Gas Central Heating Costs

LisaW123

We live in a 3 bed, 30's semi and our gas central heating costs seem extortionate. We've worked out roughly how much we pay per hour for central heating using the following formula:

Convert cubic feet to cubic metres by multiplying the units used by 2.8316736.

Multiplying the cubic metres by the correction factor shown on the of bill then multiplying the result by the calorific value.

Dividing this amount by 3.6 to get the number of kilowatt hours used, and multiplying that by the cost of each kilowatt hour (kWh).

Using this formula, our central heating costs are working out at £1.15 an hour.

Does anyone know if this is unusually high? We have already shopped around for the best online deal but I wonder if it would pay us to replace our boiler/central heating system. Our boiler is a baxi we inherited from the previous owners. It is probably around 19 years old. We have no thermostat, just a setting on the boiler that goes from 1 to 5. We've often thought of replacing the boiler but have heard mixed reports about the reliability of condensors and are concerned about the cost of spares for these boilers. Although we know our current boiler will not be particularly efficient, it is very reliable.

Any advice anyone has would be appreciated, along with an idea of the costs per hour others are paying for their gas heating.

We were also wondering if anyone has an oil free column heater and how these perform? We were thinking of using the gas central heating less and buying a dimplex 2Kw oil free column heater, so at least we could keep the living room warm all the time. 2Kw of electricity at the rate we pay should work out at about 25p an hour.

Cardew

The first thing is conversion of Gas units to kWh. You can work it out exactly, but as the calorific value(CV) of the gas is variable it will differ slightly every time the CV changes. However for all practical purposes if you have an Imperial gas meter(cubic feet) a gas unit is approx 31.5kWh. A Metric meter(cubic metres) gas unit is approx 11.2kWh.

The setting on the boiler is for the temperature of the water the boiler will produce; normally from around 55C to 82C.

With regards to boiler replacement, there are lots of threads on this and the consensus of opinion is never replace a working boiler. The older non-condensing boilers tend to be very reliable and there are plenty of reports on MSE of boilers up to 30 years old - mine is 23. There is little a RGI fitter cannot repair and spares are still available for most(despite what BG servicing department would have you believe).

You haven't explained how you got your costs, but I suspect that your calculations of £1.15 an hour is a mistake - either you have a Metric meter and are using the Imperial calculation, or you are using the Tier 1 price of gas in your calculation.

You should always use the Tier 2 price of gas which is around 3p/kWh to 4pkWh. It is just possible that a big boiler might use close to 30kWh in an hour starting from scratch with a cold house and an cold Hot Water tank, but then the consumption shoud drop dramatically.

The use of an electric fire makes no sense financially. Your boiler should be around 65% to 70% efficient(most boilers of that vintage were on that region) so the real cost of heating a radiator with your CH boiler should be less than half the price you pay for electricity 4.5p to 6p/kWh

LisaW123

Thank you very much for your reply Cardew. The meter and calculations have been checked and they are, unfortunately, pretty accurate; well 10p out. The calculation is as follows:

Units of gas used x 2.8 = n1 1 x 2.8 = 2.8
n1 x 40.1 (calorific value) = n2 2.8 x 40.1 = 112 n2 / 3.6 = n3 112 / 3.6 = 31.1 (kilowatt hours)
n3 x 3.387 (cost per kilowatt hour) 31.1 * 3.387 = 105p per hour

Our boiler is a fairly large, floor standing unit - it must be at least two feet tall. It has no facility for central heating alone. It heats the radiators and water tank at the same time, although there is an option to heat only water.

We always knew our bills were large and have tried to limit the amount of heating we use, so it is on for an hour in the morning, off all day and then on again in the evening. We have only just worked out how much this is actually costing us per hour.

In light of this, I'd appreciate your opinion as to whether you think it is worth us holding on to the boiler?

Thanks

HappyMJ

Which model of boiler is it? I would hold on to it until it becomes uneconomical to repair or becomes economical to change to a new boiler. What is your annual gas usage?

Cardew

LisaW123 wrote: »

Thank you very much for your reply Cardew. The meter and calculations have been checked and they are, unfortunately, pretty accurate; well 10p out. The calculation is as follows:

Units of gas used x 2.8 = n1 1 x 2.8 = 2.8
n1 x 40.1 (calorific value) = n2 2.8 x 40.1 = 112 n2 / 3.6 = n3 112 / 3.6 = 31.1 (kilowatt hours)
n3 x 3.387 (cost per kilowatt hour) 31.1 * 3.387 = 105p per hour

Our boiler is a fairly large, floor standing unit - it must be at least two feet tall. It has no facility for central heating alone. It heats the radiators and water tank at the same time, although there is an option to heat only water.

We always knew our bills were large and have tried to limit the amount of heating we use, so it is on for an hour in the morning, off all day and then on again in the evening. We have only just worked out how much this is actually costing us per hour.

In light of this, I'd appreciate your opinion as to whether you think it is worth us holding on to the boiler?

