width of gas intake pipes

[picasso]

I cant see how there is any confusion, if your installing a boiler you are allowed 1mb drop across the carcass with all other appliances running, it does not matter what the minimum manufacturers allow you to run their boilers at if your doing an install, it only matters when your doing a service or llgc and the boiler cant achieve minimum working pressure.

 

[RickMoore]

Sorry Rick on one line you say that "boiler manufacturer states min 22 mm then that superseeds the regs" but you are arguing about an excess of a 1 mb drop across the carcass is what the the regs state where some manufacturers clearly state in the MIs that they will accept 16mb at the appliance ? I agree that it is a nightmare to get it right but also agree that our only get out clause is to install to Manufacturers instructions and if these contravene GSIUR then make sure it is noted in writing somewhere,

If its a new install then 1mb across the pipework is what's allowed. If the manufacturer says MINIMUM 22mm, they don't mean you can use 22mm so long as inlet pressure is atleast 16mb, you should use larger pipe so that the drop is less then 1mb across the carcass. What you can't do and should be able to IMHO is use 15mm at all. For example, 28kw boiler 1m above the meter, no other appliances connected, no bends or elbows. Calculate it and 15mm is fine to the regs, but according to the manufacturer you can't do it.
If it's a service or LLGS then anything over 1mb drop is NCS provided it meets the manufacturers requirments, and causes no operational issues on any appliances. You can't NCS your own work so the install has to be done correctly.

 

[Dan Robinson]

Ian, in all cases I know of, the 16mBar some MI's refer to is a the reference test point. Not the appliance service valve. Neither does it negate the 1mBar pipe work drop.

 

[bolshy]

The average modern combi uses 2.5 - 3 cubic metres of gas per hour. A 22mm pipe of 8 metres length, assuming the usual 3 elbows off the meter and a couple of machine bends and extra elbows along the way should deliver that amount of gas to the new boiler with a pressure drop of less than 1mb, with NO OTHER APPLIANCES. 15mm is likely too small. If there are other appliances, the gas pipe size may need increasing again to meet current standards. When I go to set a price for replacement gas appliances, I often find the gas pipework is under size - in some cases dangerously so. Most good installers will recognise a possible need to increase gas pipe size just by estimating the distance to and the output of the existing appliances. Checking the inlet pressure at the existing boiler with all appliances at full rate will confirm this. Failing to comply with manufacturers installation instructions is falling at the first hurdle as far as safety and any warranty is concerned. Preventing a gas appliance from operating at it's intended rate can lead to all kinds of combustion problems and flame instability. Why not just do it RIGHT?

 

[joe-90]

Because doing it right costs money and the punter of today doesn't want to pay.