reduation in temperature and a nice warm bed will feel more appealing and aid going to sleep.

Tony

 

[johndm1957]

I fitted a programmable roomstat (Heatmiser) a few months ago, boiler left on constant 24/7

Just had a quarterly bill.......£215

Stat programmes..

Weekdays
16 deg 10pm to 5am
19 deg 5am to 7am
17 deg 7am to 3.30pm
21 deg 3.30pm to 10pm

Weekends
20 deg all day

This is in a modern well insulated 4 bed detached, but open plan downstairs with 2 sets of french doors (double glazed).

We only moved in last summer, so as yet unsure how we compare to similar properties....

 

[Bon]

Leaving your heating on all day means your boiler will only occasionally fire in order to maintain the temperature of the area.

However should you set your heating to come on twice a day, the room will lose heat inbetween the operating times. When the heating comes on, your boiler will be firing at full pelt for a constant period of time in order to heat the space (which has cooled down) which in theory uses more gas.

This was the arguement one of my old lecturers used to use, however I still can't seem to justify leaving my heating on all day when no-one's in!!

 

[wilhelm]

what really winds me up is folk with swimming pools.

they go in for a dip (ooer) for 30 mins. maybe per day.


them boilers on 24/7 more or less.

ah well. kieth moon had the right idea, use em as a car wash.

 

[croydoncorgi]

There's more rubbish put out on this debate than on any other heating-related topic I know!

A few facts (please excuse some repetition):

- a building loses heat in DIRECT proportion to the difference in temperature inside to outside (disregard issues like evaporative cooling off damp walls, wind-related effects,etc.)

- a CH system can put heat into a building at a rate determined by radiator sizes, the difference in temperature between water in the radiators and the air in the room. Automatic operation of TRVs will affect heat flows from individual radiators. So will manual adjusment of TRVs and other types of valve.

- the heat source (boiler) raises the temperature of the water in direct proportion to the rate of fuel burn AND will also waste heat through the flue at a rate depending on the fluegas temperature, whether there is airflow through the boiler, condensing or not, and other factors. Depending on the boiler, it may modulate the burn-rate according to setpoint(s), Return temperature or other factors. If it's 'all or nothing', chances are it will cycle on, off and on again at some rate, depending on its own thermostat setpoint and other factors, even though the call-for-heat from the roomstat may be continuous.

Considering all these related and unrelated variables, it's virtually IMPOSSIBLE to predict with any accuracy the EXACT energy consumption of a system.

BUT it should also be obvious that if the burner in the boiler is OFF, then no energy is used at all.

The only issue then is the difference in total energy use between continuous operation at a low roomstat setting and heating from cold (say 10 degrees) to comfortable (say 20 degrees). Considering all the above factors, I suggest that more energy MUST be used, in total, in continuous than in cyclic operation of any given system. The only issue is how much more. The energy lost up the flue ONLY when the burner and fan are operating (the case with most modern boilers) will be a significant cost which will ALWAYS swing costs strongly in favour of two warm-ups from 'cold' per day if there is no actual requirement for heat during the majority of the day in between (say) 0900 and 1700. I believe this would still be true ignoring boiler losses and in all cases, considering only heat-loss from the building as a whole.

 

[baxpoti]

depending on its own thermostat setpoint and other factors, even though the call-for-heat from the roomstat may be continuous.

incorrectly sized rads, incorrectly set room stat or under powered boiler

Considering all these related and unrelated variables, it's virtually IMPOSSIBLE to predict with any accuracy the EXACT energy consumption of a system.

you can get a pretty good approximation

BUT it should also be obvious that if the burner in the boiler is OFF, then no energy is used at all.

If no energy is used at all, why does it start getting cold?

The only issue then is the difference in total energy use between continuous operation at a low roomstat setting and heating from cold (say 10 degrees) to comfortable (say 20 degrees). Considering all the above factors, I suggest that more energy MUST be used, in total, in continuous than in cyclic operation of any given system.

what about one with zero heat loss?

The energy lost up the flue ONLY when the burner and fan are operating

About 9%

I believe this would still be true ignoring boiler losses and in all cases, considering only heat-loss from the building as a whole.

How do you work out radiator sizes?