What Size Heater Do I Need?

Choosing the right size heater is one of the most important parts of buying an electric heater.

If the heater is too small, it may run constantly without making the room feel warm enough. If the heater is too powerful for the space, it may be unnecessary, harder to control and less suitable for everyday comfort.

The right heater size depends on the room size, insulation, ceiling height, how cold the space gets, how quickly you need warmth and whether you are heating a bedroom, office, garage, workshop or industrial unit.

This guide explains what size electric heater you need, how to compare wattage and kilowatt output, and which CoolEasy heater range is best suited to different spaces.

You can also browse our portable heating units, view our 3kW and below portable heaters, or compare higher output options in our industrial portable heater range.

As a simple starting point, smaller rooms usually need a heater between 1.5kW and 2kW, while garages, workshops and larger spaces often need 3kW, 5kW or more.

For industrial and commercial spaces, heater size can increase significantly. Larger workshops, warehouses and industrial units may need 9kW, 15kW or 30kW heaters, especially where the space is poorly insulated or has high ceilings.

The table below gives a practical starting guide.

Heater Output	Typical Room Size	Best For
1.5kW	Small rooms and personal spaces	Bedrooms, small offices, desks and occasional top up warmth
2.0kW	Small to medium rooms	Home offices, spare rooms, lounges and garden rooms
3.0kW	Medium rooms, garages and workshops	Colder rooms, garages, workshops and practical spaces
5.0kW	Larger workshops and small commercial spaces	Workshops, garages, storage rooms and unheated work areas
9.0kW	Large workspaces	Industrial units, workshops and commercial environments
15.0kW	Large industrial areas	Warehouses, factories and demanding workspaces
30.0kW	Very large industrial spaces	Large warehouses, industrial units and high demand heating

This should only be used as a guide. A well insulated bedroom is much easier to heat than a draughty garage of the same floor area.

Heater Wattage Explained

Electric heater size is usually shown in watts or kilowatts.

1 kilowatt is the same as 1,000 watts. So a 2kW heater is a 2,000 watt heater, and a 3kW heater is a 3,000 watt heater.

The higher the kW rating, the more heat the heater can produce at full output. However, bigger is not always better. The right output depends on the space you are heating.

Rating	Same As	What It Means
1.5kW	1,500 watts	Compact heat for smaller rooms and personal spaces
2kW	2,000 watts	Popular domestic size for small to medium rooms
3kW	3,000 watts	Stronger output for workshops, garages and colder rooms
5kW	5,000 watts	Higher output for larger workspaces
9kW plus	9,000 watts plus	Industrial heating for larger commercial spaces

A heater’s wattage tells you its maximum heat output, but it does not tell the whole story. Insulation, draughts, ceiling height and how long the heater runs all affect how warm the space will feel.

Quick Heater Size Guide By Room Type

The easiest way to choose a heater is to start with the type of room you are heating.

Room Or Space	Recommended Starting Point	Suggested Range
Small bedroom	Compact portable heater	1.5kW to 2kW
Home office	Portable electric heater	1.5kW to 2kW
Living room	Portable heater or fitted system	2kW or heating and cooling system
Conservatory	Portable heater or fitted heating and cooling system	2kW to 3kW, or fitted system for regular use
Garden office	Portable heater or heating and cooling system	2kW to 3kW depending on insulation
Garage	Workshop heater	2kW to 5kW depending on size and insulation
Workshop	Workshop or industrial heater	3kW to 5kW plus
Warehouse	Industrial heater	9kW, 15kW or 30kW

If you are heating a normal domestic room, start with the domestic portable heater range. If you are heating a garage, workshop or warehouse, look at more rugged workshop and industrial heaters.

What Affects Heater Size?

Room size matters, but it is not the only thing that affects heater choice.

Before choosing a heater, consider the following factors.

Room Size

A larger room needs more heat than a smaller room. This is usually the first thing to consider when choosing heater wattage.

