Pipe size to combi boiler question

[mylesy]

pressure is highest at the meter so 22mm connections is fine, obviously the further away you get reistance will reduce the pressure. so 28mm going on 22mm at meter is fine.

 

[GrahamM]

you can run a 24kw boiler on a 30m equivelent pipe run (actual pipe length + 0.5m per bend)

Been a while since I done sizing and I may be a bit rusty, but the average 24KW boiler I see on a daily basis consumes 2.5-2.6m³/hr of gas. So how can you run 30m of 22mm pipe plus elbows and supply the gas required at max rate to the boiler.

 

[stani]

24kw gross input = 2.21cu/m gas total 30metres == 1mb drop over the length

 

[GrahamM]

24kw gross input = 2.21cu/m gas total 30metres == 1mb drop over the length

Bear with me here. Had a few tonight. Worc. 24i Junior. (quite an average boiler I think) requires 2.6m³/hr of gas at max rate. 30M of 22mm pipe will only supply 2.3m³/hr of gas. Even without bends that reduces the rate further this does not go!!!
Am I getting confused here?

 

[stani]

sorry mate I am being a lazy get, and using an iPhone app to work out rates, 2.6m3/hr works out at 28.29kw it might be that the manufacturers give different figures to what the iPhone works out, perhaps someone else can throw some light on this.

 

[GrahamM]

2.6m³/hr is the MI stated figure for the Greenstar junior. Not some approx calculation. So obviously we should be taking the Manufactures published figures and sizing accordingly? That being said 20m of 22mm + handful elbows would be the max length we should run. Not taking into account any extra load for cooker etc.

 

[helix]

Agreed with GrahamM. The BG man 's suggestion is appropriate and it looks like the cost of up grading supply pipe is substantial, unless the distance between gas meter and boiler is less than 10m away, taking into account elbows and a gas cooker in the flat!

 

[kirkgas]

??? Scottish special ??? lol

No offence Kirk :wink:

tam i'm even older than that remember SSHA and the yellow and black vans, went to supervise the gas work out at the old depot at Mayfield many times

 

[kirkgas]

Been a while since I done sizing and I may be a bit rusty, but the average 24KW boiler I see on a daily basis consumes 2.5-2.6m³/hr of gas. So how can you run 30m of 22mm pipe plus elbows and supply the gas required at max rate to the boiler.

to calculate consumption you multiply max HI by 0.094 (24x0.094= 2.256m3/hr) my post said you can get this gas from an equivelent 30m length (which INCLUDES ALL BENDS @ 0.5m per bend) which i took from the tables in BS6891

 

[GQuigley67]

Im goin to see the job tonight i will let u know

 

[SafeGasInstall]

well done

 

[GQuigley67]

I checked out the job today, there is no way of actually knowing the exact pipe length and how many bends, I'd say total length in the region of 25-30m, but I checked out the existing boiler and was getting 2.25 m3/hr at the boiler, and with the boiler and hob running I was getting around 2.8 m3/hr with the hob being 0.6m3/hr with 3 burners on, there is a possibility of replacing around 3m of 22mm with 28mm in the flat which could help with any pressure loss issues.