13.
3.
Gas rating of Burley Flueless Appliances
Burley’s Flueless Gas Appliances are all gas input rated in the factory and undergo further line tests
for combustion, sooting and visual performance. For Installers who wish to gas input rate
appliances we need to establish tolerances for pass and fail.
Manufacturers Tolerances
The Heat Input on appliances can be expressed as either a Nett or a Gross figure. When the installer
is gas rating from the meter they will be using gross heat input which is 10% higher than Nett. This
conversion has to be taken into account if the manufacturer has quoted a nett figure.
The manufacturer also has to account for production tolerances on pipes, injectors, valves etc and
is allowed a f/-5% tolerance on the maximum rate.
Burn Down
Cold appliances generally allow a greater rate of gas to pass through them and once the appliance
warms the gas density alters and causes the rate to reduce to the figure stated. This is known as
Burn Down.
Manufacturers carrying out their technical tests allow appliances to be fully warm and burn down
before taking readings and this is typically after 1 hour. Some appliance manufacturers quote a
‘cold’ figure for the gas rate so that installers can measure this immediately.
Installer Tolerances
It is important to take a gas rate test over a reasonable period of time so that the capacity of the
meter is used. On low Input appliances such as our flueless this is even more critical because
uncertainties can creep in. It is worth measuring over a 5 minute period to make sure.
It is also important to get your inlet pressure to 20mBar.
In a gas appliance factory compensation is also made for variations in
•
% Saturation of Gas
•
Variation in Calorific Value
•
Variation in Gas Density
•
Gas Temperature
•
Gas Pressure
•
Atmospheric Pressure
•
Meter Calibration
•
Stopwatch Calibration.
In the home it is not possible to correct for these therefore an uncertainty factor needs to be built
into all measurements.
Currently Gas Safe™ (formerly CORGI) does not quote a figure on this uncertainty but the measured
gas rate could vary by +/-5%.
Conclusion
In adding all the variables together,
•
an appliance quoting Gross Heat Input could be anything from +/-10% of the quoted heat
input
•
an appliance quoting Nett Heat Input could be anything from 0% to +20% of the quoted
figure when measured as a Gross figure.
•
If the appliance is cold anything up to a further 10% error could be expected and we don’t
quote these figures because they change rapidly. The figures shown below are hot figures.
Model
Heat Input
Quoted
Minimum (Gross) Maximum
(Gross)
Cu Ft Per Hour
Environ, Esteem
2.5kW Nett
2.5kW Gross
3.0kW Gross
8.49
Ambience 4121
3.5kW Nett
3.5kW Gross
4.2kW Gross
11.67
Acumen / Elan 4111
4.2kW Nett
4.2kW Gross
5.3kW Gross
14.85