However, two rooms with the same floor area may need different heaters if one is well insulated and the other is cold, draughty or has more external walls.

Ceiling Height

Higher ceilings mean there is more air to warm. A room with a high ceiling may need more heater output than a standard room with the same floor size.

This is especially important in workshops, warehouses, industrial units and converted spaces.

Insulation

Insulation makes a huge difference.

A modern insulated home office will usually need less heating than a garage, conservatory or workshop with the same floor area. Poor insulation means heat escapes faster, so the heater has to work harder.

Draughts

Draughts make rooms harder to heat. Gaps around doors, windows, garage doors and poorly sealed walls can allow warm air to escape and cold air to enter.

If a space is draughty, you may need a more powerful heater, but it is also worth reducing draughts where possible.

How The Space Is Used

A heater used for occasional top up warmth is different from a heater used every day.

If you only need to warm a room for short periods, a portable heater may be enough. If the room is used all day, every day, you may want a more efficient long term solution, such as a fitted heating and cooling system.

Power Supply

Smaller portable heaters can usually plug into a standard socket. Higher output industrial heaters may require a suitable electrical supply, especially three phase models.

Always check the power requirements before buying a larger heater.

What Size Heater For A Bedroom?

For most bedrooms, a compact 1.5kW to 2kW heater is a sensible starting point.

Bedrooms usually need a heater that is easy to control, safe to position and not oversized for the space. You are normally looking for gentle top up warmth rather than industrial level heat.

A small bedroom may only need a compact personal heater, especially if the room is already insulated and only needs extra warmth during cold mornings or evenings.

For bedroom use, consider:

Room size
Noise level
Thermostat control
Safety features
Where the heater will be placed
Whether the room is used occasionally or every night

Good starting options include the Glaziar 1.5kW Globe Personal Heater and the Glaziar Portable 2kW PTC Heater.

What Size Heater For A Home Office?

A 1.5kW to 2kW portable heater is usually a good starting point for a home office.

Home offices are often smaller rooms where you spend long periods sitting still. Because you are not moving around much, the room can feel cold even when the rest of the house is comfortable.

A portable heater can be a practical choice because it lets you heat the room you are using rather than turning up the whole heating system.

For home offices, look for:

Compact size
Easy portability
Thermostat control
Stable placement
Enough output for the room
A style that suits the room

The 3kW and below portable heater range is a good place to start for home offices and small rooms.

What Size Heater For A Living Room?

For a living room, a 2kW portable heater may be suitable for top up warmth in a small or medium space.

If the living room is larger, open plan or used every day, you may need to think beyond a small portable heater. A fitted heating and cooling air conditioning system can be a better long term choice if you want both winter heating and summer cooling.

For living rooms, consider:

Floor area
Ceiling height
Open plan layout
Number of external walls
How often the room is used
Whether you also need cooling in summer

If you only need occasional extra warmth, browse portable heating units. If you want an all season solution, browse heating and cooling systems.

What Size Heater For A Conservatory?

Conservatories are often harder to heat than standard rooms because they usually have more glass and can lose heat quickly.

A 2kW heater may be suitable for a small conservatory used occasionally, but a colder or larger conservatory may need more output. If the space is used regularly, a fitted heating and cooling system may be more comfortable and practical.

When choosing a heater for a conservatory, think about:

How much glass the room has
Whether the roof is insulated
Whether the room has draughts
How often you use the space
Whether it gets too hot in summer as well as too cold in winter

If the conservatory is uncomfortable in both summer and winter, a heating and cooling system may be a better solution than a heater alone.

What Size Heater For A Garden Office?

For a garden office, a 2kW portable heater is often a good starting point, but insulation makes a major difference.

A well insulated garden room may warm up quickly with a compact heater. A poorly insulated cabin, shed office or garden building may need a more powerful heater or a fitted heating and cooling system.

