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How to install a single room heat recovery unit

Updated: 22 October 2026

You are standing at an outside wall with a core drill still to hire, and you want the hole right the first time. This is how to install a single room heat recovery unit in a UK house without pretending every listing uses the same bit, the same tube or the same electrician. The sequence is a survey, a diameter, a fall to outside, then a hard stop at bathroom wiring. It is not a ranking. If you have not chosen the unit, start with the [single room heat recovery comparison](/hub/heating/single-room-heat-recovery). Peter F. checked the listings and public UK sources, with no lab test. A qualifying purchase can earn a commission at no extra cost to you.

You are standing at an outside wall with a core drill still to hire, and you want the hole right the first time.

Our top picks

Kair Kair K-HRV150/12RH

Best overall

Kair Kair K-HRV150/12RH
8.4/10about £323.94
View offer
LIRAST LIRAST EER100 white

Best value

LIRAST LIRAST EER100 white
7.8/10about £123.12
View offer
LINGGONGAIR LINGGONGAIR VT100

Rank 3

LINGGONGAIR LINGGONGAIR VT100
7.2/10about £159.60
View offer
On this page
  1. 1.Before you hire a core drill
  2. 2.Diameter and fall
  3. 3.Wall thickness in this set
  4. 4.Plug, SELV, or a new circuit

Before you hire a core drill

Find an outside wall, not a partition or a chimney breast you cannot identify. Mark pipes, cables and any steel before the bit spins. Permagard's Kair notes start with that survey. Put the unit high. Approved Document F expects extract within about 400 mm of the ceiling, where steam collects. A fan at shoulder height misses that layer. Kair's own page says that model can be installed from inside. Other sleeves still need a grille from a ladder. If you rent, the wall is a party wall, or the cavity fill is unclear, stop and get someone who will own the repair.

Diameter and fall

Match the hired bit to the unit, not to a generic fan hole. LIRAST and Brookvent's ONE 100 are 100 mm, with LIRAST also printing 106 mm. The VT125-WIFI is 125 mm. EUROPLAST, Weiworld and the ONE 150 are 150 mm. Kair states 152 mm. Confirm the VT100 carton, because the title says 125 mm and the opening fields say 10–16 cm. Envirovoid's 100–160 mm sentence is not a hire size. A hole a size too small wastes the sleeve. Slope the tube down to the outside by about 1–2 degrees, the fall in the Kair instruction pattern, so condensate leaves the building. A tube that falls into the room drips indoors. Keep the outdoor cowl clear of a boiler flue and a neighbour's window, then follow the manual that arrived with your model.
Kair Kair K-HRV150/12RH

Testsieger

Kair Kair K-HRV150/12RH
8.4/10about £323.94
View offer

Wall thickness in this set

Measure both skins, the cavity and any dot-and-dab before you order. LIRAST's telescopic duct is stated at 300–555 mm. A UK review of a 275 mm wall was already a difficult fit, so do not pack a short sleeve with foam. Kair's page describes about 229–356 mm, and an extension when the run is longer. One amazon.co.uk review bought that pack at £41.17 with delivery because the outside wall was about 3 m away. The VT125-WIFI dimension line is about 39.9 cm deep. If the listing is silent, measure and ask the seller before the drill comes off hire. The HR100R does not use this hole. It is a loft box with ducts and a condensate drain that one buyer received bent. If that is the unit on the floor, plan ducts, insulation and a fall on the drain instead.

Plug, SELV, or a new circuit

A plug-in fan is not a promise that you need no electrician. LINGGONGAIR's VT100 plugs in, and UK reviews confirm a UK plug. That is a reasonable DIY finish in a bedroom, on a sound circuit, once the hole and the outside grille are done. It does not authorise a new spur in a bathroom. The room type on that listing is bedroom, with no IP rating. Kair is 12 V in the capture, with hard-wiring required, and the manufacturer puts the transformer outside bathroom zones 1 and 2. The Amazon lines also mention a BS 1363 connector, so let a competent person reconcile that on the unit you received. IET guidance on BS 7671 is that an isolator for a bathroom fan sits outside zones 0 to 2. Weiworld states 230 V and a 3-pin connector. EUROPLAST prints both Type G and Schuko, so look at the plug before you cut a socket. Fixed wiring in a bathroom is the moment to book an electrician. Open the box before you drill. Brookvent's ONE 100 and ONE 150 omit the controller. Reviews put the extra near £40 and £53.20. The ONE+ states the controller inside. If a EUROPLAST switch legend is reversed, label it on the first run. If the fan hunts, smells hot, or the breaker opens, isolate it and get an electrician.

Common questions

What diameter core drill do I hire?
The diameter of the unit you have bought. Use 100 mm for LIRAST and the ONE 100, 125 mm for the VT125-WIFI, 150 mm for EUROPLAST, Weiworld and the ONE 150, and 152 mm for Kair. Confirm the VT100 carton because the title and the opening fields disagree. Envirovoid's range is not a hire size until the manual names one hole.
Which way should the tube slope?
Down to the outside, about 1–2 degrees, so moisture leaves the wall. A fall back into the room drips indoors. This is the pattern in the Kair instructions that installers repeat. Your own manual still wins if it states a different fall for that sleeve.
How thick can the wall be?
As thick as that model's sleeve. LIRAST states 300–555 mm. Kair's page is about 229–356 mm, with a paid extension beyond that. The VT125-WIFI is about 40 cm deep on the dimension line. A wall outside the printed range is a different product, not a tube of sealant.
Do I need an electrician for a plug-in unit?
Not always, for a VT100 in a bedroom on an existing socket, once the hole is made. You do for a new circuit, a bathroom zone, a fused spur, or any doubt about the circuit you are plugging into. Kair's 12 V transformer and any hard-wired 230 V fan are electrician work. The plug-in row does not set the rule for the others.
Where does the isolator go in a bathroom?
Outside zones 0, 1 and 2, where you can switch it off without entering the wet area. That is the IET position on bathroom fans. Do not hide the switch above the shower because the cable run was shorter. IPX4 and SELV, before you choose the zone, are on the bathroom heat recovery fan page.

Related pages

Single room heat recovery buying guide

Single room heat recovery

Bathroom heat recovery fan: the IP rating and airflow

Best single room heat recovery UK: who should skip

Heat recovery fan vs extractor fan: hours or boost

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these twelve listings were taken from the listings saved on 20 October 2026. Page updated October 2026.

  1. Approved Document F Volume 1, 2021 (retrieved 20 October 2026)
  2. GOV.UK Approved Document F (retrieved 20 October 2026)
  3. Elta Trade, Part F 2021 (retrieved 20 October 2026)
  4. IET BS 7671 Section 701 FAQ (retrieved 20 October 2026)
  5. BEAMA specifier ventilation guide (retrieved 20 October 2026)
  6. Kair heat recovery room ventilator (retrieved 20 October 2026)
  7. Permagard Kair install guide (retrieved 20 October 2026)
  8. MDPI Energies, ceramic-core measurements (retrieved 20 October 2026)