New Hot water cylinder - connection height query

[bhm1712]

Im looking into buying a rapid recovery cylinder for my old gravity HW system. Im having a few problems identifying standard connection heights.

All the ones i have found say that for the 117 litre cylinder, the lower coil connection is 100mm from the base and the top coil connection is 400mm. The cylinder i have at the moment is a 23 year old "crown brand" and although the top connection measures in at 400mm from base to centre of the connection, the lower one seems to be 95mm to centre, not 100.

Has the 100 and 400mm always been a standard height for the coil tappings?

 

[HERTS P&D]

When changing cylinders there is always adjustments to pipe work.

Andy

 

[mickyg]

Im looking into buying a rapid recovery cylinder for my old gravity HW system.

i wouldnt do that if i were you

 

[D_Hailsham]

Im looking into buying a rapid recovery cylinder for my old gravity HW system.

I wouldn't do that if I were you

I think the OP may mean gravity fed, i.e there's a cold water tank in the loft feeding the HW cylinder, not a "gravity" primary system.

 

[stardanny]

Rapid recovey cylinder is not suitable for gravity primary hot water. Only for fully pumped system.

All cylinders vary in size so a small pipework change need to fit it.

Dan.

 

[JohnD]

Rapid recovery cylinder is not suitable for gravity primary hot water. Only for fully pumped system.

Why?

 

[stardanny]

Rapid recovery cylinder is not suitable for gravity primary hot water. Only for fully pumped system.

Why?

Because rapid recovery cylinder has muiti-coils inside which is small bore and requires the primary circuit to be fully pumped.

Dan

 

[bhm1712]

The one ive been looking at doesnt say whether it is suitable for gravity systems but when i phoned up and spoke to one of the engineers he said he always fits them to gravity primary HW systems when the customer does not want to upgrade the boiler due to the faster heat up time over normal cylinders. He actually said that its ideal for this situation as gravity system usually takes 60mins + to get to temp and a fast heat recovery one makes it alot quicker.

http://www.mcdonald-engineers.com/fastheat.html

 

[JohnD]

If you are going to the trouble of fitting a new cylinder, I would recommend that you also consider converting to fully pumped. The pump will improve heat-up time a lot.

Or at the very least fitting a cylinder stat if you do not already have one. it will improve economy, especially in summer.

(The cylinder in the link looks like it has an ordinary bore coil)

 

[bhm1712]

i have a cylinder stat, i converted to C plan a couple of years ago.

i dont plan on staying here for more than a couple more years and so cannot justify having a new boiler, or modding the system extensively. I thought paying out £250 for the cylinder and fitting it myself would be ideal for this situation. I must admit though, looking at other manufacturers rapid recovery cylinders they all state fully pumped. Maybe im being mislead for a quick sale?

 

[stardanny]

The one ive been looking at doesnt say whether it is suitable for gravity systems but when i phoned up and spoke to one of the engineers he said he always fits them to gravity primary HW systems when the customer does not want to upgrade the boiler due to the faster heat up time over normal cylinders. He actually said that its ideal for this situation as gravity system usually takes 60mins + to get to temp and a fast heat recovery one makes it alot quicker.

http://www.mcdonald-engineers.com/fastheat.html[/QUOTE]

Bit small for 117 litres at 630mm x 400mm. Look like it got 22mm primary might need to be fully pumped.

This is not a rapid recovery cylinder, just a cylinder with high effIcient coil.

If you want 117 litres a 900mm x 450mm cylinder will do.

Dan.

 

[bhm1712]

yeh, the one in the pic is the bog standard smallest size, but they do all other sizes. The one im after is the 117litre 900 by 450mm.

I will ring up and verify this tomorrow as i dont want to order something that wont work with my system.

 

[mickyg]

there's a fair chance if you install a high recovery to a gravity circuit that it won't work properly, and at the very least won't make any difference and may even make it slower. For high recovery cylinders to work properly it needs a decent flow of water through the coil, that wont happen with gravity. Dont waste your money. You ideally want with the smallest rated coil you can find, so the circuit can circulate well with less restriction

 

[JohnD]

but surely we have established that the cylinder he is looking at, is not really a high recovery, as it seems to have a coil of big tubes?

 

[transam]

Were is the cylinder in relation to the boiler ??