For garden offices, consider:

Wall, roof and floor insulation
Window quality
How long you work in the space
Whether the room is used all year
Whether you need cooling in summer
Whether you want a portable or fitted option

If the garden office is used daily, a fitted heating and cooling system may be worth considering because it can heat in winter and cool in summer.

What Size Heater For A Garage?

Garages usually need more heat than a normal room because they are often poorly insulated, draughty and colder to begin with.

For a small garage or occasional hobby use, a 2kW workshop heater may be a useful starting point. For a larger or colder garage, a 3kW or 5kW heater may be more suitable.

A garage heater should be practical, rugged and suitable for the environment. A small domestic heater may struggle if the space is cold, uninsulated or used with doors opening regularly.

For garage heating, look at:

Garage size
Insulation level
Door draughts
How quickly you need heat
Whether you are heating people, tools or the full space
Whether a fan heater would circulate warm air better

The Olympus 2.0kW Portable Fan Heater for Garages and Workshops is a good starting point for smaller garage spaces, while larger garages may need a 3kW or 5kW heater.

What Size Heater For A Workshop?

Workshops usually need a heater with stronger airflow and a more practical design than a standard home heater.

A 3kW heater is a useful starting point for many small workshops. Larger or colder workshops may need 5kW or more.

For workshop heating, think about:

Floor area
Ceiling height
Insulation
Door openings
How many people use the space
Whether heat needs to reach one workbench or the whole area
Available power supply

Good workshop options include the Olympus Pro 3.0kW Workshop Heater, Trotec 3.0kW TDS 20 R Electric Fan Heater and Trotec 5.0kW TDS 30 R Electric Fan Heater.

What Size Heater For A Warehouse Or Industrial Unit?

Warehouses and industrial units often need high output heating because they are large, open and can have high ceilings.

For these spaces, standard domestic heaters are usually not enough. You may need an industrial portable heater, a 9kW and above heater, or a three phase heater if the site has a suitable electrical supply.

For industrial spaces, consider:

Total floor area
Ceiling height
Insulation level
Open loading doors
Whether you need spot heating or full space heating
Working hours
Power supply
Portability requirements

For larger workspaces, browse our industrial portable heaters, 9kW and above portable heating units and three phase portable heating units.

Domestic Heater Size Guide

For domestic use, the most common heater sizes are 1.5kW and 2kW.

These are popular because they are portable, simple to use and suitable for targeted warmth in smaller spaces. They are best used for top up heating rather than replacing a full central heating system across the whole home.

Domestic Heater Size	Typical Use	Recommended Products
1.5kW	Personal warmth and small rooms	Glaziar 1.5kW Globe Personal Heater
2kW	Bedrooms, home offices and small living spaces	Glaziar Portable 2kW PTC Heater
2kW to 3kW	Garden rooms, conservatories and colder spaces	Portable or workshop style heater depending on the room

For smaller rooms and home use, view our 3kW and below portable heating units.

Workshop And Garage Heater Size Guide

Garages and workshops normally need more practical heaters because they are colder, more open and less insulated than domestic rooms.

For these spaces, heater output and airflow both matter. A fan heater can help push warm air into the area, which is useful if you are working at a bench, inside a garage or in a small unit.

Heater Size	Best For	Example Use
2kW	Small garage or occasional workshop use	Hobby work, small garage, garden building
3kW	Workshops and colder rooms	Garages, workbenches and small units
5kW	Larger workshops and commercial rooms	Unheated workspaces and larger garages
9kW plus	Industrial spaces	Large workshops, warehouses and commercial units

For this type of space, browse our industrial portable heater range.

Industrial Heater Size Guide

Industrial heaters are designed for larger, colder and more demanding spaces.

These heaters are suitable for environments where a standard portable heater would not provide enough heat. They are often used in warehouses, workshops, factories, construction areas and large commercial units.

