Have you seen users complain about mould in their adventure vehicles despite having a beasty-looking fan roof vent? Yes, that still happens, as good ventilation requires more than just a large roof fan. An effective caravan ventilation system should provide complete cross-ventilation without creating negative pressure. Otherwise, the presence of negative pressure will only lead to "dead zones" of hot, stale or moist air.
If your caravan, campervan, RV or motorhome has a powerful low-voltage fan like a Maxxfan but still has these "dead zones", you'll end up with incomplete air exchange. Any space that does not receive fresh airflow will experience condensation (which leads to mould) and other issues related to poor ventilation. For most people with a standard adventure van, a single roof fan vent, a slightly opened window and one circulating fan are usually enough to achieve maximum air exchange and fresh air movement throughout the space.
In this article, we'll go through the various steps that will help you determine how many fans your adventure vehicle needs for proper air exchange and maximum comfort throughout the year.
Recommended Supplies
- A 900+ CFM roof fan vent: Maxxfan Deluxe Rainproof Vent or Maxxfan Plus Rain-Sensing Vent
- An adjustable circulating fan: Sirocco II Fan or Sirocco Elite Fan
Roof Fan or Circulating Fan: What's the Difference?
Before determining how many fans your caravan needs, it's important to understand that there are two distinct types: roof fans and circulating fans. Each type has unique applications, features and limitations.
In caravanning and RVing, the term roof fan generally refers to fan-assisted vents mounted on the roof of your van. Their primary role is to draw in or expel air. Dual-airflow roof fans feature a reversible fan that allows you to switch between intake and exhaust with ease.
As roof vents, these fans have closable lids that allow air to move in or out of the van. Some models, such as Maxxfan vents, can continue operating with the lid closed (in ceiling fan mode) to circulate air inside the vehicle.
A circulating fan, on the other hand, is a compact, low-voltage fan designed to move the air already inside your van. Thanks to its small footprint, it can be used anywhere inside your caravan, campervan, RV or motorhome without taking up much space.
While circulating fans can improve general airflow, they're especially useful for directing air to specific areas, such as your bed, workspace or resting zone. They feature adjustable heads, with Sirocco models offering the most flexible designs, with near-limitless directional adjustments.
What Determines How Many Fans Your Caravan Needs?
What's the Size of Your Adventure Vehicle?
The first step in determining how many fans your adventure van needs is assessing its internal volume. You can measure the physical dimensions manually or estimate based on its general classification—small, medium or large.
- Small caravans and campervans have an average volume of 450–530 cubic feet
- Medium/standard caravans and campervans have an average of 530–1060 cubic feet
- Large RVs, motorhomes and 5th-wheelers have an average volume of above 1060 cubic feet
Regardless of your vehicle size, the general rule of thumb is that your fans should be able to deliver at least 40 air changes per hour (ACH). This ensures safe and comfortable ventilation, even on very hot days.
What Time Will You Be Off-Grid?
What season do you intend to be on the road? Different times of the year come with different temperature ranges, which will influence how many fans your camper needs. Hotter months require more fresh and cool airflow.
Below is a weather chart showing average seasonal temperature ranges across major regions in Australia:
| Region | Summer | Autumn | Winter | Spring |
|---|---|---|---|---|
| Melbourne Areas | 12.9–25.9°C | 23.9–8.6°C | 6.0–15.0°C | 10.3–24.0°C |
| Brisbane Areas | 19.8–29.1°C | 28.1–13.8°C | 9.5–21.7°C | 12.5–27.3°C |
| Sydney Areas | 17.5–26.4°C | 25.2–10.9°C | 7.1–18.3°C | 10.3–24.0°C |
| Adelaide Areas | 15.1–28.5°C | 26.0–10.4°C | 7.5–16.1°C | 9.2–24.4°C |
| Canberra Areas | 11.4–28.0°C | 24.5–3.2°C | 0.1–13.0°C | 3.3–22.7°C |
| Hobart Areas | 10.8–21.6°C | 20.1–7.0°C | 4.6–13.0°C | 6.4–18.7°C |
| Perth Areas | 14.8–31.9°C | 28.1–10.4°C | 8.0–18.9°C | 8.9–25.8°C |
| Darwin Areas | 24.7–32.6°C | 32.7–22.1°C | 19.3–31.3°C | 23.1–33.3°C |
Does Your Van Have Functional Windows?
