how much heating oil does the boiler use?

I have data from several sensors that record how much heating oil* is used at home daily and this page explains how you might do this calculation yourself and answers the following:

• how much heating oil do I use each year?
• how much heating oil might I use month by month?
• how much heating oil do I use in a day / hour?
• can the heating boiler power / fuel nozzle be adjusted?
• could I save money by changing my oil boiler for a new one?
• how to monitor your heating oil use in a day
• a diy sensor to monitor heating oil use by the hour
• how can I turn an oil hour meter readings into litres?

*our central heating boiler burns ‘heating oil’ (= diesel) from a tank in the garden – we do this here because we have no access to the ‘natural gas’ (=methane) that’s piped around the UK. Oil costs £0.07 / kWh – just a bit more than natural gas at £0.06 /kWh.

how much heating oil do I use each year?

Of course it depends but reckon on needing to order 1000 to 1600 litres a year for heating your rooms and bath water. (For US gallons divide litres by 4). In terms of money that’s £700-£1000 a year. Here are two benchmarks, based on several year’s records, to compare with your setup.

• A flat /apartment (50 sqm) with 4 or 5 radiators has a 15kW/h oil fired boiler uses 800-1000 litres each year for water and space heating.
• A 4-bed house with 7-14 radiators has a 36kWh oil fired boiler uses 1500 litres each year. (Usually 7 of the 14 radiators are turned off. I’ve since added smart radiator valves to improve economy and the saving will soon pay for the equipment).
• The table below shows more detail on my measurements

aside: calculating your oil or gas use based on an EPC kW/sqm

The two oil use benchmarks above are based on metered usage but the heating requirements of a property, as kWh/square meter, can be calculated using various websites or using an energy assessment. (In the UK every sold house has an energy performance certificate which will have this data and may be public and online).

Example: a flat/apartment with 50 sq m of floor area was said to need 150 kWh/square metre. This is based on room volumes, how much window, how many exterior walls and how much insulation there is. The figure is unique to the property. The calculated figure for heating the flat over six winter months comes to 6200 kWh plus 2400 kWh for 12 months of water heating. Adding that up gives us 8600 kWh – which is 50 sq m x 150kW/sq m

Take your EPC figure (or 8600 kWh) and divide that by 9 kWh per litre of oil = 950 litres a year. This 9kWh is the power in a litre of heating oil. If the heating boiler is only 90% efficient then the amount of oil required in a year would be 950 x 90% (1050 litres a year). During winter 20% of this oil usage seems to involve heating water for baths and so on.

how much heating oil might I use month by month?

On average you might use 150 to 200 litres a month based on 1050 litres per annum. This depends on the climate and my figures show that we require heat in six months of the year. Of the six months, four months have larger bills – January and February has the largest bills. In terms of ordering oil, if your tank held 1200 litres, to keep a good supply on hand, you’d probably fill up the oil tank 2-3 times a year.

how much heating oil do I use in a day / hour?

The rough answer for a domestic central central heating boiler is 1.5 litres to 2.5 litres an hour if it’s continuously alive and burning oil. In reality the boiler is using half of this because the boiler stops running when the system gets up to temperature. If I watch my boiler, it’s active for 40% of the time that it is switched on – so my boiler is using 0.60 to 1 litre per hour (ie costing £0.60 to a £1 per hour at £1/litre)

Only on the coldest days is the boiler is as active as 80% of its ‘on’ time*. *(A nest thermostat tells me the number of hours that I have scheduled while my hour meter tells me the number of hours that the oil boiler is making a noise burning oil)

estimate how much heating oil you use in a day:

find how many hours of heating you’ve programmed into your boiler. If you had scheduled six heating hours a day, half that to get 3 (= 50% active) and multiply those 3 hours … by 1.5 litres for a flat/condo boiler or 2.5 litres for a 4-bed house boiler. So the 4-bed house boiler uses roughly 3 * 2.5 = 7.5 litres a day depending on weather and house insulation.

how to do the calculation: If you know the boiler kW rating its ‘nozzle size’ can be found in the table below. My boiler spec sheet shows that a boiler nozzle* size of 0.5 will lead to a certain flow rate – the rate may be quoted in US gallons per minute or kg per hour. My 0.5 nozzle gives a flow rate of 1.895 litres per hour. (That’s the theory, as I measured that as 1.6 litres an hour).

If heating oil costs £1 per litre, the flat/condo boiler costs 1.6 * £1 (about £1.50) to run continuously for an hour. Each hour the meter clocks up costs £1.50. On the coldest of days we used 30 litres of heating oil. That’s 18 hours of burning time in 24 hours. The graph shows a rough correlation between outdoor temperature and how much we turned up the heating.

is it better to use a fan heater to heat up a room rather than heat the whole house?

