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Old 19-03-2010, 16:49   #46
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Originally Posted by D_e_n_n_i_s View Post
I don't get why the major diesel heater/oven manufacturers like Taylor, Dickenson and Sigmarine (to name a few) don't jump onboard with the coaxial flue design (Pipe in a pipe for both intake & exhaust)? Well, it seems some do for propane, but not for diesel. Is there a reason for this ???
Why is coaxial flue important?

I have a Dickenson Newport and it works great without the coaxial flue.
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Old 20-03-2010, 05:37   #47
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Why is coaxial flue important? ...
One major advantage of a Co-Axial (or any) Direct Vent (Sealed Combustion) unit is that it draws no (heated?) air from the boat. The fresh air is piped in to the combustion chamber from outdoors, and the flue gases are then exhausted directly to the outdoors.
Sealed Combustion (direct vent) appliances are generally:
More efficient
Cleaner
Safer
than indirect units.
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Old 20-03-2010, 21:25   #48
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I think Gord May has it summed up. The key for me is that there is no chance for fumes to get into the cabin and you don't have any concerns with oxygen being burned from the cabin air as you draw all air for the fire externally.

I think going with the Origo 6000 for cooking will eliminate the heat of diesel cookers, which will be great in summer. A closed system diesel heater would take care of the winter. I'm glad to hear direct experience that the Newport works so well. I like the similar Dickinson model that has the small cooking area (Great for winter and I would think also hotter for cooking than alcohol) and the water heating is a plus.

Does anyone know of any marine diesel or kerosene closed combustion heaters? If you have any name, I'm happy to run it down. I'm just looking for something simple, but if it happens to heat water too, then that's just icing on the cake.

At this point, I would also appreciate feedback on draft diesel/kerosene heaters too as I seem headed this way - Preferably something with high BTU output (16K BTU or anything remotely close). I just know that 6-7K BTU isn't cuttin' it. Thanks !!!
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Old 22-03-2010, 11:51   #49
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Originally Posted by GordMay View Post
One major advantage of a Co-Axial (or any) Direct Vent (Sealed Combustion) unit is that it draws no (heated?) air from the boat. The fresh air is piped in to the combustion chamber from outdoors, and the flue gases are then exhausted directly to the outdoors.
Sealed Combustion (direct vent) appliances are generally:
More efficient
Cleaner
Safer
than indirect units.
I understand that coaxial doesn't draw air into the burner from the inside of sailboat. I understand that is more efficient. I have real questions how much efficiency is gained. My guess is not much.

Further the influx of new air (and subsequent exhaust of that air out the flue) has it's own benefits particularly if you have been cooking, say, fish. Sailboats can get stale air and as a general rule some reasonable amount of air flow is healthy. Ask mold about it.

The idea of staying in a sailboat with no vented breathing air doesn't appeal to me--at all. When it's cold, raining buckets, and the boat is buttoned up at anchor and you're cooking, making tea, reading a book, is exactly when I want a little bit of air flow to keep the inside air from going completely stale. As soon as you open the air flow inside the boat to keep your breathing air from getting so stale, like opening the dorades, then the benefits of coxial are lost.

As to cleaner and safer, prove it. I don't buy it.

Flue gases are exhausted directly to the outdoors for the non-coxial units too. Combustion is sealed also.

So I repeat, what's the big deal about coaxial? Nobody has made any concrete claims, just glib and vague intimations. They are slightly more efficient, at the cost of a stale interior.

The vast majority of heaters are not coaxial and their users have no complaints. Why is that?
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Old 22-03-2010, 11:57   #50
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The key for me is that there is no chance for fumes to get into the cabin and you don't have any concerns with oxygen being burned from the cabin air as you draw all air for the fire externally.
1. Coaxial has nothing to do with a chance of fumes getting into the cabin. My first heater did not have a seal combustion unit, and I had the fumes problem. Installed a non-coaxial unit with sealed combustion and solved my fumes problem.

FWIW, I'm not aware of any non-propane units on the market today that are not sealed combustion. If there is one, so what. The vast majority of heaters today are sealed combustion. The unit I threw out is no longer offered for sale. It's a discontinued model, for good reason.

2. The concerns about oxygen being burned from the cabin air are solved simply by making sure the boat is not air tight. If your dorades are open, that problem has been solved. So long as air is coming into the cabin at the same rate as it's being burned by the heater, there is no problem. This is not rocket science, which is why there are so very few coaxial units offered for sale. Coaxial solves a largely non-existent problem.
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Old 22-03-2010, 13:39   #51
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Hiracer - The efficiency of the coaxial flue to me stems from the fact that cold air coming in, say through the outside pipe, gets warmed by the exhaust fumes, say through the inside pipe. The heat that would be lost from exhaust is captured better by heating the cold incoming air (Greater thermal difference). I'm just thinking about it logically so I'll let others confirm my initial thoughts on this. I'm not sure how much of a difference this makes, but is seems like it would help some (no down side).

Safer - That to me comes from not sucking oxygen from the cabin and not putting fumes into the cabin as well. This to me is the most critical piece. I wonder too if you had a flare up or blow out, I wouldn't think you would get flames into the cabin as easily (without an explosion) or wouldn't get fluid leaking into the cabin as well if the flame goes out. I could be very wrong here - just throwing those thoughts out for others to correct or tweak.

