Choosing between MVHR and PIV is less about finding a universally “best” system and more about matching ventilation to your property, moisture problems, installation access and maintenance capacity. This guide gives you a repeatable way to compare the two systems, estimate the likely installation workload and decide when a professional survey is worthwhile.
Overview
Mechanical ventilation with heat recovery (MVHR) and positive input ventilation (PIV) are both whole-home approaches, but they work in different ways.
An MVHR system extracts stale, moist air from rooms such as kitchens, bathrooms and utility rooms. At the same time, it supplies filtered outdoor air to living rooms and bedrooms. A heat exchanger transfers some of the warmth from outgoing air to incoming air, while the two airstreams remain separate. This makes MVHR particularly relevant to well-insulated homes where controlled airflow and energy efficiency are important design goals.
A PIV system introduces a measured supply of filtered air into the property, often from a loft-mounted unit or an internal location designed for the installation. The incoming air gently increases the pressure inside the home, encouraging stale air to leave through existing gaps, vents and normal leakage paths. PIV system installation is often considered for existing homes with condensation, musty odours or persistent humidity where installing a complete duct network would be disruptive.
Neither system replaces good moisture control. Cooking, bathing, drying clothes indoors, leaks and inadequate heating can all contribute to condensation. A ventilation survey should consider the source of moisture, the building fabric, existing fans, windows, loft conditions and the way rooms are used.
As a general comparison, MVHR offers more direct control over where air is extracted and supplied, but normally requires careful design and ductwork. PIV can be simpler to retrofit, but it relies more heavily on the building’s existing airflow paths and may be less suitable where the property is very leaky, unusually compartmentalised or affected by significant local moisture sources.
How to estimate
Start by scoring the project against four practical factors: property suitability, installation complexity, ongoing maintenance and the result you need. This is more useful than comparing equipment labels alone.
- Define the problem. List where condensation appears, when it occurs and whether there are odours, mould patches, cold surfaces or poor airflow. A single damp bathroom may need improved local extraction rather than a whole-house ventilation system.
- Map the property. Record the number of floors, bedrooms, bathrooms, kitchen position, loft access, ceiling voids and likely routes for ducts or electrical supplies.
- Check the building fabric. Note draughts, open fireplaces, blocked airbricks, replacement windows, insulation work and signs of penetrating or rising damp. Ventilation cannot correct every type of damp.
- Estimate installation work. For MVHR, count the supply and extract rooms, the likely duct routes, access panels, external terminals and commissioning requirements. For PIV, check the unit position, supply route, filter access, power supply and how air can move between rooms.
- Estimate maintenance effort. Include filter changes, cleaning, inspection of grilles and ductwork, fan checks and any future access needed for servicing.
A simple comparison worksheet can use a score from 1 to 3 for each factor: 1 means straightforward, 2 means moderate and 3 means demanding. Add separate notes rather than treating the total as a technical verdict. A high installation score for MVHR may reflect ductwork access, while a high property-suitability score for PIV may indicate that the home lacks reliable routes for displaced air.
For financial planning, request itemised quotations rather than relying on a single headline figure. Ask installers to separate equipment, labour, ductwork or alterations, electrical work, commissioning, remedial building work and ongoing maintenance. This makes the comparison more reliable when designs differ. For broader budgeting, see Home Ventilation Costs in the UK.
Inputs and assumptions
Your decision should be based on the following inputs, not on property size alone.
Property type and airtightness
MVHR generally benefits from a home where the ventilation strategy can be designed as a controlled system. Newer or substantially renovated homes may offer easier access to ducts and fewer uncontrolled air paths. Older homes can still use MVHR, but the survey should consider draughts, room layouts and the practical route for ductwork.
PIV may suit an existing house where a loft installation is feasible and air can circulate from the supply point to rooms that need fresher air. If internal doors are tightly sealed, rooms are divided into many separate zones or the property has unusual air leakage, the installer should explain how the system will perform in practice.
