Job takeoff
Bathroom ventilation takeoff
Extract airflow for the room, and the hangers, wrap and mastic for the duct that carries it.
A takeoff is the trade word for the shopping list a job produces — every material, and how much of each, worked out by its own cited calculator.
- 7Measurements in
- 4Trades out
Give the job once
Every figure on the right follows these, in the units you choose.
Been given a quote for this job?
Paste it into the bathroom extractor fan quote check: each line is read against these same calculators — what it leaves out, what it adds, and what to ask.
Check the quoteEvery trade, from those dimensions
then change a dimension, and each line shows what moved.
| Trade | Quantity | |
|---|---|---|
Bathroom Extract Fan Rate and Duct Resistance CalculatorAirflow the room's volume calls for.How this figure was reached
Resting on
Change any other figure on the Bathroom Extract Fan Rate and Duct Resistance Calculator | 55.47 CFM | |
HVAC Duct Hanger Support Spacing CalculatorSupports along the run — a sagging duct is a duct that holds water.
Why this quantity?
Resting on
Change any other figure on the HVAC Duct Hanger Support Spacing Calculator | 3 hangers | |
Duct Insulation Wrap Area CalculatorWrap for the length passing through cold space, round a duct of that diameter measured over the wrap — π × (diameter + twice the thickness).
Why this quantity?
Resting on
The waste allowance: the calculator's working figure, a trade convention. Change any other figure on the Duct Insulation Wrap Area Calculator | 22.46 ft² | |
Duct Sealing Mastic CalculatorMastic round every joint in the duct — the joints times π times the diameter — which is what tape only pretends to do.
Why this quantity?
Resting on
The brushing waste: the calculator's working figure, a trade convention. Change any other figure on the Duct Sealing Mastic Calculator | 1 quart | |
Bathroom Extract Fan Rate and Duct Resistance CalculatorAirflow the room's volume calls for.How this figure was reached | 26.67 L/s | |
HVAC Duct Hanger Support Spacing CalculatorSupports along the run — a sagging duct is a duct that holds water.
Why this quantity? | 3 hangers | |
Duct Insulation Wrap Area CalculatorWrap for the length passing through cold space, round a duct of that diameter measured over the wrap — π × (diameter + twice the thickness).
Why this quantity? | 2.07 m² | |
Duct Sealing Mastic CalculatorMastic round every joint in the duct — the joints times π times the diameter — which is what tape only pretends to do.
Why this quantity? | 1 quart |
Estimates, not a quote. Each row gives its base, the allowance on top, the adjusted figure and what to order; change an allowance on the row, or open its reasoning to see every figure it rests on. A trade's own page carries what it does not cover — open the one you are about to order against.
Labour and programme
Person-hours for the rows going in, from trade rules of thumb: a range for each piece of work, never a price.
No row going in carries a rate yet.
4 rows carry no hours of their own
- Bathroom Extract Fan Rate and Duct Resistance: a size or a check, not a piece of work
- HVAC Duct Hanger Support Spacing: Ductwork is not rated here: it is installed to a ventilation design by the installer who commissions it, and the design, not the length of duct alone, sets the time.
- Duct Insulation Wrap Area: Ductwork is not rated here: it is installed to a ventilation design by the installer who commissions it, and the design, not the length of duct alone, sets the time.
- Duct Sealing Mastic: Ductwork is not rated here: it is installed to a ventilation design by the installer who commissions it, and the design, not the length of duct alone, sets the time.
Labour and programme
Person-hours for the rows going in, from trade rules of thumb: a range for each piece of work, never a price.
No row going in carries a rate yet.
4 rows carry no hours of their own
- Bathroom Extract Fan Rate and Duct Resistance: a size or a check, not a piece of work
- HVAC Duct Hanger Support Spacing: Ductwork is not rated here: it is installed to a ventilation design by the installer who commissions it, and the design, not the length of duct alone, sets the time.
- Duct Insulation Wrap Area: Ductwork is not rated here: it is installed to a ventilation design by the installer who commissions it, and the design, not the length of duct alone, sets the time.
- Duct Sealing Mastic: Ductwork is not rated here: it is installed to a ventilation design by the installer who commissions it, and the design, not the length of duct alone, sets the time.
Setups you have saved
The build-up, the dimensions and any allowance you changed — kept on this device, and reusable on any job. Your prices are not copied in: they stay in your price book, so a setup never holds a stale one.
