Can I use 22mm from hot water supply tank?

[zetland76]

My old galvanized tank is about 3 feet above the hot water cylinder which it supplies by a 28mm pipe. The hot from the cylinder is taken from the cylinder on a 22mm pipe. I am replacing the tank with a plastic one in the loft (about 6 feet above the cylinder), can I use 22mm feed?
The fittings and pipe work are considerably cheaper in 22mm than 28mm, and if the outlet is 22mm what's the point of feeding the cylinder with a 28mm pipe?

Thanks

Mike

 

[BingoBongo]

My old galvanized tank is about 3 feet above the hot water cylinder which it supplies by a 28mm pipe. The hot from the cylinder is taken from the cylinder on a 22mm pipe. I am replacing the tank with a plastic one in the loft (about 6 feet above the cylinder), can I use 22mm feed?
The fittings and pipe work are considerably cheaper in 22mm than 28mm, and if the outlet is 22mm what's the point of feeding the cylinder with a 28mm pipe?

Thanks

Mike

you have answered your own question in the first sentence

 

[bengasman]

Maybe the original installer/designer was looking at ways to reduce his profit, or he had shares in the plumber's merchant.

 

[kirkgas]

in the original install the tank was only 3' above the cylinder so 28mm was the correct (not cheap) way to do it, but if you are doubling the head of water pressure then dropping to 22mm will be fine, try to keep bends to a minimum as 6' head is ok if tank is as near above cylinder as possible, you will have problems if tank is 6' above then several feet to the side as the horizontal pipework could kill the pressure.