Moisture sources
Identify whether humidity is general or concentrated. Persistent steam after showers may call for better bathroom extraction, while widespread condensation across several rooms may justify a whole-house assessment. Drying laundry indoors, inadequate cooker extraction and unvented tumble dryers can all change the ventilation requirement.
Access and disruption
MVHR installation UK projects can involve duct routes above ceilings, within service voids or through cupboards. The design should show where grilles, ducts, silencers, condensate drainage and the central unit will be located. PIV installation usually has fewer distribution ducts, but the unit still needs accessible filters, a suitable discharge or supply arrangement and safe electrical installation.
Maintenance assumptions
Every system needs maintenance. MVHR filters need checking and replacing at intervals suited to the home and local air conditions. Extract valves and supply grilles should remain clean, and the system should be checked if airflow, noise or odours change. PIV filters also need regular attention; a blocked filter can reduce performance. Keep the installation manual and record filter changes so future servicing is straightforward.
Ask the installer how the system will be commissioned and what measurements will be provided. A correctly installed unit is not enough if airflow rates are not checked and controls are not explained to the homeowner.
Worked examples
Example 1: An older house with widespread condensation
Suppose a two-storey house has condensation on bedroom windows, a musty loft and moisture after bathing. There is good loft access, but limited space for concealed ductwork. The first step is to rule out leaks and check bathroom and kitchen extraction. If moisture is spread across the property and the loft can accommodate a suitably positioned unit, PIV may be a practical option to investigate.
The estimate should include the unit, electrical connection, filter access, any loft insulation or cold-surface considerations, commissioning and follow-up checks. The homeowner should also improve moisture habits and confirm that air can move beneath or around internal doors where required. If the bathroom remains humid after showers, a dedicated extractor fan may still be needed.
Example 2: A renovation with accessible service routes
Consider a home renovation where ceilings are already open, insulation is being upgraded and the owner wants controlled supply and extraction in bedrooms, bathrooms, the kitchen and utility area. This is a stronger case for assessing MVHR. The project estimate should list the central unit, duct sizes and routes, terminals, condensate drainage, controls, electrical work, making good, commissioning and maintenance access.
The key risk is not simply the equipment cost. Poorly planned routes, inaccessible filters, excessive bends or inadequate acoustic treatment can affect the finished result. A detailed design review before ceilings are closed is therefore part of the installation value.
Example 3: A flat with limited external alterations
For a flat, first establish what changes are permitted to external walls, communal areas, loft spaces and existing ventilation routes. A whole-house system may not be appropriate or permitted without coordination. The comparison may instead include improved continuous extract, a local bathroom fan, kitchen extractor replacement or a compact ventilation approach. Read more about options in Ventilation for Flats and Apartments.
When to recalculate
Revisit the MVHR versus PIV decision whenever the property or the ventilation problem changes. Recalculate the installation scope after an extension, loft conversion, window replacement, insulation project or change of room use. A new open-plan kitchen, for example, can alter extraction needs and duct routes.
Update your comparison when you receive a quotation with different assumptions, such as included electrical work, building repairs, commissioning or maintenance. Equipment availability and labour rates can also change, so use current written quotations rather than old online price examples. The same applies when planning permission, building-control expectations or manufacturer requirements may affect the proposed work: confirm the current position for your project.
After installation, reassess performance rather than judging it only by appearance. Check whether condensation is reducing, whether rooms feel stuffy, whether fans or grilles are noisy and whether filters are accessible. If mould continues, investigate the underlying cause instead of simply increasing fan speed. A useful next step may be a humidity assessment, targeted extractor fan installation or inspection for damp unrelated to ventilation. The room-by-room guidance in How to Stop Condensation and Mould in Your Home can help structure that review.
In short, choose MVHR when you need a designed supply-and-extract system and can support the ductwork and commissioning it requires. Investigate PIV when you need a simpler retrofit approach and the property offers suitable airflow paths. Before committing, obtain a room-by-room assessment, an itemised quote and a clear maintenance plan. That process is the most dependable way to identify the best ventilation system for your house.
