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Old 30-10-2020, 17:40   #1
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Gusts blowing out / downdrafting diesel heater chimney

We have a Sigmar 170 diesel heater (similar to the Dickinson ones) we use during winter cruising. The one problem I haven't been able to solve is downdrafting of smoke into the cabin when hit by strong gusts on the beam. It's pretty awful when it happens as the smoke is quite noxious and it can extinguish the diesel pot or cause it to flare up.

The anchorages we're commonly in are tree-lined and well protected but this means gusts coming over the trees can oscillate along a 180 degree arc and go from 5 kts to 15 or 20 in the space of 60 seconds - and our boat will often be spinning through 180 degrees on the compass. Very tough situation for a diesel heater when a direct gust hits on the port beam where the heater cap is.

Here are the things I've tried which haven't worked:
  • Increasing fuel + air mixture to strengthen the draft column
  • Rotating the flue cap to avoid primary wind direction. Helps sometimes but no guarantee. We have the "H" style flue cap which Dickinson says is the best for wind.
  • I use a draft assist fan when starting the fire, but even with this, it has still blown out as a gust rushed down.

Some ideas:
  • Has anyone tried the VacuStack cap? I heard this may be better. It's not made by Dickinson, it's sold by chimney supply companies; https://www.chimneydirect.com/vacustack-chimney-cap
  • A barometric damper? I'm not sure this would prevent gusts from getting in and it would require cutting and replacing part of our interior chimney.
  • I could add a 2 foot extension above deck between the cap and the deck fitting (raising the cap). It would block our boom though so I'd have to swap it out regularly.
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Old 30-10-2020, 17:58   #2
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Re: Gusts blowing out / downdrafting diesel heater chimney

Definitely try the flue extension. It seems pretty short for a system with 2 bends. Also try a different chimney cap, the circular ones generally tend to work better.


http://dickinsonmarine.com/product/s...p-exhaust-cap/
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Old 30-10-2020, 18:00   #3
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Re: Gusts blowing out / downdrafting diesel heater chimney

My heater is a Refleks which has similar issues. I have added a half meter extension under the H cap on deck, this helped a lot and made it easier to light. I have also added a strong computer fan blowing through some ducting to the air intake primarily to assist in lighting but it also helps in gusty conditions. Opening a porthole facing the wind can be useful in pressurising the cabin and preventing backdrafts. Conversely opening the main hatch can induce a negative pressure causing a backdraft.
Its been recommended to me to use an insulated stack pipe outside to keep it warm for a better draft, I haven't tried this yet.
Refleks offers a outside air supply option where the combustion air is supplied through another identical stack which is supposed to prevent backdrafts. I have avoided this as I dont really want two stacks on deck.
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Old 30-10-2020, 18:01   #4
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by Westcliffe01 View Post
Definitely try the flue extension. It seems pretty short for a system with 2 bends. Also try a different chimney cap, the circular ones generally tend to work better.


http://dickinsonmarine.com/product/s...p-exhaust-cap/
The interior chimney is 4' in length (with the 45 degree bend).
My understanding is the Dickinson DP cap is *less* tolerant of high winds. They say in their documents that the H cap is better for wind and the DP cap is preferable only for sailboats worried about snagging lines on the H cap (this isn't an issue for us).
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Old 31-10-2020, 01:46   #5
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Re: Gusts blowing out / downdrafting diesel heater chimney

To minimize these effects, you definitely need to get the on deck chimney much higher off deck. And... you’re not going to like this: a straight chimney without all those bends and running diagonal as you have it.

I used to use a Charlie Noble like this one pictured , but it was 4’ above the deck,, with a perfectly straight chimney,. No backdraft issues in any winter storms.

It’s not the heater itself. It’s your installation.

Start with a 4’ extension on deck. Use metal guy wires to hold it in place if necessary. If that doesn’t work, you’ll need to do better with the chimney inside the boat. Get rid of that diagonal part.

