WATTCOSTLAB / ENGINEERING KNOWLEDGE BASE
Ten calculation-focused guides that explain the physics and equations behind WattCostLab's building-wall and solid-fuel combustion tools.
These guides are designed to support the interactive calculators rather than replace them. Use the articles to understand the equation sequence, units, assumptions and common interpretation errors, then change the inputs in the calculator for your own scenario.
Open Building Wall Heat Transfer Calculator →
A multilayer wall U-value is calculated by adding the thermal resistances of the indoor surface, every solid layer and the outdoor surface, then taking the reciprocal of the total resistance.
Read guide →R-value measures resistance to heat flow, while U-value measures overall heat-transfer conductance. In the same complete wall model, U is the reciprocal of total R.
Read guide →To estimate added insulation thickness for a target U-value, convert the target U to required total resistance, subtract the wall’s current total resistance, then multiply the missing resistance by insulation conductivity.
Read guide →For a steady-state plane wall, heat flux is q = UΔT and total wall heat flow is Q = U·A·ΔT. The result is an instantaneous thermal load under the selected conditions.
Read guide →Thermal conductivity k tells the wall model how readily a material conducts heat. At the same thickness, lower k produces a larger layer resistance R = x/k.
Read guide →Open Solid Fuel Combustion Calculator →
Combustion-air demand can be calculated from the fuel ultimate analysis by first determining stoichiometric oxygen and then converting that oxygen requirement to theoretical dry or wet air.
Read guide →Stoichiometric air is the theoretical air requirement in the model. The excess-air coefficient λ scales the air supplied above that baseline in the real-flue-gas calculation.
Read guide →Flue-gas volume can be built from the major species terms calculated from ultimate analysis, air humidity and excess air, then summed to obtain stoichiometric or real gas volume.
Read guide →Coal and biomass should be compared from their actual ultimate analyses. The calculator does not assign air demand from a fuel label; it derives oxygen and air requirements from C, H, O, S and the other entered inputs.
Read guide →In the WattCostLab source model, fuel moisture W contributes directly to water-vapor volume, while air humidity x affects wet-air volume and the water carried with combustion air.
Read guide →The building-physics cluster is linked to the peer-reviewed wall heat-transfer publication used by the calculator, and the combustion cluster is linked to the peer-reviewed solid-fuel combustion-air/flue-gas publication. See Sources & Data for the citations and DOI links.