Damp House Ventilation: The Complete VMC, VMI, VPH Guide
Proper ventilation is the key to eliminating condensation dampness. This guide compares all solutions: single-flow, double-flow, humidity-controlled VMC, VMI, and VPH. Find the system adapted to your situation and your budget.
Why ventilation is essential
A family of 4 produces an average of 12 liters of water vapor per day(breathing, cooking, showers, laundry). Without effective ventilation, this moisture condenses on cold surfaces and causes mold and damage.
1. The role of ventilation against dampness
Ventilation's mission is to evacuate stale and humid air from your home and replace it with fresh outdoor air. This is the most effective way to fight against condensation.
Sources of indoor humidity
Breathing
1 to 1.5 L/day/person
Shower
0.5 to 1 L per shower
Cooking
1 to 2 L/day
Drying laundry
2 to 3 L per load
Air renewal flow rate
French regulations impose a minimum air renewal flow rate, calculated according to the surface area and number of rooms. For a 3-room home, the total flow rate must be at least 75 m³/h in the kitchen + 30 m³/h in the bathroom.
Insufficient flow = moisture accumulation = condensation and mold.
2. Single-flow VMC: the standard
Single-flow VMC (Mechanical Controlled Ventilation) is the most widespread system in France. A motorized extractor, generally placed in the attic, sucks stale air from humid rooms (kitchen, bathroom, WC) via extraction vents.
Fresh air enters through air inlets located on the windows of main rooms (bedrooms, living room). Circulation occurs naturally from dry rooms towards humid rooms.
Pros
- • Affordable price (500-1500€ installed)
- • Simple and fast installation
- • Little maintenance (filter cleaning)
- • Quiet operation
- • Low electricity consumption
Cons
- • Significant heat losses in winter
- • Constant flow (over or under-ventilation)
- • Air inlets can create drafts
- • Noise from air inlets can sometimes be annoying
3. Humidity-controlled VMC: the smart evolution
Humidity-controlled VMC is an evolution of single-flow VMC. It automatically adjusts its flow rate according to the detected humidity level. When humidity increases (shower, cooking), the vents open further. When it drops, they partially close.
Two types exist: Hygro A (only extraction vents are humidity-controlled) and Hygro B (air inlets also humidity-controlled, more efficient).
Pros
- • Automatic adaptation to actual needs
- • Heating savings (30% vs single-flow)
- • Fewer drafts in winter
- • Eligible for grants (CEE, MaPrimeRénov)
- • Optimal comfort
Cons
- • Higher price than single-flow
- • Still some heat losses (lesser)
- • Humidity-controlled vents to be replaced (10-15 years)
4. Double-flow VMC: the high-end choice
Double-flow VMC is the most energy-efficient system. It uses a heat exchanger to recover up to 90% of the heat from the extracted air and transfer it to the supplied fresh air.
Unlike other systems, the fresh air is preheated before entering the home. No more need for air inlets on windows: air is supplied mechanically into living rooms.
Pros
- • Major heating savings (up to 25%)
- • No cold drafts
- • Filtration of incoming air (pollen, pollution)
- • Optimal thermal comfort
- • Eligible for significant grants
Cons
- • High price (3000-7000€ installed)
- • Complex installation (double duct network)
- • Regular filter maintenance
- • Higher electricity consumption
- • Difficult in renovation without an attic
5. VMI: ventilation by positive pressure
VMI (Ventilation Mécanique par Insufflation) works the opposite way of a VMC. It supplies filtered and slightly preheated fresh air from the attic or a technical room. Stale air is naturally evacuated through passive extraction vents.
This system creates a slight positive pressure in the home, which prevents the infiltration of uncontrolled outside air and reduces condensation problems on cold walls.
Pros
- • Very effective against condensation
- • Filtered air (pollen, dust)
- • Air preheating possible
- • Simple installation (single point)
- • Well-suited for renovation
Cons
- • Higher price than single-flow VMC
- • Electricity consumption (preheating)
- • Requires air outlets (to be created if missing)
- • Less efficiency in summer (without air conditioning)
6. VPH: Humidity-controlled Positive Ventilation
VPH is the evolution of VMI with humidity-controlled regulation. It automatically adjusts the supplied air flow rate based on the ambient humidity level. It is currently the most effective solution for treating condensation problems in old houses with poor ventilation.
The system generally includes air preheating (electric resistance or heat recovery) and high-performance filtration.
Pros
- • Very effective against humidity
- • Smart automatic regulation
- • Optimal air filtration
- • Simple installation
- • Ideal for renovation
- • Improves indoor air quality
Cons
- • High price (3000-6000€)
- • Significant electricity consumption
- • Regular filter maintenance
- • Fewer grants available than VMC
7. Full comparison table
| System | Installed Price | Cost/year | Anti-humidity | Renovation |
|---|---|---|---|---|
| Single-flow VMC | 500-1500€ | 20-40€ | ⭐⭐ | ⭐⭐⭐ |
| Hygro B VMC | 1000-2500€ | 15-30€ | ⭐⭐⭐ | ⭐⭐⭐ |
| Double-flow VMC | 3000-7000€ | 50-100€ | ⭐⭐⭐⭐ | ⭐⭐ |
| VMI | 2500-5000€ | 80-150€ | ⭐⭐⭐⭐ | ⭐⭐⭐⭐ |
| VPH | 3000-6000€ | 100-200€ | ⭐⭐⭐⭐⭐ | ⭐⭐⭐⭐ |
8. How to choose according to your situation
🏗️ New construction
Opt for a double-flow VMC. Installation is simpler in new builds (ducts integrated into partitions) and energy savings will offset the extra cost.
Recommendation: Double-flow VMC with heat recovery
🏠 Old house with condensation
Prioritize a VMI or VPH. These systems are easy to install in renovation (single supply point) and very effective against condensation thanks to positive pressure.
Recommendation: VPH if budget allows, otherwise VMI
💰 Small budget
The Hygro type B VMC offers the best value for money. It is eligible for grants (CEE, MaPrimeRénov) which can cover part of the cost.
Recommendation: Hygro B VMC with grants
🏢 Apartment
In condominiums, you generally cannot modify the collective VMC. However, you can install an autonomous air extractor in the bathroom or opt for an individual VMI.
Recommendation: humidity-controlled extractor or compact VMI
In summary
Ventilation is the key to eliminating condensation dampness. For an old house with humidity problems, VMI or VPH are generally the best options. For new construction or a complete renovation, double-flow VMC remains the optimal choice.
Don't forget that ventilation must be adapted to your home and your usage. Have a professional carry out a study to correctly size your installation.