Martin Lewis’s 4pm Rule Locks Heat In With Closed Curtains
Martin Lewis's 4pm rule asks households to close all curtains around 4pm to keep daytime warmth inside. Heating expert Ant Langston cites University of Salford estimates of 11-19% less heat loss through windows. Lewis also advises thermal-lined curtains and draught-proofing.
Martin Lewis's 4pm rule locks heat in the home by having households close every curtain at about 4pm. Heating expert Ant Langston of HeatandPlumb.com says University of Salford research estimates 11-19% less heat loss through windows when curtains are drawn.
The habit takes two seconds. It aims to keep leftover warmth from the day inside the house, so people reach for the thermostat later in the evening.
How the rule works
Lewis created the rule to help homes save energy and stay warmer for longer in winter. Closing the curtains at around 4pm seals in residual heat from the day. Less heat escapes, so households are less likely to switch the heating on or turn it up early.
Martyn Fowler, founder of Elite Renewables, called it "a good habit". He said not to get too caught up on the 4pm part. The idea is to close curtains when the sun goes down and the outside temperature starts dropping.
Windows are usually one of the weaker points for insulation. Curtains add an extra layer between the warm room and the cold glass. Fowler said that makes a noticeable difference if you have older double glazing or single-glazed windows.
Langston said the rule "isn't exact". Once the temperature drops and daylight fades, he said, it is a good moment to do some deliberate curtain-drawing.
Getting more from your curtains
Lewis's first suggestion is thermal-lined curtains. They are thicker and better at reducing heat loss than lightweight ones. They should cover the whole window and extend a little beyond the frame towards the windowsill, so no gaps let cold air through.
Watch the radiators. If curtains cover a radiator under a window, warm air gets trapped behind them instead of circulating into the room. Tie back excess fabric to expose the radiator, or choose made-to-measure curtains that sit a couple of inches above it.
Lewis also suggests draught-proofing. Check the seals around windows and doors for obvious gaps.
Moving a lit candle carefully around the frames will reveal leaks. If the flame dances, you can look at re-caulking or using draught excluders.
Langston said not to forget keyholes and letterboxes. He warned against blocking vents that matter for ventilation. He also cautioned against blocking radiators with furniture, because that stops warm air circulating.
Furniture, clothes and even dust on radiators all reduce how well they heat a home. As a guide, keep furniture about 30cm away.
Bigger upgrades and morning sun
For more impactful upgrades, Lewis points to loft insulation. He said it is one of the first things he would check in an older house, because a considerable amount of heat can be lost through an uninsulated roof.
He said curtains should be opened when there is daylight. South- or east-facing windows that catch the morning sun can bring in what he called passive solar gain, which he described as "essentially free heating". The sun heats a home through radiation, and that stops once it sets.
