A Diesel Heater On Your Boat

After purchasing my last sailboat, a 1978 Union 36, I was faced with a five-day midwinter trip to relocate her from New Bern, North Carolina, to my slip in Norfolk, Virginia. The day of our departure was an amazingly warm January day, with temperatures reaching almost 70 degrees. I began to believe Old Man Winter was going to give me a pass on this trip. But the following day, temps plummeted into the teens, with howling winds and daytime highs in the mid 30s for the remaining four days.

After battling freezing temps, ice, sleet, and snow along the way, the day I moored up in Norfolk I promised myself I’d install a diesel heater. Here’s a look at how I fulfilled my promise to keep a warm boat while underway and at anchor.

The search heats up

While there are several heater choices available to boat owners, diesel was really the only viable option for my boat. I didn’t have a generator, so electric heat while away from the dock was out of the question. An LPG (liquid petroleum gas) heater was also not an option, as my new boat used CNG (compressed natural gas) for cooking.

During a fit of childhood nostalgia prompted by memories of the old wood stove at my grandpa’s house, I briefly considered a solid fuel heater – i.e., one that could burn kindling, charcoal, peat, or wood pellets. Memories of cleaning ash and the mess it made quickly snapped me out of it.

Diesel remained the best choice, particularly as I could pull from my existing engine fuel tank, eliminating the need to carry solid fuel or install a second fuel system.

After looking at available diesel heater options, I settled on a Dickinson Newport diesel heater ­(dickinsonmarine.com). It’s a salty, good-looking heater (photo 1), and the window showing a dancing flame seemed just the ticket to stave off those cold winter nights. Well-built and robust, I viewed it as a value-added installation for the boat, both in comfort and resale value.

Is it drafty in here?

Diesel heaters are natural draft appliances, so they require plenty of fresh air. While in operation, the chimney stack creates draft pressure, just like the chimney in a wood stove. The hot air in the chimney pulls fresh air into the heater as it rises up the chimney and exits the flue or exhaust cap.

For the heater to operate properly, there must be sufficient ventilation to replace the air inside your boat at the same rate that the heater is removing it. Doing so allows greater draft pressure (the rate of heated air exiting the chimney). The greater the draft pressure, the better the heater will be able to resist downdrafts (due to strong winds) and overcome venting resistance (such as caused by flue elbows) while providing better, more efficient heating.

Part of any diesel heater installation must also include the installation of marine-grade smoke and carbon monoxide detectors located to monitor the atmosphere in both the main cabin and each sleeping area.

The heater installation instructions called for a permanently open fresh-air inlet into the cabin of at least 3 inches in diameter. As I had four 5-inch dorade vents that would remain open during heater operation, we were good to go from a draft/ventilation standpoint.

Location, location, location

The next step was choosing a place to mount the heater. It had to be a spot that was functional (with regard to heat radiation about the cabin) but also didn’t block the flow of traffic or present a contact safety hazard during operation for those moving about the cabin. Another major consideration was placement of the chimney exhaust cap, as even the best cabin location would be a no-go if these issues couldn’t be addressed. This had to be away from the boom, not interfere with any deck equipment operation (such as mainsail or jib sheet routing) and enough out of the way that it didn’t become an impromptu grab point or handhold to someone working on deck. Installation of the fuel lines was another consideration, but one that was easily solved with proper routing and a few holes.

I finally chose a spot on the forward main cabin bulkhead at the foot of the pilot berth (photo 2). It was an unused spot that worked well for both heat radiation and safety as well as placement of the chimney. Another benefit was that it didn’t reduce any functionality or get in the way of main cabin activities.

Installation instructions called for orienting the heater so that it faced either the bow or stern (particularly on a sailboat), and my location met that requirement.

A final advantage (although certainly not a crucial one) was the ability to view the flame (i.e., viewing the combustion chamber) from most of the main cabin – particularly the aft corner seat of the dinette, which serves as my floating office/writing nook.

The main disadvantage from an installation standpoint was the flue pipe. I’d be unable to meet the minimum recommended 4 feet of flue pipe between heater and chimney (we missed that by about 6 inches). The second was the necessity to use angled elbows to make the heater-to-chimney connection rather than the preferred straight flue-pipe installation. All things considered, however, this location checked the most installation requirement boxes, and I believed any disadvantages could be overcome (or at least mitigated to a tolerable level).

Getting warmer

Now came mounting the heater. Installation instructions require that combustible material closer to the heater than the specified safety clearances be lined with insulation or millboard and a metal liner with a ½-inch standoff for air movement behind. My solution was a thick, trimmed-to-fit piece of stainless-steel (photo 3). To soften the harsh, shiny reflection of the plate, I used a palm sander and 120 grit paper to rough up the outward-facing surface, giving it a nice satin finish.

