Has anyone installed a diesel heater in their 310/315?

jssailem · Feb 18, 2026

Many boat owners install heaters for exactly the reason you mentioned. My sailing buddy installed a Russian made heater (wabasto like) unit in his port lazarette of his Catalina 36. Worked like a bear keeping us warm during our 2019 winter cruise.

Be sure that the design is what you desire. I have a Wallas on my boat and it runs quiet. keeps the boat at 72F using very little energy and is miserly on fuel.

The wabasto and Espar units can sound a bit like a small jet engine. The Russian model had a noisy fuel pump. The manufacturer produced a quiet pump. We just removed the original and installed the replacement 3 weeks ago in his boat.

dlochner · Feb 18, 2026

Mainesail just released a video on installing marine heaters, as usual with Rod, lots of good insights and advice.

jssailem · Feb 18, 2026

My Cal35Cruiser came with two 75-gal diesel tanks (thanks to a previous owner who wanted to cruise to Alaska. I plumbed directly into the Starboard tank as it was the closest to the location I planned to install the heater. So that I would not carelessly run out of fuel in the Starboard tank, I made the heater intake tube 2 inches shorter than the engine intake tube. I installed a transfer pump so that I can move fuel from either tank to the other.

Adding a second tank has been done by boat owners. My friend plumbed his heater to the main fuel tank on his Catalina.

Whether you take either path, you will want to have a fuel management process where you keep track of the fuel on board and your consumption.

Hayden Watson · Feb 18, 2026

jssailem said:
...
The wabasto and Espar units can sound a bit like a small jet engine. ...

I have an Espar hydronic heater on my C30 and when originally installed without a muffler, it did indeed sound like a Boeing 707 on take off roll. It was especially loud when on the dock across the Thorofare off the stern. @jssailem slept on Papillon just after I installed it and he can attest to how very loud it was.

I installed a muffler and now it is whisper quiet and can only just barely be heard from a couple of feet away. Here is a short video of the burner on its highest burn rate. I can barely be heard over the sound of about 10-kts of wind. Espar S3D5E hydronic heater with muffler

jssailem · Feb 18, 2026

@Hayden Watson brings up another great point about heaters. I utilize the forced air variety of heater. It requires air circulation using a 2 to 3-inch-diameter vent hose and a fan on the heater.

Hayden's heater pumps hot fluid throughout the boat to warm the spaces.

Each system has its benefits. You will need to consider the factors when planning your installation.

Bob S · Feb 18, 2026

We have an Espar hydronic heater. Love that it can heat our hot water. We plumbed it with a summer loop so we have hot showers without heating the cabins during the summer months.

east coaster · Feb 19, 2026

I have the Russian "espar" installed in the port lazarette on my Catalina 310. It runs great and is quiet with the intake and outlet silencers installed. I can't stress enough to watch Rods you tube on this. It is invaluable, has sound advice and will help you with the layout of yours. I also use a separate fuel tank with a 50/50 mix ofa Diesel and kerosene which prevents gelling and prevents carbon build up which is a apita to remove.

Hayden Watson · Feb 19, 2026

east coaster said:
I have the Russian "espar" installed in the port lazarette on my Catalina 310. It runs great and is quiet with the intake and outlet silencers installed. I can't stress enough to watch Rods you tube on this. It is invaluable, has sound advice and will help you with the layout of yours. I also use a separate fuel tank with a 50/50 mix ofa Diesel and kerosene which prevents gelling and prevents carbon build up which is a apita to remove.

You said that you installed the intake and exhaust silencers. Did you use the muffler that comes with those units that is built in a similar fashion to a car muffler out of pressed steel and roll crip joint? These work great of cars and truck but not so much on a boat. The The roll crimps will leak a bit of exhaust which in a car or truck will not cause a problem because they are in free air under the rig. On a boat, any leakage is inside the cabin and can be deadly.

Only fully welded mufflers are approved for use on a boat. they are pricy but much safer and very quiet.

Hayden Watson · Feb 19, 2026

jssailem said:
@Hayden Watson brings up another great point about heaters. I utilize the forced air variety of heater. It requires air circulation using a 2 to 3-inch-diameter vent hose and a fan on the heater.

Hayden's heater pumps hot fluid throughout the boat to warm the spaces.

Each system has its benefits. You will need to consider the factors when planning your installation.

My reason for hydronic was first lead by wanting to put heat into the head. On my boat, I could not find any way to get a3"ø hole into that space that would not compromise structure. The secondary reason is its ability to also heat my domestic water.

I really like that my heater also heats my domestic water. In the summer time, I fire up the furnace every morning for one hour which heats the domestic water and the tank insulation works well enough that we still have hot water for dishes at night. That short run of heat also dries out all of the condensation we get overnight.

east coaster · Feb 20, 2026

The question about the exhaust muffler is very important. My Russian espar from British Columbia came with the proper sealed muffler. I tested it by blocking one end and filling it with hot water. Waiting for about 10 minutes for any leaks or seepage . There was none. So I lagged the muffler with exhaust wrapping(available in any auto parts store) securing it with the stainless steel ty wraps provided and it works great. Also installed a smoke detecter as well as a CO2 detector in the compartment. Have run the unit at full heat a number of times with no issues, even ran a co2 detector over all exhaust piping and no alarm or untoward indication of any leakage. Rod in his very comprehensive u tube covers this issue particularly carefully and he also sells the proper muffler and exhaust hoses for a safe install. He is trustworthy and since his stroke has continued to provide advice, services and products to all boaters. It is also his only source of income so if you need any bits and pieces for your heater install please buy from him. Let's keep him going. Thanks

Perphoto Canada · Mar 4, 2026

We have an 2018 315 that came with the Espar furnace when we purchased it. Our boat is in Vancouver. We spent a couple of weeks living on it in January and February and it is very comfortable to live on in the winter. You will notice in the photo of the cabin that the heat vents are near the floor in the main cabin and forward berth. There are several vents, one in the aft berth and one in the forward berth, and I believe there are four in the main cabin. I highly recommend having a furnace if you are in a cooler climate.

