Fitting new cylinder - pipe size?

[tonym]

Hi,

I've moved into a new home and the existing hot water system is 'strange'.
It's a direct cylinder but has been 'converted' to indirect (using the direct cylinder).
The direct feed boiler water connections have been capped off, and an indirect 15mm feed from the boiler (fully pumped) goes into the cylinder where the immersion should be as a sort of heating coil. However, the 'coil' must only be short as only the top 1/5th of the tank gets warm(!).
So I'm going to replace the cylinder with a more modern one, with a much more efficient coil (like the centercyl or similar).

My question is : Is it acceptable to use the existing 15mm pipes from the boiler via adaptors to the 1" coil connections on the new cylinder, or should I replace the boiler pipes with 22mm. The existing system works OK with regards to the pumping of the water so I'm guessing that 15mm would be ok but as I'm an electrician, not a plumber, I'd like a bit of advice about this.

Thanks in advance.
Tony

[DONFRAMAC]

My 210 litre indirect cylinder, ( heated from a 40,000 BThU/hr gas boiler), needs all the flow the 22 mm supply/return boiler pipes can muster, as the shower can turn chilly when the wife uses the hot tap in the kitchen, or the washing M/C takes a slug of hot rinse-water. The tank temperature does recover, but I'm glad that I don't have 15 mm boiler-pipes.

[tonym]

Thanks for your comments.
I'm gonna fit an 85 litre. We all have showers (electric) so only need the hot water for the occasional bath and the washing up.
I'll suck it and see and if it doesn't work, I'll change the pipes.
I'd rather not though cos I replaced the upstairs floorboards before Xmas and would rather not lift them again. However at least that means I know where the pipes run (and I laid th new floor with screws not nails hehe).

I'll be doing it in a few weeks so will post my results here when I've done it.

Wish me luck.

Tony

[tonym]

Well it was more than a couple of weeks since I said I was going to do it.
We had a lot on at work and with one thing or another I had the cylinder in the garage for more than 2 months before I fitted it !

So it's now installed and working a treat.
The 15mm pipes from the boiler are fine. I get a full tank (80 litres) in under 30 minutes with the central heating on at the same time and under 20 minutes with just the hot water on.

So now we can have 2 baths with the water in the cylinder and more ready for another bath by the time the bath is emptied again. And I've been able to turn the boiler temp right down now that the cylinder is mroe efficient.