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Old 31-10-2020, 04:24   #6
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Gusts blowing out / downdrafting diesel heater chimney

Iíve had success with these caps in gusty Wyoming conditions that used to backdraft into the house.


https://www.luxurymetals.com/wind_di...YaAsarEALw_wcB

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Old 31-10-2020, 07:31   #7
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Re: Gusts blowing out / downdrafting diesel heater chimney

A barometric damper will help a lot. Adding pipe above deck might do the trick. If you insulate the above deck section, you improve the draft and it helps to steady the flame. We stayed aboard all winter in New Bedford harbor and experimented with different caps. The round cap is also called a Concordia cap because it was the preferred cap for offshore in Concordia yachts. Expensive and difficult to build. We used the H cap and four feet of copper pipe which we insulated and covered with another thin stainless pipe. I think insulating and extending the pipe is more important than the cap.
Be very careful about an increase in the air temperature in the boat and outside.
A big swing can get the stove going really hot. Much too hot. The glass will be black and more and more fuel will be pulled into it and the exhaust temp will become dangerously high. Donít open the door, shut off the fuel.
These heaters are not very efficient but nice in a smaller yacht. We added a tee rather than an elbow below the burner which makes cleaning easier. You must move the correct fuel valve for whatever diesel you use. A small fuel filter too.
Fire and carbon monoxide alarm are a must.
We had several gales and two full storms and never had a blow out with the H cap once we increased and insulated the stack. Nice heater, just be careful.
Happy trails to you.
Captain Mark and his toasty toe manatees
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Old 31-10-2020, 08:16   #8
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by Chotu View Post
To minimize these effects, you definitely need to get the on deck chimney much higher off deck. And... youíre not going to like this: a straight chimney without all those bends and running diagonal as you have it.

...
Thanks. I'm not sure I understand the issue with the diagonal bends - seems counterintuitive. If anything I'd expect the angles to improve the deterrence of any gusts making their way down the pipe. If that's not the case, perhaps it's because the bends decrease the strength of the draft, by making it take longer for the hot air to rise (possible cooling more in the process)?

Of course, moving the hood for a straight run is not easy. A prior owner installed it, and although it looks like a straight run would be possible from the interior, I think on deck that would put the cap so close to centerline / boom that it might interfere with the boom vang.

I can try a different hood, extension above-deck and barometric damper. (knowing which of those is most effective would help since these parts add up in cost quickly! Getting all 3 will be over $250)
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Old 31-10-2020, 08:18   #9
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by Sailmonkey View Post
Iíve had success with these caps in gusty Wyoming conditions that used to backdraft into the house.


https://www.luxurymetals.com/wind_di...YaAsarEALw_wcB

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That's a very cool design (with the ball bearing races for rotation), however it appears it's designed for house chimneys but not boats - the smallest size they have is 4", but boat heaters like ours have 3" piping.
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Old 31-10-2020, 09:06   #10
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Re: Gusts blowing out / downdrafting diesel heater chimney

Why not just install it as designed? Its a 'balanced draft' heater and should have a second 3" flue coming out the bottom and back up to the deck. I sold these new back in the 90s and installed the 120 model in my 30ft sloop. Never had any problems.
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Old 31-10-2020, 09:58   #11
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by Chotu View Post
To minimize these effects, you definitely need to get the on deck chimney much higher off deck. And... you’re not going to like this: a straight chimney without all those bends and running diagonal as you have it.

I used to use a Charlie Noble like this one pictured , but it was 4’ above the deck,, with a perfectly straight chimney,. No backdraft issues in any winter storms.

It’s not the heater itself. It’s your installation.

Start with a 4’ extension on deck. Use metal guy wires to hold it in place if necessary. If that doesn’t work, you’ll need to do better with the chimney inside the boat. Get rid of that diagonal part.

