Cost of Central Heating

paperclap

Hi all,

We've recently moved into our first home.

It's a 1955 2-bed semi-detached bungalow, with cavity wall insulation, fibreglass loft insulation (between roof joists), and polystyrene board roof insulation (between roof rafters).

We have a Potterton Profile 40e conventional boiler. I think it was installed around 25 years ago.

We typically put our thermostat to 18 degrees (in a bid to save money), and have the central heating on for 2 hours in the evening, from 5pm-7pm. We have a smart meter, and have worked out that it costs on average 30p per hour for central heating.

However, since it's been abnormally cold recently, we tried a little experiment: having the central heating on "continuous", in hopes that once the house was up to temperature (18 degrees), the boiler would simply be maintaining said temperature, and therefore cost much less than the average 30p per hour.

At face value, it looks like this is the case, as the boiler clicks on for a few minutes, then off again for a few minutes (though, perhaps this is too frequent?). But, after looking at the smart meter, it still seems to average out at around 30p per hour.

What gives? Is our boiler faulty (clicking on and off too frequently)? Do we have poor insulation? Is it a simple case of external temperature battling our internal temperature?

Any thoughts and advice welcome!

matelodave

The amount of heat lost to the outside is directly proportional to the insulation value of the walls, floors, ceiling windows etc and the temperature difference between the inside and outside temperature. When its 18 indoors and 0 outside it will lose more heat than when it's not as cold outside or not as warm inside so although it will lose slightly less heat to the outside when the place is cold. Not only has the boiler got to recover all the heat that's been lost but also compensate for the heat that's still being lost to the outside.
That means it might have to flog away almost continuously for a couple of hours just to get it back up to temperature. However once its up to temp then the boiler will just fire up as necessary to maintain the set temperature to compensate for the heat loss to the outside
Older boiler just turn on and off and the internal temperatures can over and undershoot by several degrees.whereas more modern boilers with more sophisticated controls can turn themselves up and down (modulate) to adjust their heat output and with weather compensation even reduce the flow temperatures when its not so cold outside. Lots of more modern thermostats can also adjust their operation to reduce cycling but in the end all an older boiler can do its turn on and off, so it probably doesn't really make a great deal of difference.

The only way to really find out what is going on is to measure the inside, outside and boiler flow temperatures together with the gas consumption using a data logger to see how all they all interact and interrelate with each other, 

paperclap

Thanks for the reply matelodave.

It's true that all these older boilers can do is turn on and off.

The first hour, it is firing away, and using the most gas. Understandable, as it is bringing the central heating water up to temperature. But, once that water is up to temperature, and the house is up to temperature, the boiler trickles on and off to maintain said temperature. Thus, it is "on" far, far less. Yet, it still seems to cost the same / use the same energy.

matelodave

The problem with an older boiler is that when it comes on it comes on at full blast runs for a few minutes until the thermostat tells it to shut off and all that residual heat just sits there getting cold until the next firing. The boiler may also have a pilot light instead of an electronic igniter. Pilot lights use energy continuously. 

The house probably still requires roughly the same amount of energy in a day to heat it whether you give it a short fast blast for a couple of hours and then let it get cold and have to recover the lost heat as it does if you heat it gently all the time. Try turning the boiler flow temperature down a bit - it might take a bit longer to heat the place initially but it might reduce the running costs. Trying to establish the most efficient way to set it up takes time, patience and taking a lot of measurements not forgetting the variables of the temperatures outside which can make a significant difference to your heating requirements from one day to the next and even between daytime and overnight.

Modern boilers tend to regulate their output more efficiently, they usually run the pump on after the boiler has shut down to dissipate the heat into the system and don't waste gas on a pilot.They are also extract heat from the flue and so are usually a lot more efficient. However the cost of a new boiler against any savings could take a very long time to payback.

FreeBear

matelodave said: The problem with an older boiler is that when it comes on it comes on at full blast runs for a few minutes until the thermostat tells it to shut off and all that residual heat just sits there getting cold until the next firing.

I now have a control system that can switch the boiler and CH pump on/off independently of each other. The pump is set to run for an additional 15 minutes after the boiler shuts down. Gives me another 0.5°C of temperature increase throughout the house.

Boiler is a vintage Baxi back boiler - Not the most efficient of boilers, but it is not worth changing until it is beyond economical repair. Wouldn't save much on an annual £300 bill to justify the expense.

YorkieB

My central heating boiler is set to a very low temperature during the night so it switches off. Sadly, in the morning, it doesn't come back on. The troubleshooting guide says it's due to "low water pressure" but simply switching the electricity supply off and on again solves the problem. I've asked an engineer to come and look at it but I'd like to have some idea what's wrong before they come. Any advice?

JJ_Egan

Thermostats ???

PS this is Oil LPG board .