How far does a budget go?
At your own prices, with this build-up unchanged.
About this job
An extract fan is only as good as the duct behind it, and the duct is where nearly every bathroom ventilation failure lives. A fan rated at 100 m³/h (about 60 CFM) on the box delivers a fraction of that through 4 m (13 ft) of crushed flexible duct with two tight bends, and the room stays wet while the fan makes a noise that everyone reads as working.
The wrap row is not about efficiency. A cold duct running through a loft condenses the moisture it is carrying, and that water runs back down the duct to the fan or drips through the ceiling — which is read as a roof leak and chased for weeks. Insulating the duct is what stops it, and the quantity follows the run and the duct's size rather than the room.
The mastic row is the other half of the same problem. A duct that leaks into a loft is a duct delivering warm wet air into a cold space, which is the exact recipe for condensation on the underside of the roof. Tape ages and lets go; mastic does not.
How each line reads
- Base
- What the calculator gives for these dimensions, before anything is added.
- Allowance
- Cutting waste, a lap or spare stock — named, with where it comes from, and changeable on the row.
- Adjusted
- The base with its allowance on top.
- Order
- What to buy: the adjusted figure in whole boards, bags, rolls or lengths.
The order this happens in
Quantities do not tell you the sequence, and on this job the sequence is where the money goes wrong.
- Size the fan for the room, then choose a duct that does not throttle it.
- Plan the shortest, straightest route to outside — never into a loft or a soffit void.
- Use rigid duct where you can and pull flexible duct taut where you cannot.
- Seal every joint with mastic, then insulate the whole run that passes through cold space.
- Fit a terminal with a proper backdraught damper and a free area that matches the duct.
- Test the actual flow at the grille rather than trusting the fan's rating.
What this takeoff does not cover
- The fan, its controls, the humidistat and the terminal.
- The duct itself and the fittings on the route. Its diameter is asked for only to size the wrap.
- Make-up air. An extract fan in a sealed room extracts very little; something has to let air in.
- The pressure drop of the actual route, which is what decides whether the rated flow is achieved.
Quote check
Been given a quote for this job?
Paste it into the bathroom extractor fan quote check. Every line of it is read against these same calculators and your measurements. Quantities only, never prices.
What it leaves out
Every line this takeoff has that nothing on the quote reads as.
What it adds
Labour, removal, hire, fees — each named for what it is.
What to ask
One list of questions, ready to copy. Never a verdict.
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Run this takeoff
Frequently asked questions
- What does the bathroom extractor fan takeoff give for a typical job?
- Opened at Room length 2.5 m · Room width 2 m · Ceiling height 2.4 m · Duct run 4 m · Duct diameter 0.1 m · Wrap thickness 0.03 m · Duct joints 6, it orders: Bathroom Extract Fan Rate and Duct Resistance, 26.7 L/s; HVAC Duct Hanger Support Spacing, 3 hangers; Duct Insulation Wrap Area, 2.07 m²; Duct Sealing Mastic, 1 quart. Opened at Room length 8 ft · Room width 6.5 ft · Ceiling height 8 ft · Duct run 13 ft · Duct diameter 4 in · Wrap thickness 1 in · Duct joints 6: Bathroom Extract Fan Rate and Duct Resistance, 55.5 CFM; HVAC Duct Hanger Support Spacing, 3 hangers; Duct Insulation Wrap Area, 22.5 ft²; Duct Sealing Mastic, 1 quart. Every figure follows the dimensions you give it.
- Which calculators does the bathroom extractor fan takeoff run?
- 4 calculators, one to a line: Bathroom Extract Fan Rate and Duct Resistance Calculator, HVAC Duct Hanger Support Spacing Calculator, Duct Insulation Wrap Area Calculator, Duct Sealing Mastic Calculator. Each has a page of its own with its formula and its sources; the takeoff runs them all on one set of dimensions.
- What does the bathroom extractor fan takeoff leave out?
- 4 things, each named on this page: The fan, its controls, the humidistat and the terminal; The duct itself and the fittings on the route; Make-up air; The pressure drop of the actual route, which is what decides whether the rated flow is achieved.
- Can I check a quote for this job against the takeoff?
- Yes. The bathroom extractor fan quote check reads a quote's lines against these same calculators and your measurements, and reports what it leaves out, what it adds and what to ask. It reads quantities, never prices.