In order to cruise year-round in the Northwest, cabin heat is essential. On cold, wet days you don’t want to be shivering at anchor while the temperature drops to 35 F. So around October, repairing the Sig Marine diesel heater that came with our boat became a #1 priority.
Working on a diesel heater was scary to me though – these heaters involve setting a fire inside your boat! Fire is usually the last thing you want on a boat. But, as I learned more about it I gained confidence. It was a bigger project than expected though.
On a club meetup at Port Orchard last month with the Puget Sound Cruising Club, we were on 3 or 4 other boats in 30 degree weather that had nice, calm burning diesel heaters keeping their boat nice and toasty. This was a stark contrast to our heater which had flared up into an angry inferno a couple weeks ago. Getting the fuel and air mixture right on a heater that hasn’t been used in a number of years is more difficult than it seems.
The first thing to decide is the fuel type. You basically have three choices: #2 diesel (what your diesel engine runs on), #1 diesel (aka stove oil), or kerosene. Some people install the heater fed directly from the engine’s diesel tank, or from a smaller day tank that is fed from the larger tank – in that case, the choice is already made for you.
Since we already had a system installed, we knew we had a dedicated fuel tank in the stern area which gravity fed to the cabin heater about 15 feet forward. I decided to use kerosene because I heard it is cleaner and less smelly than diesel. Actually picked up a kerosene substitute, Klean Heat, from Home Depot, because kerosene was fairly difficult to find (Home Depot may sell it, but the employees didn’t seem to know where it was).
Kerosene has a lower viscosity than diesel, meaning it flows faster through the metering valve. The Sig Marine manual says it’ll mean a 50% faster flow rate than #2 diesel. #1 diesel, aka stove oil, is slightly thicker but less so than #2 diesel, which is what you put in your engine. #1 diesel has a 30% faster flow rate than #2 diesel.
You can get valves calibrated for kerosene or #1 diesel, but unless you specifically requested that, most valves are made for #2 diesel.
Exhaust Hood / Conduit
As mentioned in a previous post, rebuilding the deck exhaust cap was one of the things we had to do to get the heater working. The deck cap had been mounted on some kind of wood that easily rotted, and it was falling apart and leaking water into the cabin and deck. Eliminating leaks in an opening this large isn’t easy, but at least we know the deck penetrations are sealed (epoxy potted) now.
Fuel Line Issues
The first problem with a cabin heater that hasn’t been used in 4+ years is that the fuel line is probably clogged. It was. We had some fine adventures with trying to unclog the fuel line while having kerosene drip – or spray – into the bilge, and onto the floor and hands.
If you have trouble clearing the clog you can try sticking some old electrical wire through it or a coat hanger. Or blow through it with you mouth, while trying not to swallow any kerosene.
You also want to make sure the fuel hose from the heater valve to the heater pot is clear, so we opened that up and blew through it.
Lighting the Burner
The instructions recommend making a wick out of a piece of paper towel and dropping it in to start the starter fuel. This is harder than I expected, and it often takes 10 minutes or more to start the burner.
The first time consuming part is getting the starter fuel into the pot – you need about 2 tablespoons. Opening the valve to setting 1 like recommended it’ll take 6 minutes or more just for that part of the process. Sometimes there’s an air bubble in the fuel line so you need to tap on it or tap the valve to get that cleared. Usually I’ll turn the valve up to 3 or 4 to get it started.
Then once I dropped the flame in, it often got extinguished by the air flow as it dropped or the kerosene itself extinguished it. Kerosene (and diesel) really aren’t that easy to light, especially when the fuel is cold. It needs a big enough flame on it for a long enough time to heat it up a bit and start combustion.
With practice I found a better wick shape. When I made a thin candle-like wick, the paper ended up burning slowly – like a candle wick – with the kerosene soaking providing some longevity to the candle wick (it took close to 5 minutes to burn out) but not enough to light the kerosene.
But a wick with a largish unrolled section in the middle, and twisted ends (like a cigarette with the middle unwrapped) worked better. The twisted ends burn slowly and allow me to light the end and drop it in before it starts to burn my fingers, and when the flame gets to the middle section it flares up into a larger flame that lights the kerosene.
I’m sure there are other ways to do this. Perhaps I could just use one of the long-necked butane lighters we use to light the propane stove.
Controlling the Burn
Getting the flames to burn right is a delicate balance of fuel control and air control. The first few times we ran the burner, the flames were much too high and resulted in carbon buildup. Having a raging inferno isn’t very safe either, and creates too much heat. After some adjustments to the metering valve to decrease fuel flow, it got better, but we still had issues with the flames growing much too high after 30 minutes or so. Most likely the fuel warmed up and the flow rate increased.
The meter has always been on setting 1 (lowest fuel flow rate) and increasing air flow didn’t help – that just caused the flames to jump around even more, making agitated rushing air sounds (kind of hard to describe). It’s possible the flue was downdrafting, which can happen when it’s windy out or air pressure in the cabin drops below the outside air pressure (if you don’t have adequate ventilation into the boat). We have excellent ventilation however, and it was only slightly windy out (and we have the “H” style cap, which is the more wind resistant design).
Here’s a video of a pretty well controlled flame we had going for about half an hour: