I want a dual-coil water cylinder for use with a (potential) solar heating system. However there are a few issues...
- I'd like to keep my existing airing cupboard un-cylindered. (We have a Combi that can also be configured to heat a tank.)
- It would be nice to mount the cylinder in the loft
- (Most important) Have you seen how much unvented dual coil cylinders cost!! £1200 when the the same size single coil cylinder from the same supplier is £300!!
So.. what I was thinking, this being the DIY group and all, is of DIY'ing it. But in an unusual way.
I was thinking of using several 3m long 100mm or so PVC pipes to store the water, with screw on endcaps. These would be laid along the joists in the loft to spread the weight (smallish house, so only 120l or so total volume). I was thinking of making a frame or backplate they could be fixed to so they could sort of zigzag at a shallow angle upwards to allow the conventional 'hot draw from the top' to work.
I'd put a loop of copper pipe along the bottom pipe for solar preheat and another loop along the next one up for boiler top up heating. That gives over 5m pipe length in contact with the water, which AFAICS is roughy equivalent to the standard coils in a conventional cylinder. Having it done as a loop keeps the connections all at one end for simplicity.
I could also make a temporary cover to box it all in then use expanding foam to superinsulate it - as much as needed.
So...
- Does anybody not think I'm mad yet?
- Is PVC pipe up to the temperatures and pressures you'd get in an unvented system?
- Any other gotchas?
- If unvented is a no go for whatever reason, could I use this scheme and go vented? It is mainly for central heating use, DHW would still be combi, I think.
Cheers
Paul