Maine Sail · Mar 4, 2026

VFR750 said:
Late April-May and late September-Oct mornings are pretty cold in Connecticut. We'd like to extend the weekends as far into the season as possible.

I'm thinking of a Webasto diesel fueled heater. Located in the port lazarette.

Has anyone done this, or knows some who did it?

This will help.

Hayden Watson · Mar 16, 2026

Perphoto Canada said:
We have an 2018 315 that came with the Espar furnace when we purchased it. Our boat is in Vancouver. We spent a couple of weeks living on it in January and February and it is very comfortable to live on in the winter. You will notice in the photo of the cabin that the heat vents are near the floor in the main cabin and forward berth. There are several vents, one in the aft berth and one in the forward berth, and I believe there are four in the main cabin. I highly recommend having a furnace if you are in a cooler climate.

I also love my hydronic system. right after I finished the install, I decided to test it on a very cold [for the PNW] night when the temperatures dropped to 10ºF to 15º over night. When I got to the boat, the inside temperature was about 45º and 32º outside. The cabin warmed up to where I did not feel that I needed my coat on but was not warming up enough to be comfortable sleeping. I then turned on the engine start loop which runs the hot water through the engine to preheat it. That 500-lbs of hot iron in the bilge soon warmed up the cabin very nicely.

max_sailing · Apr 12, 2026

I installed an Autoterm 2D diesel heater. The intent was not to heat the whole boat, but to get heat into the head to act as a drying locker for wet gear and into the aft berth to warm up cold crew. I'm excited to see how it works on my upcoming coastal trip from Portland, OR to my new home in Berkeley, CA.

Here are some pics of my install:

The unit is installed in the steering/fuel-tank/water-heater room on the port side.

Note that this picture is with my original exhaust design that mounted the silencer way up high to provide lots of protection should the output port get flooded. This did not work as it created too much back-pressure and resulted in the heater shutting down after a few minutes of running and outputting lots of smoke. I later reverted to a simple pipe from the heater to the output, with a best-effort little hump in it for fooding protection. At the moment, I'm running without a silencer and it's still very quiet in the cockpit. I plan to upgrade the exhaust with better flooding protection, a condensation drain, and a silencer in the future.

I also used a dedicated 7 liter fuel tank, which will run the unit on high for around 30 hours. The bottom of the tank is bolted to the fiberglass rib of the liner and conveniently tucked tightly behind the macerator for upper support. I didn't want to mess with installing a new suction tube into my main tank, but may do this if I ever have to pull the tank again.

For the combustion air intake, the included silencer is mounted just behind the unit and draws air from this compartment directly below the open vent in the transom.

The 60mm intake duct runs across the steering room to the starboard side, and the intake vent is in the cabin here:

For the hot air output, I ran the 60mm intake duct around the corner of the waste tank and into the void behind the aft berth cabinets. I tucked a Y-fitting right back in there and connected one vent back in the corner of the aft berth and the other in the head:

I figured I would need to install a vent in the door to the head to allow the return air to escape back to the intake in the aft berth, but without it the head still gets nice and toasty. There must be enough air the leaks out of the head back to the cabin through other spots.

The wiring was straightforward, I connected it to a spare 20a breaker in the main panel and installed the Autoterm "Simple" mini control panel and temp sensor next to my VHF.

It is very bad for the heaters to cut power while they are running, as it prevents the "purge" cycle from clearing the chamber. I'll use one of these BlueSea toggle guards to protect against accidentally breaker flip, like I do on my macerator pump: https://www.bluesea.com/products/4100/A-Series_Circuit_Breaker_Toggle_Guard

Once I sorted the exhaust issue noted above, the unit runs well and made plenty of heat in my Portland December test. I will report back how it works after our 700NM trip down the Oregon / Northern California coast.

Hayden Watson · Apr 12, 2026

max_sailing said:
I installed an Autoterm 2D diesel heater. The intent was not to heat the whole boat, but to get heat into the head to act as a drying locker for wet gear and into the aft berth to warm up cold crew. I'm excited to see how it works on my upcoming coastal trip from Portland, OR to my new home in Berkeley, CA.
...

Nice install. Is that really on a C25? If so, it should provide all the heat you need. I have a 5kw heater on my C30 and it has no problems keeping the whole boat warn even in the low 20's.

What did you do for exhaust? Most of the non-marine kits come with a single spiral exhaust pipe which is fine for a truck install but is not safe for a boat. Marine installations need to have double spiral fume-tight exhaust. It should also have a condensation drain. If you put a silencer on it, it must be a fully welded airtight marine muffler. The silencers that come with the kit leak air and can kill you.

max_sailing · Apr 13, 2026

I need to figure out how to update my profile. My boat is a Catalina 310.

Autoterm claims in the manual that the exhaust line shipped with their kit is suitable for marine installs including their silencer. I will be carefully monitoring CO in the installation compartment with my low-level CO meter (measures down to 10ppm).

I do plan to do the condensation drain next. I've read varying/conflicting feedback if they're needed in the moderate ~50 degree F environments I'm running in. It will add a handy 90 degree bend which will allow me to get more "hump" in my exhaust for back-flood presentation.

Has anyone installed a diesel heater in their 310/315?

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