I will explain how to calculate the cost of heating from different fuels and also the size of boiler you need.

Relative costs:

The simplest unit of energy when doing comparisons is the KWH (kilowatt hour). This is what is commonly known as a unit of electricity.

If we use electric to heat with a direct heating element (kettle or electric heater) then each KWH will cost       18 cents day rate and 9 cents night rate. If we use a heat pump with COP of 4 then heating by electricity will cost 4.5 cents daytime and 2.25 cents night time.

One litre of heating oil contains 10 KWH and so each KWH of heat will cost 10 cents when we take the efficiency of the boiler into account.

One kg of wood pellets contains 5 KWH and so each KWH of heat will cost 5 cents when compared on the same basis.

You can compare the cost, calorific value and conversion efficiency of any fuel.

The cheapest method of heating is a heat pump run on off-peak electricity. You need to be able to store the heat produced at night for use when needed. Buffer tanks can be used to store hot water or underfloor heating for domestic use is a very viable option.

Boiler size:

The simplest way to check the boiler size required on a mushroom farm is to check the oil usage over say 1 week. Then work out usage per day and per hour.

If we use 10 litres per hour, then we are using 100 KWH of heat per hour.

The heating demand will be 50% higher at night so we will need 120 KW boilers at night and 80 KW daytime. A good choice would be a boiler of 150 KWH capacities. This should be used as a guide only.

Any grower using 8 -10  litres per hour per boiler will get maximum benefit from the RHI (renewable heat incentive).