Windows are essential for proper ventilation in caravans, campervans, RVs and motorhomes. They facilitate airflow into and out of the vehicle, helping maintain comfort and safety while reducing condensation.
How windows affect the number of fans you need depends on several factors:
- Opening type: This highlights the opening style of the window, which can be sliding, tilt-style, top-hung or side-hung. The most common choices are top-hung windows (ideal for airflow even during rain) and sliding windows that can remain open while driving.
- Window size: This refers to the physical dimensions, ranging from small to large options. A small window is usually excellent for improving insulation, whereas large ones allow faster air exchange.
- Number of windows: The more windows your camper has, the more natural airflow is possible, which reduces the number of fans needed.
- Window placement: The location of windows is also crucial. Stacked windows—those placed at both low and high points—promote continuous air circulation. Warm, moist air rises through the higher openings, while fresh, cooler air enters through the lower ones.
Is Your Adventure Vehicle Properly Insulated?
Insulation is another critical factor when determining how many fans your camper requires. It helps separate indoor temperatures from outdoor conditions by keeping heat out and slowing heat transfer. As a result, good insulation reduces peak temperatures, slows heating and speeds up cooling.
While real-world results vary, insulation generally provides:
- Lower peak temperatures: A well-insulated adventure van can stay 15–25+° cooler on a hot sunny day.
- Slower heat-up rate: Proper insulation significantly slows down how quickly your van heats up. For example, a well-insulated van may take 2–4 hours of direct sunlight to reach a temperature that a poorly insulated van hits in 20–30 minutes.
- Faster cooling: Insulated campers also cool down faster. Poorly insulated vehicles retain heat longer because the metal structure continues radiating heat inward even after the sun is gone.
Other Important Factors to Consider
The four points above are the primary aspects to consider when determining how many fans your camper needs, but they aren't the only ones. You still need to account for the number of occupants on board, available mounting space, your budget and how much power you can safely draw without straining your battery system.
- Occupants of the camper: The more people (and pets) sharing your van, the higher your ventilation needs will be due to increased body heat and moisture.
- Available power supply: The more fans you install in your caravan, campervan or RV, the higher the overall power consumption.
- Space available: The more roof and interior space your camper has, the more fans you can potentially install.
- Budget at hand: Your available budget will also determine the number, type and size of fans you can install. With a sufficient budget, you can install as many fans as you need and choose premium options such as Maxxair or Sirocco, along with the most suitable sizes.
Note: When sizing fans for caravans and other adventure vehicles, the focus is usually on the airflow capacity. Airflow—expressed in CFM (cubic feet per minute) or CMM (cubic metres per minute)—is a measure of how much air a fan can move in a given time. The higher the airflow capacity, the faster the air exchange in your van.
How Many Fans Does a Standard Caravan Need? A Worked Example
Let's assume you have a decent budget, your van has enough installation space, and your off-grid power system is adequate. How many fans can you install for optimal air exchange and ventilation? Here's the breakdown:
- Size of the adventure vehicle: A medium-sized campervan with an interior volume of 1,036 cubic feet.
- Time of year you'll be off-grid: Around 10–15 days every month of the year, switching between your family house in Victoria and the van.
- Does your van have functional windows? Yes. The living area has two large top-hung windows and two compact sliding windows. Each side is fitted with a sliding window at the front door and a large top-hung window at the bunk area (the passenger-side rear).
- Is your adventure vehicle insulated? Yes. The van is properly insulated with XPS board on the floor and polyiso on the walls and ceiling.
