diesel heater ducting

[paulga]

this video discusses the easy installation of a diesel heater. in the setup, the exhaust hose, warm air ducts and fuel supply hose are already in place, so it really is plug and play. If these hoses and connections are not there yet, how to design and install them?

 

[psneeld]

I just ran mine to where I thought I could use the most heat. I unfortunately placed one for convenience of hose running and it wound up behind the helmsman's legs and it gets VERY warm there.

 

[paulga]

first, there should be a cold air intake hose to the unit. where does this hose connect to? is the air from outside of inside?

 

[Bmarler]

first, there should be a cold air intake hose to the unit. where does this hose connect to? is the air from outside of inside?

There are a couple of ways to do it. You can use air from inside the cabin and circulate it which re-warms it, or my preferred way is to bring in outside air. Outside air helps keep humidity levels lower, and slightly pressurizes the cabin.
Combustion air is usually pulled from the compartment the heater is installed in.

 

[psneeld]

My boat had so many air leaks, outside air was not really needed (if humidity was an issue, cracking a door or hatch near the source was preferred).

I just didn't add an in air duct, I just put a filter on the back side of the louvered door close to and facing the units air intake.

 

[SeaDogAK]

Just make sure the cold air intake isn’t anywhere near where the exhaust goes out. Also, I would not pull cold air from the engine room because any kind of exhaust leak would put CO into your cabin. It’s fine to pull combustion air from the engine room.

 

[Carriage Guy]

I installed a Wallas in our Rosborough 246 during Covid and love it. The Wallas stuff is eyewateringly expensive but provides quiet, warm heat that dries out the boat on cold, snotty days because it is continually bring in and heating fresh air. Wouldn't go in cold weather without it, you will be very pleased when you get your unit operational. Can't overstate the advantages of forced air warm heat on a boat.

Bought our heater and some Wallas ducting parts from Scan Marine, the (exclusive?) US distributor for Wallas, and also some Webasto diverter valves and other items direct from online sources in Europe (Webasto parts were cheaper delivered to me direct from Europe (England I think) than from domestic sources like Ebay or Amazon and amazingly fast delivery, like 3-5 days!).

Webasto seems to be the go-to brand for van conversions and has a bigger catalog of ducting parts and gizmos to choose from but there is a slight difference between Webasto and Wallas nominal duct size, 60mm (Wallas) vs 75mm (Webasto) if I remember correctly. Nothing a little wrapping with some foam strips couldn't handle.

The Wallas heater has two air ports on either end of the box. The general recommendation is to feed one input air port with cabin air and the other input port with external fresh air so there is a blend of recirculate and fresh air. Don't think it matters which input source goes where.



On the air output side, the lower air port provides the hotter air of the two as it is closer to the burner. You would run that port to the area of the boat that is larger volume and/or that you want to be warmer.



Our "hotter" output is routed to the main cabin area under our dinette and is lovely on cold mornings when we're just running the heater for 30 minutes to take the chill off the cabin. Our "cooler" output is routed to either our helm or V-berth through one of the Webasto diverters which allows us to share all or some of that airflow between those two locations.

Which highlights a caveat about these heaters, all but the latest design units must always be "on" at least at idle to keep the flame alive after the cycle starts so will always be producing X amount of heat and the maximum output of the unit is typically only 3X that of idle. (The majority of fielded units use a glow plug that draws ~10A for a couple of minutes until the flame stabilizes so you wouldn't want to keep re-doing that startup cycle every few minutes anyway. The newer units must have spark ignition or something else to allow it to cycle on and off more frequently.) Between those X and 3X limits, the unit is thermostatically controlled but on a smaller boat like a Rosborough the idle heat output can be an issue at moderate outdoor temps if not planned for. The upshot is give some serious thought to where you want to distribute and manage the heat output before you start drilling holes for your ducts.

The Walls heater uses a separate air path for combustion supply and exhaust air, that port is on the top of the unit. The exhaust gases come out through the smaller tube and the air supply for the burner goes into the unit through the annular plenum between that inner smaller tube and the larger tube surrounding it. One visible pipe but two airflows going in opposite directions internally.



Wallas sells coaxial metal tubing stock by the foot IIRC and a high temp sleeve "sock" material that fits over that tube if you want to further protect the tube or store your chocolates next to your heater exhaust pipe, lol. We installed the sleeve but I'm not sure it's necessary in most applications due to the cooling of the exhaust stream from the inbound combustion air. The pipe is probably hottest immediately next to the unit and I've never touched it there.

