I'm in the process of converting part of my house into a holiday let but have had 2 different solutions suggested on how to heat and provide water to both properties. I only have oil as the fuel option. 1 plumber has quoted for 2 separate boilers; one is a system boiler to replace our current one in the main home, which we were going to do anyway because it's very old, and a second boiler - combi - in the holiday let as space is very limited in there for HW tank etc. This gives 2 completely separate heating and water systems. The other plumber has suggested one big system boiler and a mains pressure hot water cylinder (all located in the main house) for both properties with various zone valves etc to effectively make heating and water controllable from each property. The quotes are fairly similar so I'm unsure but leaning slightly towards the mains pressure tank solution as I also have a oil fired Rayburn which is on all the time and is currently providing all our hot water so I'm assuming that could also be connected to the mains pressure cylinder to supplement the heating for hot water and central heating? Any advice on which way to go would be much appreciated, thanks.
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My preference would be the "other plumber". But is there any reason to go for a mains pressure hot water cylinder? If you already have a conventional HW cylinder (fed from the main storage tank) and it's OK, perhaps you only need to change the boiler.
the current hw cylinder is too small to do both properties so ideal opportunity to swap it out but just wasn't sure if mains pressure cylinder was the way forward
I wouldn't know, sorry, but sounds like your plumber is OK with it. It has advantages, like mains pressure to shower, but doesn't give a store in event of mains failure, and probably has more instrumentation and needs more inspection/maintenance. A friend of mine in St. Albans installed one a few years ago and he's happy with it.
Thanks for all the replies, it's looking like the consensus is a big system boiler with mains pressure hw tank rather than a combi
You can have your oil boiler as a cheaper option, by not opting for a system boiler, but purchasing the non system boiler and adding sealed systems components (expansion vessel, filling loop, etc) outside the boiler. The filling loop could be installed at the unvented cylinder.
It doesn't have to be a system boiler (with built-in pump a expansion vessel). As it's an old set-up you probably have a F/E tank in the loft, and an external pump, which could be re-used, with a regular boiler. But if the cold feed is to the boiler return, don't forget to re-pipe it - boiler, open vent, cold feed, pump!
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