Let There be Heat!

rev. 3-9-2010
rev. 9-19-2016 
rev. 2-1-2020 

(I first posted this 10 years ago, but the system still works, it's cold outside, and I though you might want to know. I installed a more primitive heating system in my F-24, which will soon be seen in Good Old Boat. No spoilers.)

The Problem. The delivery trip of Shoal Survivor, from Deltaville, VA to Deale, MD took place between Christmas and New Year's (2008-2009); while it was actually quite comfortable at the helm during the day, protected behind the windscreen, it was decidedly chilly watching movies at night, and my daughter and I vowed that we would install heat before the first frost visited us in the next winter.  

The Solution. I belabored the different types of heaters at length. We already had propane, and a spare propane tap existed. The boat was equipped with propane leak detectors and a solenoid valve, further simplifying the decision.  I had a fair idea of the BTU requirement, having spent a few nights on the boat last winter when the temperature dropped into the 20s. I learned that a single 1500 watt space heater didn't quite do it at all and two were just about right. I learned that a vented heater was an absolute requirement, as even cooking with propane in a sealed cabin brought on a slight headache; I'm not certain whether it was lack of oxygen or carbon monoxide.  Applying an appropriate conversion factor (about 3.3 BTUs/watt) and estimating the thermal efficiency at 85%),  5,800 BTUs seem to be the minimum requirement, and perhaps 10,000 BTUs would serve better. The Sig Marine / Dixon P-9000 (5500-7500 BTU output) seemed a reasonable choice and was also the most we really have room for.  A 10 pound bottle of propane should last 50-70 hours, depending on the rate, or most of a season for a $12 refill. Time will tell.

Note on photo: there is a short gap above the heater, between the heater and the air intake pipe. Installation was not finished and this was sealed.

 I  taped a cardboard of the approximate sized to the wall and we lived with it all summer to prove that it was not in the way.

Note 2-19-2010. Winter experience has proven the above numbers. We burned through 20 pounds in 14 very cold December - February days and nights on the boat. I except when on the hook, I have turned the gas off at night and used dock power to run a single 1500 watt space heater. On one very windy 22F night I had to run the heater on low and 2 x 1500 watt heaters in order to keep the entire boat over 70F. I turned the gas off to sleep.

Note 3-24-2013. 3-day cold weather trip (27F-46F). Heater ran most of the time (sometimes on low), plus cooking, and burned about 2-3 pounds each 24 hours. It was off when we left the boat, generally for about 3-6 hours per day.


Installation isn't overly difficult, but it does require meticulous attention to detail:

*  The gas line must run through a vapor-tight fitting from the propane locker into the cabin. This is a standard item through West Marine, Defender Marine, or Sig / Dickson. The hose is typically pre-assembled with 3/8" flare fittings on each end, so it is a bit fat. The vapor-tight fitting will accommodate this.
*  12 volt electric is required for the fan.  The unit will run without it, but the heat output will be somewhat less and it will not be as well distributed. This is another reason we chose this over the Cozy Cabin Heater. The shut-off safety is not dependent on electricity.
*  Installation side clearances are actually quite small for this unit, because the fan circulates cold air around the firebox.  Additionally, the combustion air is drawn through the deck, and around the flu via a double wall pipe. Thus, smokestack never really gets hot on the outside.  The required clearance around the firebox is only 2 inches, and a little bit more around the smokestack. The smoke stack is almost cool enough to hold in your hand by the time it reaches the deck, so no special insulation is needed. The back of the stove and surfaces only a few inches away stay quite cool and no discernible heat is transferred to the bulkhead.
*  Mounting. I suppose I could have simply placed screws in the wall, but it's rather heavy and I decided through bolting made more sense.  The backside ( visible inside the head) fold heads are covered with decorative caps matching those used throughout the boat, and I used acorn nuts and on the heater side of the bolts. The holes were over-drilled, filled with epoxy, and re-drilled. ahead is a shower compartment as well and thus is quite wet.  The bulkhead is foam cored.
*  Through-deck hole for the smokestack. This was the most stressful step, I assure you.  Boring a 3 1/2-inch, gaping hole through the deck and through the salon roof and extremely visible place - not relaxing at all the first time you commit this sort of surgery on the new boat. It went smoothly enough. After drilling the core was removed extending about 1/2-inch back from the edges and the space filled with epoxy thickened with Cabosil (fumed silica) to a peanut butter consistency. The small holes for the mounting screws were also over drilled and, epoxy-filled, and then re-drilled as well. The smokestack comes with a very thick rubber gasket that is not drilled for the mounting screws; the screws drill their own holes through the rubber and make a very tight fit.
* Heat and epoxy. It is perfectly acceptable to use moderate heat to encourage epoxy to cure more quickly in cool weather. However, there are some caveats: Do not apply significant heat before the epoxy reaches a gel state, as it will become very runny; do not heat thick layers until you are certain they will not exotherm and get hot on their own; it is better to warm the substrate than either the epoxy or the curing mixture after it has gelled.
*  Passing the electric wires and gas lines through the bulkhead near the heater was quite simple. I purchased an assortment set of rubber grommets from Home Depot; the largest and second largest nested fit the gas line, and the smallest one accommodated the 2 x 16 gauge wires.
*  There is a gap in the flue in the picture - that was covered by a collar, not yet installed, that allows for deck movement.Remember that distance between the heater and the roof changes as you go through waves and as people walk on the deck There is also thermal expansion to consider. Provide for some movement.
* I checked for gas leaks with diluted dish washing liquid and a brush. I have added a simple carbon monoxide detector.  

