Expansion tank is it big enough.

[Old Account]

I'd recommend an Plumbing and heating engineer.

 

[Chuck]

Now I have some 22 rads and what with a run to and from the boiler I recon there is roughly about 300 litres in the system.

That seems rather a lot. Between two and three times what I'd expect for a domestic system. DId you measure it by counting buckets when you drained it?

How big was the old expansion tank? If you look carefully inside it you can probably see the high-water and low-water levels represented by rings of crud and corrosion.

 

[Bogart]

Are we not at apples and pears here. Assuming the expansion tank in the loft is for a vented gravity system and the tanks he is looking at are pressure vessels for an unvented sealed system ? although i dont have any trouble sizing vessels in small increments here

No tanks am looking at are for gravity fed system.

 

[Bogart]

Twin 18ltrs.

Did actually think of that still a possibility.

 

[Harvest Fields]

No tanks am looking at are for gravity fed system.

So are you trying to convert the system or trying to keep it as a gravity fed?

 

[Bogart]

That seems rather a lot. Between two and three times what I'd expect for a domestic system. DId you measure it by counting buckets when you drained it?

How big was the old expansion tank? If you look carefully inside it you can probably see the high-water and low-water levels represented by rings of crud and corrosion.

I think I am not too far of the volume. Worked it out by radaiator size and then adding volume in pipework. The boiler is some 15m plus away from the house and feed and return are in 32mm plus there is a fair bit of 28mm and 22mm knocking about soon adds up. Old expansion tank was I reckon a good 100 litres minimum has been at the tip for weeks so no chance of looking at levels.

 

[Bogart]

So are you trying to convert the system or trying to keep it as a gravity fed?

Keeping as gravity fed.

 

[Chuck]

I think I am not too far of the volume. Worked it out by radaiator size and then adding volume in pipework. The boiler is some 15m plus away from the house and feed and return are in 32mm plus there is a fair bit of 28mm and 22mm knocking about soon adds up. Old expansion tank was I reckon a good 100 litres minimum has been at the tip for weeks so no chance of looking at levels.

Fair enough. As a rule of thumb, you want 10 cm depth of water in the FE tank when the system is cold and then space for an additional 5% of the system water to expand into. So, by this method you would need a bit more than 18 litre.

Polytank, for example, do 55 litre rectangular tanks in three shapes:

RECTANGULAR

I'd consider a single tank as a nicer solution than two 18 litres linked into a pair. The footprint will be smaller and easier to install and insulate.

The fact that the previous tank was 100 litre suggests that the previous installer decided (or discovered!) that a standard 18 litre (4-gallon) FE wasn't big enough.

[Afterthought: Check before buying that Polytank approves use of their rectangular tank as a CH FE application. I'm 99% sure they're suitable, but I can't find it explicitly specified on the website.]

 

[Bogart]

Strangely enough I had seen their tanks before online and at the back of my mind thought might be the solution. They have today confirmed suitable, suppose is obvious as they supply the B and Q feed and expansion tank.