Industrial Heater Size	Typical Application	Best For
9kW	Large workshop or smaller industrial space	Focused industrial heating
15kW	Medium industrial area	Warehouses, factories and larger units
30kW	High demand industrial space	Large open areas and heavy duty heating

High output heaters need the right power supply. Check whether the heater requires standard single phase power or a suitable three phase electrical connection before buying.

Single Phase Vs Three Phase Heaters

Power supply is important when choosing larger heaters.

Many smaller portable electric heaters are designed for standard domestic or commercial plug in use. Larger industrial heaters may require a different electrical supply.

Three phase heaters are designed for commercial and industrial environments with compatible electrical infrastructure. They are not usually suitable for normal domestic homes.

Heater Type	Typical Use	Power Consideration
Small portable heater	Bedrooms, offices and domestic rooms	Usually plug in
Workshop heater	Garages and workshops	Check output and plug requirements
Industrial heater	Warehouses and large spaces	May require higher capacity supply
Three phase heater	Industrial and commercial sites	Requires compatible three phase power

If you are unsure whether your site has the correct supply, check before ordering or speak to the CoolEasy team.

Should I Choose A Bigger Heater?

It can be tempting to choose the most powerful heater available, but bigger is not always the best choice.

A heater should be suitable for the room and the way it will be used. A high output industrial heater is not appropriate for a small bedroom, while a compact domestic heater may be underpowered for a warehouse.

Choose a bigger heater if:

The room is large
The space has high ceilings
The area is poorly insulated
You need faster warm up times
The room has frequent draughts or open doors
You are heating a garage, workshop or industrial unit

Stay with a smaller heater if:

The room is compact
You only need personal warmth
The space is well insulated
You need occasional top up heating
You are using the heater in a bedroom or office

How Much Does Heater Size Affect Running Cost?

Heater size directly affects running cost because a higher kW heater uses more electricity when running at full output.

The simple calculation is:

Heater running cost = heater kW x hours used x electricity cost per kWh

For example, a 2kW heater uses up to 2kWh of electricity per hour at full output. A 3kW heater uses up to 3kWh per hour at full output. A 5kW heater uses up to 5kWh per hour at full output.

However, thermostats, insulation and room temperature make a difference. Once the space reaches the target temperature, a heater with a thermostat may cycle on and off rather than running at full power constantly.

For more detail, read our guide on how much an electric heater costs to run.

How To Make Your Heater Work More Effectively

Choosing the right size heater is important, but how you use it also matters.

To get better performance from your heater:

Close doors to keep heat in the room you are using
Reduce draughts around windows and doors
Keep the heater on a stable, level surface
Do not block the air inlet or outlet
Use thermostat control where available
Use timers to avoid unnecessary running
Match the heater to the actual room size
Use a workshop heater for garages and workspaces rather than a small domestic heater
Use industrial heaters only where the space and power supply are suitable

A correctly sized heater in a well managed space will usually perform better than an oversized heater used in a draughty room with doors left open.

When A Portable Heater Is Not The Best Choice

A portable heater is useful for quick warmth, but it is not always the best long term heating solution.

You may want to consider a fitted system if:

You use the room every day
You need heating for long periods
You also need cooling in summer
You want a neater permanent installation
You are heating a home office, garden room, conservatory or living space all year

In these cases, a heating and cooling air conditioning system may be more suitable than a portable heater alone.

Recommended Heaters By Size

Here are some useful starting points from the CoolEasy heating range.

1.5kW: Glaziar 1.5kW Globe Personal Heater

The Glaziar 1.5kW Globe Personal Heater is a compact option for personal warmth, small rooms, bedrooms and home offices.

2kW: Glaziar Portable 2kW PTC Heater

The Glaziar Portable 2kW PTC Heater in White and Glaziar Portable 2kW PTC Heater in Black are good starting points for small to medium domestic rooms and offices.

2kW Workshop Use: Olympus 2.0kW Portable Fan Heater

The Olympus 2.0kW Portable Fan Heater for Garages and Workshops is designed for garages, workshops, small warehouses, trade vans, site work and garden buildings.

