What’s preventing you from taking your boat out more often these days? If it’s the thought of being chilled to the bone in an icy cabin and sleeping in multiple layers, we feel your pain.

With Northwest winters averaging in the mid-30s to the mid-40s, it might be time to consider installing a heating system on your boat. Since your Three Sheets crew is about to do just that, we consulted with a few heating experts about how to choose a system, what the considerations are and how much the various options cost.

The bad news: heating a boat can be costly, but depending on the size of your vessel, it can be done without landing you in the poorhouse. And look at it this way—a boat’s an investment and the more you use your investment, the lower the cost per use.

“Heating is expensive, but boating is fantastic in the winter time,” said Roger McAfee, author of the book “The Warm Dry Boat,” who lives in Burnaby, B.C. “You can go places where there’s nobody and have a great time. It’s beautiful.”

Beyond electric space heaters, which can only be used at a dock with AC power unless your boat has a generator, there are three main types of heating systems for boats—potbelly burners, forced air diesel heaters or hydronic systems that use water to heat the boat. All have advantages and drawbacks.

Potbelly burners, the least expensive option, are considered suitable primarily for small boats and can be purchased for around $1,000. The burners require a stack that vents outside of the boat, like a chimney, and are not meant to be used underway since a backdraft could blow soot and smoke into the boat. Fans can be used to circulate heat from the burner to other areas of the boat, but depending on your boat’s layout, you may not get enough heat at either ends.

Hydronic heaters, like this one by Webasto, are the preferred choice for larger boats.

A forced air diesel heater pumps warm air around the boat and requires a ducting system. Hot air systems start at around $2,000 to $3,000, and the general wisdom is that they will sufficiently heat boats of up to about 38 to 40 feet only. For larger boats, a hydronic system is the recommended choice.

Hydronic heating systems, the most expensive option, pump coolant to a radiator with a fan, producing heat that can be controlled by a thermostat. The systems allow heating zones to be set up around the boat so you can control heat in different areas—for example, you could shut off the heat in the galley while keeping it on in your stateroom. Hydronic systems also require ducting, are more complex to install than hot air systems and start at around $5,000.

A fourth and less common option is a diesel stove. Cooking is by far the greatest contributor to moisture inside boats—most boaters cook on propane stoves, and burning a pound of propane produces about 1.5 pounds of water, McAfee said. Butane and compressed natural gas produce even more.

Wallas, a Finland-based company, makes diesel ovens and stoves that draw air from inside the cabin and vent water vapor outside, keeping the cabin dry. Closing a lid on the stove turns it into a cabin heater. Doug McElroy, the co-owner of Scan Marine Equipment in Seattle, which carries Wallas systems exclusively, said the company’s diesel stoves are easily his best-selling item.

“Those are our bread and butter,” he said.

So how do you decide which system is best for your boat? Here are some factors to consider.

Boat use – If you use your boat primarily in summer, with the occasional winter outing, a smaller system may suffice. But if you live aboard, you’ll need a heating system that can hold up to the amount of hours you’ll be using it and with enough output to keep you toasty in all types of weather.

Boat size – It’s important to calculate how much heat you’ll need. Eric Hinze, president and CEO of Sure Marine Service Inc. in Seattle, said boaters often make the mistake of thinking they can just heat the boat’s main cabin. “The heat is going to leach into the rest of the boat and they’ll end up undersized,” he said.

A diesel forced air heater made by Espar

Hinze uses a calculation of cubic footage times 15 for powerboats and cubic footage times 12 for sailboats to determine how much heat—measured in BTUs—is needed.

McAfee emphasizes that boat owners must also take into account the efficiency of the heating unit. Most units are around 80 percent effective, he said, meaning you need to subtract 20 percent from a unit’s listed BTU output to determine how much heat it will really provide.

“In a lot of cases people are forgetting to do that, so they buy a unit that cannot heat their boat,” McAfee said.

But bigger isn’t always better. If a heating system is oversized for the boat it’s in, it will cycle on and off, not running long enough to heat up properly, which can lead to carbon build-up and extra maintenance. Conversely, if the system is too small, it will be running too often and may wear out.

Placement of unit – Because heat rises, heating units should be located low in the boat. Forced air systems should be situated in a location that keeps the ducting as short as possible, since hot air cools as it travels to the output point. With 30 feet of ducting, Hinze said, temperature losses can be as much as 30 degrees. Placement is not as important with hydronic systems, he said, since the temperature differential between the water going into the system’s boiler and the water being pumped around the boat is only about 10 degrees.

Hot water needs – With a forced air system, you may need to run the engine for a while to have hot water. One advantage of a hydronic system is that hot water is available at all times. Ironically, Hinze said, the biggest complaint about hydronic systems is running out of cold water, since boaters that have them tend to take longer showers.

Cost – Smaller hydronic systems can be comparable in price to hot air systems, Hinze said, but as the units get larger, the price difference increases. The least expensive option is a potbelly furnace; for larger boats, you might consider installing two potbelly furnaces as a less costly alternative to a forced air or hydronic system.

Ventilation – Adding heat to a boat allows the air to hold more moisture, increasing the likelihood of developing mold and mildew. Be sure your boat is well-ventilated to allow fresh outside air in. Even when it’s raining, outside air will have a lower relative humidity than the air trapped inside a boat.

Using a dehumidifier can reduce the amount of heat your boat needs while also drying out the air. Use a small, portable home dehumidifier; the few made for marine applications are very costly. But don’t overdo it—over-dehumidification will cause wood to crack.

Combustion air – Some heating systems draw combustion air from outside the boat, while others draw from inside. McElroy likes a heating system to use half inside air, which is warm and also needs to be dried out, and half outside air, which is drier and contains a high amount of oxygen. McAfee cautions that if the system draws outside air only, it won’t dry out the humid air inside the boat and without adequate ventilation, can make a boat damp.

One final consideration: warranties. McAfee said though warranties are ostensibly valid for a specific time period, they are usually based on the number of hours the unit is used. That means they’ll only cover you up to a certain number of hours of use, calculated by average boating habits. He recommends asking a dealer to guarantee in writing that the warranty will cover the time frame specified, regardless of use.

“In most cases, you can’t buy an extended warranty,” he said. “You want the dealer to give you a letter.”