# How to heat a cold garage, and why the heater comes last

_Published by CAVE4MAN (https://cave4man.com) — storage, workshop and man-cave kit for UK home garages. The shop has not opened yet; nothing here can be ordered today._

_Updated 2026-09-20 · 10 min read_

**The short answer**

Heating an uninsulated single-skin garage is mostly wasted: the slab, the metal door and the roof lose heat as fast as you make it. Seal the door, insulate the roof and door, get off the bare slab, then heat the person or the corner you work or sit in rather than the room. Never run a fuel-burning heater without ventilation.

**In this guide**

1. [Why the heater is the wrong first purchase](https://cave4man.com/guides/cold-garage-how-to-heat#why-the-heater-is-the-wrong-first-purchase)
2. [Do these before you buy a heater](https://cave4man.com/guides/cold-garage-how-to-heat#do-these-before-you-buy-a-heater)
3. [Heater types, compared honestly](https://cave4man.com/guides/cold-garage-how-to-heat#heater-types-compared-honestly)
4. [Carbon monoxide and ventilation, said plainly](https://cave4man.com/guides/cold-garage-how-to-heat#carbon-monoxide-and-ventilation-said-plainly)
5. [Heat the person, then the bench, then the room](https://cave4man.com/guides/cold-garage-how-to-heat#heat-the-person-then-the-bench-then-the-room)
6. [Heating a man cave: sitting still changes the sum](https://cave4man.com/guides/cold-garage-how-to-heat#heating-a-man-cave-sitting-still-changes-the-sum)

## Why the heater is the wrong first purchase

Most people who ask how to heat a garage have already bought a heater, run it for an evening and been disappointed. A single-skin garage with a metal door and a bare slab is a cold box with a gap round its biggest opening. Heat the air and the air leaves round the door. Stand on the slab and it pulls heat out through your boots. Sit in front of a radiant heater and your front is warm while your back is cold.

None of that is the heater's fault. It is the building. Until the door is sealed and the worst surfaces are insulated, a heater is paying to warm the street, and the bigger the heater the faster it does it. The honest order is: seal, insulate, get off the slab, then heat. Done that way round, a small heater does what a large one could not.

There is a separate guide on insulating a single-skin garage that covers the door, roof and walls in order. This one assumes you have at least read it, and concentrates on what heating can and cannot do, which type suits which job, and the safety rules that are not optional in a small enclosed room with a car and a shelf of aerosols in it.


## Do these before you buy a heater

Every one of the steps below is cheaper than a decent heater and every one makes the heater you eventually buy smaller. The partition is the one people skip. A heavy curtain hung from the ceiling between the car bay and the workshop end turns a double garage into a single room you can actually keep warm, and it comes down in five minutes when you need the space.

A word on the floor. Standing on bare concrete in winter is the reason garages feel colder than the thermometer says. The slab is in contact with the ground, it never warms up, and it conducts heat away from anything touching it, including you. A floating floor of interlocking tiles over the slab, or a mat at the bench, is the difference between an hour in there and an afternoon.

1. **Seal the door** — Brush strip along the top and sides of an up-and-over door and a rubber seal along the bottom. This is the largest draught in the building and the cheapest fix.
2. **Find the other gaps** — Where the roof meets the wall, the eaves, around pipes and cables, and the side door. Mastic and foam close most of them.
3. **Insulate the door and roof** — Foil-faced foam board in the door panels, insulation under the roof. These two change how the room feels more than the walls do.
4. **Get off the slab** — A floating floor, interlocking tiles, or a thick rubber mat where you stand. Cold concrete draws heat out of your feet all day.
5. **Shrink the space you heat** — A curtain across the garage, or heat only the bench end. Half a garage is far easier to keep warm than all of it.


## Heater types, compared honestly

There is no best garage heater, only the right one for the size of the room, how sealed it is and what you want from it. The table groups them by what they are good at and what they cost you in return. Running cost is deliberately not a column: it depends on your tariff, the room and how long it runs, and any figure given here would be a guess dressed up as advice.

