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Duct Routing for Diesel Heater

Oct 17, 2020
3
Hunter 410 North Weymouth
I’m getting ready to install a Wallas 40D (purchased new in the box from someone who bought it to install and never did) on my 2001 Hunter 410. I still need to buy the ducting and registers from ScanMarine.

Does anyone have pics of how they routed the warm air ducting to the saloon? It looks like I’ll have to drill holes in several spots and am thinking this is the best route to under the settee on the starboard side.

And yes, I’ll be re-doing all the wood backed thru hulls this winter!

77E8DCF5-E6D6-4D39-A56C-6FC7B3B19DB5.jpeg
 
Last edited:
Apr 8, 2010
1,436
Ericson Yachts Olson 34 Portland OR
Major Stress/Strength issues, from opening up 3" holes in a grid structure??
Best to check in with the factory, first.

Coincidence: I am now installing a new furnace in our smaller boat -- after some pondering we are running ductwork higher up closer to the underside of the deck behind cabinetry. A lot of "imagineering" goes into a project like this. (sigh)
 
Jan 11, 2014
6,159
Sabre 362 113 Fair Haven, NY
Major Stress/Strength issues, from opening up 3" holes in a grid structure??
Best to check in with the factory, first.

Coincidence: I am now installing a new furnace in our smaller boat -- after some pondering we are running ductwork higher up closer to the underside of the deck behind cabinetry. A lot of "imagineering" goes into a project like this. (sigh)
Those beams are important structures. Big holes would probably compromise the structure.
 
Mar 6, 2008
536
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
Yes, I agree with number 2 and 4 posts above. Making such large holes in sheer walls or bulkheads is sure to weaken the structure. I would not buy a boat with such holes in them.
 
Jan 1, 2006
5,179
Slickcraft 26 Greenport, NY
And if that isn't bad enough, running ducts low in the boat puts the ducts in an unfavorable heat gradient. Better to be higher. On my 356 the A/C ducting was behind cabinetry, thru settee lockers and inevitably thru bulkheads for the aft cabin and fore cabin. For the main cabin it's more difficult. The 356 had a heat pump and the same ducts for heat and cooling. They worked better for cooling. I wonder if the best you can do is place the duct exit in the riser for settee. And get some wool socks. Something in the head would be nice.
 
Oct 17, 2020
3
Hunter 410 North Weymouth
And if that isn't bad enough, running ducts low in the boat puts the ducts in an unfavorable heat gradient. Better to be higher. On my 356 the A/C ducting was behind cabinetry, thru settee lockers and inevitably thru bulkheads for the aft cabin and fore cabin. For the main cabin it's more difficult. The 356 had a heat pump and the same ducts for heat and cooling. They worked better for cooling. I wonder if the best you can do is place the duct exit in the riser for settee. And get some wool socks. Something in the head would be nice.
That’s what I’m leaning towards now!
 
Oct 22, 2014
13,132
CAL 35 Cruiser moored EVERETT WA
running ducts low in the boat puts the ducts in an unfavorable heat gradient
Running heat ducts low along the side of the boat in voids is my preference. This is not for AC, it is for Heat from a forced air diesel heater. While I am not a HVAC specialist like some on this forum, what I have heard from them is heat rises. Placing the ducts in straight lines and as short as is practical to reach all of the spaces to be heated is the goal. Every turn/bend you place on the duct will reduce the flow of the heated air you want to reach the cabins.

I would search for a better routing than through the cross beams that are designed to hold the hull in shape.

In or better behind cupboards/cabinets would be my go to approach. Then I would exit the vents low into the space.
 
Oct 22, 2014
13,132
CAL 35 Cruiser moored EVERETT WA
Insulation wrapped around the ducts will reduce the heat loss along the ducts. You will get maximum heated air delivered to the vents into the cabin.

I found that one wrap of the foil bubble wrap around the duct increased the air temp at the vent by 10 degrees.
 
Jan 1, 2006
5,179
Slickcraft 26 Greenport, NY
And I think a fan high in the cabin could blow the warmer air down to the feet area which is the problem with heat on a boat - too warm high up, too cool at foot level.
 