That coaxial metal tubing mates with various (above water) thru hull or deck fittings offered by Wallas. Ours is located on the side of our hull as high as possible but low enough to still have an inverted splash loop before going down to the heater box.

There are other guidelines about the location (relative elevation) of the fuel source, maximum duct lengths and electrical cable sizes (to minimize voltage drop the glow plug sees during start up). Look online for a copy of the Wallas installation manual and/or give Scan Marine on the west coast a call, you will have to purchase at least your combustion tubing from them if not other ducting materials. They provide good service support.

 

[paulga]

There are a couple of ways to do it. You can use air from inside the cabin and circulate it which re-warms it, or my preferred way is to bring in outside air. Outside air helps keep humidity levels lower, and slightly pressurizes the cabin.
Combustion air is usually pulled from the compartment the heater is installed in.

reminds me of one post: https://www.trawlerforum.com/forums/s31/opinion-diesel-heaters-58635.html

"expanded that 3:1 heat output ratio by adding a diverter valve on the heater air input duct so we can adjust the mix of fresh and recirculated air. On cool but not cold nights, we can "force" our heater to heat 100% fresh cooler incoming air which can reduce the output temperature. On very cold nights, we can recirculate 50% of the pre-warmed cabin air if needed. The diverters were not Wallas brand but were easily adaptable"

 

[paulga]

There are a couple of ways to do it. You can use air from inside the cabin and circulate it which re-warms it, or my preferred way is to bring in outside air. Outside air helps keep humidity levels lower, and slightly pressurizes the cabin.
Combustion air is usually pulled from the compartment the heater is installed in.

do you need to drill on the hull a lead-through for the cold air intake? another drill for the exhaust?

I called local west marine, they cannot provide contacts who can do the install. called the marina, they will need a month to run the estimate, or start asap without doing the estimate. but they don't give a firm price, only a do and charge manner, "about 2 weeks".

 

[Carriage Guy]

Air exhaust, no, you wouldn't need an exit vent hole in your boat. The air will naturally leak out through the small gaps in your window, doors, wiring runs, etc. That is probably preferable to having a single exhaust vent anyway since your moist air will be naturally flushed out from many points instead of a single place.
Cold air intake, you just need a reliable source of outside air that can effortlessly feed the one or two 3-1/2"-4" diameter duct(s) to your heater. That can be from a vent fitting on the side of a cabin wall or somewhere on your flybridge, a dorade box on your roof, from underneath an overhang or even a locker if it passed enough air freely and didn't otherwise stink with mold or have a risk of blocking your vent with equipmet.
A 4" diameter duct has about 13 square inches of area so wherever you draw air from, you want at least that same open area between the end of your intake duct to the outside. If you were drawing air from some type of locker for example, you would want that locker to also have an opening to the outside world that is at least 1" x 13" or 2" x 6-1/2", or etc. so that the air flow you are drawing can easily be supported without causing the heater to have to "suck" the air.

 

[paulga]

Air exhaust, no, you wouldn't need an exit vent hole in your boat. The air will naturally leak out through the small gaps in your window, doors, wiring runs, etc. That is probably preferable to having a single exhaust vent anyway since your moist air will be naturally flushed out from many points instead of a single place.
Cold air intake, you just need a reliable source of outside air that can effortlessly feed the one or two 3-1/2"-4" diameter duct(s) to your heater. That can be from a vent fitting on the side of a cabin wall or somewhere on your flybridge, a dorade box on your roof, from underneath an overhang or even a locker if it passed enough air freely and didn't otherwise stink with mold or have a risk of blocking your vent with equipmet.
A 4" diameter duct has about 13 square inches of area so wherever you draw air from, you want at least that same open area between the end of your intake duct to the outside. If you were drawing air from some type of locker for example, you would want that locker to also have an opening to the outside world that is at least 1" x 13" or 2" x 6-1/2", or etc. so that the air flow you are drawing can easily be supported without causing the heater to have to "suck" the air.

Without exhaust, would the cabin be filled with diesel soot?
This pic is taken from the installation manual, it says the heater need to have a dedicated through hull for exhausting

 

[paulga]

Another slide on exhaust system

 

[Carriage Guy]

There are two air flows

These forced air diesel heaters have two separate airflow paths that only contact each other in the heater "box" through a heat exchanger. Let me call one path "combustion air and exhaust" and the other path "cabin air". So all forced air heater boxes have 4 openings for the two air paths: 1)combustion air in
2) exhaust gas/air out
Those two heater box openings are for the first path and typically enter/leave your boat through a hull or roof fitting or fittings.

