12th Nov – 8th Dec: The Cabin Heater evolves!

Most of November was either too rainy or too windy (or both) for me to be tempted to take Seatern sailing. However I spent most nights on board and tried out the cabin heater. I soon learnt that heating technology is more complicated than I had supposed! My optimism after my first experiments with the new chimney (see my 9th/10th November entry) was premature.

In order to prevent sooting up of the heat exchanger the suppliers of the PAN2000 heater suggest that when used on a spirit stove (as shown in the photo left), the stove should be set at level 2 (i.e quite low). The result is a relatively low level of heat production and not enough heat to prevent condensation in the chimney. Despite a jubilee clip, this condensation dripped out of the pipe connection at the top of the chimney fan unit.

Since running the spirit stove at a higher setting did indeed produce soot I decided to try a camping stove of the type which uses an A4 Butane/propane gas cartridge. This was produced much more heat without sooting but it meant that the fan unit and the fitting through the cabin roof became hotter. While both could still be touched by hand they were now uncomfortable to hold for more than a few seconds. I was no longer happy with the installation of the fitting through the cabin roof which was only insulated by a small (about 1mm) air gap (as specified in the PAN2000 instructions). While that might be OK in normal use, I wanted to be sure it was safe if the chimney somehow started to over heat.

To provide better insulation I made a larger (56mm) hole through the cabin roof and insulated the 50mm stainless tube by wrapping it in woven glass stove ribbon. I bolted the stainless fitting to a Tufnol board with insulation between the nuts and the plywood. The Tufnol (which can withstand up to a few 100C ) was bolted through the cabin top to another piece of Tufnol (see diagram). Thus all parts of the chimney fitting were now heat insulated from direct contact with the cabin roof.

To minimise condensation in the chimney I insulated it with the foam that is put around scaffolding to limit the damage to pedestrians who walk into it. This also has the advantage of butting against the deck socket, cutting down the risk of rain water penetration between the socket and the chimney. I’m using copper grease on the chimney threads which I’ve been told is important to keep the joint free should it get hot.

In case the PAN2000 heater itself is getting too hot, for example due either to failure of the 12V supply or the heat exchanger fan, it has a heat activated alarm independantly powered from a 9V battery. I mounted the alarm buzzer on a box which also holds the 9V battery, a switch for the chimney fan, and a potentiometer to control the speed of that fan. Connection to the PAN200 is through a 6 pin Bulgin socket. The chimney fan power is connected to the Bulgin plug with an RCA plug and socket so that it can be removed from the system if it breaks down, or turns out to be not needed.

The fan is now held in place by Tufnol squares which are epoxied into short lengths of 50mm alloy tube. Rather than sealing the top pipe onto the fan unit I created a condensation trap (from a Co-op pineapple chunks tin) with a drain pipe (aquarium supplies) which can be led into the portaloo. The end is weighted with an RF choke (Maplins!). Although the flexible exhaust pipe is a tight fit on the alloy tube, water still manages to get past the jubilee clip.

I was worried in case the computer fan gets too hot so I tested a broken one to destruction using a hot air gun. The plastic melted but it did not catch light. Similarly, although the insulation around the chimney is described as self-extinguishing, I tested a small sample which simply melted and shrank under the heat gun.

The underside of the gas stove gets warm and, since used as a heater it will be on for longish periods, I mounted the stove on a metal cooking tray which in turn was mounted above a plywood base. The latter slides into teak holders screwed onto the forepeak floor. These can also hold the gimballed spirit stove unit if I want to use that as a heater.

A remaining problem is the poor performance of gas stoves in cold weather (which was why I originally chose a spirit stove). The Bright Spark “Butane Battery” cartridges containing a Butane/propane mix, which helps. However in very cold weather I can imagine having to sleep alongside a new cartridge in order to keep it warm enough to use. Provided the cartridge has enough pressure, the gas stove raises the cabin temperature quite rapidly. For example with 3C outside the inside temperature was raised from 5C to 21C in an hour with the burner on it’s lowest setting.

[Note added August 2017: although the illustrations in this post show a BrightSpark 110 stove, I obtained and use a BS 100 stove which is designed for indoor use and has a safety cut-off if the flame goes out (see 13th December entry). I now also use a similar stove for cooking in place of the spirit stove.]

[Note added October 2018: I soon did away with the condensation trap. When I light the stove I wait until the flexible chimney tube is becoming hot before switching on the heat exchanger fan thus ensuring a good updraft through the chimney.]