A modular home is an airtight structure — far tighter than classic brick construction. Without deliberate ventilation you get moisture, stale odors and mold within weeks. This guide shows when gravity flow is enough and when a heat recovery unit is worth the investment — with the full bill of costs.
Short answer: it depends on how the home is used and by whom. A modular home is factory-tight — aluminium windows with gaskets, doors with a sealed threshold, walls with a vapor barrier layer. That's great for holding heat, but it kills passive air exchange. In a classic brick building, air moves through thousands of tiny gaps in the structure. In a modular home, those gaps essentially don't exist.
The consequences of insufficient ventilation show up within 2–3 months of moving in:
The walls of a modular home have a timber core — a stud frame plus mineral wool insulation. Wood is hygroscopic: it soaks up moisture from indoor air and releases it when the air is dry. The trouble starts when indoor relative humidity stays above 65% for more than 3 weeks. Then:
More on how good insulation and airtightness protect a home from losses: Insulation and airtightness of modular home walls.
In a modular home we use three approaches. Each has its place — the table below shows the differences in numbers for a year-round 38 m² home (2 occupants, 8-month heating season):
| Parameter | Gravity | Mechanical exhaust | Heat recovery |
|---|---|---|---|
| Installation cost | PLN 1,500–3,000 (EUR 330–670) | PLN 4,000–7,000 (EUR 890–1,555) | PLN 12,000–18,000 (EUR 2,670–4,000) |
| Electricity use / year | PLN 0 | PLN 150–250 (EUR 35–55) | PLN 350–550 (EUR 80–125) |
| Winter heat loss | High (30–40%) | High (25–35%) | Low (5–10%) |
| Heating savings | — | — | PLN 800–1,400/yr (EUR 180–310) |
| Heat recovery efficiency | 0% | 0% | 85–92% |
| PM2.5 filtration | None | None | 65% (F7) up to 99.95% (HEPA) |
| Humidity control | None | Partial | Full |
| Unit noise | 0 dB | 25–35 dB | 18–28 dB |
| Annual filter change | — | — | PLN 120–350 (EUR 27–78) |
| Service every 3 years | — | PLN 200 (EUR 45) | PLN 400–600 (EUR 90–135) |
Simplest of all: window inlets plus exhaust ducts in the bathroom and kitchen with a plain grille. It runs on a pressure differential — the colder it is outside, the stronger the exchange. In summer, on a still day, it basically stops. A good option for a recreational cabin used from April to October.
A fan pulls stale air out of the bathroom and kitchen; fresh air enters through window inlets. Constant exchange, independent of weather. In winter it pulls cold air into the interior — that is a direct heat loss. A sensible minimum for a 38 m² home used all year if you don't invest in heat recovery.
A central unit with a cross-flow or counter-flow exchanger. Outgoing stale air warms the incoming fresh air — without the two streams mixing. Recovery efficiency: 85–92%. Extra features: dust filtration, humidity control, night mode, summer bypass. Makes sense from the moment the home is lived in year-round, every day.
Central unit capacity is sized to the home's air volume (not just floor area) and the number of permanent occupants. Rule of thumb: two air changes per hour in standard mode, four changes in boost mode (cooking, showering).
More on matching heating to home size: Heating a modular home — heat pump, electric, air conditioning.
Clients often ask whether heat recovery can be added after the home has been delivered. Answer: yes, but at higher cost and with limits. You have to find space for the central unit (min. 55 × 55 × 65 cm), route 125–160 mm ducts, and design a condensate drain. In a modular home there are three scenarios:
Practical advice: if you're considering heat recovery, commit at the order stage. The manufacturer then prepares the ceiling with ready-made pass-throughs and a spot for the central unit. You add PLN 12,000–18,000 (38 m² home) to the price of the home, instead of PLN 15,000–23,000 after delivery.
A standard heat recovery unit ships with an F7-class filter on the intake — it catches 65% of PM2.5 particles. That's enough in most situations. But during the heating season in many Polish cities, PM2.5 concentrations exceed WHO limits 3–5 times over — and then F7 still lets too much through.
The fix: upgrade to a HEPA H13 filter. It stops over 99.95% of 0.3 μm particles. The effect: indoor air with operating-room parameters — without letting the smog from outside get in.
| Filter | PM2.5 efficiency | Cost / unit | Change interval | Annual cost |
|---|---|---|---|---|
| G4 (basic) | 30% | PLN 15–30 | 3 months | PLN 60–120 |
| F7 (standard) | 65% | PLN 60–120 | 6 months | PLN 120–240 |
| HEPA H13 | 99.95% | PLN 200–400 | 12 months | PLN 200–400 |
It also pays to add a PM2.5 + CO₂ sensor (cost PLN 300–600) — it shows in real time how air quality changes when you activate boost or open a window. Brink Plus and Zehnder Q series units include this on the control panel from the factory.
How good ventilation affects your bills: Bills and running costs in a modular home — real numbers. And how to prep the home for winter when ventilation is under the heaviest load: Wintering a modular home — checklist.
Yes — in bypass mode it skips the heat exchanger and lets in fresh, cooler air without warming it. In the evening you can effectively "air out" the home without opening windows and letting mosquitoes in.
No — the unit's exhaust diffuser replaces the fan. It ramps up automatically based on a humidity sensor or the light switch.
The unit stops. The home stays airtight — if the outage lasts more than 6 hours it's worth cracking a window for 10 minutes. Modern units feature SMS alerts plus an automatic emergency intake damper.
Economically calculated lifespan: 15–20 years. EC-type fans are replaced after 12–15 years (PLN 500–800); the ceramic or aluminum exchanger essentially never wears out.
Yes. A filter swap takes 3 minutes: open the unit door, pull out the old one, slide the new one in. Manufacturers class filters as a consumable — it doesn't affect the warranty.
Heat recovery in a modular home pays off when at least two of three conditions are met:
For a weekend 20 m² cabin, gravity is enough. For a 38 m² year-round home with 2 occupants, mechanical exhaust is the minimum and heat recovery is an investment with a 6–8 year payback. For a 74 m² home with 4 occupants, heat recovery is essentially standard. Ask MP Modular for a quote sized to your model and usage profile — we'll show you concrete numbers for your plot, electricity tariff and regional climate.
Call us — we'll prepare a heat recovery quote and annual cost comparison for your model. No obligation.
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