Property: Doctor On The House: Do you blow hot and cold? Shut that door

Were you born in a barn? No? Good - then shut the door. Here are five good reasons for closing doors.

One - heat. Heat is a precious commodity. Internal doors keep it where it is needed. If you leave the doors open the heat goes upwards and outwards. Remember that central heating does not in itself warm the whole house; the term means that one central heat source (boiler or heat exchanger) provides heat that is distributed to the rest of the house via radiators, hot air ducts or whatever. There it ends up as warm air, which has to be kept in place long enough to heat the fabric of the room. Closed doors are vital for the success of the whole operation. If the internal doors are left open the upstairs rooms will get most of the heat, and the downstairs will stay cold, which may lead to ...

Two - condensation. Inside air always contains more moisture than outside air. The extra moisture is produced by people - breathing, sweating, washing, cooking. Keeping the doors shut keeps the moisture where it is produced; it should be allowed to escape only to the outside by opening windows. If you leave the doors to "wet" rooms open you get condensation on cold surfaces all around the house, especially in cold corners downstairs. Is there mildew on your leather jacket when you get it out of the wardrobe? Try closing the bathroom door after you shower.

Three - fire. Even an ordinary timber-panelled door can keep a fire at bay for hours. It stops flames and smoke from spreading and, more importantly, stifles the fire by limiting the air supply. Open the door and - whoosh - a fire can engulf the house in minutes. Modern doors are fire-rated, which refers to the time they can contain a blazing fire - half-hour, one-hour and so on. Old period doors can have their fire ratings increased by attaching fire-resistant boarding on one side, preferable to replacing them with featureless fire doors in converted houses.

Four - noise. Closed doors and windows are surprisingly effective at keeping sounds within rooms. Closing your own internal doors can even help deaden noise from outside and from neighbours. If the doors are open the sound can move around, by reflection, reverberation and resonance and come out in different places, like the openings in a loudspeaker cabinet. Closing doors divides the building up into separate compartments and reduces these effects.

Five - privacy. Until recently doors opened in towards the centre of the room, so someone standing at the half-opened door had a restricted view into the room. Now, concepts of privacy and personal space have changed and doors are generally hinged to open the other way, back against the end wall, offering an uninterrupted view. Funny, that.

Six - er, was there a six? Oh yes, as my old man used to say: "Because I bloody say so!"

You can contact Jeff Howell at the Independent on Sunday or by e-mail on: Jeff@doctoronthehouse.demon.co.uk