I need to replace a Fortic cylinder that has 2 immersion heaters (there is no boiler). This is in my Mother's 1 bedroom small flat. I want to use an unvented cylinder with power from an off-peak supply. There is no gas in the flat, and just bath, basin and kitchen sink need to be supplied. I have good experience of a 'Hotflo' feeding a single basin, but need something bigger.
Any ideas on what capacity and manufacturer please? She does not use a lot of hot water.
Just buy the biggest she can fit in the space (within reason) if she has Economy 7. Then she'll never have to use peak rate boost.
I doubt, however, it is worth going over 200 litres, if you say she doesn't use a lot. You could get away with a lot smaller if there wasn't the space, although a 130 litre will only supply one bath and washing up water before needing peak boost.
Installation of an unvented HW cylinder comes under part G of the Building Regulations. This is concerned with hygiene and in this case with safety. The requirement is that such a cylinder be installed by a qualified plumber or heating engineer with acreditation for installation of sealed cylinders. It is also a requirement for them to be serviced annually. In other words this is not a DIY job
However, the part G requirement only applies if the volume of water stored under pressure exceeds a certain limit (45 litres I believe). Thermal stores can have the bulk of the water in the cylinder open vented and avoid the volume rule. In that scenario, only the heating circuit (which heats the cylinder through a coil) and the mains water being heated re under pressure and the rules don't then apply. You can also have a direct thermal store where there is no coil and the heating and cylinder water are open vented. These can be a DIY job
There is a further Building Regulation, Part L which has to do with energy conservation. This applies to all cylinders and heating systems. A professional fitter such as plumber/heating engineer (above) or CORGI person can self certify such installations. If you DIY, you can apply to the local authority for a Building Notice to notify the work to them. In all probability, they will collect your money and file the paperwork and you won't hear from them again.
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