Sizing & fitting

Multiply floor area by ceiling height. Multiply again by a room factor: 45 for a living room, 40 for a bedroom, 45 for a bathroom. That's your BTU target.

Add 15% for single-glazed sash windows, 10% for an open chimney, 10% for uninsulated period walls, and 5% for coved ceilings above 3m.

Pipe centres approximately width + 495mm. Floor-to-tapping min. 150mm. Wall-to-centre tapping 88mm on cast iron.

Cast iron is heavy. Fit into masonry with correctly rated fixings. On stud walls, use a horizontal timber batten across at least two studs.

Flush the system, add inhibitor, pressure-test to 1.5 bar. Bleed the top tapping. Balance the flow after a full warm-up.