Fabric loss
–
Heating. Water. Air.
Engineeredproperly
Building services engineering calculators
Heat loss, pipe and duct sizing, plant duty. Done properly, for free.
Standard CIBSE methods, laid out so you can see every step. Method and source on every sheet, so you can check it against your own code before you rely on it.
Designed byA 4th year Energy Engineering student, Galway
Method basisCIBSE Guides A, B, C, G · TGD F/L · BS EN 806-3 · switchable per sheet
UnitsMetric and imperial
Calculation register
Pick a sheet. Every calculator shows its method and cites its source.
Why this exists
The checks building services engineers run most often were never in one place. Now they are. Each one is the standard method, laid out so you can see exactly what it's doing.
What's new in v12
- Live 3D scenes on every page - the heat pump, AHU and chiller pull apart as you scroll, every valve on the riser says what it does
- Heating: radiators from a BS EN 442 catalogue at your flow temperature, and underfloor loops checked against the 100 m / 29 °C / W/m² limits
- Pipe sizing on real copper (EN 1057) and steel (BS EN 10255) bores, not nominal sizes
- 3D room builder: click a wall, add a window or door, cited default U-values (TGD L 2022, SEAI DEAP)
- Every pipe and duct size checked at your flow, the one to use marked
- Index run in kPa and a Grundfos pump picked on its real curve with the duty point
- Real datasheet PDFs, exact product pages and transcribed capacity data for every unit
- PDF calc sheets on every calculator - free
Design the
heating
Heating · Sheet 01
Space Heat Loss
Fabric loss (U·A·ΔT per element) plus ventilation and infiltration loss, with the TGD L backstop check on every element.
Heating · as installed in Irish buildings
Heat every
Underfloor manifolds, radiators, TRVs and the plant room behind them: the kit this sheet sizes.
square metre
Fabric loss first, then the emitter, then the plant.
0.18
W/m²K wall backstop, TGD L 2022 Dwellings
0.15
W/m²K floor with underfloor heating
≤5
m³/(h·m²) @ 50 Pa air permeability
−3 °C
external design temperature commonly used in Ireland - confirm with CIBSE Guide A weather data for the site
Note: this is a steady-state fabric + ventilation loss (U·A·ΔT + 0.33·n·V·ΔT, after CIBSE Guide A and the principles of BS EN 12831-1). It is not the full EN 12831 method: it leaves out thermal bridging, temperature factors for unheated spaces, the ground-loss method and heat-up allowance. U-values shown are typical starting points - overwrite them with the actual build-up from your project specification or the Part L / TGD tables.
Fabric loss
| Element | U-value (W/m²K) | Area (m²) | Loss (W) | TGD L backstop |
|---|
The five standard elements are filled from the room builder above - overwrite any U-value or area with the project figure. Backstops are the TGD L 2022 Table 1 maximum area-weighted average U-values (Um) for the building type you pick. Dwellings: pitched roof 0.16, flat roof 0.20, walls 0.18, floors 0.18, windows / doors / rooflights 1.4 W/m²K. Buildings other than dwellings: pitched roof 0.16, flat roof 0.20, walls 0.21, floors 0.21, windows / personnel doors / rooflights 1.65, curtain walling 1.8, vehicle and large doors 1.5 W/m²K. Underfloor heating: floor 0.15. Individual elements may be worse up to roof 0.3, wall / floor 0.6, openings 3.0 (both verified against the gov.ie PDFs).
Add another element
Garage door, party wall, rooflight, conservatory glazing, exposed soffit - anything not in the list above. Name it, give it a U-value and an area, and it joins the table with its own loss and backstop check (matched on the words wall / roof / floor / window / door).
W/m²K
m²
Ventilation / infiltration loss
m³
°C
°C
Fabric check
Ventilation loss
–
Total heat loss
–
Emitters that meet this heat loss
What goes in the room to put that heat back: a radiator from a real BS EN 442 catalogue at your water temperatures, or an underfloor circuit checked against the loop, floor-temperature and output limits.
