Here is the mistake most people make with a cold house: they spend money before they know where the heat is going. New radiators, a smarter thermostat, thicker curtains, all bought on a hunch. The cheaper and far more effective move is to spend an evening finding out where the warmth actually escapes, because the biggest losses are often invisible and rarely where you would guess. This guide is about the hunt, not the fix, and almost all of it costs nothing.
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Two different ways heat leaves a house
It helps to know what you are hunting, because heat escapes by two routes that need different cures. The first is draughts: warm air physically leaking out through gaps around doors, windows, floorboards, the loft hatch and an open chimney, with cold air dragged in to replace it. You feel these as moving air. The second is conduction: heat soaking out slowly through the solid fabric of the house, the walls, the roof and the glass, with no air movement at all. You feel this as a surface that is colder than the room, a wall or window that chills you when you sit near it even though nothing is draughty. A candle finds the first kind. Your hand, and sometimes a camera, finds the second.
The walk-round that finds the draughts
Pick a cold, breezy day, because the pressure difference between a warm house and cold wind outside is what makes draughts show themselves. Turn off any fans and shut the windows, then walk the house slowly with a lit candle, a stick of incense, or just the back of a damp hand. Hold it close to the edges of things and watch. Where the flame leans, the smoke streams sideways, or your wet skin feels a cool line, air is moving through a gap.
Work methodically rather than wandering. Trace the whole frame of every external door, top, sides and especially the bottom. Run along the opening edge of each window and across the meeting rail of any sash. Follow the skirting boards at floor level in older houses. Check the loft hatch, the letterbox and keyhole, any old wall vents, the gaps where pipes and cables pass through outside walls, and the fireplace. Note each one as you go, because you will not remember them all later. The draught-proofing guide covers how to seal everything on that list once you have it.
The rooms and spots where losses hide
Some places leak so reliably that it is worth going to them first. An open, unused chimney is often the single biggest hole in the house, drawing warm air up and out around the clock. The loft hatch is another classic, a small uninsulated panel in the middle of your biggest heat-loss surface. The bottom of an external door, the point where floorboards meet the skirting in a house with a suspended timber floor, and the void behind fitted kitchen units all leak more than their size suggests.
For conduction losses, the usual culprits are a cold solid wall, an uninsulated or under-insulated loft, and single glazing. Run your hand over a large area of outside wall on a cold day: if it feels markedly colder than an internal wall, heat is pouring through it. Do the same at the ceiling of the top-floor rooms, which will feel cold if the loft insulation is thin or has been squashed. Glass almost always feels cold, which is why sitting by a window chills you even with the heating on.
Reading the clues the house already gives you
You do not always need to go looking, because a cold house drops hints if you know how to read them. A room that never quite warms up however long the heating runs usually has either a large unaddressed loss or a radiator problem. Patches of condensation or black mould appear first on the coldest surfaces, so a damp patch in a corner, behind a wardrobe or along a window reveal is pointing straight at a cold spot or a thermal weak point. On a frosty morning, the parts of a roof where the frost melts first are the parts losing the most heat from below, which is a free thermal survey if you glance up at the neighbours' roofs too for comparison.
Inside, a telling test on a winter evening is to turn the heating off for an hour and notice which rooms cool fastest. The quick coolers are the leaky ones. If a particular radiator is cold at the top while hot at the bottom, that is trapped air rather than a fabric problem, and bleeding it is a five-minute job; if a radiator stays cold all over, the issue is elsewhere in the system. Keeping a cheap thermometer in a problem room for a few days tells you more than a vague sense that it feels chilly.
Thermal cameras and phone apps
A thermal camera makes heat loss visible, showing cold walls, gaps around frames and missing insulation as blue streaks on a screen. It is the one tool here that earns its place, and the clip-on units that plug into a phone have come down in price, while some councils and community energy groups lend proper cameras out in winter or run thermal-imaging evenings. If you can borrow one for free, an hour on a cold night will teach you more about your house than anything else here.
Buying one purely for your own home is harder to justify, since you will use it once or twice and the hand-and-candle method already finds the big draughts for nothing. The very cheap phone apps that claim to turn an ordinary camera into a thermal one do not work; genuine thermal imaging needs a dedicated infrared sensor, not a software filter on a normal photo. So borrow before you buy, and treat a camera as a way to confirm and prioritise what your hands have already told you, not as a first step.
Turning what you found into a fix list
Once you have your list, order it by value rather than by how annoying each item feels. The draughts almost always come first, because sealing them is cheap, quick and makes a room feel warmer the same evening at a lower thermostat setting. Next come the cheap conduction fixes for the surfaces you found cold: topping up thin loft insulation, fitting reflectors behind radiators on external walls, and hanging heavier curtains over cold glass. The bigger fabric jobs, insulating solid walls or replacing single glazing, cost far more and belong further down the list, chosen only after you know they are where your worst losses actually are.
The point of the hunt is to spend in the right order. A home energy survey is the formal version of all this, and worth it for a complex house, but an evening with a candle and a cold hand gets most people most of the way for free. Do the finding before the fixing and you avoid the common fate of pouring money into the thing that was easiest to buy rather than the thing that was actually losing the heat.
What I would do first
On the first cold, windy evening of autumn I would light a stick of incense and walk the house in half an hour, writing down every gap the smoke finds, then run my hand over the top-floor ceilings and the biggest outside walls to feel for cold fabric. That alone tells you whether your problem is mostly air leaking out, which is cheap to fix, or mostly heat soaking through solid surfaces, which is dearer and slower. Start the sealing straight away while the list is fresh, and fold the bigger finds into the winter checklist so nothing gets forgotten by the time the weather really turns.