Central heating. Bursts or constant? My results

ToTo_Man

As fuel prices continue to surge I am trying desperately to cut our central heating bills.

My original thread on this topic can be viewed here: http://forums.moneysavingexpert.com/showthread.html?t=1259041

A recap of our house:
100+ year old sandstone detached villa in Scotland with no modern insulation. Walls are solid sandstone, probably at least 1ft if not 2ft thick (i.e. no scope for cavity insulation!), lots of rooms (many of which large!), double glazing, large hallway with draughty front door, a total of 17 radiators (some modern but most old).

Since my initial post I have taken the bull by the horns and made a few changes.

Two small but effective changes have been the draughtproofing of the front door and ensuring that all room doors are also closed. Trying to get my father, gran and dog to remember to close doors as they enter/exit rooms is an endless pursuit, however the message is slowly sinking in!....

Biggest change has been to the CH setup. Our boiler is a Vokera combi, and most likely is too small for our size of house (we were ill-advised by our original heating engineer), however the fitting of an external pressurizer tank a couple of years ago has boosted its performance. There is no room thermostat in our house, only a thermostatic valve on all but two of the radiators.

Until recently, my father has been in charge of the CH system and has operated it under the approach of running all radiator thermostatic valves fully open and turn off the CH when the house gets too hot. Funny enough the house rarely got too hot so the heating stayed on for several hours at a time. I then recently took control of the CH and the first change I made was to turn the radiator thermostat valves down in the rooms that weren't used as much. This resulted in the radiators in the used rooms heating up both faster and to a hotter temperature, meaning that the periods we ran the CH for before getting too hot had shortened.

Note: by too hot I am referring to a maximum temperature of 16C , not the 20C+ "sauna" temperatures that you find in schools and nursing homes. Even if we kept our heating on 24/7 during the summer I doubt we'd reach those temperatures!

I then decided that it would be more practical (and cheaper!) if the CH could keep the house at a consistent temperature so that we don't feel the house getting hotter the longer the CH is on. With no room thermostat, this meant I had to march round the house for several days, setting the thermostat valve on each radiator so that the temperature of each used room was "comfortable" to sit in with a jumper and jacket on, probably around 13-14C, no matter what time of the day it is.

With this setup, I then took measurements of 3 different approaches.
Approach 1: run the CH for a short burst in the morning and a short burst in the evening.
Approach 2: run the CH constantly during the day.
Approach 3: run the CH constantly 24/7.

The results:

Approach 1
Time = 5.30am-9.00am and 6.15pm-10.45pm
Hours = 8
Units Used = 20
kWh = 226
Cost = £9.43

Approach 2
Time = 5.30am-10.30pm
Hours = 17
Units Used = 23
kWh = 261
Cost = £10.90

Approach 3
Time = 5.30am-5.30am (with rolling start)
Hours = 24
Units Used = 27
kWh = 306
Cost = £12.80

Note: I don't know how accurate the costs are as I am not sure whether I have entered the ratio of primary-to-secondary units correctly in the spreadsheet, however the Units Used is a reliable reading.

So, from purely a cost perspective, it is cheapest to run the heating in two short bursts during the day. However, this is the worst value for money, as it means that my gran and myself are spending a large part of the day frozen stiff sitting in rooms that are 11C! Interestingly, running the CH for 3-times longer (i.e. 24hrs) only costs an extra 35%, which is the best value for money as it keeps the house at a constant temperature day and night. This small cost increase is good to know, especially when sub-zero temperatures threaten to burst pipes. However, unless there is really cold weather, I think I'll use Option 2, as keeping warm during the day is most important, and my dad worries that the boiler will break down if I run it 24/7 for a prolonged period.

I do have one question though. To fine tune the CH, all I did was adjust the thermostat valves on the radiators, I did not touch any flow valves. The flow valves had been previously adjusted, by a combination of my dad and the plumber, so that the radiators furthest from the boiler still got sufficient heat. My dad doesn't want me messing with the valves unless I'm absolutely sure about what I'm doing, as he fears that if I close too many the boiler will explode! Are the flow valves something I should consider experimenting with? Will fine tuning the flow valves increase the boiler's efficiency, or does it merely redirect heat to other radiators?

linnister

Hi
this is a great post - i have been experimenting with this idea but not quite as methodically as you! Have managed to get most rooms at 18 degrees and now need to experiment with timings etc. but this has given me a good start! Thanks

Cardew

Hi,

Interesting post. However I suggest that it would have been better to put this post on the other thread you staerted on this subject as the earlier posts give more information.

A couple of comments.

Firstly you don't say how long the experiments for the 3 stages lasted - a day, a week?

The outside ambient temperature will have a considerable bearing on the results as will any 'residual' heat in the house.

I don't know how accurate your temperature measurements are but most people simply could not tolerate temperatures as low as you quote.

16C is the minimum recommended working temperature for offices and at the 11c you speak about, your Gran is quite seriously in danger of suffering from hypothermia - and I do mean that.

Far from 20C being like a 'sauna' it is slightly below what many people consider comfortable.

