Library
Guides and calculators for UK building services
Size faster. Design with standards. Learn the method - then take it into your project.
Calculators
Run the numbers
One guide per calculator - inputs explained, live calc on the page, UK practice notes.
Thermal
- U-valueCalculate wall, roof or floor U-values and check against Part L limiting values. Free UK U-value calculator for building services and compliance screening.
- Flue sizingPreliminary common flue diameter from connected gas input. Velocity check per draft type — final design per BS EN 13384-2.
- Heat loadEstimate room or building heat loss and heating plant duty. Free UK heat load calculator for first-pass boiler and emitter sizing.
- Part O assessmentSimplified Approved Document O check for glazing limits and opening areas in UK dwellings. Free Part O overheating calculator.
- Quick SAP estimateIndicative SAP/EPC screening before sending to a SAP assessor. Free quick SAP estimate calculator for Part L compliance checks.
- Duct coil heatingSize ducted heating coil airflow or off-coil temperature from heat loss. Free duct coil heating calculator for AHU and FCU design.
- Duct coil coolingSize ducted cooling coil airflow or off-coil temperature from sensible cooling load. Free duct coil cooling calculator.
- Oil tank sizingFuel oil storage from boiler/generator output, days and hours. Free UK oil tank sizing calculator with thermal guidance.
- Boiler plant dutyPlant kW from AHU coils, emitters, DHW appliances and failure scenarios. Free UK boiler plant duty calculator with thermal guidance.
Ventilation
- Ventilation rateWhole-dwelling and room extract rates under Approved Document F. Free Part F ventilation calculator for MVHR, MEV and extract fan sizing.
- MVHR sizingSize mechanical ventilation with heat recovery — supply and extract flow rates under Part F. Free UK MVHR sizing calculator.
- Duct sizingCheck duct velocity, Pa/m, equivalent diameter and sound power from airflow. Free UK duct sizing calculator for circular and rectangular ductwork.
- Duct heaterSupply air / duct heater kW from airflow and entering → leaving air temperatures (Q = V̇·ρ·cp·ΔT). Free UK duct heater calculator with ventilation guidance.
- Refrigerant charge limitCheck maximum refrigerant charge and minimum room volume per BS EN 378. Free calculator for split systems and VRF installations.
- Heat recovery tempCalculate MVHR/HRV supply air temperature from heat exchanger efficiency. Free heat recovery temperature calculator.
- Stack dischargeCalculate kitchen exhaust discharge cone pressure drop per DW172 guidance. Free stack discharge calculator for commercial kitchen ventilation.
- Kitchen canopyDW172 thermal convection canopy extract and make-up air from equipment schedule. Free commercial kitchen ventilation calculator.
- Equipment finderSize FCU, DX, MVHR, AHU, fans, pumps, heat pumps, radiators, chillers and boilers from design duties with correct units. Instant equipment selection brief for UK MEP.
- AHU coil capacityCalculate AHU heating and cooling coil duties from fresh air and room loads. Free air handling unit coil sizing calculator.
- AHU / fan ESPFan external static from components, duct friction, bends and fittings. Free UK ahu / fan esp calculator with ventilation guidance.
- Louvre sizingSize W×H from flow for face velocity ≤ 1 m/s (lockable), free area, ΔP and indicative dB. Free UK louvre sizing calculator with ventilation guidance.
Water
- Pipe sizingSize copper, steel, or plastic pipework from flow rate or loading units. BS EN 1057 trade sizes with BS 8558 guidance — free UK pipe sizing calculator.
- Loading unitsSum fixture loading units per BS 8558 and convert to diversified design flow. Free UK loading units calculator for pipe sizing.
- Hot water storageSize calorifier storage volume and recovery from building type or loading units. Free UK hot water demand calculator.
- Pipe water contentCalculate heating or chilled water system volume from pipe lengths and internal diameters. Free pipe water content calculator.
- DHW return pumpSize secondary hot water return flow and pump head from pipe heat loss. Free DHW return pump calculator.
- Expansion vesselSize expansion vessels for DHW, LTHW or CHW per BS 7074. Free expansion vessel sizing calculator.
- Cold water storageSize cold water storage from IoP daily demand tables or check 24-hour tank level. Free UK cold water storage calculator.
- Pump sizingHydronic pump flow and duty head from pipe lengths, bends, outlets, valves and margin — with PN rating. Free UK pump sizing calculator with water guidance.
Drainage
Electrical
- Voltage dropCalculate cable voltage drop and check conductor CSA per BS 7671. Free UK voltage drop calculator for single and three-phase circuits.
- Design currentDesign current Ib from kW / kVA (no diversity). Free UK design current calculator with electrical guidance.
- Max demand & diversityDiversified ADMD and incomer fit check (OSG App. A). Free UK max demand & diversity calculator with electrical guidance.
- Cable sizingRecommend live CSA and MCB from Ib, length and installation method. Free UK cable sizing calculator with electrical guidance.
- Earth fault loop ZsZs check, max circuit length and CPC / curve guidance. Free UK earth fault loop zs calculator with electrical guidance.
- Adiabatic CPCMinimum CPC from fault level and disconnection time. Free UK adiabatic cpc calculator with electrical guidance.
- Prospective fault currentPFC from Ze/Zs and check against device breaking capacity. Free UK prospective fault current calculator with electrical guidance.
- Protective device helperRecommend MCB rating and curve for load / inrush / Zs. Free UK protective device helper calculator with electrical guidance.
- Power factor correctionCapacitor kVAr to move from existing PF to target PF. Free UK power factor correction calculator with electrical guidance.
- Motor starting currentStart current from FLC and DOL / SSD / VSD factor. Free UK motor starting current calculator with electrical guidance.
- RCD selection helperRCD type and IΔn for sockets, EV, inverters. Free UK rcd selection helper calculator with electrical guidance.
- Cable containmentCheck trunking, conduit and cable tray fill per IET On-Site Guide. Free cable containment capacity calculator.
Design guides
How to design the system
Topic guides for temperatures, ventilation, lighting, and the checks that sit around a single calc.
- ThermalTemperature designDesign temperatures for UK offices, classrooms, corridors, and plant rooms - winter and summer setpoints from UK design guidance and common practice.
- VentilationDwelling ventilationWhole-dwelling and room extract rates under Approved Document F Volume 1 - MVHR, MEV, trickle vents, and kitchen/bathroom boost.
- ElectricalLighting designMaintained illuminance (lux) by space type under BS EN 12464 - offices, classrooms, corridors, and emergency escape.
Design tutorials
Walk a whole job
Step-by-step walkthroughs for a space or sector - follow them when you are starting from scratch.
Docs
Notes and practice
Standards context, method explainers, and the why behind common MEP rules of thumb.