°C
°C
Method: Fabric: Σ(U×A×ΔT). Ventilation: 0.33 × ACH × Volume × ΔT (0.33 Wh/m³K ≈ ρ·cp of air). ΔT = internal − external design temp.
Design the
waterservices
Water Services · Sheet 02
Pipe Sizing
Flow rate in, velocity and Pa/m out — circular or rectangular, metric or imperial. Limits from CIBSE, the Irish TGDs, British Standards or your own company rules. Demand from BS 8558 loading units if you don't have a flow yet.
Water services · as installed
Move every
Copper, press-fit and stainless distribution, booster pumps and the valves between them.
litre
Demand → flow → pipe size → index run → pump.
2.0
m/s max in distribution pipes, I.S. EN 806-3 cl. 4.4
4.0
m/s on a pipe serving one fitting, cl. 4.4
0.30
l/s at 10 LU on the BS 6700 chart
9.81
kPa per metre of static lift
Method: Darcy-Weisbach + Colebrook-White (laminar below Re 2300 uses f=64/Re). Rectangular sections use hydraulic diameter for the friction calc. Roughness values are typical starting points — verify against your project spec.
Design the
ventilationservices
Ventilation · Sheet 03
Duct Sizing
Flow rate in, velocity and Pa/m out — circular, rectangular or flat oval, metric or imperial. Limits from CIBSE, the Irish TGDs, British Standards or your own company rules. The sizing table shows every standard duct size for your flow and marks the one to use.
Ventilation · as installed
Breathe every
Spiral and rectangular galvanised duct, hangers, dampers and the AHU or MVHR feeding it.
litre per second
Size for noise first, then Pa/m, then the fan.
10
l/s per person, non-dwellings, TGD F 2019 §1.3.1.7
6.0
m/s main duct, private offices NR30–35, CIBSE Guide B2 (2016) velocity table
1.0
Pa/m equal-friction target for low-pressure systems (CIBSE)
0.3
l/s per m² dwelling MV minimum, TGD F 2019
Method: Darcy-Weisbach + Colebrook-White. Rectangular ducts use hydraulic diameter (2ab/(a+b)) for the friction calc — a good approximation for most aspect ratios; very flat/elongated ducts want CIBSE Guide C's additional aspect-ratio correction, not yet included.
Further reading (CIBSE)
Guide B2: Ventilation and Ductwork
Guide C: Reference Data — duct sizing spreadsheets
What are you designing?
Pick one first. The 3D model below becomes that unit and pulls apart as you scroll; the calculator fields change to suit it.
Design the
heat pumps& AHUs
Refrigeration & Heat Pumps · Sheet 04
Heat Pump / AHU / Chiller Duty
Pick what you're sizing first — the right fields show up for it. Then match the load against real Irish supplier ranges.
Heat pumps, AHUs and chillers · as installed
Pump every
Monoblocs on plinths, cascades on roofs, VRF and chillers on the plant deck.
kilowatt
Duty, then the real unit, then its datasheet COP.
4.91
COP A7/W35, Grant Aerona³ HPID6R32 (BS EN 14511)
2.85
COP A7/W45, Ecodan CAHV-R450 (EN 14511)
640
kW cascade ceiling, 16 × CAHV-R at A7/W35
813/2013
Ecodesign regulation setting minimum efficiency (via TGD L)
Scope note: this doesn't model actual refrigerant properties (P‑h enthalpy data for R32/R410A/R290 etc. is proprietary/complex and varies by manufacturer selection software) — it works off duty and COP/EER, which covers most day-to-day sizing checks. If you want true refrigerant-side mass flow, that needs a manufacturer's selection tool.
Calc sheets
Every calculator. Every calc sheet. Free.
Each calculator prints a signed-off style calc sheet - project, reference, revision and engineer on the header, every input and result, method and source cited. Set the header once here; it's saved on this device only.
Calc sheet header
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