Adding a new heat source is in an essential part of turning that dull grey and cold garage into a warm inviting room. It can also be a bit of a minefield as you try to work out whats feasible vs upfront costs vs running costs vs personal preferences.

I'm going to state early on that insulation is critical to the comfort of your new space and the ongoing running costs of the heating system. This post assumes you have already, or will be adding sufficient insulation to the garage. Remember the building regulations are the legal minimum that you have to meet, but it often makes sense to exceed these. Although the extra insulation will increase the initial cost of your garage conversion, you will retain more heat and reduce your energy demand, which is often the smartest long term choice. 

Pushed for time?

This article is a deep dive into the subject, to skip to our general recommendation click here

Overview of this post

Ok so on to the heating options where will be discussing the most popular and feasible solutions you should consider. These boil down to extending your current system and introducing a completely new system and the reasons why you would do choose this option. I also rank the various solutions for the different type of garage conversions

  • An Integral Garage Conversion
  • A Detached Garage Conversion

These tables highlight the solutions that are more relevant to your garage conversion.

Do we really need to heat the new space?

In most instances yes a heat source will be needed, although it is optional and in some cases such as a gym in a detached garage you may be able to manage without. That being said, missing the opportunity to install heaters during the conversion is something you may regret if you later decide to retrofit a heating system. The reason for this is the works to retrofit a system could be invasive and involve ruining your previously plastered and decorated finished walls. Or even worse you may need ugly trunking and surface mounted cables that stretch over and around your room. With the cheapest of options being a simple panel heater which could be supplied and fitted for under £100 I would highly recommend you fit something while the main build is in progress.

Types of heating solutions

The post doesn’t consider all of the options as some such as underfloor heating and log burning stoves I would consider as uneconomical or of a limited application. However, if you feel we have missed an option you are considering for your own project please reach out and we can look to update the post.

Central heating (GAS WITH WET RADIATORS)

The most popular way of heating homes in the UK is a mains gas wet central heating system using radiators. Gas is burned in the boiler to heat water that is then pumped through the pipework and into radiators which dissipate heat from the water to the surrounding air. Extending your central heating system to add a radiator into the new room is a great option and a sensible solution if possible. 

electric convector heaters - (wall mounted)

A panel heater on convector heater is connected to the electrical system by a fused spur or in larger applications and new supply from the consumer unit. Heat is provided by air passing over an element that is electrically charged and is same method as the ubiquitous freestanding heaters that are often rolled out as supplementary heating during the colder months of the year. 

Electric radiators

That’s right electric radiators, just to throw a bit of confusion into the plethora of heating options available manufacturers have developed a heater that looks a bit like a wet radiator but uses electricity like the convector heaters mentioned above however they produce heat in a different way. Stick with me now, these heaters use electricity to heat element or fluids such as oil which then provide radiant heat as well as heat from air (convection). We will discuss the benefits of radiant heat later in the post. 

Electric Storage heaters

Storage heaters also known as night store heaters generate heat by first passing an electric current through an element which is surrounded by dense ceramic blocks. The purpose of the blocks is to store that heat within their thermal mass so that it can be released later. This storage of heat allows a cost saving to be made from cheaper night time electricity rates which are offered by most suppliers. 

air conditioning

Traditionally only considered for cooling applications modern systems can also run in reverse to provide warmth. A wall mounted unit on the inside works with a unit on the outside of the building to provide warm or cool air on demand. The science behind the operation of these units offers what is known as a coefficient of performance. Translation they offer a running cost benefit which could be 50-75% cheaper than convector heaters, which can't be ignored. 

What is a coeffecient of performance?

Coefficient of performance (COP) is a measure of a heating systems efficiency and is calculated by dividing the heat energy produced by the energy consumed to produce that heat. Example 1kw produced / 1 kw consumed = 1 . A COP of 1 means the heater is 100% efficient which is typical for a electric heater with no moving parts. 


