What can I do next?

Contact Build Test Solutions or Veritherm to access heat loss measurements for your project. Contact Elmhurst Energy Consultancy to access their measurement-informed BS EN12831 heat loss calculator or for heat loss measurement training.

Should I use a monitoring or overnight test?

Both measurement methods return the same result, the measured rate of heat transfer from the building. This means that you can likely use either test method, choosing based on the practicalities of your situation. If you need a result quickly and can vacate the property, an overnight measurement could be best, if you don't want to disturb the residents a monitoring test may be more convenient.

What are the practical limitations?

The measurements must be carried out when there is a significant temperature difference between inside and out in order that there is enough heat transfer to be accurately measured, this typically restricts them to winter use. SmartHTC requires that all energy inputs to the building are measured, this makes the test hard to use when there are significant unmetered heat sources like bottled gas, unmetered heating oil or solid fuels.

Who can carry out performance measurements?

Measurements are typically carried out by trained testers, the training doesn't require previous experience and can be easily accessed through BTS or Veritherm. Our trained testers include people working with buildings in lots of different ways, including building surveyors, retrofit assessors and coordinators, heat pump installers, architects and community groups. 

What is an HTC?

The Heat Transfer Coefficient (HTC) of a dwelling is the rate of heat transfer between inside and outside per degree of temperature difference. In the winter it defines how much heat is required to make it 1 degree warmer inside than outside, a lower HTC means less heat loss and therefore less energy required to make it warm inside. The HTC is calculated in any energy model or alternatively can be directly measured for greater accuracy. The HTC is a commonly used term across different applications.

How can heat loss measurements be carried out?

There are two main options for heat loss measurements, by non-disruptive monitoring or by a shorter but more invasive overnight test. Monitoring allows the home to be lived in as normal, but takes a minimum of 3 weeks to gather enough data for a heat loss measurement. Overnight testing is much quicker, providing an answer in a single night but requiring that the home be vacated during testing. Both options return the same measurement, just by different methods.

When can heat loss measurements be carried out?

At the moment measurements can only be carried out during winter when the temperature inside is significantly warmer than the temperature outside, in these conditions there is enough heat transfer to be accurately measured.

What's the difference between measuring heat loss and energy models like SAP or PHPP?

Heat loss measurements are carried out in a particular building and measure the amount of heat transfer through the building fabric. Energy models calculate the thermal performance of a building based on measurements of the physical dimensions and either assumed heat loss characteristics of construction types or heat loss calculations based on known materials in the construction. Energy models can be prone to inaccuracy as some of the inputs are hard or impossible to assess by a visual survey.

Can measurements and energy models be used together?

Yes. Measurements of overall building heat loss, or metrics like airtightness or U-values, can be used to calibrate an energy model to a specific building. This will make the outputs of the energy model, like predicted energy use, cost or carbon emissions, more accurate.