Free HVAC Tools & Engineering Resources: 8 Calculators Worth Bookmarking

Good HVAC design starts long before anything is ordered: room loads, air change rates, duct sizes, refrigerant charge, attenuation. This page collects eight free, browser-based HVAC tools and engineering resources that do those calculations in minutes — no subscription, no login, no spreadsheets.

The short answer

Bookmark these once, use them on every job. Together they cover the full design chain — from estimating a room’s heating and cooling load, through Part F ventilation rates and duct sizing, to refrigerant pre-charge, silencer selection and psychrometrics. Every tool below opens in a new tab and gives instant results in UK units.

Heating, cooling and ventilation rates

1. Cooling & Heating Load Estimator

Start every project here. Enter the room size, occupancy, glazing and heat gains and the Cooling & Heating Load Estimator returns the capacity the space actually needs, in BTU and kW. It stops the two classic air con mistakes — undersizing a sunny office, or paying for a unit twice the size the room will ever use.

2. Part F Ventilation Calculator

Building Regulations compliance without the paper chase: the Part F Ventilation Calculator checks supply and extract air volumes against occupancy, room type and Approved Document F guidance. Useful for MVHR commissioning figures too — if heat recovery is new territory, read What is MVHR? first.

3. Duct Sizing Calculator

The Duct Sizing Calculator works out duct cross-sections by the velocity and pressure-drop methods, for both rectangular and circular ductwork. Right-sized ducts mean lower velocities, lower pressure drop and quieter terminals — and if one branch still overblows, an inline foam damper trims it without adding noise.

Air conditioning and refrigerant

4. Refrigerant Pipe & Pre-charge Calculator

For split and multi-split installs, the Refrigerant Pipe & Pre-charge Calculator takes the system type, pipe length and diameter and returns the additional refrigerant charge required. A quick sanity check before the gauges come out — made for F-gas engineers who would rather not do it longhand on the van bonnet.

Acoustics

5. Silencer Configurator

Feed the Silencer Configurator your airflow and system details and it identifies a suitable acoustic attenuator, with insertion loss and pressure drop. Pair it with a plenum chosen for the duct entry — our Acoustic Box vs Thermo Box guide explains which plenum keeps a slot diffuser quiet.

Air distribution

6. Plenum Configurator

When a standard box will not fit the void, the Bespoke Plenum Configurator lets you pick the dimensions, connection type and configuration to match your ceiling diffuser. For standard sizes, Ventmann’s own plenum boxes and Product Selector cover the common cases from stock.

Reference tools for engineers

7. Interactive Psychrometric Chart

The Interactive Psychrometric Chart plots temperature, humidity, enthalpy and dew point in the browser — the fastest way to check a coil condition, a dew-point risk or a mixed-air state without digging out the paper chart. A favourite with building services students as much as consultants.

8. Performance Curve Interpolator

Manufacturer fan data never lands exactly on your duty point. The Performance Curve Interpolator reads between the published curve points so you can check what a fan or unit will actually deliver at your flow and pressure.

How the tools fit together

• Size the load first — the Cooling & Heating Load Estimator tells you what the space needs.
• Set the air volumes — the Part F Ventilation Calculator confirms the supply and extract rates.
• Size the ductwork — the Duct Sizing Calculator keeps velocities and pressure drop in range.
• Quieten the system — the Silencer Configurator picks the attenuator; the right plenum box and an inline foam damper finish the job at the terminal.
• Finish invisibly — deliver the air through frameless LINE or PLINE slot diffusers that plaster in flush with the ceiling.

Quick answers

Are these HVAC tools really free?

Yes — every tool linked above is free and browser-based, with no subscription and no login. Open it in a new tab and start calculating.

Do the calculators use UK standards?

They are built for UK practice — the ventilation calculator follows Approved Document F guidance, and outputs come in the units UK installers and consultants actually use.

Do they replace a full M&E design?

No. They are fast, accurate estimating and checking tools. For a full specification — airflow calculations, diffuser schedules, plenum and spigot sizing — send us your plans and we will do it for free.

Which tool should I start with?

The load estimator for air con jobs; the Part F calculator for ventilation and MVHR work. Everything else follows from those two numbers.