Choosing between MVHR and PIV depends less on which system sounds more advanced and more on your property’s layout, airtightness, moisture problems, installation access and maintenance expectations. This guide compares the two whole-house ventilation options, provides a repeatable way to assess suitability and costs, and shows when your decision should be reviewed.
Overview
MVHR means mechanical ventilation with heat recovery. The system continuously extracts stale, humid air from rooms such as kitchens, bathrooms and utility rooms while supplying filtered fresh air to living rooms and bedrooms. A heat exchanger transfers much of the heat from outgoing air to incoming air without mixing the two air streams. MVHR normally uses a network of ducts connected to a central unit.
PIV, or positive input ventilation, introduces filtered air into the property, commonly through a unit installed in a loft or another suitable location. The additional air pressure encourages stale, moist air to leave through existing vents, gaps and purposeful extraction points. Some systems use warmed input air, while others are designed for different installation locations and property conditions. The exact arrangement should be confirmed during a survey.
Both can form part of a whole-house ventilation system, but they solve the problem in different ways. MVHR is a designed supply-and-extract system that suits homes with a reasonably controlled air envelope and enough space for ductwork. PIV is often considered for retrofit projects where installing multiple ducts would be disruptive, particularly in homes with loft access and persistent condensation concerns.
| Consideration | MVHR | PIV |
|---|---|---|
| Air movement | Mechanical supply and mechanical extract | Mechanical input with air leaving through existing routes and extraction points |
| Heat recovery | Yes, through a heat exchanger | Not normally the defining feature |
| Best starting point | New-builds, major refurbishments or homes where duct routes can be planned | Many retrofit situations, especially where loft installation is practical |
| Installation complexity | Higher because of the central unit, ductwork, terminals and commissioning | Usually simpler, but performance depends on the property and existing air paths |
| Maintenance | Filter changes, cleaning checks and periodic inspection of the unit and ductwork | Filter changes, fan checks and inspection of terminals, vents and air paths |
There is no universal answer to “the best ventilation system for a house”. A well-designed system that is correctly sized, commissioned and maintained is more important than choosing a particular label. If you are also considering local solutions, compare them with a whole-house approach in this room-by-room ventilation guide.
How to estimate
Start with a simple decision-and-cost worksheet rather than asking for a price based only on floor area. Record the following:
- Property type: detached, semi-detached, terraced, flat, bungalow or a converted property.
- Number of rooms: note bedrooms, bathrooms, kitchen, utility spaces and rooms where people spend substantial time.
- Access: identify loft access, service cupboards, ceiling voids, risers and possible routes between the central unit and each room.
- Moisture symptoms: record window condensation, mould, musty odours, peeling finishes and humidity readings by room and time of day.
- Existing ventilation: list extractor fans, trickle vents, airbricks, passive vents and any systems that no longer work effectively.
- Fabric and occupancy: note insulation improvements, replacement windows, solid walls, occupancy levels, drying laundry indoors and cooking or bathing patterns.
Then request a written quotation that separates equipment, ducting or terminals, electrical work, access preparation, commissioning, controls and future maintenance. This makes it easier to compare like with like. A low installation price may not represent good value if it excludes difficult access, required repairs, balancing or commissioning.
A useful comparison is to calculate an estimated whole-life cost:
Whole-life estimate = installation cost + planned maintenance + replacement parts − avoided remedial work.
This is not a promise of financial savings. It is a way to include items that are often overlooked, such as filter purchases, fan replacements, cleaning, electrical work and repairs to moisture-damaged finishes. Use the same time period and assumptions for each option, and ask the installer to identify which figures are estimates.
For an MVHR quotation, check whether the design includes supply and extract terminals, insulated ductwork where needed, condensate drainage, controls, access for filter changes and commissioning. For PIV system installation, check the unit location, input route, filter specification, discharge paths, interaction with existing extractor fans and whether the loft or other installation space is suitable.
Inputs and assumptions
Several property conditions can change the recommendation.
Airtightness and air leakage
MVHR works most predictably when air movement is controlled through designed supply and extract routes. Excessive leakage can reduce the amount of air passing through the heat exchanger and make balancing more difficult. This does not mean every older home needs major building work, but the installer should consider the condition of doors, windows, loft hatches, service penetrations and other leakage paths.
