At Brimstone Energy, we are committed to helping you understand the thermal efficiency of your home.

This is because we know that the great majority of your domestic energy usage comes from space heating and water heating.

Only a relatively small amount comes from household appliances (TV, radio, etc) and lighting, with the balance coming from cooking, dishwasher, washing machine and tumble dryer usage.

To reframe this another way, turning off your LED light when you leave a room makes hardly any difference to your annual energy bill. And who wants to live in darkness anyway? You need to cook, and in the twenty first century we believe that people everywhere should be able to cook heathy meals without worrying about the cost of energy required to cook the meal.

Washing your clothes at a lower temperature may help reduce your bills a little, but as my washing machine repair technician said to me recently “washing your clothes at 30 degrees won’t save the planet but it will cause your machine to stop working sooner”.

No. The big gains, and the permanent gains are to be made in the area of space heating.

And consider this. It is possible to basically not heat your home at all. A Passive Haus does exactly this.

So the question you need to ask yourself is, do I want to permanently reduce my annual spend on space heating? If so, reach out to Brimstone Energy for a heat loss survey of your home. This will identify the heating loss of each room in your home.

So, what exactly is a U-Value?

“U-Value – is the measure of the overall rate of heat transfer, by all mechanisms under standard conditions, through a particular section of construction.”

In other words, a U-value is used to measure how well or how badly a component transmits heat from the inside to the outside.

The slower or more difficult it is for heat to transfer through the component, the lower the U-value. This means that we are looking for a lower U-value.

The lower the U-value the better.

When we talk about a component, we mean any aspect of the structure – a pane of glass, a timber door, or a complete cavity wall. We can work out how much heat passes through each element of the building assembly and determine the U-value based on the amount of energy lost through a square metre of material.

Modern materials have U-values determined by their manufacturers, and architects, builders and building control can refer to technical specifications to determine the U-value of a particular construction method.

So what?

How do you as the consumer put any of this information into a useful context?

What do these U-values mean in practice?

What about a cottage constructed in 1780? Or the 1970s house you call home?

This is where the heat loss survey comes into play….!

For example. Your typical Victorian cottage with solid brick walls will lose heat through its external walls at a rate of 2.11 W/m²K compared to an external wall built to 2022 Building Regulations at 0.18 W/m²K.

This means that the modern wall is almost twelve (12) times as thermally efficient as your ‘period’ cottage.

So what? You really need to upgrade your wall to benefit from a permanent reduction in your space heating costs. Insulation is a ‘no-regrets’ measure.

For anyone who wants a more technical discussion of U-Values, please read on:

What are the units for U-Values?

The U-Value is measured in W/m² K

This is broken down as: The rate of heat flow (in Watts) through 1m² of a structure when there is a temperature difference across the structure of 1 degree (K or ˚C).

Example:

Wall 1 with U-Value of 0.3 W/m2 K will lose heat at half the rate of Wall 2 which has a U-Value of 0.6 W/m2 K

So, the LOWER the U-Value, the BETTER.

The lower the U-value the more efficient the construction is at keeping heat flow through the structure to a minimum.

In June 2022 Building Regulations in England were updated to further improve the specifications for new dwellings and extensions.

• U-value requirement External Walls 0.18 W/m²K
• U-value requirement Party Walls 0.0 W/m²K
• U-value requirement Floor 0.13 W/m²K
• U-value requirement Roof 0.11 W/m²K
• U-value requirement Windows (whole window U-value) 1.2 W/m²K

Thermal Resistance (R)

U-values are calculated from the thermal resistances of the parts making up a particular part of the structure. Transmission of heat is opposed in varying amounts dependent on material and surface. Thermal Resistance is defined as a measure of the opposition to heat transfer offered by a particular component in a building element.

In order to calculate thermal resistance, you must know the thickness of the material and the Thermal Conductivity (K) value.

R=d/k

Where

R= Thermal Resistance (m2K/W)

d= Thickness of material (in Metres – very important)

k= thermal conductivity of the material (W/m K)

You must know the thermal resistance (R) in order to calculate the u-value. If you are specifying standard products it is often easy to find the resistance values for these elements. Sometimes it is worth having a look at specific manufacturers websites for these details.

Ra is airspace cavity

How do you know the Rso and Rsi Value?

Rso is the outside surface resistance, and Rsi is the inside surface resistance. These values are specified in the Architects Pocket Book as:

U-Value

Now you have your Rt value, the calculation is simple, one divided by the Rt. There you have your U-Value.

Let Brimstone Energy be your guide. We’ll cut through the complexity to help you benefit from the Green Energy Transition.