We fitted a Baxi 825 onto a ground floor system of a larger 3 storey house. It did the UFH, approx 110sqm and also utility/downstairs wc taps. Check with Baxi beforehand and they were happy with the installation. From memory the system was split into 4 zones, each approximately 5kw. Been in for a couple of year and boiler is like new on the annual service. My main concern was if it would modulate low enough but appears fine and flow temp set for about 48 degrees constantly.