With the squeeze on family finances looking set to continue and the only predictable element relating to energy prices being the increasing cost, energy efficiency has to be the main factor in addressing high-energy bills.
Perhaps you have an old but seemingly reliable boiler, or you have recently installed a new A rated boiler that is claimed to be ultra-efficient. How do you know that they are operating to, and within, acceptable and efficient operating tolerances?
There are procedures that can be used that will give a reasonably accurate indicator of how efficient a gas appliance is under normal operating circumstances. They can also give an indicator of problems relating to the appliance or the system to which it is connected.
The gas rating of an appliance to check its efficiency is not a complicated task.
It is simply a procedure used to measure the volume of gas consumed by an appliance during a timed period. A reading is taken at the gas meter and from this it is possible to establish if the appliance under test is using the amount of gas it was designed to.
First look on the appliance that you wish to rate for some indication of its expected operating fuel consumption. If it is illegible, refer to the manufacturer’s guidance notes if you still have them. This information may be provided in Btu’s. There is a conversion that can be applied. We will cover that shortly.
Next, locate your gas meter and determine which type is installed.
There are three types in use. A digital metric meter, a digital imperial meter and the old-fashioned dial meter. The latter is almost obsolete.
Essentially, the task with the meter is to discover whether the meter is measuring the gas flowing through it in metric or imperial units.
Metric meters measure gas in cubic meters (m3).
Imperial meters measure gas in cubic feet (Ft3).
This is usually clearly marked on all three types of meters, normally to the right of the four or five digit number displaying the units of gas used. When reading the displayed meter numbers ignore any numbers in red sections or red dials. On metric meters, ignore any numbers after the decimal point.
You are now ready to start the procedure.
As a gas boiler is perhaps the most likely appliance to be gas rated to check its efficiency, the procedure for doing so will be used as the example.
It is a good idea to run the boiler on full capacity for around ten minutes to start with. This just ensures that it is operating at normal running temperature. Whilst this is happening; ensure all other gas appliances are turned off.
After ten minutes, turn off the boiler.
Now, return to the gas meter with some means of timing. A stopwatch or a watch with a second hand is ideal.
Take a reading from the meter and record this on a sheet of paper.
Return to the boiler and ensure that the thermostats and system programmers are over-ridden. This will guarantee that the boiler will operate at full capacity.
Turn on the boiler and at the same time start the timing. Continue timing the running boiler for exactly two minutes and then switch the boiler off.
Return to the gas meter and take a second reading from the numerical display and record this on the sheet of paper with the first reading.
You now have the information that is required and the appliance, and any others, can be returned to normal functioning.
Of the two sets of numbers you have recorded, subtract the lesser set of numbers from the greater. This will provide you with a number, which represents the number of units that the appliance has consumed in two minutes.
Multiply this figure by thirty to establish the number of units used in one hour.
This number will then represent either ft3 or the m3 of gas used.
If your meter has registered output as m3 it will need to be converted to ft3.
To convert m3 to ft3, multiply the m3 units used by 35.37.
Now for the three types of meters you will have a value expressed in ft3
It is now necessary to establish the calorific value (C.V.) of natural gas. All domestically used gases have a known calorific value.
Natural gas has a C.V. of 1040 Btu/ft3
(If you have a system which runs on propane the C.V. will be 2496 Btu/ft3).
Multiply the value of used gas in ft 3 that you calculated earlier by the C.V. of your fuel type. For natural gas that figure will be 1040.
This will give you a figure which represents the number of Btu’s that your appliance uses in one hour.
To calculate the kW-h multiply by 0.000293 (2.93×10-4)
Either the Btu/hr figure or the kW-h figure should correspond to the rating indicated by the boiler specifications.
The kW-h figure will certainly allow for comparison with other appliances and aid the understanding of which appliances are contributing most of the cost to your energy bill, which will invariably be referenced and calculated in kW-h.