Choosing between MVHR and PIV is less about finding a universal winner and more about matching the system to your property, airtightness, layout, moisture sources and maintenance capacity. This guide explains how each system works, how to compare installation and running considerations, and how to make a repeatable decision when renovating, moving home or reviewing indoor air quality.
Overview
MVHR and PIV are both whole-house ventilation approaches, but they solve the air movement problem in different ways.
Mechanical ventilation with heat recovery (MVHR) uses separate ductwork to extract stale, moist air from rooms such as kitchens, bathrooms and utility rooms. At the same time, it supplies filtered fresh air to living rooms and bedrooms. A heat exchanger transfers warmth from the outgoing air to the incoming air without mixing the two airflows.
Positive input ventilation (PIV) introduces filtered air into the property, commonly from a loft-mounted unit or an indoor location. The additional air creates a gentle positive pressure that encourages stale air to leave through gaps, vents and existing openings. It is often considered for properties where condensation is linked to insufficient background ventilation and where installing a full duct network would be disruptive.
In simple terms, MVHR is a balanced, ducted system with controlled extraction and supply. PIV is generally a simpler input-led system that relies more on the building fabric and existing routes for air to escape. Neither is automatically the best ventilation system for every house.
Property condition matters. A well-designed MVHR system usually benefits from a reasonably airtight home and enough space for insulated ductwork. PIV can be more practical in some older homes, flats or retrofit projects, but its performance depends on providing suitable routes for stale air to leave. For room-specific moisture problems, such as a bathroom with heavy condensation, an appropriately sized extractor fan may still be needed alongside—or instead of—a whole-house system.
For a room-by-room starting point, see Which Home Ventilation System Do I Need?. If you are diagnosing a problem rather than selecting equipment, review the signs of poor ventilation first.
How to estimate
Compare systems using a consistent checklist rather than focusing only on the equipment price. A useful decision estimate has five stages:
- Define the problem. Record where condensation, musty smells, mould or stuffiness occurs, and whether the issue is seasonal or continuous.
- Describe the property. Note the floor area, number of bedrooms, storey layout, construction age, loft access, available service routes and whether major renovation work is planned.
- Map moisture sources. List bathrooms, kitchens, utility rooms, drying areas and occupancy patterns. A system must be capable of dealing with the actual moisture load, not just the number of rooms.
- Estimate installation complexity. Allow for core drilling, electrical connections, ductwork, grilles, fire-stopping, access panels, making good and commissioning. These items can affect the total more than the fan unit itself.
- Compare the ongoing commitment. Consider filter replacement, cleaning, access for servicing, electricity use, noise and whether occupants will use boost controls correctly.
For a simple scoring method, give each system a score from zero to three against each requirement: property suitability, condensation control, installation disruption, filtration, heat retention, noise, maintenance and future flexibility. Use zero where the system appears unsuitable, one where substantial compromises are likely, two where it is workable, and three where it fits well. The scores are not a substitute for a survey, but they make assumptions visible.
Do not compare a basic PIV quotation with an MVHR quotation that includes extensive ductwork, electrical work and making good without separating the line items. Ask for the same information from each installer: equipment, controls, ducting or air routes, terminals, insulation, commissioning, user instructions, warranty terms and planned maintenance.
Inputs and assumptions
A reliable comparison starts with accurate inputs. Check the following before requesting an installation proposal.
Property and building fabric
MVHR generally needs planned routes between the central unit and supply or extract terminals. New-build properties and homes undergoing major refurbishment may make this easier because ceilings, floors and cupboards can be opened. In a finished home, duct routes may require boxing-in or access through cupboards and loft spaces.
PIV needs a suitable position for the unit and a clear discharge path for displaced air. Existing background ventilation, trickle vents, open chimneys and uncontrolled leakage can influence the result. A survey should consider whether the property can accept the airflow without creating draughts or transferring odours between rooms.
