Gas Rate Help

[Cheech]

Hi im studying for my ccn1 test and im still confused with gas rating. I know the calculations but i have just been told the tolorence is 5% but 5% of what can someone give me an example , say i have a 37kw boiler and my gas rate is coming out at 45kw is that to high ? or say a 30kw boiler what is the lowist kw i can have and whats the highist. Thanks

 

[villa_tom]

5% of what your gas rate on the data badge, so say you have 100kw boiler you could be 105kw or 95kw

 

[kirkgas]

Hi im studying for my ccn1 test and im still confused with gas rating. I know the calculations but i have just been told the tolorence is 5% but 5% of what can someone give me an example , say i have a 37kw boiler and my gas rate is coming out at 45kw is that to high ? or say a 30kw boiler what is the lowist kw i can have and whats the highist. Thanks

i dont think there is an actual written min & max allowance, however the only way to get a 100% accurate gas rate is to know the Calorific Value of the gas being burnt, and also to measure it very accurately, the exact gas rate therefore is difficult to get, so an allowance is made, some say between 5-10% below or above is acceptable, i have heard some people saying 5% over and 10% under as over gassing is potentially dangerous, as others have said you need to check MI or data badge to confirm max HI, then gas rate the appliance to confirm the actual reading is within the tolerance you have decided to use

 

[Cheech]

ok still confused, does that mean that if its 5% over and 10% under a 37kw boiler would be ok if it rated 42kw highist and 27kw lowist what would i do if it was getting a gas rate of 44kw or 45 ??

 

[gasmarc]

I make you right Kirkgas , I had this today on a boiler after taking the burner pressure of 12mb then I gas rated it and came up with a larger consumption , then confirmed max burner pressure should be 11mb, learning everyday

 

[desrob]

Hi im studying for my ccn1 test and im still confused with gas rating. I know the calculations but i have just been told the tolorence is 5% but 5% of what can someone give me an example , say i have a 37kw boiler and my gas rate is coming out at 45kw is that to high ? or say a 30kw boiler what is the lowist kw i can have and whats the highist. Thanks

say you get a reading of say 12.5 kw, but data badge says 14kw,....12.5 divide by 14kw =0.89, 0.89 x 100 =89percent, 89 - 100 =minus 11percent, this shows the appliance is 11% under gassed not within + - 5%

 

[kirkgas]

ok still confused, does that mean that if its 5% over and 10% under a 37kw boiler would be ok if it rated 42kw highist and 27kw lowist what would i do if it was getting a gas rate of 44kw or 45 ??

sorry to confuse you what i mean is taking your 37kw boiler if it rates between 38.85kw (5% over the 37) and 33.3(10% under the 37) then i would say it was fine, if i am getting 44kw on a 37kw boiler the first thing i would do is recalculate just to check my figures, then if still 44 i would be looking at checking the standing and working pressure at the meter in case the regulator was goosed

 

[stewm]

Just in case your maths is wrong,a really good download is available from www. GB-GAS.co.uk you can work all your gas rates from this,and plenty more on site which is handy, online training free stuff

 

[Cheech]

ok thanks for the help guys. is there any other cause for getting a higher reading eg.44 kw than the regulator not working ?

 

[SafeGasInstall]

gas valve ,but how can you sit exam when this is a GREY area to you ,you need to go on side and get more training gas rating gas fired appliances IMHO

 

[Cheech]

cause i got made redundent as a plummer and am now training to get my ccn1. i dont have anyone else to ask and the books just tell you how to gas rate, nothing about what to do if you are not getting right kw. So the gas valve could be faulty if your not getting right kw ? or is it something you can adjust like the high and low flame ?

 

[stevie]

Hi , you can set the high and low limits on the gas vales on older boilers to get the correct gas rate, you can't so do this on newer "A" band boilers due to the modi reg.Another cause can be a faulty meter reg supplying to high a pressure, what is your supposed appliance inlet working pressure ?Cheers

 

[Cheech]

Hi i dont have a working pressure its just an example but once on a job asking an engineer to show me how he did a gas rate it was a 37kw new worcester cdi and the kw came up as 44kw when i asked the gas engineer he said that was ok. did not want to quiz him to much abought it but i did not think that was ok.

 

[stevie]

Well he has either not done the gas rate cal right or there are problems with the boiler, 44kw on a 37kw boiler aint right or acceptable .

 

[armourer]

Its not that far out if the calculated 44Kw reading was gross?
Or did he test on Dhw? a lot of boilers run above what they are badged at for Dhw.(by that I mean model number not data plate reading).

 

[Cheech]

Its not that far out if the calculated 44Kw reading was gross?
Or did he test on Dhw? a lot of boilers run above what they are badged at for Dhw.(by that I mean model number not data plate reading).

now you say it armourer when he was doing it the water was on full. I did not know that dhw mode have done that says nothing about that in the books.