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Likes: Boomer54
Jan 12, 2016
252
Hunter 410 Ladysmith, BC
Access is really tight. I had a local marine HVAC expert do a consult when trying to decide which heating system to install on our 410. We ended up hydronic because it was much easier to run coolant hose than 3" duct with the tight clearances below the floor. No way was I cutting open structural beams. The only thing I would have done differently was spend the extra $$ for a Hurricane branded heater rather than Espar. Espar has been trouble free, but the Hurricane is a better unit and allows you to eliminate your hot-water tank.

Maybe you could run it below the stove/fridge above floor level, (insulated of course so you don't leak heat into these areas) you could run down the starbord side of the boat, but once you hit the starbord settee there is a lot of plumbing there that could make things challenging to find room. The other option could be to use reducers to get the hose to a smaller diameter but this would no doubt kill efficiency. Unfortunately the H410 isn't laid out well to install forced air heat easily. I posted about our hydronic install almost four years ago. I don't know if there is anything in that thread that can help you. Those Wallas heaters are very nice, if you can make it fit cleanly without too much surgery I'd love to learn what you end up doing.
 
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Likes: Hayden Watson
Apr 8, 2010
1,436
Ericson Yachts Olson 34 Portland OR
Another piece for the puzzle is how and where for ducting.
A friend of mine installed a furnace in his 38 footer, and since he knew the usual problems with the install and also the ensuing heat loss for a duct forward..... he decided to not do that. Besides rebuilding his boat, he's an A&P mechanic and pretty savvy about mechanical projects.
Blasphamy? :)

Well, in use it's great! He put in a system with the 4" main duct, and fed it into the main cabin from aft. The vent faces forward, and the air flow is strong and hot. I recall that he put a small circulation fan up somewhere forward.

This saved a buttload of money, time, and saw-and-drill bush-whacking thru a lot of cabinet woodwork.

(Full disclosure: this is the general plan for our present furnace install, as well. Main duct up to the rear of main cabin, with a small outlet for the aft head. Our boat, like many 'modern' interior layouts has the head and aft cabin geography, with the boat mostly open forward to a large V berth. We already have Hella fans for circulation in three areas of the interior.)

Do post up more pix as the project moves along.
 
Apr 5, 2009
1,244
Catalina '88 C30 tr/bs Oak Harbor, WA
Cutting big holes in the floor grid is a bad idea. On my C30 I could not find a good way to run 3" or 4" ducts to the forward end of the boat. In the end, I installed a small hydronic system and the 3/4"ø hoses were easy.
 

Bob S

.
Sep 27, 2007
1,596
Beneteau 393 New Bedford, MA
Hurricane is a better unit and allows you to eliminate your hot-water tank.
I believe you can eliminate your hot water heater with any hydronic system or just run it through your domestic hot water. I hope to install heat on ours some day.
1603045821809.jpeg
 

dLj

.
Mar 23, 2017
1,245
Hunter 30 Snug Harbor, Lake Champlain
Just an observation, in the forced air systems I'm not hearing anyone talking about return cold air flow. Is that not done with boat forced air systems?

In forced hot air systems in other structures the most critical aspect is the cold air flow. How is that being handled in boats? I've never worked with forced hot air systems in a boat. But this aspect is commonly overlooked in other systems I have worked with.

dj
 
Oct 22, 2014
13,132
CAL 35 Cruiser moored EVERETT WA
return cold air flow.
Good point. The Wallas install info encourages you to use the two cold air intakes in two ways.
One should be drawing in fresh air. I chose to position the intake duct next to a cowl off the stern near the unit.
The second is connected in the bulkhead that draws air near the top of the space of the salon.

So far it is working as expected.
 
Jan 12, 2016
252
Hunter 410 Ladysmith, BC
I believe you can eliminate your hot water heater with any hydronic system or just run it through your domestic hot water. I hope to install heat on ours some day.
We plumbed ours through the hotwater tank and used a summertime loop to get more efficiency in the warm weather months when it is only used for water heating. Hot showers in the morning after a night on the hook are a wonderful thing.
 
Apr 5, 2009
1,244
Catalina '88 C30 tr/bs Oak Harbor, WA
I believe you can eliminate your hot water heater with any hydronic system or just run it through your domestic hot water. I hope to install heat on ours some day.
View attachment 186238
No reason to eliminate the HW tank to use hydronic or this type of heat exchanger. I plan to add one of these after my HW tank and have the outlet go through a mixing valve. That way, when the tank is hot, I do not need to fire the boiler just to heat water. When the tank is cold, I can still get hot water by using the boiler. Best of both.