Heat loss guides and calculation notes
Heatworx is built around transparent room-by-room heat loss calculation. These guides explain the principles behind heat loss, what the app calculates, where assumptions are used, and why any result should be treated as a design estimate rather than an exact measurement.
Every guide is written for homeowners and installers. Plain English first, technical detail where it earns its place.
Videos
Watch Heatworx do it before you read how it does it.
For homeowners
No jargon, no formulas you have to follow: what heat loss means for your home, your bills and your next heating system.
Start here
What heat loss is, why room-by-room matters, and how much you should trust any calculated number.
What is heat loss?
A plain-English introduction to domestic heat loss — fabric losses, ventilation losses, and why the total is always an estimate.
Why room-by-room heat loss matters
Why whole-house figures are not enough for radiator sizing or heat pump decisions.
How accurate is a heat loss calculation?
An honest look at where the uncertainty sits and why transparent inputs beat false precision.
How Heatworx works
How the app turns a room scan into a structured heat loss estimate.
How Heatworx builds a room model
What happens when you scan or manually capture a room, and what you can edit afterward.
Measured, assumed and editable inputs
Which inputs come from the scan, which are assumed, and which you should review.
How Heatworx calculates heat loss
The full calculation chain from survey inputs to room heat loss, emitter comparison and whole-house summary.
CIBSE vs MCS — choosing a calculation method
Two calculation methods, one measured survey. What differs, how switching works, and when to use each.
Standards and industry news
What new guides, editions and corrections from the standards bodies mean for your surveys.
CIBSE Domestic Heat Pump Design and Installation Guide 2026
The new monobloc-only companion to the Design Guide — two heat-loss numbers, the reused-radiator method, whole-house flow temperature and the signed system criteria document.
CIBSE Domestic Heating Design Guide 2026
What the new guide means for heating engineers — airtightness routes, build-year temperatures, reheat allowances, party walls — and the July corrigendum.
Building fabric
How heat escapes through walls, windows, floors and roofs.
Walls, windows and floors
Fabric heat loss explained: area, U-value and temperature difference.
U-values explained
What a U-value means and why construction assumptions matter.
Finding the right U-value for an existing building
Five routes, how to read a wall on survey, and a stone wall worked insulated and not — around seven times apart.
Thermal bridging
Cold bridges at lintels, junctions and corners — and the uncertainty they add.
Thermal bridging: psi and y-values
How the allowance is chosen and applied under CIBSE 2026 and MCS, where they differ, and a 1930s room worked through both.
Air movement and ventilation
Heat lost through air moving in and out of a building.
Ventilation heat loss
Infiltration versus intentional ventilation, air change rates, and airtightness uncertainty.
Airtightness and draughts
Background vents, trickle vents, MVHR, suspended floors, and survey evidence.
q50 to air changes per hour
One room worked through CIBSE 2026 and MCS side by side: the scaling, the party-wall difference, the 0.5 ach floor, and what it means in watts.
Heating system fit
Whether the heating system can deliver the heat each room needs.
Radiator and emitter sizing
Comparing room heat loss with corrected emitter output. Why catalogue ratings mislead.
What flow and return temperatures should you use?
They're assumptions you test, not measurements: how they move radiator output without moving heat loss, and what to start with.
Flow temperature and Delta T
How Delta T affects radiator output and why this matters for heat pumps.
Boiler sizing
Why many boilers are oversized and why minimum modulation matters.
Heat pump readiness
Why heat pumps need accurate room-by-room heat loss and what to check first.
Reference notes
Background topics that support the main guides.
Design temperatures
What design outside temperature means and why location matters.
Internal room temperatures
Why different rooms use different design temperatures.
Common survey mistakes
Rules of thumb, wrong Delta T, and treating estimates as measurements.
Glossary
Short definitions linking to the relevant guide.