Heating & heat loss
- Radiator / Emitter Correction CalculatorAdjust a radiator's rated output for your system temperatures.
- Heat Loss CalculatorWork out how much heat a building loses, to size the heating.
- Heat Network DHW + Space-Heating Diversity CalculatorFind the realistic peak demand on a heat network riser.
- Heat Network Distribution Loss CalculatorEstimate the heat lost from heat network pipework.
- Heating Output & Flow Rate CalculatorConvert between heat output and the water flow needed.
- Radiator Selection from Room Load CalculatorFind the catalogue size of radiator a room needs.
- Room-by-Room Heat Loss CalculatorWork out heat loss room by room to size radiators.
- Underfloor Heating Loop Sizing CalculatorSet pipe spacing and loop lengths for underfloor heating.
Hot & cold water services
- Cold Water Storage Sizing CalculatorWork out how much cold water storage a building needs.
- DHW Cylinder Recovery CalculatorSee how long a hot water cylinder takes to reheat.
- DHW Storage Sizing CalculatorSize a hot water cylinder for the number of people using it.
- Hot Water Secondary Return CalculatorSize a secondary return so hot water arrives quickly at the tap.
- Mixing / Blend Temperature CalculatorFind the blended temperature when hot and cold water mix.
- Pipe Sizing by Loading Units CalculatorSize domestic water pipework from the fittings it serves.
- Unvented Discharge Pipe Sizing CalculatorSize the discharge pipe from a cylinder relief valve.
Pipework & flow
- Control Valve Sizing (Kv) CalculatorPick the right size of control valve for a heating circuit.
- Glycol / Antifreeze Properties CalculatorSee how antifreeze changes freezing point, flow and pump duty.
- Pipe Pressure Drop (water) CalculatorFind the pressure drop along a run of water pipe.
- Pipe Sizing CalculatorFind the right pipe size for the flow you need to carry.
- Pipe Thermal Expansion & Compensation Legs CalculatorSee how far a pipe moves as it heats, and allow room for it.
- Pipe Weight CalculatorFind the weight of pipework, empty and full, for support design.
- System Volume & Water Content CalculatorEstimate how much water a heating system holds.
Pumps & pressurisation
- Expansion Vessel SizingSize the expansion vessel for a sealed heating system.
- Pressurisation Unit CalculatorSet the fill and pre-charge pressures for a sealed system.
- Pump Affinity Laws CalculatorSee how flow, head and power change when pump speed changes.
- Pump Duty CalculatorFind the flow and pressure a pump has to deliver.
- Pump Selection CalculatorEstimate pump duty, power, running cost and carbon.
Cooling, heat pumps & refrigeration
- Cooling Load CalculatorEstimate how much cooling a room needs on a hot summer day.
- Heat Exchanger Sizing CalculatorSize a heat exchanger, or predict the temperatures it will give.
- Heat Pump Buffer Vessel / Volumiser Sizing CalculatorSize a buffer vessel so a heat pump does not short cycle.
- Psychrometric CalculatorConvert between air temperature, humidity and moisture content.
- Refrigerant Charge / Room Concentration Limit CalculatorCheck a refrigerant charge is safe for the size of the room.
Gas & compressed air
- Compressed Air Pipe Sizing CalculatorSize compressed air pipework so pressure reaches the tools.
- Compressed Air Receiver & Leakage Cost CalculatorSize an air receiver, or cost up what your leaks are wasting.
- Gas Pipe Sizing CalculatorSize gas pipework so every appliance gets the pressure it needs.
- Gas Rate CalculatorCheck an appliance is burning gas at the rate it should.
Drainage & rainwater
Supports & plant noise
About these mechanical calculators
These are the day-to-day sizing calculations behind a mechanical building services design: how much heat a space loses, how big the pipe needs to be, what duty the pump has to meet, and whether the supports will carry it.
The methods follow the references UK engineers actually work to. Heat loss uses the BS EN 12831 approach; pipe sizing and pressure drop follow CIBSE Guide C tabulated data with CIBSE Guide G for public health services; emitter output correction uses the BS EN 442 characteristic power law; hot and cold water services follow BS 8558 and BS EN 12056-2. Where a calculator applies a coefficient or a table value, the source is stated on the page rather than buried.
They are built for mechanical designers, estimators and contractors who need a defensible number quickly - during a tender, on site, or as a sense-check on someone else's figure. Every calculation runs in your browser; nothing is uploaded and nothing is stored.
These are design aids, not a substitute for a full design. They will get you to a sound working figure and show you the arithmetic behind it, but the finished design remains the responsibility of a competent engineer.
Frequently asked questions
Which heat loss method do these use?
Room and building heat loss follows the BS EN 12831 approach - fabric losses from element areas and U-values, plus ventilation or infiltration losses, at your chosen internal and external design temperatures. The calculator shows the fabric and ventilation components separately so you can see which dominates.
Can I use these for a tender submission?
They are intended to produce a defensible working figure and each states the standard and coefficients it applies, so the arithmetic can be checked. For anything issued for construction or contractually relied upon, have the result verified by the responsible engineer.
Do I need to install anything?
No. Every calculator runs entirely in your browser. There is no sign-up, nothing is uploaded, and no inputs are stored or transmitted.