Energy Saving Trust Q&A Centre

Berger · 5 December 2010 at 3:48PM

zeupater wrote: »

Hi

If your heat requirement in that room is only 400/800W then running the central heating and turning all of the other radiators off will probably not be efficient/practical. Modern CH boilers can modulate their output from full power to around 25% of their rated maximum, so if you have say a 30kW boiler it could attempt to match it's output to as low as 8kW, which would be far too high for the radiators in a standard room .... the boiler will therefore be cycling on/off at a high frequency and become far less efficient than it could be .... probably not a practical solution for one room.

The only thought on the gas is that if you're running the heating in the evening anyway, what would the cost of running it for the extra hours be ?. If you're currently using an average of say 600W, that's around 5kWh of electricity/day costing around 50p to 60p, which could buy around 15kWh of additional gas heating/heatloss .... If your house isn't too large and is well insulated it might be an idea to test how much extra gas is used by taking some meter readings.

You could possibly look at installing a small ASHP (Air to Air) for the room, but if you're looking at moving within the timescales mentioned it would never pay for itself, you might as well run your CH full blast and be comfortable. If you're not going to move this could be a viable one-room option.

HTH

##Note ..... Just checked, it looks like the potterton boiler you have is non-condensing/non-modulating with an efficiency of 78.2% (ish - when new) .... therefore it will not be able to adjust it's output to meet requirement.

thanks for that answer, really thorough. Especially the last bit, which confirms what I thought re: the boiler

Ken68 · 5 December 2010 at 6:47PM

I trust your Accreditation scheme is whiter than white.A programme on Radio 4 just now reports that the same money was used for different applications.

http://www.energysavingtrust.org.uk/Resources/Energy-saving-news/Renewable-energy2/Green-fraud-could-increase-during-recovery9

geoff07 · 6 December 2010 at 8:33PM

Just because a boiler cannot modulate does not mean that it runs flat out regardless of heat demand. The job of the boiler is to heat the circulating water to a set temperature. This is thermostatically controlled. The job of a radiator is to cool the water by heating the room. If fewer radiators are in circuit then less heat is required and the water will be cooled less, so the boiler will heat it less. It is much better to have a modulating (i.e. variable flame) condensing boiler at say 94% efficiency than a non-condensing one at say 74%, but turning radiators off still makes sense. If your gas bill for CH and water heating is £500/year then at 74% efficiency you are throwing away £100 of gas each year: change the boiler. A decent boiler might cost £800 plus fitting and last 20 years. And gas isn't going to get cheaper.

zeupater · 6 December 2010 at 9:13PM

geoff07 wrote: »

Just because a boiler cannot modulate does not mean that it runs flat out regardless of heat demand. The job of the boiler is to heat the circulating water to a set temperature. This is thermostatically controlled. The job of a radiator is to cool the water by heating the room. If fewer radiators are in circuit then less heat is required and the water will be cooled less, so the boiler will heat it less. It is much better to have a modulating (i.e. variable flame) condensing boiler at say 94% efficiency than a non-condensing one at say 74%, but turning radiators off still makes sense. If your gas bill for CH and water heating is £500/year then at 74% efficiency you are throwing away £100 of gas each year: change the boiler. A decent boiler might cost £800 plus fitting and last 20 years. And gas isn't going to get cheaper.

Hi geoff07

Isn't it the case that when heating only one(?) radiator, even the best modulating/condensing boiler would be cycling on/off regularly, and with very much reduced radiator panel area, the return temperature would be far too high to allow condensing anyway which, in turn, would reduce the boilers efficiency to close to that achieved from the current unit, so changing the boiler would not help in this situation anyway, although there would be a long term saving on the normal heating if Berger was not looking at moving within the medium term.

I am in a position where I do something similar to Berger. My property generally doesn't usually need heating at all until November, the log burner copes with all space heating demand until early/mid December, then the main heating gets switched on too, but it only gets used in the evening (except weekends) .... this year there was only about a week between firing up the log burner and the CH going on too

Cardew · 6 December 2010 at 10:29PM

geoff07 wrote: »

Just because a boiler cannot modulate does not mean that it runs flat out regardless of heat demand. The job of the boiler is to heat the circulating water to a set temperature. This is thermostatically controlled. The job of a radiator is to cool the water by heating the room. If fewer radiators are in circuit then less heat is required and the water will be cooled less, so the boiler will heat it less. It is much better to have a modulating (i.e. variable flame) condensing boiler at say 94% efficiency than a non-condensing one at say 74%, but turning radiators off still makes sense. If your gas bill for CH and water heating is £500/year then at 74% efficiency you are throwing away £100 of gas each year: change the boiler. A decent boiler might cost £800 plus fitting and last 20 years. And gas isn't going to get cheaper.

Welcome to the forum.

The problem is that it is difficult to fit a new boiler for under £2,000 these days - power flushing is mandatory and the regulations for flue, condensate drainage, ventillation add loads to the cost.

If you are changing from a system boiler to a combi it is even more cost.

In any case, many people think that the 94% efficiency figures are much like car fuel consumption figures of 70mpg etc - i.e. rarely achieved in practice.

Berger · 7 December 2010 at 12:30PM

cheers for the input Geoff. As the other chap says, I am looking at moving next year, so a new boiler would be money down the drain (I doubt a potential buyer will ask for a reduction because a working boiler is 7 years old).

I am getting better insulation put in, which should help, but I think for now I will stick with the halogen heater.

Actually, today I am putting the central heating on, because it's still -5 outdoors at 11.30!!

mjjordan · 8 December 2010 at 9:31AM

Can you tell me please, what is the evidence for or against having central heating on/off several times a day at say 26 degree roomstat or leaving on all waking hours at say 22 degrees roomstat?

cassandra@walpole · 8 December 2010 at 9:38AM

I live in n Suffolk in a modest 400 year old listed old timber-framed house with my husband and daughter.She is 14: we are retired and on relatively low incomes, with no capital.
We are very well aware of the need to use more renewables and are founder members of Cookpole Energy Action.
In terms of what we can do in our own home - we are limited by the fabric and structure of the building, ie no loft or cavity walls,and an old oak, plaster and brick structure.There is no gas pipeline in the vicinity.We use oil and electricity, and have a wood burning stove and an open fire. While the old structure is surprisingly warm and weatherproof, the windows and doors are ill-fitting even with draughtproofing.
Can you advise on any grants, opportunities etc which might help us to fund eg new double glazed windows or renewable energy sources, bearing in mind the listed building restrictions, and are you aware of any likely relaxation or concessions in the listed building regulations in the foreseeable future?

Energy_Saving_Trust_company_representative · 8 December 2010 at 1:50PM

mjjordan wrote: »

Can you tell me please, what is the evidence for or against having central heating on/off several times a day at say 26 degree roomstat or leaving on all waking hours at say 22 degrees roomstat?

Hi mjjordan,

If you have your heating on for say 6 hours a day (1 hour in the moring just before you wake up and 5 hours in the evening when you get home from work) appose to having it on for 16 hours a day (7am - 11pm) then you will be wasting heat when you do no need it.

The most efficient way of using your heating system is setting it to the lowest comfortable temperature for the times when you need it.

Richarrow · 8 December 2010 at 1:54PM

I have a house with dormer windows in every upstairs room and these rooms are set partially into the roof. I am not sure how much insulation was possible / was installed on the dormer sides or the sloping interior surface of the roof.

Is there a thermal imaging service (affordable of course) that would come and view my house and give me an indication of where the greatest heat loss is occurring? Could you provide the names of any such service providers?

Thank you

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