LPG running cost

DailyClicker

Hello,

I have a Greenstar 36CDi Compact ErP LPG boiler, and with Calor Gas (39.9p per litre). 

From looking online it says it has an output of 36 kW, so trying to work out the running cost. 

1 Litre of LPG = 7.08 kWh

So if I run the central heating for 8 hours (4 hours morning + evening), it would need 36 kW x 8 hours = 288 kWh.

Then 288 kWh / 7.08 kWh = 40.68 litres. 40.68 litres x 39.9p = £16.23 per day (£486.90 per month - winter).

This seems pretty excessive - are my calculations right?

Thanks

Reed_Richards

DailyClicker said:

This seems pretty excessive - are my calculations right?

No.  36 kW is the maximum power that your boiler can provide.  The actual power it uses will depend on how hot you keep your house, how cold it is outside and how much hot water you use.  It's very unlikely you will require anything like 36 kW for heating your house.  The reason you have a 36 kW boiler is so that it can heat your hot water sufficiently quickly.    

QrizB

As R_R says, a good part of that output will only ever be seen when heating water.

A moderately-sized nouse will have radiators capable of dissipating 10-15kW of heat (mine are about 11kW total, R_R do you know yours?). This will limit the peak amount of space heating your boiler can provide. Also, unless it's really cold your thermostat will restrict the running time of the boiler and reduce the actual output further. (Clever boiler controls will achieve a similar result.)

If you're interested you can estimate yours by measuring them and then comparing them to similar radiators eg. on the Screwfix website.

Reed_Richards

QrizB said:

A moderately-sized house will have radiators capable of dissipating 10-15kW of heat (mine are about 11kW total, R_R do you know yours?). 

I know my radiator heat output very precisely.  It is 9.73 kW assuming that the rooms are at 21 C and the radiators are at their specified operating temperature (which in my case is a Delta T of 25.5 C but that's by-the-by).  The radiators are oversized by 8.7% for what is calculated to keep my house warm enough 99.6% of the time if the radiators are on continuously.  I live in a four bedroom bungalow.

I estimated that my old heating system (same house) had 12.7 kW worth of radiators assuming they were operated at Delta T = 50 C.      

DailyClicker

Thanks both, that's really useful. I've got 15 radiators but even with the heating on 8 hours a day, cannot get the temperature to reach 20C, and drops pretty quickly. 

https://www.screwfix.com/p/acova-classic-vertical-2-column-radiator-2000-x-490mm-white-4709btu/81335
https://www.screwfix.com/p/acova-classic-horizontal-3-column-radiator-500-x-812mm-white-2992btu/57982

I can't seem to find the kWh on the Screwfix website for these ones?

lohr500

You could try entering the dimensions and radiator types into this website to get an estimate of the outputs :
https://www.castrads.com/uk/resources/calculators/panel-radiator-outputs/

Do you have thermostatic valves on the radiators?
Where is the central heating thermostat located relative to the closest radiator? 
Where are you measuring the 20C.
Is the house well insulated?
With the thermostat cranked up to the maximum, can you sill not achieve 20C?

We have 17 radiators in our house, with a theoretical T50 output of 16kW. 
Our 30kW oil boiler is more than capable of maintaining a 20C temperature, even in the coldest periods.
And we live in an old exposed converted farmhouse with poor insulation.

We are on oil, and over the past few weeks it has been costing us around £8.25 per day for heating and hot water, running the heating at 19C for a couple of hours in the morning and four hours in the evening, with a day time setting of 16C and an overnight setting of 13C.

In comparison, mid summer, it was costing around £1 per day, for hot water only. Four of us with lots of baths and showers.

I can measure our oil usage reasonably accurately as I have an inline low meter on the oil line to the boiler.

Do you know how many litres of LPG you have used over a 12 month period? 

QrizB

DailyClicker said:

Thanks both, that's really useful. I've got 15 radiators but even with the heating on 8 hours a day, cannot get the temperature to reach 20C, and drops pretty quickly. 
https://www.screwfix.com/p/acova-classic-vertical-2-column-radiator-2000-x-490mm-white-4709btu/81335
https://www.screwfix.com/p/acova-classic-horizontal-3-column-radiator-500-x-812mm-white-2992btu/57982
I can't seem to find the kWh on the Screwfix website for these ones?

In the description:

• The first one says 4709BTU, 1380W.
• The second says 2992BTU, 877W.

The BTUs are in the product name and the URL. If you ever can't find the wattage, divide that by 3.4 and you'll be close enough.

Reed_Richards

QrizB said:

DailyClicker said:

Thanks both, that's really useful. I've got 15 radiators but even with the heating on 8 hours a day, cannot get the temperature to reach 20C, and drops pretty quickly. 
https://www.screwfix.com/p/acova-classic-vertical-2-column-radiator-2000-x-490mm-white-4709btu/81335
https://www.screwfix.com/p/acova-classic-horizontal-3-column-radiator-500-x-812mm-white-2992btu/57982
I can't seem to find the kWh on the Screwfix website for these ones?

In the description:

• The first one says 4709BTU, 1380W.
• The second says 2992BTU, 877W.

The BTUs are in the product name and the URL. If you ever can't find the wattage, divide that by 3.4 and you'll be close enough.

BUT those figures will be for a radiator temperature that is 50 C higher than your room temperature, averaging the input and output flow temperatures to determine the radiator temperature.  Your boiler could be set to make your radiators hotter or colder than 50 C above room temperature.  

KathysBoy

We have a 4 bedroom house, with a study. There are two of us, and we are retired, so home most of the day. I thought it might be helpful f I shared my usage figured.

We have an Ideal S30 LPG boiler, and we set the heating to start at 6.30am (6.00am if below freezing). It’s set to 21c, which when the temperatures are low like the last few days, it reaches about 8.30. At 9.00am it’s set to 20.5c for the rest of the day until 5.00pm when it resets to 21until 9.30pm. 

I took the reading this morning, and since the last reading on 31st December we have used an average of. 8.50 litres. Our usage during December was about the same.

markin

The flow temp on the boiler could be set to low for winter use, have you just moved in/ got a new boiler? *(2015 boiler)

Maximum rated heating is stated as 24KW

Maximum rated heat output Water 36KW

Gas flow rate LPG - Max. 10 minutes from lighting  2.8KW

Water heating energy efficiency  85

Seasonal space heating energy efficiency  94
Daily fuel consumption 20.7

Annual fuel consumption  18 , Averaged?