IMHO. This is correct.
I use a Chalie Noble Cap with my Newport Dickenson Diesel Heater.
As my Set up in the interior is minimal as to stack height I just add a 1 foot extension on the stack outside when I use the stove, cap it when I'm off the boat.
Never had any puffs down the stack yet, had 30+ winds and sailed while running it.
Do look at the insides of your stove pot for cokeing up and clean it really well often.
There are also updated components that are used for problems with low sulphur diesel.
Your stack may need a dampener as well because of length.
Read the literature provided by Dickenson, on their web page.
They speak a lot about stack height minimums and maximum heights.
Happy Sailing‼️
SV Cloud Duster
PNW

Also the flex pipe is much better for overcoming bend issues, 1 continuous piece.
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Old 31-10-2020, 10:01   #12
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by Tessellate View Post
That's a very cool design (with the ball bearing races for rotation), however it appears it's designed for house chimneys but not boats - the smallest size they have is 4", but boat heaters like ours have 3" piping.
These won't work for long in Salt Conditions.
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Old 31-10-2020, 10:29   #13
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by Tessellate View Post
We have a Sigmar 170 diesel heater (similar to the Dickinson ones) we use during winter cruising. The one problem I haven't been able to solve is downdrafting of smoke into the cabin when hit by strong gusts on the beam. It's pretty awful when it happens as the smoke is quite noxious and it can extinguish the diesel pot or cause it to flare up.

The anchorages we're commonly in are tree-lined and well protected but this means gusts coming over the trees can oscillate along a 180 degree arc and go from 5 kts to 15 or 20 in the space of 60 seconds - and our boat will often be spinning through 180 degrees on the compass. Very tough situation for a diesel heater when a direct gust hits on the port beam where the heater cap is.

Here are the things I've tried which haven't worked:
  • Increasing fuel + air mixture to strengthen the draft column
  • Rotating the flue cap to avoid primary wind direction. Helps sometimes but no guarantee. We have the "H" style flue cap which Dickinson says is the best for wind.
  • I use a draft assist fan when starting the fire, but even with this, it has still blown out as a gust rushed down.

Some ideas:
  • Has anyone tried the VacuStack cap? I heard this may be better. It's not made by Dickinson, it's sold by chimney supply companies; https://www.chimneydirect.com/vacustack-chimney-cap
  • A barometric damper? I'm not sure this would prevent gusts from getting in and it would require cutting and replacing part of our interior chimney.
  • I could add a 2 foot extension above deck between the cap and the deck fitting (raising the cap). It would block our boom though so I'd have to swap it out regularly.
We extended the stack four feet and put the H-pipe on top of that. The extension was two sections of smoke stack which fit into each other, therefore was removeable. The smoke stack passess close to the shroud so we could wire the top of the stack to a shroud to keep it steady.

The second improvement we made was to pressurize the interior of the boat by judicious use of cowl vents, which also helped keep the boat dry (cold dry air comming in, and hot humid air burned and exhaused out the stack).

With these two changes we kept the"blow outs" to a minimum for the 10 years we lived on and cruised in PNW.
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Old 31-10-2020, 10:35   #14
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Re: Gusts blowing out / downdrafting diesel heater chimney

Quote:
Originally Posted by rphdiego View Post
Why not just install it as designed? Its a 'balanced draft' heater and should have a second 3" flue coming out the bottom and back up to the deck. I sold these new back in the 90s and installed the 120 model in my 30ft sloop. Never had any problems.
Burning outside air defeats one of the major benifits of these heaters, which is to consume the humid air from inside the cabin and exhaust it outside.
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Old 31-10-2020, 12:06   #15
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Re: Gusts blowing out / downdrafting diesel heater chimney

I used stove pipe above my cabin, two 45* elbows, then another section of stovepipe capped everything with the H cap.

The two 45’s allow me to twist the pipe down towards the horizontal when underway so the boom clears the pipe.

Works very well for us. I just have to remember to twist the chimney down before raising the main.
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