FAQ
MVHR questions, answered
Short, direct answers from working MVHR engineers.
The basics
- What is MVHR?
- MVHR (Mechanical Ventilation with Heat Recovery) is a whole-home ventilation system that extracts stale air from wet rooms, supplies fresh filtered air to living areas and bedrooms, and transfers heat between the two airstreams through a heat exchanger.
- How do I know if I have MVHR?
- Look for a white or grey box in a loft, utility cupboard or ceiling void with two sets of ducts, and valves in the ceilings of kitchens, bathrooms and bedrooms. It usually has a fused spur and a controller or boost switch. Your building's O&M manual or EPC may also state it.
- Does MVHR need to run all the time?
- Yes. It is designed to run continuously at a low background rate and boost when needed. Turning it off allows moisture and pollutants to build up in airtight homes.
- Is MVHR the same as air conditioning?
- No. MVHR provides ventilation and recovers heat. It doesn't cool the air actively, although the summer bypass can stop it warming incoming air on hot days.
Servicing & filters
- How often should MVHR be serviced?
- Once a year, with filters checked every 3–6 months and replaced every 6–12 months.
- How much does an MVHR service cost in London?
- With MVHR Expert it is £140 for a 1-bed, £160 for a 2-bed and £200 for a 3-bed, including filters, heat exchanger clean and an airflow check. Larger homes and multiple units are to be discussed.
- What happens if MVHR filters are never changed?
- Airflow drops, fans work harder, moisture isn't removed properly and the heat exchanger gets dirty. Condensation, mould and stale air usually follow.
- Can I wash MVHR filters?
- Most MVHR filters are disposable and shouldn't be washed. Only reuse a filter if the manufacturer states that it is washable.
Faults & repairs
- Why is my MVHR noisy?
- Common causes are dirty or imbalanced fans, clogged filters, loose ducting or mounting, and valves set to pass too much air.
- Why is my MVHR leaking water?
- Almost always the condensate drain: a dry or blocked trap, a kinked pipe, or an unlevel unit.
- How much does MVHR repair cost?
- A £140 call-out covers attendance and full diagnosis. We quote any repair before starting work.
- Why do I have condensation or mould with MVHR?
- Usually the system isn't moving enough air: blocked filters, switched off or turned down, unbalanced airflow or a fan fault.
Replacement & regulations
- Do you install new MVHR systems?
- No. We service, repair and replace existing MVHR units on existing ductwork. We don't design or install new duct systems.
- Does MVHR need to be commissioned?
- Yes. In England, the commissioning of new fixed mechanical ventilation must be recorded and notified to building control under Approved Document F.
- Do you cover all of London?
- Yes. We cover Greater London (all 32 boroughs and the City of London).
Need an MVHR engineer in London?
Tell us the make of your unit and what's wrong. We'll confirm price and availability the same day.