Air quality and moisture
Identify whether the priority is condensation control, filtration, odour removal, reducing stuffiness, protecting a refurbished airtight home, or several of these at once. MVHR offers controlled extraction from wet rooms and filtered supply to habitable rooms. PIV can improve background air movement, but it does not replace local extraction where steam is produced quickly.
Measure humidity in representative rooms rather than relying on one reading. A hygrometer can help reveal patterns, but readings vary with temperature, position and time of day. The guide to indoor humidity levels can help you create a more useful monitoring routine.
Installation and maintenance assumptions
Include access for future filter changes, fan cleaning and inspection of duct connections. MVHR filters need regular attention according to the manufacturer’s instructions, and neglected filters can restrict airflow. PIV units also require cleaning and filter replacement at the specified intervals.
Noise depends on equipment selection, airflow settings, duct design, terminal position and installation quality. Ask to see the proposed unit locations and request commissioning records. A system that is technically capable but poorly balanced may not deliver the expected comfort.
Worked examples
Example 1: An older house with local condensation
Suppose a traditional house has condensation on bedroom windows, limited loft access and a bathroom extractor that is noisy but weak. The owner is not planning a full refurbishment. The initial estimate might favour a retrofit-friendly PIV assessment because the installation could be less disruptive than installing a complete duct network. However, the bathroom still needs effective local extraction, and the installer should check background ventilation and the routes available for stale air to escape.
The decision should not be recorded simply as “PIV is cheaper”. Instead, record the assumptions: no major ceiling works, one main condensation pattern, suitable unit location, acceptable air discharge routes and a separate plan to improve bathroom extraction. If those assumptions change, the recommendation should be reviewed.
Example 2: A renovated or new airtight home
Consider a home being renovated with accessible ceilings, improved airtightness and several wet rooms. The owner wants controlled fresh air in bedrooms, heat recovery and a clear maintenance plan. MVHR may score more strongly because supply and extract can be designed together, with heat recovery and filtration included in the system concept.
The estimate must include insulated ductwork, terminal positions, condensate drainage where required, commissioning and access for filters. It should also allow for coordination with heating, electrics, lighting and joinery. If duct routes cannot be accommodated, a simpler system may become more practical despite the original preference.
Example 3: A flat or apartment
In a flat, check lease restrictions, external-wall permissions, shared ventilation arrangements and the location of existing exhaust terminals before choosing equipment. A whole-house system may be limited by space and the building’s communal design. A targeted solution, such as improved bathroom extraction or a suitable PIV arrangement, may be more realistic, but it must not interfere with shared systems. See the guide to ventilation for flats and apartments before committing to a quotation.
When to recalculate
Revisit the comparison whenever a key input changes. That includes moving from a leaky older home to a refurbished property, replacing windows, adding insulation, converting a loft, changing the number of occupants or creating a new bathroom or utility room. These changes can alter moisture production, airtightness, airflow routes and the amount of ductwork that can be installed.
Recalculate after recurring mould or condensation remains despite normal heating and sensible moisture control. Check the original design, airflow measurements, filter condition, fan settings, ductwork and extract terminals before replacing equipment. A maintenance visit may identify a blocked grille, disconnected duct, dirty filter or incorrect control setting.
Costs should also be refreshed before requesting quotes because labour, access, electrical work, building alterations and equipment availability change over time. Ask installers to separate fixed equipment costs from property-specific work so that quotations remain comparable. For smaller interventions, compare the condition and ducting of an existing fan; the guidance on extractor-fan ducting explains why the route can affect performance.
The practical next step is to create a one-page brief: property type, rooms affected, humidity observations, planned renovation, available installation routes, preferred controls and maintenance access. Obtain a survey rather than choosing from a product label alone, request a written design and commissioning plan, and keep the brief with your maintenance records. That gives you a repeatable way to compare MVHR, PIV and targeted extractor solutions whenever the property or your priorities change.
