A small piece of hardware with a big job to do

Few things in a British home work harder than the letterbox. It takes the post in horizontal rain, keeps the February wind out of the hallway, and sits on the front door where every visitor can see it. Yet it is often the last thing chosen and the first thing to be regretted. A plate that looks handsome but rattles, drips onto the mat or refuses to admit a padded envelope will irritate you every single day. Choosing well is not difficult, but it does mean thinking about size, draughts, finish and position before you pick a colour to match the knocker.

Get the size right before anything else

Postal guidance in the UK asks for a minimum aperture of roughly 250mm wide by 40mm high, and for the opening to sit somewhere between 0.7m and 1.7m above ground level. Most domestic plates are sold as 10 inch (about 250mm) or 12 inch (about 300mm), and the outer plate is always larger than the slot itself, so check the internal aperture measurement rather than the decorative size.

• Aperture width and height: A 40mm slot accepts standard letters, but thicker card, board-backed envelopes and small parcels need more. Measure a typical week's post before deciding.
• Door thickness: The sleeve or liner that runs through the door must match its thickness, including any panels or insulation.
• Door type: uPVC and composite doors often need a specific telescopic sleeve or an internal liner, and some composite doors should have the letterbox factory-fitted so the guarantee stays intact.
• Fire doors: A flat entrance door that is a certified fire door must not be cut for a letterbox unless you use an approved intumescent letterplate kit fitted exactly as specified.

If you regularly receive bulky items, be honest about it. A letterbox is not a parcel box, and no amount of clever design will change that. A separate outdoor parcel container or a wall-mounted post box may be the more practical answer.

Draughts, rain and heat loss

A letterbox is a hole in your front door, and an unsealed one can undo a great deal of the insulation behind it. The best plates combine an outward-opening external flap with a brush or rubber seal, plus an internal flap or brush strip to stop the wind that gets past the first line of defence. Double-flap designs cost a little more and are worth it in exposed locations.

Rain matters as much as cold. Water running down the door will find any gap, so look for a plate with a slight drip lip or a hooded profile, and avoid designs where the external flap sits flush against the door with nowhere for water to go. The sleeve itself should be sealed into the door with a bead of suitable silicone or foam, top and bottom, not just around the visible plate.

If you live on a coast or a hilltop, prioritise sealing quality over ornament. A well-sealed, modest-looking plate will serve you far better than a decorative one that sings in the wind.

Finishes that survive British weather

Material matters more than colour. Thin pressed steel with a bright plating is the classic false economy: it flexes, the plating lifts and rust appears within a couple of winters. Better options include:

• Cast brass or bronze: heavy, smooth in operation and beautifully long-lasting. Unlacquered versions develop a patina, which some people love and others do not.
• Stainless steel: grade 304 is fine inland, while grade 316 is the sensible choice within a mile or two of the sea.
• Cast aluminium: light, rust-free and often powder-coated in a range of colours to match composite doors.
• Polished or satin chrome and nickel: crisp and contemporary, but they show fingerprints and water spots, so they need the occasional wipe.

Whatever you choose, match the finish to your handle, knocker, hinges and house numbers. Mixed metals can look deliberate, but only if the tones are clearly different rather than nearly the same.

Where to fit it

The classic position is around 1.2m to 1.4m from the ground, comfortably inside the recommended range and at a comfortable height for the postie. Keep the plate clear of the handle, lock and any door furniture so the flap can open fully, and avoid placing it hard against the frame, where the slot may be partly blocked. On the inside, fit a basket, cage or internal hood: it catches wet post, stops letters landing on the floor and softens the draught.

Think about the route from door to doormat, too. A letterbox positioned above a tiled floor with no basket means soggy envelopes and a permanent cold spot by your feet. A few centimetres of forethought saves years of annoyance.

Fitting and looking after it

Use stainless screws of the right length, and do not overtighten, as this bows the plate and jams the flap. Check the flap falls shut under its own weight, and adjust if it stays open. Every year or so, clean the plate with a soft cloth and a mild soap, lubricate the hinge points with a drop of light oil, and replace worn brush seals, which flatten and stop doing their job after a few seasons. Ten minutes of attention keeps a good letterbox working properly for decades.