width of gas intake pipes

[Mignonnette]

I'm getting my gas boiler replaced. The current intake pipes are 15mm. Distance of boiler from meter is about 8-10 metres. I'm getting conflicting info: British Gas salesman says all pipes must be 22mm because the intake on new condensing boilers is 22mm. Two of independent engineers say yes this is right. Two others say no, that's just how British Gas make money out of people.

Who's right please? Is it 1. illegal 2. dangerous to have a boiler with 22mm intake fitted to 15 mm pipes?

Or is it in fact possible to get boilers with 15mm intake? I was told they no longer exist. Is this true?

Many thanks for any help, am going round in circles on this.

 

[Dan Robinson]

Depends on the boiler output.

I think BG are offering Worcester Bosch and it states in their manual (as do a lot of others) that the incoming supply must be no smaller than the connection on the boiler.

Ultimately though the power of the boiler determines the amount of gas it needs. The amount of gas the pipe can provide is a product of length and number of fittings.

 

[Biggles..]

Like Dan has said lots of boiler manufacturers now stipulate the gas supply to the boiler should be no smaller than the inlet connection.
WB being 22.

You then have to size it based on length and fittings.

If you want to keep your 15mm look at ideal/Vaillant they have a 15mm inlet but then it could still need some pipe upgrading anyway.

 

[ianmcd]

As you have been correctly advised it all depends on which boiler but most combis will require at least part of the supply to be at least 22mm (if not all of it) at that length, if it is just a system boiler and not a large one it might be possible to be left in 15mm, we need more info on the proposed appliance to give you an exact yes or no

 

[Mignonnette]

Thanks, the guy is installing a Vaillant and he is saying that the boiler I need (1 bedroom flat) doesn't need the increased capacity that 22mm pipes would provide so from what you all say it looks ok.

I'm female by the way, guys are born knowing stuff like this, I thought?

 

[Dan Robinson]

Thanks, the guy is installing a Vaillant and he is saying that the boiler I need (1 bedroom flat) doesn't need the increased capacity that 22mm pipes would provide so from what you all say it looks ok.

I'm female by the way, guys are born knowing stuff like this, I thought?

Unless they're called Joe, natch. Mustn't feed the troll.

Do you know the exact model?

For every 90 degree bend or tee connection you have to add ½m of pipe (equivalent length).

SO - you don't have a lot to play with. If you have the gas metre right under the boiler you might get away with it.

Most Vaillants have a 15mm inlet. So it boils down to gas pressure at the boiler.


*edited* Schoolboy error.

 

[Tibbot]

A pipe sizing calculation is mandatory with the work you're having done. The result will determine what's required.

 

[Mignonnette]

Well the current Potterton combi which has just expired at 14 years of age has been fine. It's about 8 m from the gas meter to the boiler. I don't know what model Vaillant he is thinking of, I will have to check.

And btw BG are offering Bosch for rich people or Potterton for the rest of us.

 

[Dan Robinson]

If you are talking Combi's then the smallest will be 24kW.

You have no chance of fitting it to 8m of 15mm.

 

[Dan Robinson]

If we say 8 metres of pipe, with a measly 4 elbows then your pressure loss will be over 2mBar. Too much.

If you up the size to 22mm then it will be fine. Not taking into account any cookers or fires.

4 bends is also a lot less than you probably have.

 

[Mignonnette]

so how come the combi I have had for 14 years has been ok? Is this because the new one is a condenser.

Part of the pipe is 22mm but we don't know how much because it disappears under the floorboards.

Have a gas hob but nothing else, no fires.

 

[Dan Robinson]

Has any one measured the pressure at the old boiler with it running full tilt?

Lots of boilers back then were put in incorrectly.

If the pipe is 22mm all the way under the floor to the boiler and reduces to 15mm just underneath then it might well be fine.

You'd be surprised how much gas a hob can consume.

 

[BertieGas]

If the instructions say the pipe must be 22mm then anything less would have to be labelled as sub standard. I often run a new 22 pipe and leave the old 15 pipe in and connect them together below the boiler for a bit more gas supply I lose loads of quotes when I tell people it needs a new feed from the meter to the new boiler. They get someone to do it who says it doesn't matter and pay the price later.

 

[Mignonnette]

don't know if anyone ever measure the gas pressure with the boiler running. Having said that, the pipes were new 14 years ago, this was a new conversation when I bought it from a housing association, so I would guess they stuck to the regulations but spent not a penny more than they needed to.

don't know to be honest where the pipe reduces to 15 mm.

 

[Dan Robinson]

Now that feeling Bertie.

Really annoying when that happens.