3) cold cabin air in

4) warm cabin air out
Those two heater box openings are for the second path and only the air in typically needs an opening in the cabin wall or elsewhere.

There is a small combustion chamber that takes in the combustion air, adds fuel, burns it, passes it over an internal heat exchanger before exhausting it from the boat. That combustion air in/exhaust gas out is the first of the two airflow paths.
Some heaters have a separate duct for the incoming combustion air and outgoing exhaust that require two holes in your hull or roof, others (Wallas for example) have a single co-axial duct where there is only one hole in your hull with a special coaxial fitting that handles both the incoming and outgoing combustion airflow through that single hole.

The heater also has a fan that sucks in outside air, passes it over the heat exchanger to be heated up by the outflowing exhaust gas mentioned above, then dumps that warm, fresh air in your cabin wherever you route it. That is the cabin air, the second air flow path.

The combustion airflow and the fresh cabin air paths meet each other at the heat exchanger but never mix. One airflow is on one side of a metal wall and the other airflow is on the other side of the metal wall. The combustion airflow path heats up the metal which in turn heats up the cabin air.

My most recent post was in reference to your question about "cold air intake" which I took as referencing the cabin airflow. Re-read that post from the point of view of where to get your fresh cabin air input from and it should make more sense to you.

Of course you need to exhaust the combustion air outside your boat. The location on your hull or roof needs to be selected so you don't accidentally allow that heater exhaust gas to be drawn into your living space through windows, doors or vents. The Wallas manual you have should give you some tips as to how to avoid that.

I'd suggest you google "How to install a diesel heater on a trawler yacht" and watch some of the YouTube videos on what others have done on trawlers and sailboats. Looks like I see at least a half dozen that look pretty good. That should give you a better insight as to the location, venting, ducting and installation needs of these types heaters as well as an overview of the various brands and models of heaters available. There are lots of different heater price/feature/quality combinations out there and like everything, there is always a tradeoff to be made.

 

[paulga]

Thanks for the introduction. I was able to get a picture view of the framework.
does the fuel supply fitting usually need to drill a hole from the top of a fuel tank? this is not doable as the tanks are wholly insulated behind panels. the tank's top or sides are not accessible. so the heater would need a dedicated day tank if I do it.

 

[Cigatoo]

Thanks for the introduction. I was able to get a picture view of the framework.
does the fuel supply fitting usually need to drill a hole from the top of a fuel tank? this is not doable as the tanks are wholly insulated behind panels. the tank's top or sides are not accessible. so the heater would need a dedicated day tank if I do it.

I am also contemplating a diesel heater. I was going to tap into my generator fuel line after the Raycor for fuel. Drilling into the fuel tank or adding a dedicated fuel tank is out of the question for me.

 

[Bmarler]

It’s not recommended to share a fuel supply with the engine or genset. The issue is that one can starve the other in some instances.
That said, I’ve done it, and it works fine. Best to have a manifold to pull from. I put the manifold before the primary filters and put in a separate small racor for the espar.

 

[Marco Flamingo]

My boat had a Wallas diesel heater. When that needed parts that were no longer available, I went with a $150 Chinese diesel heater (3 years ago). Some of the old ducting I used, some I improved. The Wallas had a fresh air intake to the outside. I eliminated that and now simply take air from my well ventilated engine room.

I added both a muffler and an intake silencer. The original install made for a whining noise outside the hull. More irritating to a neighbor than to me, less irritating than a generator, but still something easy to eliminate. I fabricated a muffler (as the common diesel heater mufflers are not suitable for interior spaces) similar to a "glass pack" muffler out of common copper pipe (shown in this thread at post 37). Wallas makes an exhaust muffler out of $tainless $teel for about $300. My silencer on the air intake is one from Ebay. Recommended as the intake whines almost as much as the exhaust. Both are now silent.

The little heater fuel pump is a tick type and could be heard when at anchor. I suspended the pump from the rubber fuel lines and wrapped the pump in pipe insulation (the brown "smurf tube" commonly sold at hardware stores). It now can't be heard in the cabin.

The air duct is not a common size and one is generally forced to buy small lengths. The air is quite hot (it melted one of my crocs on the cabin floor, also shown in the above thread at post 53). I would use the special heat-tolerant aluminized duct when near the heater. However, that duct is usually kind of an accordion pleat and therefore not that efficient for longer runs. Turns out that long runs and lots of elbows are what kills these little heaters as they can't "breathe" and coke up. That said, I needed to run one "Y" over 8 feet through the cold bilge to get to the V berth. I used 3" pipe insulation as the duct (the brown stuff, again) to keep the air warm. Worked fine and can apparently take more heat than a pair of crocs.

