Gas Fire Output Measurement

[Willum08]

Hi,
I have a problem related to my Kohlangaz Gosford HE Gas Fire and wonder if anyone can give me some advice..
The problem is that when it is set to its lowest output it seems to be producing too much heat output. It has recently been serviced by a Gas registered engineer and he is of the opinion that every thing is OK. Having had the gas fire for a number of years (January 2017) we are perfectly used to the amount of heat which the fire produces when set to the minimum output. Sitting in our normal positions in the room which we have done since installation, we now find that our legs are uncomfortably hot when the fire is on its lowest setting. This was not the case, prior to the recent service.....
The engineer made another visit in response to my complaint but still stated he could not see any problem.. I did not witness any instrument being used to measure the heat output of the fire at its various settings as can be adjusted by the fire's remote controller.
My question... How is the actual heat output from the front of a gas fire measured ?

The specifications of the fire state that the Maximum Gross Heat Input is 5.0 kW and the Minimum Gross Heat Input is 3.5 kW. Presumably these quoted Max and Min ratings relate to the heat settings of Max and Min as selected by the Remote Controller.
The Efficiency as specified in BS 7988-1 is quoted as 80%

So using these figures I would think that the Maximum Heat Output = 80% of 5 kW or 4kW
and the Minimum Heat Output = 80% of 3.5 kW or 2.8 kW or is this too simplistic ???

If these Output figures are correct, How can they be verified by testing ??

 

[Deleted member 267285]

Hopefully, your engineer would have gas rated the appliance, which a calculation is used to determine if the fire is within the kw rating. If this is correct, then I’m not sure there’s much more he can do.

 

[Harry Bloomfield]

If these Output figures are correct, How can they be verified by testing ??

With only that fire on, you can record the gas meter reading, record it again in one hour, the difference between the two is either (depending on your meter type) either in cubic meters, or Kw of gas used. There is an easy formula to convert from cubic meters to Kw, it should match your fires 100% input rating.

I doubt anyone doing a serice, could possibly adjust the minimum out setting.

 

[Willum08]

Thank you to both for taking the time to reply.... Much appreciated....
CBW you state. "Hopefully, your engineer would have gas rated the appliance, which a calculation is used to determine if the fire is within the kw rating.
I don't know if this procedure has been carried out. If you have the time, could you explain what the calculation involves....
The fire is working OK - it is just that the Heat output on its lowest setting is definitely much higher now, compared to what it has been since it was first installed. Is there an instrument which service engineers use to measure the actual heat output of a gas fire ?
Kind Regards......

 

[Deleted member 267285]

No, they measure the burner pressure at the fire if possible, or the heat input. Harry has already given you an insight. There’s a few ways of doing it, but all roughly similar. We let the fire heat up for about 10 mins (not everybody does), take a meter reading, time the appliance burning for 2 minutes, then take the meter reading again, this is how much gas is burnt in 2 minutes, then multiply this by 30, to give gas burnt in an hour, multiply by a factor number (this can vary, as can the calorific value of gas), and divide by 3.6, and then it’s converted to a net figure.

 

[Willum08]

Thank you for your help.. much appreciated.. regards & Stay Safe

 

[gasbanni]

With only that fire on, you can record the gas meter reading, record it again in one hour, the difference between the two is either (depending on your meter type) either in cubic meters, or Kw of gas used. There is an easy formula to convert from cubic meters to Kw, it should match your fires 100% input rating.

I doubt anyone doing a serice, could possibly adjust the minimum out setting.

Sorry Harry an hour !!!!!

All you need to do is operate the fire on maximum for two minutes if its a metric meter or one revolution if its imperial then do it on low setting.
From these figures the heat input can be ccalculated and checked against the spec. I have found gas fires overgassed because some idiot had drilled out the injectors.

Your fire can be easily checked using the gas meter with everything else gas rated off and it only takes a few minutes. So providing the fire is checked for spillage and the gas rate is correct he's done a good job !!!

 

[Harry Bloomfield]

Sorry Harry an hour !!!!!

No problem - The longer the measurement, the greater the readable accuracy from the meter and more easily timed..

 

[gasbanni]

No problem - The longer the measurement, the greater the readable accuracy from the meter and more easily timed..

It's never done that way Harry, under any circumstances, I couldn't help but laugh when you said an hour ! One full revolution of an imperial gas meter or two minutes on a metric one is accurate.
A little calculation then gives you what you need.
With a boiler this enough time on a cold heating system for it to ramp up and fire on max without the boiler reaching temp and modulating down.
Even then sometimes on max two minutes is too long and the boiler stat cuts in so you get s false reading.!

 

[Harry Bloomfield]

It's never done that way Harry, under any circumstances, I couldn't help but laugh when you said an hour ! One full revolution of an imperial gas meter or two minutes on a metric one is accurate.
A little calculation then gives you what you need.

However, you agree in principle, that one hour for a gas fire, which will not by itself ramp up or down, will give a suitable value.

 

[gasbanni]

However, you agree in principle, that one hour for a gas fire, which will not by itself ramp up or down, will give a suitable value.

No Harry it's a pointless exercise it's wasting gas.
It was a good guess I'll give you that but honestly pointless. What your saying to me is an hour spent on minimum.and an hour spent on maximum and you'll have the results that can take one or two minutes ! The original poster can even do this himself !

If he posts the readings I'll tell him the heat inputs.

By the way gas pressure at the appliance is not thecway to test a fire .....what if some idiot has enlarged the injectors oressure wouldn't show this heat input would.