I found some small ¾-inch aluminum tube sections of the correct diameter to fit the mounting bolts and used them as standoffs. I placed them between the stainless-steel heat shield and bulkhead when bolting the plate into place (photo 4). I also installed stainless-steel washers on the bulkhead end of the standoff to help spread the load and protect the wood when tightening the bolts. This worked so well, I later used the same method to install additional heat shields to a small section of the coach roof outboard of the heater, as well as the side of a nearby support knee facing it (photo 10).

Once the stainless-steel plate was mounted, I drilled holes for the heater mounting feet through both the stainless-steel plate and bulkhead, added standoffs, and securely bolted everything together (photo 5).

Building the chimney

Now that I had the heater mounted, it was time to tackle the chimney stack. As mentioned earlier, a long, straight chimney stack is preferred but, alas, in my installation, it was not to be. I was unable to mount the thru-deck fitting directly above the heater (due to a handrailing), so I had to shift its location about 6 inches inboard. I then had to “Frankenstein” a connection between heater and thru-deck fitting using two 45-degree fittings and three sections of stainless modified chimney pipe.

Snug as a bug

After marking the location, it was time to cut the hole for the deck fitting. Installing the deck fitting requires 1 inch of clearance all around the chimney pipe. As the exhaust pipe for the Newport is 3 inches, this means the deck hole had to be 5 inches to provide the required 1 inch air gap. The simplest way to cut this was using a hole saw. After cutting the hole, I sealed the exposed coring with thickened epoxy to prevent water intrusion into the deck (photo 6). Although probably not necessary, I also installed a ring of tin around the hole to further protect the epoxy sealed coring against heat. The instructions don’t say anything about the need for the extra shielding because as long as you have the recommended air gap and the stack is of the required length, the stack shouldn’t get hot enough to require it. But I added some because I had the leftover tin. And I was a bit concerned as the stack was 6 inches too short, but, again, it probably wasn’t crucial or necessary.

Another issue that needed addressing was the contour, or camber, of the coach roof where I’d be mounting the deck fitting. It wasn’t level, so I fashioned an angled base for the deck fitting out of wood (photo 7). After drilling and dry-fitting the base, I found the angle was a tad off, so I used thickened epoxy to level it up and mount it to the deck (photos 8 & 9).

Once the epoxy hardened, I was able to fit the chimney pipe into place (photo 10). Everything looked like it would work, but I still didn’t like using so many elbows in such a short run. I was at a loss for a better solution, however, so I moved on to plumbing the fuel supply.

Adding fuel

This was the most straightforward part of the heater installation. After my initial reading of the installation instructions, I decided to use my existing diesel tank to provide fuel to the heater. The only “extra” fitting I had in my fuel tank had been used a few years earlier to install a fuel polishing system. (See page 84 to learn more about that.) I decided to “T” into this fitting to simplify things.

I had outfitted this fitting with a pick-up tube that reached within an inch of the tank bottom, so I knew it would be able to provide fuel until the tank was pretty much empty. I believed the diameter of the tube was sufficient to provide fuel to both systems, however, if not, I wouldn’t be polishing fuel while operating the heater anyway. The fuel consumption (per the manufacturer) every 24 hours is 1.3 gallons (low setting) and 3.2 gallons (high setting).

After choosing the best route to run the fuel hose to the heater, I selected a good place to install the in-line filter and heater fuel pump (photo 11), and continued the hose run to the heater.

I then wired the fuel pump to a dedicated on/off switch via an extra breaker at the main DC panel (photo 12). I used a Walbro #20-000 low-pressure pump recommended by Dickinson. The pump will slow almost to a stop when the stove or heater is in use and the pump outflow pressure limit of about 3 psi is reached.

Once this was completed, the only thing left was plumbing the fuel overflow fitting. The Newport heater has an overflow safety feature designed to allow the controlled escape of fuel from the heater in case of overpressurization or minor leaking at the valve due to dirt or debris. If the main tank is used as a fuel supply, the instructions call for installing a fuel line to return the overflow back to the main tank. If a day tank is used, however, the overflow line can be plumbed to a small container located away from the heater.

I didn’t have an extra fitting at the primary tank, so opted to install a small container instead. I repurposed an empty metal paint thinner can for the job, mounting it on the opposite side of the bulkhead and below the heater so any escaping fuel would gravity feed into it (photo 13). The overflow is an emergency system only, and while I never saw any fuel enter the tank, the installation looked professional, and I was confident it would work great should the need ever arise.

Firing it up

Now that I had everything installed, it was time to fire up the heater and give it a test (photo 14). Once the heater was lit, I monitored the temperature of the surrounding wood (and any nearby combustible materials) as it reached operating temperature to verify that nothing got excessively hot.

Everything worked as planned, and I used the heater over the next few months with good results. I still didn’t like the chimney pipe configuration, so I was stoked when I found a neat solution to rectify it. I discovered semi-flexible stainless-steel tubing at a fireplace store that is used inside older chimneys when installing heaters. It was robust-looking and of the proper diameter, so I bought a section and installed it (photos 15 & 16). It fit perfectly, looked great, and has worked flawlessly ever since.