Converting to a sealed/pressurised central heating system-Expansion vessel size

[firebladerrw]

Does anyone have a link or could assist with assessing size for the expansion vessel? It doesn't look as though it'd be too expensive.

My boiler can be used in a pressurised system, and I'm keen to convert to a sealed system to stop air getting into rads, see my other post.

I've got 12 radiators, of which 3 are towel radiators, the rest are usual mix for bedrooms, living room etc. It's a 4 bedroom house.

Any help would be appreciated.

 

[oldbuffer]

1. Theoretically, 104% of the volume of the water in the system. In practice, a 12litre vessel is fine for all but the larger systems.
2. Be aware that pressurising the system can cause leaks in pipes / radiators / fittings, for example if are already thin through corrosion. Chances are small, but it can happen.
3. You'll need the expansion vessel, pressure relief valve and filling loop. You can get it all as a kit, e.g. http://www.advancedwater.co.uk/prod-014-146-0122.html

 

[firebladerrw]

1. Theoretically, 104% of the volume of the water in the system. In practice, a 12litre vessel is fine for all but the larger systems.
2. Be aware that pressurising the system can cause leaks in pipes / radiators / fittings, for example if are already thin through corrosion. Chances are small, but it can happen.
3. You'll need the expansion vessel, pressure relief valve and filling loop. You can get it all as a kit, e.g. http://www.advancedwater.co.uk/prod-014-146-0122.html

Thank you for that. Many of my radiators have been swapped out, but understand risk of leaks etc.

Last question; for space reasons, I'd like it fitted in the loft where the current F&E tank is, would that pose any problems?

 

[winston1]

Air should not get into your radiators anyway. I've never had that problem in 30 years of open systems.

Are there any advantages of a sealed system? You lose the header tank and have an expansion vessel etc, so what.

 

[firebladerrw]

Air should not get into your radiators anyway. I've never had that problem in 30 years of open systems.

Are there any advantages of a sealed system? You lose the header tank and have an expansion vessel etc, so what.

Thanks for your input, but I have had issues with air getting into the system. You're lucky I guess.

So back to my question.....

 

[Mottie]

Thank you for that. Many of my radiators have been swapped out, but understand risk of leaks etc.

Last question; for space reasons, I'd like it fitted in the loft where the current F&E tank is, would that pose any problems?

Our one is fitted in the loft where our old F&E tank was fitted but the filling loop and gauge are fitted in the airing cupboard downstairs where it is easy to access. I did have two radiators spring a pinhole leak after the conversion to a sealed system but they were nearly 50 years old!

 

[firebladerrw]

Our one is fitted in the loft where our old F&E tank was fitted but the filling loop and gauge are fitted in the airing cupboard downstairs where it is easy to access. I did have two radiators spring a pinhole leak after the conversion to a sealed system but they were nearly 50 years old!

Thanks for that, sounds encouraging!

 

[John D v2.0]

Does anyone have a link or could assist with assessing size for the expansion vessel? It doesn't look as though it'd be too expensive.
d.

If you Google there are formulas for working it out especially if you know system volume, but as above 12l is probably fine.
You can measure the expansion by measuring your feed expansion tank water surface area and then the change in depth from cold to hot. Then multiply by cold pressure over 3 bar to get the minimum required volume.
But being honest there's no down side of oversizing other than cost and space, so go bigger.

 

[firebladerrw]

If you Google there are formulas for working it out especially if you know system volume, but as above 12l is probably fine.
You can measure the expansion by measuring your feed expansion tank water surface area and then the change in depth from cold to hot. Then multiply by cold pressure over 3 bar to get the minimum required volume.
But being honest there's no down side of oversizing other than cost and space, so go bigger.

Thanks mate, I'm going to get the Altecnic 18 litre kit, which has the expansion vessel, pressure gauge, pressure relief valve and filling loop with n/r valve.

My loft is easy access, so going to keep it all up there. My GS mate reckons using the existing f&E tank feed pipe will be fine, and capping off the expansion pipe lower down. CW mains to the existing tank can be used for the filling loop. It's all 15mm.

 

[Phill Peck]

You will need to check and set the pressure in the vesssl correctly.
Don’t assume it’s correct.

How do you intend running your discharge from the loft?

 

[John D v2.0]

The loft is a good place because it'll be your highest point in the system so it will need no cold static pressure. As above check the vessel pressure before filing the system, but being honest you can just leave it at 0.1bar or so and just charge the system to 0.3 bar at loft level. That should give you around 1 bar at the ground floor radiator pipework and still maximum expansion space in the vessel. Your pump head should be 0.25 bar

 

[Phill Peck]

The loft is a good place because it'll be your highest point in the system so it will need no cold static pressure. As above check the vessel pressure before filing the system, but being honest you can just leave it at 0.1bar or so and just charge the system to 0.3 bar at loft level. That should give you around 1 bar at the ground floor radiator pipework and still maximum expansion space in the vessel. Your pump head should be 0.25 bar

I’ve had loads of expansion vessels come out with between 3&5 bar in them.

 

[John D v2.0]

I’ve had loads of expansion vessels come out with between 3&5 bar in them.

maybe that's from their testing in the factory

Although I'd expect them to test with water rather than air, you wouldn't want to be around if it blew with air in it!

 

[firebladerrw]

Picture of f&e tank in loft, intention is to use 22mm copper for pressure relief line using same cut out in soffit.

The pump is around 3M below the f&e tank.

 

[John D v2.0]

Picture of f&e tank in loft, intention is to use 22mm copper for pressure relief line using same cut out in soffit.

That's fine even in 15mm, just make sure it doesn't go uphill and supported properly and it terminates somewhere safe where it can't spray anyone below with boiling water! I think you can get a special end to disperse any discharge if you can't easily get it within a couple of feet from the ground