You will often see electric heater manufacturers highlighting their 100% efficiency and you would be forgiven for believing that this is a great product to buy.  However, it may be possible to get 3+kw of heat for every 1 kw of energy you feed into a heat pump based air con system, or in COP terms a COP of 3.


Translation, an air con unit with a COP of 3 will cost one third of the running costs of the 100% efficient electric heater.  

Sizing a heating system for a garage conversion

It's important that we size an appropriate heat source to the room, firstly so you don’t waste money buying something that is overkill for the room and second so that we can fairly compare the solutions by similar capability. The British Thermal Unit (BTU) is a reliable way of sizing a heating system for any purpose and not just garage conversions.

By first calculating the demand of the room in BTU's you can choose a suitable heating solution by matching the demand to the BTU's a solution offers. Most radiator manufacturers will include their BTU output within the specification while electric heating solutions traditionally supply outputs measured in watts or kilowatts which will require conversion.

In writing this article I have already done those conversions and linked below to the products I recommend for single and double garages. For those of you interested in the technical aspect and how BTUs work read more in the section below. Otherwise skip to Pros & Cons

How to: Calculate the heating demand 

To accurately calculate the BTU demand you need to know the following

  • Room Dimensions Length, Width and Height
  • Amount of Glazing
  • Type of Room (Demand by room type can be vastly different e.g. A Lounge has a higher demand than a bedroom)

To save you some time I have calculated the requirements for the average single and double integral garages below. I have used the room type as Lounge as this is the highest demand and also added a 10% increase in BTU's to allow for a margin of error (plus I like it warm). However, if your garage is a different size or you just want to perform the calculation for yourself there are a number of online calculators available. 

BTU Demand for the average garage to lounge conversion 

Single Garage

Internal Size 2850(w) x 4900(l) x 2400(h) (mm) = 4525 BTU + 10% margin = 4997.5 lets call it 5000 BTU for a single garage.

Double Garage

Internal Size 4700(w) x 4900(l) x 2400(h) (mm) = 7462 +10% margin = 8208 rounded to 8200 BTU

Garage Type

BTU/h

Single

5000

Double

8200


Assumptions standard garage to be insulated to a minimum of building regulations with a double glazed window fitted with a minimum U value of 1.4 W/m2K

Note if your garage conversion is a detached garage it will have a higher demand due to heat loss on all four sides of the structure and I recommend you calculate your own BTU demand

Heating options.

Pros & Cons

Before we look at the pros and cons I must remind you that this is based on a mains gas wet central heating system. At the time of writing UK gas cost roughly 10p per kWh. If you use an oil based system which has considerably higher running costs it can be argued that extending this system is unlikely to be beneficial.

Central Heating

Pros:

  • Economical to run
  • Relatively Simple Installation

Cons:

  • Increasing Gas consumption is not environmentally friendly
  • Potentially disruptive installation
Storage Heaters

Pros:

  • Makes use of cheaper night time rate electricity
  • Easy Installation (Although very heavy)

Cons:

  • Relatively high upfront cost compared to convectors
  • Big & Bulky
  • Unable to provide instant heat unless they were charge the night before.
Convector Heaters

Pros:

  • Cheap to buy
  • Easy Installation

Cons:

  • High Running Costs
  • No Coefficient of performance
Air Con

Pros:

  • Cheaper to run than other electric based solutions due to the 2-4 coefficient of performance offered.
  • Cooling capability for those hot summers

Cons:

  • Higher upfront cost compared to other solutions
  • Requires outside space for compressor
Electric Radiators

Pros:

  • Radiant Heat
  • Easy Installation

Cons:

  • High Running Costs
  • No Coefficient of performance
  • Relatively high upfront cost compared to convectors

Solutions by Garage Conversion Type

How to use the tables: Each table shows a different starting scenario, first find the scenario that is relevant to you. The tables then show ratings for some key criteria the importance of which will vary depending on your personal preferences and budgets.

