Small-duct high-velocity systems explained
Small-duct high-velocity, or SDHV, sounds technical, but the idea is simple — and it solves a very British problem: how to heat, cool and ventilate a whole home without radiators, wall boxes or major building work. Here is the plain-English guide.
What is a small-duct high-velocity system?
A small-duct high-velocity system has three main parts: a compact air handler (the heart of the system, tucked into a loft or cupboard), slim 50–63mm insulated ducts, and small outlets in each room. "High velocity" simply means that because the ducts are narrow, the air moves through them faster — which is exactly what lets the ducts be small enough to hide in the structure of a normal home.
How it works: aspiration, not air-dumping
Air leaves the small outlets at a higher velocity, which creates a gentle suction that draws the room's own air into the stream and mixes it thoroughly. The result is the opposite of a blast from a big grille: temperatures stay remarkably even — typically less than 2°C variance between floor and ceiling — with no hot spots, no cold corners and no draughts. Inline sound attenuators keep it quiet.
What it actually does: heat, cool and ventilate
Paired with a heat pump (or working alongside a boiler), the same system warms your home in winter and cools it in summer. Add filtration and optional heat-recovery ventilation and it also keeps the air fresh and clean year-round — three jobs from one hidden system. See the full system and components →
Why UK homes love it
- Discreet — no radiators, no wall cassettes, no rows of outdoor boxes.
- Retrofit-friendly — slim ducts thread through existing homes, including period properties.
- Even and quiet — gentle, well-mixed air rather than a noisy blast.
- Cleaner air — filtration plus optional fresh-air ventilation.
Is it right for your home?
If you only have one stuffy bedroom, a single split or portable unit may be all you need. But if your whole home is getting harder to live in across the seasons — and you would also like to modernise heating and air quality — a whole-home, heat-pump-ready system is usually the better long-term answer. It suits retrofits, period homes, flats and new builds alike.
What does it cost?
A whole-home small-duct high-velocity system typically starts from around £5,495 and varies with the size and layout of your home. The simplest way to get your figure is to configure your system for an instant indicative price — no payment, no obligation.
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Price your systemRequest a callbackFrequently asked questions
What does small-duct high-velocity mean?
It is a heating and cooling system that uses narrow 50–63mm ducts instead of large conventional ducts. Because the ducts are small, air moves through them faster (high velocity), which lets the ducts hide inside the structure of a normal home.
Is high-velocity air conditioning noisy?
No. Inline sound attenuators isolate noise and vibration, and because the air aspirates and mixes gently rather than blasting from a large grille, operation is quiet and draught-free.
Can small-duct high-velocity heat as well as cool?
Yes. Paired with a heat pump it heats in winter and cools in summer, and it can add filtered fresh-air ventilation — three jobs from one hidden system.
Is SDHV good for retrofit and older homes?
Yes. The slim, flexible ducts thread through existing voids with minimal disruption, which makes small-duct high-velocity one of the most practical ways to add whole-home comfort to older and period properties.
How much does a small-duct high-velocity system cost in the UK?
As a guide, a whole-home system typically starts from around £5,495 and rises with the size of the property. You can get an instant indicative price for your home using the online configurator.