3kW: Olympus Pro 3.0kW Workshop Heater

The Olympus Pro 3.0kW Workshop Heater is a practical option for hobby workshops, garages and spaces that need more output than a small domestic heater.

3kW To 5kW: Trotec Electric Fan Heaters

The Trotec 3.0kW TDS 20 R Electric Fan Heater and Trotec 5.0kW TDS 30 R Electric Fan Heater are suited to workshops, garages, construction sites and unheated indoor environments.

9kW And Above: Olympus Industrial Heaters

For larger spaces, browse the 9kW and above portable heating units collection. These heaters are designed for industrial and commercial environments where smaller models are not enough.

Heater Size Buying Checklist

Before choosing a heater, ask yourself these questions:

What is the size of the room or workspace?
Is the room well insulated?
Does the space have high ceilings?
Are there draughts or frequently opened doors?
Do I need personal warmth or full room heating?
Will the heater be used occasionally or every day?
Is the heater for a bedroom, office, garage, workshop or warehouse?
Do I need a standard plug in heater or a larger industrial model?
Does the site have the correct power supply?
Would a fitted heating and cooling system be better long term?

If you are unsure, it is better to ask for advice before buying than to choose a heater that is too small for the space.

What Size Heater Do I Need FAQs

What size heater do I need for a small room?

For many small rooms, a 1.5kW to 2kW portable heater is a good starting point. The exact size depends on the room size, insulation and how cold the room gets.

Is a 2kW heater enough for a bedroom?

A 2kW heater can be suitable for many bedrooms, especially if the room is reasonably insulated. A smaller 1.5kW heater may be enough for compact bedrooms or personal warmth.

What size heater do I need for a home office?

For a typical home office, a 1.5kW to 2kW portable heater is usually a practical starting point. Larger or poorly insulated offices may need more output.

What size heater do I need for a garage?

For a small garage, a 2kW workshop heater may be useful. Larger, colder or poorly insulated garages may need 3kW, 5kW or more.

What size heater do I need for a workshop?

A 3kW heater is a useful starting point for many small workshops. Larger workshops may need 5kW or a higher output industrial heater.

What size heater do I need for a warehouse?

Warehouses usually need industrial heating. Depending on the size, insulation and ceiling height, you may need 9kW, 15kW, 30kW or multiple heaters.

Does a bigger heater cost more to run?

At full output, yes. A higher kW heater uses more electricity per hour. However, the right size heater may warm a suitable space faster and cycle down if it has thermostat control.

What does kW mean on a heater?

kW stands for kilowatt. It shows the heater’s power output. A 2kW heater is 2,000 watts, while a 3kW heater is 3,000 watts.

Can I use an industrial heater at home?

Industrial heaters are designed for larger and more demanding spaces. They are not usually suitable for small domestic rooms. Always check the heater type, output and power requirements.

Do three phase heaters plug into a normal socket?

No. Three phase heaters require a compatible three phase electrical supply and are normally used in commercial or industrial settings.

Should I buy a portable heater or a fitted heating system?

Choose a portable heater for quick, flexible warmth. Choose a fitted heating and cooling system if you want a permanent solution that can heat in winter and cool in summer.

Final Advice: Choose Heater Size Based On The Space, Not Just The Wattage

The right heater size depends on the space you are heating.

For bedrooms, home offices and smaller rooms, a 1.5kW or 2kW portable heater is often the best starting point. For garages and workshops, look at 2kW, 3kW or 5kW workshop heaters with stronger airflow. For warehouses and industrial spaces, high output heaters from 9kW upwards are usually more suitable.

Always consider insulation, ceiling height, draughts, power supply and how often the heater will be used.

Explore our portable heating units, browse industrial portable heaters or speak to the CoolEasy team for help choosing the right heater size.

What Size Heater Do I Need? Room Size & Wattage Guide