Electric is the default for a domestic garage because it burns nothing in the room. The choice between fan, oil-filled and radiant is about what you are heating. A fan heater warms air, which is the thing a garage loses fastest. An oil-filled radiator warms air slowly and steadily and only makes sense once the room can hold it. A radiant panel warms surfaces and people directly and is the one that works in a room that is not yet insulated, because it is not trying to heat the air at all.

Gas and liquid-fuel heaters are in the table because people use them, not because they are recommended. They put out a lot of heat and they need no socket, which is exactly why they turn up in detached garages with no power. What they also put out is water vapour, which condenses on everything cold, and combustion gases, which in a small sealed room can kill you.

| Type | Good for | Downside | Rule |
| --- | --- | --- | --- |
| Electric fan heater | Fast warm-up of a small sealed room | Heats the air, which leaves | Fully unwind any extension reel; never leave it running unattended |
| Oil-filled electric radiator | Steady background heat in an insulated garage | Slow, and useless in an uninsulated one | Keep clear of stored material; not for an unattended night |
| Infrared or radiant panel | Warming the person at the bench without heating the room | Only warms what it faces | Mount clear of anything flammable; switch off when you leave |
| Thermostatic frost-protection heater | Keeping the space above freezing for paint, glue, batteries and the car | Comfort is not the aim | Fixed wiring is an electrician's job |
| Portable gas cabinet heater | Big, fast heat with no mains needed | Burns fuel in the room: water vapour and carbon monoxide | Ventilation is not optional; never in a sealed garage |
| Paraffin or diesel space heater | Heating a large, open, draughty workshop quickly | Fumes, smell, water vapour, carbon monoxide | Vented or outdoor-rated only, door open; never for background heat |


## Carbon monoxide and ventilation, said plainly

Anything that burns fuel in a room — a gas cabinet heater, a paraffin heater, a barbecue, a generator, a car engine — uses up the oxygen in that room and produces carbon monoxide, more of it as the oxygen runs down. Carbon monoxide has no smell and no colour. The first symptoms are a headache and feeling tired, which in a warm garage after a day's work is exactly what you would expect to feel anyway. That is how it kills people.

A well-insulated, draught-sealed garage is precisely the room where this happens, because the work you did to keep the heat in also keeps the gas in. So the rule is short. No fuel-burning heater in a sealed garage, ever. If you use one at all, a door or a window open, and a carbon monoxide alarm on the wall, tested. Never a car engine running inside with the door down, even for a minute. Never any heater, of any type, left running while you are asleep or out.

Electric heaters have their own rules. A fan heater near sawdust, rags or aerosols is a fire; keep the space around it clear. A cable reel with the cable still coiled on it heats up under a fan heater's load and can melt, so unwind it fully every time. And a heater plugged into an extension lead run from the house through a window is a temporary arrangement, not a heating system. The no-power guide covers where that line is.


## Heat the person, then the bench, then the room

The cheapest heat is the heat you do not waste on air. Aim a radiant panel at the bench and you are warm while you work whatever the room is doing. Put a mat or a tiled floor under your feet and the slab stops stealing from you. Wear the layers you would wear outside in that weather, then take one off when the panel is on. That approach works in a garage that is not insulated yet, and it is the right first step because it costs so little to find out.

Once the garage is sealed and insulated, heating the room becomes possible, and an oil-filled radiator or a wall-mounted convector on a thermostat keeps it at a temperature where the tools stop sweating and the glue does not freeze. That is a different goal from being comfortable and it needs far less heat. Cordless tool batteries, paint, wood glue and filler are all damaged by frost, and keeping a garage just above freezing protects them. In an uninsulated garage the answer is to bring those things indoors for the winter instead.

Keep the battery chargers in the heated corner too, or in the house. A cold battery charges badly and a very cold one should not be charged at all. A tool rack with its battery shelf beside the bench, in the part of the garage you actually heat, keeps everything where it works and stops the batteries living on the coldest shelf in the building.


