Boat heating

Once we had decided to move onto the boat and as we were planning to do this in January I reassigned the “heating would be great to have” from a want to a need. I started reading a lot about it and how other people had done it on small boats, there were several ideas and obviously I wanted to go with the cheapest solution that worked. There were two options really, one to go with air and one with water. With air the heater burns diesel, heats the air and blows it through large conduits to where you need it. The water heater works the same way, just with water being heated and then pumped to where you want your lovely heatedness.

I did think that the air heating with be easier but when I was looking the price seemed higher and the conduits looked very large and therefore difficult to feed through my little boats nooks and crannies. I settled on the water heater route, the price was much less which was mainly due, I think , to the fact the the Webasto heaters I was looking at were put in vans and cars so there were plenty of them around, it still wasn’t that cheap when you are trying to get money saved for going cruising but I got the heater, wiring and timer switch for about £250. It’s a Webasto Thermo Top C, a name I will remember for a long time.

After I decided on the heater I started looking at ways to distribute the heat to the boat, it was tight on space as always and I couldn’t really find any “official” boat radiators that fitted the bill, after saying “soddit” to myself I discovered how cheap normal household radiators were on ebay. I measured up and bought two radiators that fit in to the space I had, one under the table and one on the starboard side near the seat. I guess some people would hate the way they would look on their boats and I have had some funny looks when I have mentioned it from people but I was going for cheap functional not expensive pretty.

Next was where to put the heater, the only spot I could think of was under the sink in the galley, I need to take a feed from the main diesel tank as I wasn’t going to put a separate tank in, I just didn’t have the space. Once that was decided and I had figured out where I could run the wiring I installed the piping. I used push-fit pipes, nearly all 22mm apart from where I needed to join the radiators and where the header tank. The inlets and outlets on the heater are both 22mm so it meant I only needed reducers at the radiators. It may have been easier to use smaller pipe as it would have been easier to feed that through the boat, the fittings were cheaper too for 15mm, although when I started out I wasn’t exactly sure how I was going to put the radiators in, normally in a house you would have a main ring that the radiators would feed from, I ended up just feeding the water straight into the radiators and then out again. I still think it was neater having the pipe reduce at the radiators rather than the heater.

I also had to install the exhaust for the heater, another reason for putting it under the sink in the galley as I could run the exhaust past the engine, alongside the existing exhaust, and to the stern. As always with any work in the lazarette it involved a lot of swearing and fitting into spaces not intended for man. I also had to drill a hole in the stern to mount the exhaust port.

I managed to pick up a genuine Webasto exhaust port for about £25 from ebay, the exhaust was stainless steel as all the guides recommended, I did have problems joining this to the silencer and the heater as it was corrugated, not sure how you are supposed to do it but I used a lot of exhaust sealant which gave a good seal first time and also was easy to reapply when I took it all apart again. Drilling into the hull was a little nerve-racking but once I got going it was all fine and I have since sailed across the channel with no issues and had no water come through. The exhaust port comes with a nice plastic seal and I also used a lot of heat resistant sealant for good measure. To be fair I did mount it high enough not to get under water. I also put a loop in the exhaust to raise the level to just below the cockpit moulding to ensure nothing gets washed back up the exhaust. I also lagged the exhaust to ensure no expensive or firey issues, after fitting the fireproof lagging to the exhaust I would have gone for the more expensive stuff, I used a reel of it and it was an arse to fit, I think the stuff that fits like a sleeve on the exhaust pipe would be a lot easier.

I installed a small header tank as well, the system isn’t pressurized and I used a coolant tank from a mini as it was the only one I could find where the outlet was stated to be something I could connect to the system, it also only had one outlet and was large enough to hold enough water. I mounted this as high as possible in the lazerette which also made it easy to get to for me to check the water level and top up.

So with all the piping in, the heater connected and the wiring in, exhaust plumbed I was ready to fill the system with water. Obviously there were a few leaks, I had expected there to be but I had actually expected more. The pushfit piping was excellent, it also bent around curves and was really easy to fit, the leaks were mainly from the places that were in awkward places where I hadn’t been able to push the pipes on firmly. I used La-Co LAC 42018 pipe thread compound which I picked up from Screwfix to help with the joins in the tricky spots, I also ended up using this on the fuel joins as well as the compound is good for pretty much anything, it also doesn’t set which helps when dismantling everything…

Ok so once the leaks were dealt with I fired the heater up, the first few times it failed to go but then did run for a bit. The heaters were getting hot but then the heater gave up. I will cut a very long story short, some people know how much frustration this caused me and took me so long that I ended up not needing it as the weather got better and I headed over to France. I did learn a lot about Webastard heaters as they became known. The one massive piece of advice I would give to anyone installing one is fit a water trap before the heater, I don’t care if it has it’s own tank or not, they really can’t cope with moisture and on a boat fuel tanks are prone to getting moisture forming inside them. It causes issues like this:


That is looking into the combustion chamber with the top part removed that holds the glowplug and flame sensor, I think what happened was that there was enough moisture in the fuel caused the chamber to soot up and the heater wasn’t able to sense the flame was on and shutdown. There’s a video of what was happening here. I had fitted an inline fuel filter already so now it has both. It took me until the weather was threatening to get cold again before I pulled the heater out again and whilst sat in the marina in Paris de-coked it and put it back in, it’s not a nice job and I have done it three times, I don’t like the smell and the soot goes everywhere even when you are careful. So don’t forget the water-trap.

Finally the heater started and ran and….kept running. After this long trying to sort it out I kept thinking it was going to stop. It’s now been about 6 weeks and we have been using it most days for at least an hour. The only thing I would say is that the system is a little small, I think the heater starts kicking in too often after it has been on for a while, it’s not a massive deal as usually by that point the boat is toasty.

After all the hassle I have finally come to love my Webastard but it was certainly a rocky start to the relationship and the heater nearly ended up in the marina more than once.


Heater above in the centre, fuel pump to the bottom left on a home made bracket, fuel line comes in from the lazerette with tap, exhaust is just visible to the bottom right with white lagging, wiring comes in from the top.