Scenario 1

Single Integral Garage

Integral garage with external walls to front and side. Easy to extend Gas Central Heating system. E.G. boiler is in garage / radiator on adjoining wall / manifold and pipe run easily accessible. Ask a heating engineer if you are unsure about this.  Estimated minimum 5000 BTU's

Heating Type

Ease of installation

Upfront Cost

Ongoing Running Cost

Recommended Product

Gas Central Heating

Convector Heaters

Electric Radiators

Storage Heaters

Air Conditioning

Scenario 2

Single Integral Garage v2

Integral garage with external walls to front and side. Difficult to extend Gas Central Heating system. E.G. boiler is far away from garage / manifold concealed / disruption required to finished surfaces of internal house to run pipes and extend system. Estimated minimum 5000 BTU's

Heating Type

Ease of installation

Upfront Cost

Ongoing Running Cost

Recommended Product

Gas Central Heating

Convector Heaters

Electric Radiators

Storage Heaters

Air Conditioning

Scenario 3

Single Detached Garage

Single Detached garage with external walls to all sides and located approximately 15m from the main house and existing heating system. Suitable electricity supply already in place. Estimated minimum 5500 BTU's

Heating Type

Ease of installation

Upfront Cost

Ongoing Running Cost

Recommended Product

Gas Central Heating

Convector Heaters

Electric Radiators

Storage Heaters

Air Conditioning

Scenario 4

Double Detached Garage

Double Detached garage with external walls to all sides and located approximately 15m from the main house and existing heating system. Suitable electricity supply already in place. Estimate minimum of 8200 BTU's

Heating Type

Ease of installation

Upfront Cost

Ongoing Running Cost

Recommended Product

Gas Central Heating

Convector Heaters

You will need 2 of these

Electric Radiators

You will need 2 of these

Storage Heaters

Air Conditioning

Other Factors to consider when choosing a heating option

The tables above should really be considered a starting point to give you a grasp of the solutions available and how they relate to your type of garage conversion. Next you should think about your personal preferences and usage to determine how important things like running costs really are. 

Ask yourself

  • How often will you use the room? This will change the significance of the ongoing cost criteria, a home office conversion in use every day during the winter will cost more to heat than a infrequently used guest bedroom.  
  • How beneficial would cooling be? The summer of 2022 was record breaking and as someone who often works from a home office I can tell you air con would have been very welcome. If cooling is of interest to you I recommend getting an accurate air con installation quote so you can make an informed decision. 
  • How much work is involved in extending the existing system? Invasive work to the main house could be required to extend the system which could add significant costs to the job for plastering and decorating. 

Conclusion


By now you have probably realised there is no one best solution and each system must be considered on both its merits in relation to the existing home and garage as well as the individual preferences of the owner. Hopefully the scenario tables above help you to quickly do that and decide with confidence that having considered your options you have reached the optimum solution for you.

Final Thoughts & Considerations

Something we've not considered throughout the post which can massively skew results is "Man Maths". Normally used to justify the seemingly non logical allocation of large financial sums on new cars and car upgrades, Man Maths can also be used to specify air con over all the other options. I've tried to write this article objectively and leave out my own personal preference, but I must admit I'm slightly biased to this solution.  

Think about it, a click of a remote control can provide instant warm or cool air for less than half the ongoing cost of electric heating solutions and not too much more than GCH. For my own scenario, a home office which is the only room in the house that needs heating/cooling for most of the day, its possible to make a case that air con is cheaper. The reason for this is putting on the GCH is likely to heat the entire home. Whats more air con can be installed without disruption to the rest of the house.

Finally, for detached garages that already have power it could be cheaper or at least a negligible difference than digging a huge trench to bury the heating pipes or new gas line.

My advice is to at least get an accurate quote for the installation of air con from a local specialist. 

About the Author Michael NEGC


Michael is the Architectural Designer and Surveyor at North East Garage Conversions.
Michael has a HNC in Civil Engineering and a HND in Construction Management. Previous experience includes multiple renovations, a self build plus working as an Architectural Technician, Designer and Project Manager.