## Heating a man cave: sitting still changes the sum

A workshop forgives a cold garage because you move in it. A man cave does not. People sit still for hours, a film or a game of darts is a long session, and the room has to be somewhere they choose to stay. The order of work is the same as above — seal, insulate, get off the slab, then heat — but the target is higher, because usable with a jumper on is a fair standard for a bench and a poor one for a sofa. If evenings in the garage are the point, insulation is the first big spend, and the sofa comes after it.

Until that is done, the short-session rule still applies: warm the corner, not the room. A radiant panel aimed at the seating warms the people in front of it whatever the air is doing, a rug or a tiled floor keeps the slab off their feet, and the seating goes out of the draught from the door. Heating the whole garage evenly is a job for an insulated one and a heater that runs long and steady.

The problem a heated man cave creates is condensation. A cold garage is often a dry one, because cold air holds little moisture. Warm it up with several people breathing in it and the same air carries far more, and the moment it touches the cold brick, the slab, the steel door or a cold tool it condenses. That is why a garage heated for an evening in January streams down the walls in the morning. The heat did not cause the damp; it moved it onto the surfaces. Ventilate while heating, keep things off the slab, and consider drying the air with a dehumidifier before buying a bigger heater: a damp room feels colder than a dry one at the same reading on the thermometer, and drying the air is the cheaper of the two problems to fix.

Two more rules from the sofa end of the garage. Electric heaters near soft furnishings are a fire risk of their own: a fan heater against a sofa, an oil-filled radiator draped with a jacket, anything running off a coiled extension lead. Keep the heater clear of everything that burns and switch it off when the room empties. And a wood-burning stove, which turns up in a lot of man-cave photographs, is a flued installation with its own rules, not a portable heater, and it is outside this guide.

## Common questions

**What is the cheapest way to heat a garage?**

Not to heat it, at first: seal the door, insulate the door and roof, and put something between your feet and the slab. Then heat yourself rather than the room with a radiant panel aimed at where you work. Heating the whole garage only becomes sensible once it is insulated enough to hold the heat, and even then a small heater on a thermostat beats a large one on full.

**Is it safe to use a gas heater in a garage?**

Not in a sealed one. A gas cabinet heater burns fuel in the room and produces carbon monoxide, which has no smell, plus a lot of water vapour that condenses on everything cold. If you use one, ventilation is not optional: a door or window open, a carbon monoxide alarm fitted, and never while asleep or away. Electric is the safer default for a domestic garage.

**Can I leave a heater on in my garage overnight?**

A portable heater, no. The manufacturer's instructions will say so, and a garage full of timber, rags and aerosols is the wrong place to test it. The exception is a fixed, thermostatic frost-protection heater, installed by an electrician and designed to run unattended, which keeps the space above freezing for paint, batteries and the car.

**Why is my garage still cold with the heater on?**

Because the heat is leaving faster than the heater makes it. A single-skin garage with an unsealed metal door and a bare slab loses heat through every surface, and heating the air in it is filling a bucket with a hole in it. Seal the door, insulate the door and roof, get off the slab, and heat the person rather than the room until that is done.

**What is the best way to heat a garage man cave?**

Seal the draughts and insulate before buying a heater, because an uninsulated single-skin garage loses heat as fast as it is made. Then heat the person rather than the room: a radiant heater pointed at where you sit does more in a short session than warming all the air. Ventilate, and never leave any heater running unattended.

**Why does my garage get condensation when I heat it?**

Warm air holds more moisture than cold air, and when it meets the cold walls, slab and door it condenses on them. Heating a damp, unventilated garage moves the moisture onto the surfaces rather than removing it. Ventilate while heating, keep things off the slab, and consider drying the air with a dehumidifier before adding more heat.

## Kit that does the job

- **Interlocking garage floor tiles** — £59.99, not yet on sale (https://cave4man.com/product/interlocking-floor-tiles)

---

Guide page: https://cave4man.com/guides/cold-garage-how-to-heat