I am not surprised at the small differential between the 3 cases, although that differentional would increase if you kept the house at temperatures most people would find comfortable.

I also feel that you should simply use the tier 2 price for comparison and treat the Tier 1 price as simply a charge for having gas to your house.

Having 2 radiators without TRVs means no harm will come to your boiler by playing with the balancing.(obviously don't turn these radiators off completely) I would just note what adjustments you have made e.g. 1 turn Clockwise.

The boiler efficiency will not be affected by the balance valves. Generally the hotter the water the more efficient the boiler itself is operating, but of course there are more losses in pipes. However this heat lost goes into the fabric of the house so is not really lost.

Finally with a large house like yours in Scotland, you are always going to face very large heating bills. To be using 7,000kWh to 9,000kWh a month and keeping a house at barely tolerable temperatures(for most people) is a huge consumption.

Farway

Cardew wrote: »

Finally with a large house like yours in Scotland, you are always going to face very large heating bills. To be using 7,000kWh to 9,000kWh a month and keeping a house at barely tolerable temperatures(for most people) is a huge consumption.

Useful post, as Cardew says the consumption is huge, mine is around 10000kw per year, but I am in Hampshire & mid terrace

Perhaps you could cut the bills by moving sarf? :rotfl:

ToTo_Man

Hi, many thanks for your reply, extremely helpful. I'll try to provide further clarification on each point in turn.

Cardew wrote: »

I suggest that it would have been better to put this post on the other thread you started on this subject as the earlier posts give more information.

Ok, I'll try to link the two threads up.

Cardew wrote: »

You don't say how long the experiments for the 3 stages lasted - a day, a week? The outside ambient temperature will have a considerable bearing on the results as will any 'residual' heat in the house.

I only ran each of the 3 experiments once, i.e. each for 1 day, and kept the days consecutive. I did this to limit the effect of the outside temps getting progressively colder as winter progresses, although I do acknowledge that the residual heat built up would potentially make each subsequent experiment cheaper than it would be from a completely "cold start". However I don't think this makes a difference to Exp3 as a 24hr cycle implies that the CH would never have to deal with a cold start. I also acknowledge that external temps on the 3 consecutive days are never going to be identical, however all 3 days were very cold!

Cardew wrote: »

I don't know how accurate your temperature measurements are but most people simply could not tolerate temperatures as low as you quote. 16C is the minimum recommended working temperature for offices and at the 11c you speak about, your Gran is quite seriously in danger of suffering from hypothermia - and I do mean that. Far from 20C being like a 'sauna' it is slightly below what many people consider comfortable.

I don't know how accurate my temp measurements are as I took them with my alarm clock (has built in thermometer) which I moved about the house every 30mins or so. Ideally each room could do with its own dedicated thermometer but that would be an expensive outlay! I was considering buying a Grobag thermometer that changes colour as the temperature increases but then realised it would always be stuck on "BLUE"! Yes I do agree that 11C-12C is indeed to cold for my Gran. She does however stay in bed for long periods of the day with an electric blanket on, thank goodness. I'll need to take more accurate readings before I can be certain of the temperature of a particular room at a particular time of the day.

Cardew wrote: »

I also feel that you should simply use the tier 2 price for comparison and treat the Tier 1 price as simply a charge for having gas to your house.

A very good suggestion that I hadn't though of.

Cardew wrote: »

Finally with a large house like yours in Scotland, you are always going to face very large heating bills. To be using 7,000kWh to 9,000kWh a month and keeping a house at barely tolerable temperatures(for most people) is a huge consumption.

I'll drink to that! :beer:

cady

hi... im too trying this i think i might try to put my CH on as low as poss constant but im worried it will cost us loads .... what do you think??? will it cost us loads

Farway

It depends on what "low as possible" is

If it is frost setting then it will be very cheap, if you consider 20 degrees low then it will not be

As Cardew has said earlier the outside temperature will have a big bearing on it as well

ToTo_Man

Just moved my thermometer from my bedroom (13C) to my living room (15C). I find 15C just nice, but then again I'm wearing a polo neck and jacket, and my hands are like slabs of ice!

flashnazia

If your house in never getting warm despite your boiler blasting for hours on end it may be because you have the incorrect radiators for the size of your rooms.

I had the same problem and have fitted bigger radiators after working out the btu that my rooms need (worked out using factors like height, width, length of room etc).

Obviously, if you do get bigger rads you have to make sure your boiler can cope.

And fitting a room thermostat will help alot. They only cost a tenner or so. Not sure how much to fit though...

zzzLazyDaisy

[quote=__I_find_15C_just_nice,_but_then_again_I'm_wearing_a_polo_neck_and_jacket,_and_my_hands_are_like_slabs_of_ice!_:D[/quote]

NNNNNOOOOOOOOOOOOooooooooooooo!

space_rider

ToTo_Man wrote: »

Just moved my thermometer from my bedroom (13C) to my living room (15C). I find 15C just nice, but then again I'm wearing a polo neck and jacket, and my hands are like slabs of ice!

Are you doing this because you can`t afford your heating bills. Does your gran get the winter fuel allowance? I could never live like that. I would rather live off soup and bread than have a room so cold.