Stuck need some advice...Pipe size?

[BruceRee]

Stuck need some advice recently purchased a property with no central heating. Had a Worchester Bosch 24i junior greenstar Combi boiler installed a few months back opted not to have the radiators installed at the time because of the cost factor. I am a hands on practical guy and have decided to install the radiator system myself. I have done loads of reading up and asking around about the do and don’ts etc but still have some unknowns. I have calculated the total heat loss for the property @ 26827 BTU The boiler flow rate is 9.8l/min, Central heating output Min 7.2kw Max 24KW. I have opted to go for plastic pipe and push fit fittings. I will be installing 7 radiators in total and have decided to go for a feed and return system. I am now stuck at pipe size to use for the system should I be using 22mm pipe throughout and tee off to 15mm copper for radiator connections or should I be using 15mm pipe throughout (Except for 1m copper from boiler before going to plastic) ? Any advice and tips will be greatly appreciated. Thx

 

[glasgowgas]

22mm flow and return with 15mm to rads

but you will get a few "proffesors" telling you about every other size under the sun

22mm f n r 15mm to rads

 

[kevplumb]

well what i would do is

tbf you can put a couple of rads on 15 as long as they ain't huge

or put it another way if its big it costs a few bob more but won't hurt
if its small your up **** creek without the proverbial

 

[doitall]

You can comfortably take 3-4Kw of a 15mm pipe.

The normal practice would to take the 22mm to a convenient position and spit 15mm each way.

 

[kevplumb]

spit 15mm each way.

only if you get a mouth full of flux

 

[bengasman]

As it is a condensing boiler, you can easily stick 8 kw on 15 mm.
How did you installer commission the boiler without rads?

 

[BruceRee]

As it is a condensing boiler, you can easily stick 8 kw on 15 mm.
How did you installer commission the boiler without rads?

On the second day in my new property the boiler packed up and could not be repaired and thus had to fork out a large amount of cash for a new boiler + installation and could not afford to have rads installed at the time specially after putting down a 10% deposit on the new property! Property has storage heaters in and no existing radiators and central heating pipe work! So that is why no rads were installed by Mr Plumber! Central heating circuit was looped by the CORGI Engineer! So now I am fitting the rads 8 months later as a D.I.Y project....

 

[doitall]

22mmm and split it 15mm 50-50 to the rads.

8Kw is too much for 15mm whatever the boiler.

 

[bengasman]

8Kw is too much for 15mm whatever the boiler.

How come when I do it, it works fine? In fact, the only problem I have is trying to get the flow down enough to get my 20 K drop.

Last whole installation I did had 30 kW boiler, and 18 kW in rads if I recall correctly, spread over 2 floors. 22 from the boiler for about 3 metres, and then split in two 15 mm spurs of fairly equal capacity.
All rads get stinking hot and house heats up in no time.

Afaik, the revered tables date from around the fifties when we had open vent back boilers, permanently open bypasses, and half the houses had gravity hot water.

 

[D_Hailsham]

8Kw is too much for 15mm whatever the boiler.

But that's only a velocity of 0.66m/s with a 20°C differential. See Copper pipes in small bore heating systems

Copper Pipes in Domestic Heating Systems is very helpful when designing a system.

 

[bengasman]

Who gives a monkey's? It works a treat, which proves the tables don't mean 5hit.

 

[BruceRee]

Thanx for all the help guys it is greatly appreciated!!! So I am going for 22mm pipe and T off 15mm to rads... Just been looking at each room and finding out which way the joists go so I can work out the easiest pipe run without having to cross over to many joist. Now Should I use compression fittings or plastic push fit fittings? Don’t want any surprise leaks a few weeks down the line once all the floor boards and carpets are back in place!

 

[bengasman]

Only compression fittings where they can be inspected, under floors, in walls and anywhere else where they are invisible, they should be soldered or pushfit.