A complete ventilation system typically includes both an exhaust and an intake opening. The amount of air expelled must be continuously replaced at the same rate to maintain effective ventilation. This is why professional van builders emphasise the importance of cross-ventilation.
Cross-ventilation allows fresh air to move optimally through your van by having an intake and exhaust opening on opposite sides. With only one opening, your van becomes a humid, stale, mould-prone metal box due to short-circuiting airflow—a situation where negative pressure causes the intake to pull in the same exhausted air. This results in zero (or nearly zero) air exchange and creates dead zones of hot, stale, humid air.
Therefore, for a standard 1,036 ft³ camper, install two Maxxfan Deluxe roof vents placed opposite each other—say one at the front and one at the rear. Set one fan to exhaust and the other to intake to achieve balanced, effective airflow.
Calculations for Proper Sizing (Maxxfan Example)
Two Maxxfan Deluxe vents, each rated at 900 CFM, meet the ideal requirement:
1,036 cubic feet ÷ 900 CFM = 1.15 minutes per full air exchange.
This results in about 52 air exchanges per hour, which is within the recommended 40 CPH (cycles per hour).
Remember, the volume of air pushed out by the exhaust vent must be equally replaced by the intake vent. Therefore, the intake vent should also deliver at least 900 CFM.
What If You Only Have the Budget for One Maxxfan Roof Vent?
A single 900 CFM fan can still serve as the exhaust. But to maintain proper cross-ventilation, your van must have passive intake openings capable of supporting that airflow.
In this case, the passive intake opening(s) must have at least the same surface area as the Maxxfan vent (113 square inches). Two 33 × 10-inch windows placed opposite the fan will provide more than enough intake capacity.
However, it's still advisable to install one or two circulating fans to help move fresh air into every corner of the van. This is especially important in a packed van, with the circulating fans helping push air into areas like behind couches and beds.
Don't Over-Ventilate Your Adventure Vehicle
In summary, that's how you can easily determine how many fans are enough for your caravan, campervan, RV or motorhome. A single 900 CFM roof vent is usually sufficient for a standard camper when paired with a window of similar surface area and a circulating fan on the opposite side.
For larger RVs or motorhomes, you'll still use the same formula:
Interior volume ÷ fan airflow capacity = minimum exhaust and intake airflow required.
If your budget doesn't allow for multiple roof fans, consider combining one powered fan with passive window intakes and circulating fans. Where possible, aim for two powered vents of equal airflow—one for intake and one for exhaust.
That said, don't overdo your ventilation. Installing too many fans or one overly powerful fan can result in diminishing returns, increased negative pressure and uncomfortable interior conditions—defeating the goal of creating an optimal living environment.
Caravan Fan and Ventilation FAQ
How many fans does a standard caravan need?
For most standard campers, a single 900 CFM roof vent paired with a window of similar surface area and a circulating fan on the opposite side is usually sufficient. Where possible, aim for two powered vents of equal airflow—one for intake and one for exhaust.
How much airflow should my caravan fans deliver?
The general rule of thumb is that your fans should deliver at least 40 air changes per hour (ACH). For example, a 1,036 cubic foot camper with a 900 CFM vent achieves a full air exchange every 1.15 minutes—about 52 air exchanges per hour.
What's the difference between a roof fan and a circulating fan?
A roof fan is a fan-assisted vent mounted on the roof that draws in or expels air, with dual-airflow models switching between intake and exhaust. A circulating fan is a compact, low-voltage fan that moves the air already inside your van, ideal for directing airflow to your bed, workspace or resting zone.
Can you install too many fans in a caravan?
Yes. Installing too many fans or one overly powerful fan can result in diminishing returns, increased negative pressure and uncomfortable interior conditions—defeating the goal of an optimal living environment.
Ready to sort your van's airflow? Shop the Maxxfan Deluxe Rainproof Vent and pair it with a Sirocco II circulating fan at Campervan Builders.
