It’s Not (Just) the Heat; It’s the Humidity

With an electric brewing system, it’s not just a matter of figuring out how to heat water and boil the wort; ventilation is every bit as important. Here are some things you should consider as you design your dream system.

Jester Goldman Dec 23, 2016 - 7 min read

It’s Not (Just) the Heat; It’s the Humidity Primary Image

Like many beginners, I started homebrewing in my kitchen. Now I have a 10-gallon (38-liter) outdoor propane setup, but I miss the convenience of brewing indoors where weather is less of a concern. Electric brewing systems look really attractive, especially when winter blows in, but it’s not just a matter of figuring out how to heat water and boil the wort; ventilation is every bit as important, and it can be a pricey problem to solve.

Before we go any further, I want to lay down some ground rules. While it is possible to set up an indoor brewery using gas burners, it takes some serious planning and engineering to protect yourself from carbon monoxide poisoning. You have to either create a contained combustion/exhaust system or handle some extreme ventilation requirements. So, let’s just focus on electric setups.

Steamy Sessions

During a typical hour-long boil, 1 to 2 gallons (4 to 7 liters) of water are lost to evaporation. That can turn a sealed room into a sauna, with condensation dripping from the walls, ceilings, and windows. While you can wipe down those surfaces, persistent humidity in the room can lead to mold problems, water damage, and—worst of all—infected beer.

Unfortunately, opening a window while you brew won’t have much of an effect, even with a household fan to increase the airflow. To get the humidity out requires more serious air movement, and it helps if you can draw directly from the source. What you need is a hood, but a typical kitchen range hood won’t do. Its fan is underpowered, and some kitchen hoods can’t even be ducted outside.


Commercial kitchen hoods work great, but they’re usually quite expensive. If you do pick one up, note that there are two types of commercial exhaust systems, each aimed at a different application. A Type I hood is intended for use over a cooking surface where grease is a factor. A Type II hood is designed to vent moisture and heat from grease-free sources, such as a dishwasher or oven. This second type, also known as a condensate hood, is what you want.

Guide to Condensate Hoods

When designing your ventilation system, there are a few factors to consider: air intake, airflow, and condensation handling.

Air Intake

Put the intake as close to your brew kettle as possible, to draw the steam in directly before it dissipates into the room. Ideally, the hood will extend a bit outside the bounds of the top of your kettle. A box design works best, because it can accommodate both the brew pot and hot liquor tank.

Airflow Requirements

Airflow is dependent on the fan driving the system, the geometry of the ducting, and the free flow of makeup air into the system. This last item is often overlooked. Since the system is forcing air out of the room, there needs to be enough replacement air coming in from outside. If the room or house is too tightly sealed and the system is short on makeup air, it will either underperform because it can’t depressurize your house or—worse—it may backdraft your chimney or gas appliances. You may need to open a window in the room to supply the system with sufficient makeup air.

But how much air do you need to move? John Blichmann of Blichmann Engineering offers a good rule of thumb for electric brewing systems: take the size of your electrical elements in watts and divide this by 17.6 to get the number of cubic feet of air per minute (CFM). So, if you’re using a single 5,500-watt heating element, then your airflow requirement is 5,500/17.6, or 312.50 CFM. Inline centrifugal or vortex fans are the most efficient choice, and they can be sized to handle most home breweries.

Blichmann’s rule of thumb is based on running a maximum length of 100 feet (30 meters) of smooth duct. If you needed to run a longer distance than that, you’d need a stronger fan to account for the additional drag. It’s unlikely that your setup would actually need more than 100 feet, but this is where geometry has an impact. Any turns will slow down the airflow, too. Blichmann states that a 90° elbow is equivalent to 10 feet (3 meters) of straight duct, but other HVAC sources suggest an equivalent length of 20–30 feet (6–9 meters). In any case, you should avoid turns as much as possible, or you may need to scale up your fan.

Condensation Handling

The fan may suck the steam out of the room, but condensation within the system itself can become a problem. The design needs to minimize the conditions that favor condensation. In particular, you should use smooth ducting rather than ribbed flexible ductwork. In addition, insulation on the outside of the duct will reduce temperature differences that would drive condensation. You’ll likely still collect some moisture, so make sure you have a way to drain that from the system and not let it drip back into your brew kettle. Two good ideas are to install drain holes at the low points of the duct and to make sure the hood frame has a gutter along the bottom edge for water to collect.

Closing Thoughts

Indoor brewing is convenient, but building out a good electrical brew system is not a cheap proposition. Despite this, don’t try to cut corners on ventilation. Mold problems can be hard to eradicate, and a moister environment can contribute to infection problems in your beer. Learn how to convert your propane system or build an electric system from the ground up with Craft Beer & Brewing Magazine®’s How to Build Your Electric Brewery two-part online class. Sign up today!