Note: as of 1-13-2010 the CO monitor has never chirped. There is no odor, moisture, or other side effect. Just like my home gas furnace, in miniature.

*  The optional stack heat shield seems unnecessary. The stack stays pretty cool (maximum175 F with infrared thermometer - hurts, but would not burn very quickly). Also, the guard will only fit if the stack is straight.

*  The deck guard is necessary; the stack (deck cap, included with the heaters and pictured to the left) is a VERY effective sheet grabber and will foul your sheets on every tack. I built a similar custom guard from 1/8" x 3/4" aluminum strap that stands 5" high by 12" across, since the custom guard from Dickson was not streamlined enough to effectively shed sheets.
* Distributing the heat. We direct a small pre-existing fan (at first a Hella Turbo, now a Camaro Bora), set on low, at the stack and heater, blowing downwards. It increases the heater out-put by cooling the pipe and exterior, and helps spread the heat evenly throughout the cabin, floor to ceiling, without producing an objectionable draft. I'm sure location is critical, so experiment with your geometry.

Unfortunately, my deck has been attacked by the birds. I removed a nest from my boom in the spring; this must be avian retribution.


About five hours of labor, overall.  The only hideous step was drilling the hole into the propane locker.  That involved boat yoga, worming into one of the under seat lockers in the saloon, which is obviously not designed for human habitation.

Although the heater doesn't get hot on the outside, thanks to the fan and jacket configuration, the glass front gets hot enough to take some paint off your hand. My daughter has also determined that with the door open and the flame set on low, it can be used for somores!

I'm now actually looking forward to our first overnight trip in true winter weather. I like winter: in the summer, there is a limit as to how many clothes you can take off; in the winter it is a simple matter to layer up with modern fleece and stretch products, enough to be comfortable in anything. My other joy is ice climbing; watch me enjoying a New Hampshire icefall at ~ -10F... and loving every moment. There is no swimming in the winter. The wind can howl and often does. Beach combing is different. Many Bay area businesses close for the season. But it is still beautiful.

Experience note, 1-13-2010: operation at the dock and underway has been flawless. Spray and moderate wind have caused no ill effects. Wind gusts of 25 knots apparent have caused flame-outs, but the unit interrupted the gas flow quickly. The heat generally stays in the salon, leaving the cabins quite cool, and so thick blankets are required. I like it that way. At dock, we use small electric space heaters on low in the cabins.

Note on thermal efficiency. The exhaust gases go through a double-pipe heat exchanger, giving up heat to the incoming combustion air. The draft is controlled (there is not too much excess air, as the gas flame is yellow) and waste up the stack is reduced (the maximum stack temperature is only about 285 F by IR thermometer). Thus, depending on the assumptions, the of the heater is about 85% efficient , as good as you will find short of a high-efficiency condensing heater, not available for boats. Most marine heaters are 70-80% efficient and have much higher exhaust temperatures.

10-22-2011: I just returned from another cool weather trip; still working well. As it is a vented heater, it warms the boat without humidity increase, CO or CO2 risk, and is without odor. 

3-24-2013: Some continuing problems with flame blowing out if sailing with wind on beam above 20 knots. I need to upgrade the deflector. No problems at anchor, only with wind on beam. 

1-2-2020: OK, one small spoiler, because this tidbit didn't make it into the Good Old Boat article. I placed the F-24 heater flue on the aft side of the cabin bulkhead to reduce rope snagging problems. That works works fine sailing and anytime there isn't a strong aft wind.  When this did cause a problem, I taped a Tupperware container over the pipe very, very loosely, with gaps on the top. Problem solved. After that, I learned to slide a T on the end when it blew that way. Since I don't really use the heater at the dock--electricity is free where I stay--this is a vanishingly rare problem. That said, don't for get to consider wind and it's affect on draft.

A simple. dependable solution, without the complications of forced air heat.