Thanks

You have correctly worked out in this post that 1 Imperial gas unit is 31.1kWh. In my earlier post I stated that rather than laboriously working it out every time, if you used a figure of 31.5kWh then that would give approx the correct kWh figure.

However although in the first post you detailed the calculation starting with cubic feet, can you confirm that:

1. You definitely have an Imperial gas meter(marked ft3) and not a metric meter(marked M3)?

2. Is the meter a digital display, or several dials.

3. That you used exactly 1.0 gas units in 1 hour? (taking into account the decimal display)

It is a large boiler to use 30+ kWh, especially for a 3 bed semi, and whilst it is theoretically possible to use that amount of gas in an hour, in practice the boiler wouldn't be firing continuously. It cuts out when the water reaches the temperature set on the boiler.

It is however certain that you cannot use 31.3kWh per hour continously, hour after hour.

Do you not have Thermostatic Radiator Valves(TRVs) on the radiators?

Do you have every radiator in the house switched on?

How much gas( in kWhs) are you being billed for?

My gut feeling is still that you have a metric meter, or are reading the meter incorrectly.

Pincher

Potterton floor standing boiler

Input/Output in kW

Minimum 31.2/23.4

Mid-Position 34.9/26.3

Maximum 38.6/29.3


Since it is non-modulating, at minimum setting, it does indeed consume gas at 31.2kW (Exactly 1 unit imperial in one hour ), but you only get 23.4kW in heat. Maybe your thermostat is sticky, so the boiler is on all the time.

LisaW123

I have checked and the meter is definitely imperial. It is marked ft3. It is a digital display. We specifically wanted to know how much an hour's heating cost, so took meter readings before and after the heating had been on for an hour. We've checked again a few times since and it definitely moves on one unit after an hour's heating (from cold). We intend to do a bit more experimenting at the weekend, by running the system for longer and reading the meters before and after it is switched on/off. We are hoping it will not be so pricey per hour if it is run for longer. Unfortunately, we have no thermostats, either on the wall or on the radiators. Do you know roughly how much these cost to install?

We do have every radiator in the house switched on as most rooms are in use at some point. One thing we might try at the weekend is running the heating with all but the living room radiator switched off, as this is the room occupied for most of the time.

We just changed supplier in September so have not had a bill yet, but going off bills from our previous supplier, I would estimate we are being billed for about 18,000 kwh annually.

After much hunting, I have found the operating instructions for the boiler and it is a Baxi FS 601 OF. I don't think anything is sticking, as you can hear it firing up and down if you alter the numbered dial on the front of the boiler.

Thanks to everyone for taking the time to reply to my posts.

dogshome

For 3 bed 1930's semi, 18,000Kwh a year seems about right - A new boiler would reduce it, but is likely to have a shorter life, higher maintenance costs and be less reliable than your present one.

It would be better to spend cash on improving insulation in every possible area - Anywhere you can add to it will cut the gas bill, and it will continue doing it's job when that dear old tank of a boiler must be replaced for a new one

HappyMJ

18,000kWh is very good for a boiler that is 65% efficient. Let's say you spend £1,500 on a new boiler (a very conservative estimate). New ones last a maximum of 15 years so that's going to cost you £100 per year so far yours is over 20 years old and still running. It will be 90% efficient so that will reduce your usage from 18,000kWh to about 13,000kWh. Let's say your unit rate for gas is 3.5p per unit that will save you £175 per year. Insert your own figures where underlined. If you have the money saved in the bank earning 1% or less then do it and you will save about £1 per week. If you need to borrow the money or take the money from high interest savings accounts then don't do it.

Cardew

18,000kWh pa is not excessive(the UK average is 16,500) That doesn't tie in with using 30kWh an hour each hour.

Your boiler is a FS 601 OF.(I believe FS is Floor Standing) Looking at the SEDBUK tables Baxi made a whole range of boilers for several years designated 40, 50, 60, 70, 80, - all the 60 series are rated 14.95kW to 17.58kW. they have a poor efficiency of 55%. - perhaps one of the gas fitters can confirm this.

Without a room thermostat or TRVs the boiler will only be regulated by its water temperature.

HappyMJ

Cardew wrote: »

18,000kWh pa is not excessive(the UK average is 16,500) That doesn't tie in with using 30kWh an hour each hour.

Your boiler is a FS 601 OF.(I believe FS is Floor Standing) Looking at the SEDBUK tables Baxi made a whole range of boilers for several years designated 40, 50, 60, 70, 80, - all the 60 series are rated 14.95kW to 17.58kW. they have a poor efficiency of 55%. - perhaps one of the gas fitters can confirm this.

Without a room thermostat or TRVs the boiler will only be regulated by its water temperature.

65% efficient and the 14.95kW to 17.58kW is output heat the input's are higher. The "6" in the model means 60,000BTU. They also have a pilot light reducing the overall efficiency to the 65% mark.

Edit: according to the manual the inputs are from 19.5727kW to 22.91kW.