Boat Heating Boat Maintenance

Choosing a Boat Heater (Part One)

Monday, January 16, 2017S.V. CAMBRIA

When we arrived in the Pacific Northwest eight years ago, Cambria lacked one vital piece of equipment for cruising the Inside Passage: a heater. So, one of the first things we did was to rectify that. David started researching our options while we were still in California and by the time we rounded Cape Flattery, he’d made a decision.

Like everything else on a boat, heating presents some issues that can be difficult and expensive to overcome – available space for equipment and ducting, access to outside air, multiple cabins to heat (to name just a few). But there are several types of marine heaters* on the market and choosing the right one is an important step in overcoming these challenges.

Bulkhead-Mounted Diesel Heaters
Photos courtesy of Dickinson Marine.
Dickinson and others make bulkhead and floor mounted units (also known as potbelly burners) that resemble a piece of art. With the right boat, this would have been my preference. I love the idea of a working fire and, had we been able to go the wood-burning route, collecting fuel from the beach would have become a fun pastime.

In the world of boat heaters, there are a lot of positives to these types of units: They’re tried and true, use diesel fuel (as opposed to propane), have no moving parts (except a fan during startup) and are easy to use. They’re also economically priced. A Dickinson Antarctic Floor Mounted Diesel Heater (their largest unit) is $899 with an additional $300 or so in materials. And they’re economical to use, costing less than US$3.00 for 24 hours of running time.

There are also some negatives to these types of units: They’re spec’d for smaller boats (30 to 40 feet). They’re only effective at heating one space rather than the entire boat (fans can be used to circulate the heat to other areas of the boat but not efficiently). And they shouldn’t be used while underway (or sometimes in strong winds) because back-drafts can blow soot and smoke into the boat.

Unfortunately, Cambria is compartmentalized in its layout and a bulkhead or floor mounted unit in the salon wouldn’t service the aft cabin or v-berth. More importantly, we don’t have the bulkhead or floor space to accommodate one. And then, of course, there’s the chimney. Cutting a 3-inch hole through the cabin top for the flue isn’t something either of us was willing to do. So, we needed to move on to central heating, a more expensive option.

Forced Air Heaters

The simplest type of forced-air heater is probably the Red Dot which uses engine coolant that’s been circulated through a heat exchanger and a fan to blow heated air into a living space. But it only works when the engine is running so, once again, this wasn’t a viable option for us.

Webasto and Espar are probably the best known forced air heaters on the market. Both companies build for buses and trucks but also offer marinized units for boats in several different sizes to service boats up to 38 feet, though Espar has come out with a newer model (the Airtronic D5) which, according to the specs, will heat sailboats in the 45-foot range**. 

Graphic courtesy of Espar.
With forced air systems, the burner draws combustion air from outside the boat as well as from inside and burns it in a chamber with an air-to-air heat exchanger. A blower unit then forces the heated air through flexible ducting to outlets in the boat. The furnace unit is designed to be installed inside the engine room or someplace out of sight. Most burn diesel, consuming 0.02 (lowest) to 0.17 (highest) gallons per hour, so close proximity to the tanks is helpful. They also require battery power and draw anywhere from 0.67 (lowest) amps to 7.1 (highest) amps when they’re running, depending on the size.

Prices for the furnace units range from $1,000 for a 7,000 BTU unit to over $3,800 for a 18,000 BTU unit. Additional costs include the fuel pickup line, exhaust hose, through hull, electrical wiring, thermostat, ducting, fan units, and registers.

Graphic courtesy of Webasto.
While forced air systems are simpler and less expensive to install than hydronic (coolant) systems, the ducting is 4 inches and can be difficult to accommodate on some boats. Another downside is that heat is controlled by a central thermostat so all spaces are heated at the same rate – if it’s 70° F in the salon, it’s going to be 70° F in the aft cabin whether it needs to be or not. They’re also very loud. They do, however, offer heat quickly. 

Photo courtesy of Wallas.
Wallas, a company out of Finland, has introduced a forced air heating system to the market that is supposed to be quieter and more efficient than Webasto and Espar while offering options that can service boats up to 46 feet in the same price range. But they also require ample room for large duct work (3 inches) and, once again, heat is controlled by a central thermostat.

Hydronic Heaters

Graphic courtesy of Espar.
Hydronic furnaces (boilers or systems) use an air-to-water heat exchanger to heat a coolant mixture and a pump to circulate it through silicone hoses to fan-forced radiators. The fan speed can be adjusted manually (low and high speed) and temperature controlled by one or more thermostats placed in zones throughout the boat. For example, aboard Cambria, we have three zones set up – one in the v-berth, one in the salon/galley and one in the aft cabin – and can have the thermostat set at 68°F in the salon while keeping it turned off in our stateroom.

The boiler is fueled by diesel from the engine tanks and heats water that is circulated throughout the boat via silicone hoses. The hoses are attached to small radiators (heat exchangers) that trigger a fan once the water reaches a certain temperature. The fans are controlled by thermostat and can be set up to heat individual zones (as mentioned in the previous paragraph). As an added benefit, incidental heating from the circulation loop helps keep bilges, lockers and storage areas warmer and dryer when the heater is in use.

By plumbing the heated water through a water-to-water heat exchanger, the units can be adapted to heat domestic water, preheat the engine before starting and (through the same heat exchanger) heat the boat from the engine (rather than the boiler unit) while underway. Hydronic heaters also require less maintenance than forced air heaters and, according to the research we’ve done, are less expensive to maintain.

