diesel heater ducting

[paulga]

https://www.youtube.com/watch?v=qGZRqj028AA

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]

Originally Posted by 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?

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]

Originally Posted by Bmarler

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/...ers-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]

Originally Posted by Bmarler

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]

Originally Posted by 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.

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]

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]

Originally Posted by 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.

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]

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-chinoo...eating-system/
--Mike