Guest House Heating and Hot Water

A good quality light/commercial system boiler,accompanied with suitable sized indirect unvented hot water cylinder with secondary return pipework,this would suitably heat the rooms via panel radiators controlable with thermostatic valves and also allow adequate hot water supply to all bathrooms.

For something of this scale, what I have done in the past is speak directly to the boiler manufacturers, such as Worcester. As they will want you to purchase their goods they provide you with a full heating and hot water plan, boiler and cylinders correctly sized to match your demand. Then you know 100% that is what you need, no worry that your going to have to ammend, or rip out if something is installed that is undersized. Check out this link, and they will get their local rep to come out an measure up for you, all free of charge. https://www.worcester-bosch.co.uk/professional/support/local-contacts

Personally I'd say you will require at more than one unvented cylinder to cope with maximum demand. An 'average' shower uses 60L of hot water so with the recovery time of a cylinder compared to the very low heat loss of modern unvented ones I would recommend 600l of stored water to deal with demand as invariable many of the showers will be in use at a similar time.