The downside to a hydronic system is that there is a delay between turning the heater on and receiving hot air because of the additional time it takes to heat the water and circulate it to the heat exchangers. They’re also a more expensive option than forced air systems. The basic components are similarly priced, but the added cost of labour for the installation is higher due to the amount of time needed (80 to 120 hours). They’re also not as efficient. For example, the 31,000 BTU Webasto Thermo Pro 90 consumes 0.24 gallons of diesel per hour and uses 7 to 11.5 amps of power.

Hydronic systems are more difficult to price and can require working directly with a distributor for an exact quote. But you can expect to pay $2,000 to $3,500 for the furnace unit and that again for the additional required parts (fan coils, thermostats, wiring, silicone hoses, through-hull, exhaust hose, valves, fittings, pumps etc.). But while hydronic heaters may be the most expensive option on the market, they’re also considered to be the best and most versatile.

In my next blog post on choosing a heater, I’ll discuss which unit we chose and why along with information about the installation.

*Wallas and other companies also make diesel ovens and stoves that can be used as a cabin heater but, because they weren’t a suitable option for Cambria, I’ve chosen not to include them in this blog post.

**Unit size is determined by the number of cubic feet to be heated. A good rule of thumb is to multiply the cubic footage by 12 (sailboats) or 15 (powerboats) to arrive at the number of BTUs required.

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  1. Sitting here with our Sig Marine diesel fire going strong. I am always attracted to stoves on a boat. We looked at a lovely old Spencer 44 when we were first looking for our boat and it had the coolest ever wood burning stove on one bulkhead. I'm allergic to woodsmoke, however, and even at our house, it causes me sinus problems to use our wood burning fireplace insert. It's cramped my style plenty of times. We love our Sig Marine heater, but your point about these stoves heating only one space is pretty accurate. It keeps the cabin toasty warm, but the aft cabin needs its own electric heater at the dock. We have some kind of blower that circulates the heat but it is so bloody loud that it's not really useable.

    1. I envy you. There's nothing nicer than being warmed by a fire on a boat, even if it's fueled by diesel. To get my fix, I've been turning on the gas fireplace at my mom's house -- it's lovely!

  2. I love the idea of a wood burning stove but I don't think I'd ever get over a paranoia about it! When we looked at getting AC plumbed in the boat, it was just as complicated and expensive as these heating systems so we decided to sweat it out- but having climate control sure would be nice!

    1. I know what you mean. We don't run the central heating at night partly because I'm paranoid about leaving systems on unattended. Poor David, though. He's had to sleep in long johns and wooly hats some nights. Lol.

  3. A well written primer regarding the all important heat source for those of us who choose to play in cooler climes. [If you don't mind I'll add a reference to your post on our materials of similar topic.]

    I have lived with all of the heating options you mention on various boats I have had over time, and agree with your guidance and assumptions.

    It might also be worth reminding ourselves of the importance of [fresh] air exchange and moisture control- which becomes critical when living in cool climates in a vessel closed up to retain heat. [Of course, as we all know this is true for all vessels in all climates regardless of any heating/cooling requirements...]

    To facilitate this on our current boat, we introduce some centralized fresh air exchange [and consequently moisture removal...] with our forced air heating system.

    Our current vessel has a forced air diesel heater in the engine room, with a return air duct [not combustion air- that intake is part of the exhaust system...] lead to the adjoining cabin. [workroom/laundry room] That cabin has a port that can be opened to the outside in almost any conditions, allowing fresh air into this cabin where return air is drawn for the heater, therefore circulating a percentage of fresh air throughout the boat when the heater is running. [And since some air exchange is occurring in that cabin, exhausting moisture to the outside as well...

    This represents my 5th opportunity to 'experiment' with heating systems in as many live-aboard vessels above 56°N, and is perhaps the best so far...

    I, too, miss having a 'fireplace' onboard, but this boat has no place for one...

    Hydronic heat is wonderful, but recirculates air within each space, and therefore requires localized fresh air sources/ventilation/dehumidification in isolated areas to achieve this very important function. Otherwise moisture compounds in those spaces over time with the usual detrimental outcomes.

    As you mentioned, one of the great aspects of hydronic heating is localized temperature control [thermostats in every cabin...] With forced air, we control heat in remote areas with vents that have flow control- a crude and imprecise, but manageable temperature control mechanism.

    Another option for fresh air and moisture control is a Heat Recovery Ventilator. [HRV] This is a very desirable option if space permits, but also requires ducting throughout the vessel to achieve ideal results. Since ducting is required, the forced air heat already achieves the desired results when the port in the air intake cabin is open a bit...

    I look forward to reading your continuing series on this topic- and more importantly- sharing with others. Well done.

    Cheers! Bill [SV Denali Rose]

    1. Thanks, Bill. That's high praise coming from you along with excellent points on fresh air exchange -- I hope to hit some of those in Part Two.


  4. Great resource for folks looking to buy a heater for their boat! I hope we're never in the market for one. I do like wearing shorts and flip-flops. :-)

    1. I know what you mean! I'm sure I probably said this before but when David asked me if I wanted to sell up and go cruising, he dangled sandy beaches and sunshine in front of me. It was a classic bait and switch! ;-)

  5. What an extensive report so far, Stephanie. We never had a heater on board and I am with Ellen when it comes to sailing (and living in general): wearing flip flops and shorts is the way to go. Sitting by a wood fire once in a while is a nice change and oh-so cozy, though. :-)

    1. You and Ellen have excellent points and I'm really beginning to wonder how David turned me into someone who finds beauty in the changing seasons when, for most of my life, I've lived for sunshine and summertime. Talk about drinking the Kool-Aid!

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