Solid fuel heating
With plummeting temperatures in mind, a budget-conscious John Connell opts to fit a wood heater in his boat
A reader installs a wood heater in his boat
You know it’s cold when it takes two hands to squeeze the toothpaste out of the tube. When your sheepskin slippers can’t get a grip on the icy deck, it’s time for action.
There are a number of perfectly functional options for safely heating a boat. Diesel heaters seem to be the most popular these days, from the cheaper radiant-style Dickinson to the fan-forced Webasto and Eberspächer. Sig also offer propane as an option, but this requires professional installation if the insurance company is to be satisfied. In the interests of simplicity, however, I leant towards the solid fuel heaters. Several manufacturers in the UK and US sell attractive, boat-friendly, solid-fuel stoves and heaters, but the cost of these led me to have mine custom-built. I showed local blacksmith/welder Taig Simms what was on offer at various websites then left him to it.
Low-profile unit
My requirements were for a low-profile unit with a flue exiting far enough back on the heater so that I could put a kettle on top. I never intended to use it as a stove, but wanted to be able to boil water or heat up soup. The addition of a rail to hold things in place left me with enough space for a small billy or saucepan.
Talking to Taig, I was surprised to find that there was a bit more to wood heater design than I realised: it wasn’t just about keeping the burning stuff in the box. The heater is effectively a box with a damper plate at the upper rear. This damper works as a baffle to slow the escape of heated air up the flue. A grate low down allows airflow around the fire and provides a means of allowing the ash to drop through. We went for a unit 250mm square and 350mm high, excluding the short legs. (This turned out to be larger than necessary for our boat.) Taig used 5mm steel plate as too-thick material will result in poor radiation of heat.
The size of the flue is significant. If it’s too small, the fire won’t draw: it will burn poorly, and the result may be smoke blowing back into the cabin. A 5indiameter (127mm) flue might seem like overkill on a heater this small, but the large diameter has the advantage of increased surface area in radiating heat into the cabin. Wall thickness of 0.8mm is normal. Some installations might include a slight bend in the flue on its way up to the deck. This lengthens the flue a little, keeping more of the heat in the cabin – although the rising smoke needs to escape easily if it isn’t to blow back into the cabin. A butterfly valve in the flue can also regulate the flow upwards, but we decided it wasn’t necessary on this unit.
The large, removable doorway at the front allows me to tilt back the grate to shovel out the ash. It’s actually large enough for the grate and damper plates to be removed completely if necessary. The door is sealed around the edge with self-adhesive glassfibre rope. A 150mm square window in the door allows me to see what’s happening and enhances the visual effect. The heatresistant glass in the front is quite expensive, but the amount I needed didn’t blow the budget.
Fitting the heater
Installation would have been simpler if the site had been chosen before construction of the boat. I had never expected to be fitting a heater when I built my 11.6m (38ft) cat, so the location was a bit of a compromise. I decided that the settee was way longer than necessary for two residents and the occasional drop-ins, so I sacrificed one end. 12mm of cement sheeting replaced the cushion on the plywood settee for insulation, then the heater was bolted securely through this. A cutout in the front of the settee allowed access for tightening bolts and is now the storage area for firewood. The heater can be unbolted and stored below if I’m cruising warmer climes, and it’s a simple matter to replace the seat cushion to return the space to its original function.
Installation of the stainless steel flue was the trickiest part. I had it custom-made to slide through a stainless steel deck plate, which makes it removable for sailing. With my boat’s low-slung boom, a permanent fixture was never going to be feasible. With the heater in place, I could calculate the centre of the hole needed to get the flue through the deck using a plumb bob. I cut a 178mm (7in) hole for the 127mm (5in) flue.
The space around the flue was filled with glassfibre rope to insulate it from the cedar/epoxy deck. A foam/glassfibre box was shaped to create a flat exit point for the flue above deck. An inverted cone creates a weatherproof arrangement at deck