Pick a property and a ventilation system, then watch the damp air leave and fresh air arrive. It is an illustration, not a survey — but it shows exactly how each system works.
1Your home
2What to fit
3Watch it work
1. What sort of home is it?
Tap the one that looks most like yours. It does not have to be exact.
How many bedrooms?
Can you get up into the loft?
2. What would you like it to do?
Four ways to fix it, smallest job first. If you are not sure, use the
button underneath — we will pick a sensible starting point for your home.
2-Bed Terraced / Semi · with loft access · 78% humidity · mould forming on the cold-bridge areas
Pick a property type and a ventilation system first.
Each fan comes out of its own nearest wall. There is no single route to
choose, because there is no central unit — and that is what makes this the cheapest
way to do it. What decides the price is one question per room: is there an outside
wall behind it? If there is, the fan goes through it — core drill, sleeve,
louvre with a backdraught shutter — and it is a couple of hours. If the room sits in
the middle of the plan, a wall fan cannot serve it at all — and rather than draw one
that could not be fitted, the drawing leaves it out and the result panel prices the two
honest alternatives instead.
Not this property. No wet room here has an outside wall behind it, so
there is nowhere for a wall fan to go — which is why the drawing shows none. That is
not a fault, it is the answer: on a plan like this the choice is an inline fan and a duct
per room, or one MEV unit serving all of them. The result panel prices both.
No duct to outside on this one. A loft PIV draws its air from the roof
space through its own filter — the loft is ventilated at the eaves, which is what the
vents in the soffit are for. Loft air is a little warmer than outdoor air in winter, so it
arrives softer than air taken straight off a cold wall. Worth knowing: a loft PIV is
only as good as the loft’s own ventilation. Block the eaves — which is
what happens every time insulation gets topped up and pushed into them — and the unit
is just moving stale loft air about. We check that on the survey. Where a loft genuinely
is not somewhere you would want to breathe from, the unit gets a ducted intake instead.
No loft? It goes on the wall. A wall-mounted PIV sits high on an outside
wall — the hall if it has one, otherwise the living room — with a core drilled
straight through the wall behind it and a grille on the outside. It draws fresh air in
through that one hole and filters it on the way, so there is no loft needed and no
ductwork at all. It is the usual answer in a flat.
Where should the duct come out?
Every job needs a way out through the building, and the three ways
cost very different amounts. This is the bit you are normally never shown until the
quote arrives.
Straight out through the external wall. Usually the best result: the shortest run, easy to reach for servicing, and nothing on the roof that can ever leak.
How high up is the flat?
It does not change the rates — Part F sizes on bedrooms and floor
area, not on height. It changes how the air behaves at the wall, and what you are
allowed to cut into it.
Tell us more about your homeOptional — it makes the "before" match what you actually see
73%
Condensation on windows and cold walls. Mould can take hold here.
Estimated from your answers, not measured. On a survey we take a real reading in each room.
I have a hygrometer and know the reading
Mould grows where warm, damp air meets a cold surface.
⚠ Elevated mould risk in cold-bridge areas
Illustrative only. This shows how each system moves air through a home of this shape — it is not a
Part F calculation and not a system design. A site survey is the only way to size a system properly.
Not sure where to start?
Send us a message with what you have noticed at home. We will tell you honestly whether you need a survey, a system, or neither.
Or see what it costs — unlike most in this trade, we publish our prices.
Trained on the systems we install
Certificated — and here they are
Most trade sites show you a row of logos. These are the actual certificates, held by this
business. Tap either one to read it, or download the PDF.
12-month workmanship guaranteeOn top of the manufacturer’s warranty, which we register in your name. If anything we installed fails because of the way we installed it, we come back and put it right. What it covers.
Company no. 12092552Registered in England & Wales. Trading as Cavalli Ventilation since July 2019, and in ventilation since 2003.
Airflow measured on every installA calibrated anemometer at the grille, recorded and handed over. The only figure that counts is the one measured in your room.