Space for ducts and equipment
MVHR needs a practical location for the unit and routes for ductwork. Ducts may be concealed above ceilings, within cupboards, in lofts or through planned service zones. Long, poorly routed or sharply bent ductwork can affect airflow and noise, so ask for the proposed route rather than relying on a headline specification.
PIV generally requires less internal ducting, but it still needs a suitable unit location and an effective route for air to move through the home. Closed internal doors, blocked vents, inadequate extract fans or unusually airtight rooms can affect the result. PIV should not automatically be treated as a replacement for dedicated kitchen or bathroom extraction.
Moisture sources
Ventilation can help manage moisture, but it does not repair plumbing leaks, penetrating damp, rising damp, roof defects or failed seals. Identify and resolve those causes before judging a ventilation system. Likewise, heating patterns, drying clothes indoors and inadequate use of existing fans can all contribute to condensation.
Running and maintenance assumptions
Both systems require ongoing attention. MVHR filters need changing according to the manufacturer’s instructions and the property’s air quality. The heat exchanger, condensate arrangements, grilles and ductwork should be checked as appropriate. PIV filters and fan components also need inspection, while vents and extraction routes must remain clear. Include these tasks when comparing systems, not just the initial installation.
Use a reliable hygrometer to track patterns rather than relying only on a single reading. The hygrometer buying guide explains what to look for. Persistent symptoms should also be investigated alongside the wider signs of poor ventilation described in this inspection checklist.
Worked examples
Example 1: A home undergoing major refurbishment
Suppose a homeowner is replacing ceilings, improving insulation and reorganising a utility area. The property has accessible service zones and the owner wants controlled fresh-air supply to bedrooms and living spaces, with continuous extraction from wet rooms. In this situation, MVHR may be a strong candidate because duct routes can be planned before finishes are completed. The estimate should include the unit, distribution system, terminals, drainage, controls, electrical connection, commissioning and future filter costs.
The homeowner should ask for room-by-room airflow design and confirmation that the proposed terminals can be accessed for cleaning. If the refurbishment makes duct routing impractical after all, a PIV or mixed strategy may be considered, but that decision should follow the survey rather than the initial assumption.
Example 2: An occupied older house with loft access
Consider an older house with recurring window condensation, a reachable loft, limited ceiling access and no appetite for extensive redecoration. A loft-based PIV system may be easier to install than a fully ducted MVHR system. The assessment still needs to check the loft environment, insulation and air paths, as well as the performance of existing kitchen and bathroom extraction.
The quotation should make clear what the PIV system is expected to address and what it cannot address. If mould is concentrated around a cold bridge or caused by a leak, ventilation alone will not remove the underlying problem. Local extractor fan repairs or an appropriate bathroom extraction upgrade may be required as part of the wider solution.
Example 3: A flat or apartment
In a flat, the decision may be constrained by lease conditions, limited external wall access, communal shafts, fire separation and noise concerns. A central whole-house system may not be feasible without building approval and careful coordination. A survey should establish what can legally and technically be altered before an installer recommends MVHR or PIV. See the guidance on ventilation options for flats and apartments before requesting detailed quotes.
When to recalculate
Revisit the comparison whenever a major input changes. That includes a loft conversion, new windows, insulation work, a change in occupancy, a new kitchen or bathroom, persistent mould, a failed extractor fan, or a change in the intended location of the ventilation unit.
Recalculate costs when installer rates, equipment specifications, electrical requirements or access conditions change. Ask for revised written quotes rather than applying an old allowance to a new project. Product availability and manufacturer maintenance requirements can also change, so confirm filter types, warranty conditions and service intervals before ordering.
Use this final checklist before choosing a system:
- Has the property been surveyed rather than assessed from floor area alone?
- Are moisture sources and building defects being addressed separately?
- Does the proposal show where air enters, where it leaves and how airflow will be balanced?
- Are kitchen and bathroom extraction needs covered?
- Are noise, access, controls, electrical work and condensate arrangements explained?
- Does the quote include commissioning and a maintenance plan?
- Have you compared the same inclusions and assumptions across suppliers?
MVHR can be appropriate where controlled, balanced ventilation and heat recovery justify a more involved installation. PIV can be practical where a retrofit needs a simpler whole-house input approach. The best outcome comes from matching the system to the building, then keeping it correctly maintained. For broader retrofit considerations, read this guide to whole-house ventilation in older UK homes.