 

[Carriage Guy]

Our heater installation also had requirements about the relative elevation between the heater and the fuel supply. If the heater was mounted below the level of the fuel, it required an optional automatic fuel cutoff as a safety measure so it couldn't accidentally siphon and leak fuel when it wasn't running.
I'd think you could tap into the line running to your fuel filters, especially if you installed the cut off valve mentioned above on the tap to the heater. But would call the distributor for whatever heater I was installing for their advice about that and their recommendations for a separate inline filter for your heater, preferably close to your heater box. At least our heater fuel pump doesn't like ANY foreign material or algae "snot". The fuel demand of our heater is minimal compared with an engine, even at 35F and running 24 hrs, we run through only about 1 to 1-1/2 gallons per day. FYI, we draw our diesel from a day tank since our boat's engine is gas and that tank is below the level of our heater so we don't have one of the automatic cut off valves.

We chose our Wallas for it's quietness and you should look for YouTube actual start up and running demonstrations of whatever model you are looking to install to make sure it will be compatible with your type of boating. Our brand does have some drawbacks, for one it's eyewateringly expensive. It does seems well made and it is easy to service most of it's components. The US distributor provides excellent support over the phone for the stuff you can do yourself. You can replace the glow plug, thermocouple, and "innards" of the combustion chamber in just a few minutes and they provide good information for freeing a "stuck" (gummed up) fuel pump but you can't replace the fuel pump itself or the controller board in the field.

Those two items need to be "married" to each other because the fuel pump needs to be calibrated and those values need to be calculate and installed into the controller board at a service shop-- you have to ship your heater back to the shop if either of those items goes bad. And of course Murphy says you will find that out when everyone else is also starting to use their heaters at the beginning of the cold season so the shop queue time can be long. Ask me how I know......
Our Wallas does provide almost home furnace level of service and we have 3,500 hours on ours so far. Quiet, warm air at the push of a button without the need for a muffler, but that does come at a price. Another owner of our model of boat went the low cost route, simply carries a spare heater for redundancy and still came out money ahead but also runs the risk of being "that noisy guy" at an anchorage, marina or important in our trailerable trawler case, a campground. Everything is a compromise and only you can decide what features have value to you.

 

[paulga]

Thanks guys for your input.
I called Wallas for some questions and was told it may not be adequate for a 40' boat. They recommended to install a hydronic heating system.

I watched some videos but not sure if it's the one that was talked about over the phone. Is it still a diesel heater? Anyone who has installed a hydronic system could you post some photos, any idea how expensive the parts and installation are?

 

[Carriage Guy]

Hydronic

Steve Mitchell does numerous good writeups on his SeaBits site and happens to have done one two years ago for his own hydronic installation. Includes how he sized his unit for his boat, evaluation of two different models, costs of parts for DIY installation, quotes for parts with installation, and diagrams.

https://seabits.com/hurricane-chinook-hydronic-heating-system/
--Mike

 

[sunchaser]

Thanks guys for your input.
I called Wallas for some questions and was told it may not be adequate for a 40' boat. They recommended to install a hydronic heating system.

Yes to hydronic. There are many advantages over forced air one being the use of engine heat via a plate heat exchanger for vessel heating when cruising and boiler off.

One hull hole is fine with the hole utilizing a pipe in a pipe design able to provide fresh combustion air and exhaust together.

 

[paulga]

Steve Mitchell does numerous good writeups on his SeaBits site and happens to have done one two years ago for his own hydronic installation. Includes how he sized his unit for his boat, evaluation of two different models, costs of parts for DIY installation, quotes for parts with installation, and diagrams.

https://seabits.com/hurricane-chinook-hydronic-heating-system/
--Mike

I read it through. Hydronic is great, but is definitely not a DIY for me. The parts alone costs more than twice of the Wallas installation kit. The forced air unit may be the way to go

 

[psneeld]

I installed one on my 40 foot Albin. I wasn't worried about heating the lower forward galley, head and V-berth area.

I had a duct in the main salon, masted head and master stateroom and it was good for down to freezing temps and a stiff breeze.

As long as the sleeping area and head were cozy and the nip out of the main salon...I was happy. If really frigid conditions were anticipated, the bus heater worked while running and I just planned to use a marina with electric for those bad nights.

Ask Boomerang (member) who bought my boat on his opinion whether it is adequate as he has run the boat in even colder weather than I did.