Yes probably but let’s look at this. The graph above shows how long it takes to heat my room. Using the central heating system which is also heating other rooms, it takes 35 mins; using a fan heater it takes 25 mins. The calculations show that it’s faster and cheaper to heat up the room with a fan heater. For example, if you simply wanted the room warmed to get dressed in the morning, using a fan heater is a money saving strategy. It also uses a tenth of the energy to achieve this momentary and short-lived heating.

energy source	rate	cost to heat the room
central heating oil boiler – 35 mins	1.5 litres/hour at £0.60 / litre	£0.53 to use 8kWh
daytime electricity – 25 mins	1.7kWh at £0.30 / kWh	£0.21 to use 0.7kWh
off-peak electricity – 25 mins	1.7kWh at £0.12 / kWh	£0.09 to use 0.7kWh

Another way to reduce the energy used by the central heating is to make the thermostat radiator valves smarter so that different rooms have their own heating schedule. For example, the bedroom radiator is timed to turn on for a morning period and for an evening period ie bedtime. The living room only heats up at TV watching time. This setup is a DIY project and easy to achieve and I wrote about my experience with the tado system here.

can the heating boiler power / fuel nozzle be adjusted?

Most of us rely on the integrity of a oil boiler technician to service and optimise the boiler. They can be asked to make adjustments. For example, the size of the nozzle that sprays oil into the burner determines how fast fuel is burned. Having a smaller nozzle will warm the house more slowly … but also burn oil more slowly. Ask your boiler expert if fitting a smaller nozzle will be good for you. But there’s a lot to know … for example, I read somewhere that it’s good for a boiler to work and less good for a boiler to be stop-starting.

could I save money by changing my oil boiler for a new one?

No, not much if it’s a like for like swap. For example, if it gave a 5% increase in efficiency, carbon issues aside, you save £50 a year on house heating. However, replacing an old ‘conventional’ boiler with a present day condensing boiler gives an improvement from 75% to 90% efficiency. My real figures below imply that something dramatic can happen if you’re replacing a ‘conventional’ boiler with a condensing boiler. This looks like a 25% saving on fuel but there are many variables including a milder winter so I need still more data. My first thoughts (carbon emissions aside) were that if I saved £300 a year a boiler change is paid for in ten years. The second table below shows the data for replacing a larger boiler with data for 2025 to still to complete.

heating use by a flat (50 sqm)	winter burning hours	oil used over entire winter
conventional (1980 boiler) in 2022/23	796 hours (0.5 nozzle)	1294 litres (£880 @ £0.68/l)
condensing (new boiler) in 2023/24	449 hours (0.6 nozzle)	760 litres (£517 @ 0.68/l)

heating use by a 4-bed house	winter burning hours	oil used over entire winter
conventional (1980 boiler) in 2022/23	578 hours (0.85 nozzle)	1742 litres (£1185 @ £0.68/l)
conventional (1980 boiler) in 2023/24	543 hours (with smart radiator valves)	1432 litres (£974 @ £0.68/l)
condensing (2025 boiler)	TBA	x litres (£x @ 0.68/l)

how to monitor your heating oil use in a day

Buy tank sensors that have a mobile app allowing you to record usage. Examples include FoxRadar and Watchman Sensit which were not around at the time I needed them – I made my own, connected it to Home Assistant and got it to display and calculate things as needed.

My need was to meter the use of oil for billing purposes and I met that easily and inexpensively as described below. (You might care to see my display of how much energy is used. Or you might like my device that measures the oil level in the supply tank and shows me the oil usage in Home Assistant).

a diy sensor to monitor heating oil use by the hour

As there are two households drawing oil from the same tank I was keen to find a way to divide up the bill for our use of fuel. While your need will be different an oil meter can measure your oil use and help with budgeting or knowing when you’ll need to order oil.

Is there a sensor to show much oil is used by a boiler? Well, a oil flow meter needs to measure from 1 litre an hour up to 50 litres a day. Oil flow sensors that measure 100 litres a minute aren’t suitable. The two sensors below are suitable – the mini flowmeter at Rapid could measure oil consumption; the Adafruit flow meter is accurate to only 10%. However I was hesitant to mess with my fuel line … so I changed tack and found the solution below.

My solution (2016 -) is a 240v hour meter. It’s a part you’d find on a machine where it would count the time until a service was required. This timer is mechanical so it doesn’t reset if the power fails. I got the boiler service man to wire the meter in parallel with the boiler burner circuit so that the meter would only count the hours when the boiler was burning oil. You don’t want the meter to count hours when the boiler was simply ‘on’ as set by the heating programmer. The meter cost £5 – which is a more appropriate price than paying up to £150 for an oil flow meter. It’s now 2022 and I’m looking for a version of this sensor which works with Home Assistant – it needs to monitor is how long a circuit stays active while unfailingly allowing the boiler to work.

how can I turn an oil hour meter readings into litres?

The meter measures burning hours, and if we know the oil nozzle flow rate (table above), we can turn that into litres. My calculation goes like this:

The boiler spec sheet shows that a boiler nozzle size of 0.5 will lead to a certain flow rate. Nominally that is 1.895 litres per hour but further study showed that to be 1.6 litres an hour. If heating oil costs £1 per litre, the boiler costs 1.6 * 1 (about £1.50) to run continuously for an hour. For billing purposes, each hour the meter clocks up costs £1.50.