The Scan Marine guys gave me a pretty good discount being what they thought was one of the first installs on the East Coast and me being in the marine business promising to sing its praise if it was a good system.

 

[Bmarler]

I read it through. Hydronic is great, but is definitely not a DIY for me. The parts alone costs more than twice of the Wallas installation kit. The forced air unit may be the way to go

You can install multiple forced air units too. Maybe a large one for the salon, And a smaller one in the stateroom.
Maybe look at some of the knockoff ones too, lots of people use the and they’re really inexpensive.

 

[SteveK]

I have one diesel forced air in the 4588. One outlet in salon, the other in one of stair facing forward. We feel the heat at night, so one unit for us is enough since we do not want 70+ while sleeping

 

[paulga]

I took some snapshots of the aft bulkhead. is there a good location for mounting the heater?

The combustion exhaust through put would most likely on either side of this bulkhead. fuel tanks insulation panels and the bulkhead form a really pinched space. it is narrower than what the photo shows.

I need to find another location. maybe in the salon, tap into the genset fuel line, or in the sundeck, run from a daytank?

 

[Bmarler]

The heater doesn’t need to be in the engine space. Many times it’s easier to put it closer to where you want the heat to come out. An easy path for the exhaust is a high priority, followed by fuel supply. So an under settee, or other cabinet space you can sacrifice may work better.

 

[psneeld]

Put mine in the storage area under the lower helm seat sucked fresh air in through the louvers (with air filter screwed on inside) exhausted easily through hull side and running the duct work under the sidedecks to salon, aft head and aft stateroom was easy. If the heater is in the engine room and you have any fresh air intake leaks, you might get engine room odor circulated throughout the boat. The heater is quieter than air-conditioning units so it never really bothered me.

There were numerous holes already through the decks to go to a main fuel tank or a small separate tank in the engine room and I was debating to put a small tank under the step going outside next to the helm.

Whole project was a day or so.... probably took more time to pull the controller wires forward to my electrical/command power center than the rest of the project.

 

[Carriage Guy]

+1 for mounting a heater in the cabin. As you can see from our boat picture, we don't have an engine space so don't have that option anyway. The typical mounting location in our model of boat is the space between the helm seat bench and the hull. Our heater is the size of a large kids lunchbox, other brands are the size of a loaf of bread so should be easy to find a place.

The long axis of our heater is oriented fore/aft which puts the incoming fresh air duct from our cockpit and the outgoing heated air duct naturally parallel to the hull for easier routing around our boat. Our combustion air pipe rises from the heater, does an inverted "U" bend and dives down to our thru hull fitting aft of the heater.


From the online videos I've seen, I'd be a little leery about mounting the ultra low cost diesel heaters in a cabin due to the sound they make but would consider putting one in an empty lazarette locker somewhere outside.

I like the suggestion of installing a couple of heaters to get the heat output you need and provide some redundancy. I didn't think about the fuel consumption for a bigger boat, but if you need anything like Steve Mitchell's estimate of 40k BTU, keeping two big diesel heaters fed with diesel fuel from a day tank would be a task. I think each would come close to draining such a tank each day in cold weather-- truly making them "day tanks". (Google says 1 gallon of diesel has 137,000 BTU of energy so running heaters at max output to come near that 40k BTU would consume 1 gallon of fuel about every three hours, maybe more when inefficiencies are considered.)


Any chance you have vertical access above your fuel tank vent fitting? I see that heater fuel pickup tubes are available that can fit through a special combination tank vent/heater fuel pickup "T" fitting that screws into the standard vent fitting on a diesel tank. But while that eliminates the need to drill your tank for a separate fuel pickup fitting, you still need the clearance above the vent fitting to drop the long straight fuel pickup tube down into the tank and a little space to hook up the hoses.


If you don't have good vent access in your engine room, I'd imagine your tanks are outboard against your hull so maybe you would be lucky enough to have the vent fitting on your tanks located underneath some cabinet or bench where you could (very carefully!) drill an access port in the cabin floor to access that vent fitting by reaching down through the cabin floor.

 

[TJM]

Paul: As you can see there are lot of options. Insulating the exhaust pipe is an easyish task. My tube-in-tube exhaust hose touches fiberglass and wood with NO issues. Where the hose touched the boat I have wrapped high temp cloth to act as a heat shield. Fuel can be extracted thru a manifold without any more tank penetrations. I have 2 manifolds on my boat. All of the feeds have ball shut off valves so no starvation can take place. If you winterize your main engine, close the fuel valve.