I think refreshing the air in the cabin by opening a hatch is a separate issue than doing it through a diesel heater vent. By having these as separate things, you can open a hatch when you want, but don't have to worry about fumes coming at you through the heater vent while it's burning fuel. Down drafts throw out a lot of fumes (I've had this in strong winds even with my charlie noble, which works great). Besides, I know I don't have my cabin air tight so there's always a small amount of natural air flow.

I'm not sure why closed combustion would be cleaner burning - Perhaps this was a reference to the fumes into the cabin. You would still have the mess topside I would think.

Flue gases are exhausted directly to the outdoors for the non-coaxial units too, but the combustion is not sealed. Air is being sucked in from the cabin and as you learn the hard way with a strong down draft, those fumes can come right back out of those holes at you.

Coaxial specifically is just the efficiency of the pipe in a pipe for heating the cold air coming in as I see it. The closed combustion part is huge in that it stops fumes and doesn't suck oxygen out of the cabin. You can have a closed combustion system that uses two separate vents. I would be fine with that too as my main concern is safety. I just can't find either designed in a truly marine unit using diesel or kerosene anywhere ... sigh ...

FYI - I got a response from Dickinson that noted in the first paragraph:
We have been researching and developing a closed combustion direct draft diesel unit now going on 4 years. We have been playing with the size of burner, fuel flow and the size of both the inner exhaust pipe and the outer intake pipe but we are unable to find the correct fuel to air mixture to create a clean combustion. So, we continue to try to achieve this but it doesn't look like we are close to the end anytime soon.

I've been very impressed with the Dickinson Marine and how they have responded to my inquiries (as a side note).

My concern is that I don't get the balance right between fresh air coming into the boat and air being burned by the heater and I simply don't wake up to fix the problem in time. Of course, with the diesel heaters that I've seen so far, I can't run them overnight unattended anyway ... sigh ... Still, the same thing could happen while you're watching the fireplace burn ... Even worse is the fumes - They can be very, very bad and I'm sure not healthy in the long run either ...
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Old 22-03-2010, 14:03   #52
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. The efficiency of the coaxial flue to me stems from the fact that cold air coming in, say through the outside pipe, gets warmed by the exhaust fumes, say through the inside pipe. The heat that would be lost from exhaust is captured better by heating the cold incoming air ...
Sorry but this makes zero sense to me. On my heater, the lion's share of the heat transmitted to the cabin comes not from the stove but from the exhaust pipe. If you decrease the temperature of the exhaust pipe because you're using it to suck cold air to the burner, then heating efficiency goes DOWN.

And explain to me why it's important that the air feeding the burner be preheated. How does that matter? That outside air never mixes with cabin air in a coaxial design, so its temperate is immaterial.

I thought the efficiency of coaxial comes from the fact that air in the cabin (that has already been heated) is not sucked into the burner and exhausted outside, to be replace by new cold air from the outside which now must be heated (again). Coaxial avoids having to heat the new air coming into the cabin because the burner's air intake is outside, not inside, the boat.

But if it does so at the cost of reducing the temperate of the exhaust pipe, then I'm very skeptical about any energy savings. In fact, if the intake of cold outside air is reducing the temperature of the exhaust pipe, then I flat out don't believe in any alleged efficiency.

Quote:
Originally Posted by D_e_n_n_i_s View Post
. Air is being sucked in from the cabin and as you learn the hard way with a strong down draft, those fumes can come right back out of those holes at you. ...
Never had this happen, even during storms.
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Old 22-03-2010, 15:02   #53
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That's an interesting point about most of the heat coming from the exhaust pipe. I get most of my heat from the heart of my Taylor diesel heater, but there is a lot of heat too from the exhaust pipe so you make a great point. I guess someone with a thermodynamics background can speak to the actual efficiency of the transfer of energy across a greater temp differential in the pipe versus the amount of energy transferred to the air in the combustion chamber. I would think heating hot air requires less energy, but how does that compare to the heat lost heating up the incoming cold air. Hmmmmm ...

Not venting heated air in the cabin perhaps is, in fact, the greatest efficiency of a closed combustion system. Keep in mind that a coaxial flue just speaks to a pipe in a pipe design. With your initial point, it may make more sense to actually use two separate pipes for intake and exhaust both still going into a closed combustion system. Close combustion just describes the fact that there is no air going into the combustion chamber from the cabin and has nothing to do with the venting into or out of it. The venting can be two pipes or a coaxial design (pipe inside a pipe).
Also, you've made me consider that even if a coaxial design is used, it's best to have the exhaust in the external pipe with the intake on the inside pipe so that radiation on the outside of the "exhaust" pipe is released into the cabin.

You must have a much better charlie noble than what I have because when the wind was blowing very hard and when I had the unit cranked way up, I had some nasty fumes come into the cabin. Maybe I just need to clean my Taylor and I believe I had it cranked way up beyond what it recommended since it was glowing red at the time ... seriously ...
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Old 23-03-2010, 09:20   #54
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We may have a candidate !!!

I had sent an E-Mail to Wallas (Scan Marine Equipment) to see if they offered closed combustion diesel heaters and just received the following response:

Dennis:
First to answer your question: Yes, our models 30D, 2400, 1800 and 1300 all use coaxial exhaust/combustion air piping, exiting the hull or deck through a single fitment. See our accessories page on line for the different types of fitments. We typically prefer to see the fitment pass through a vertical surface (hull side, transom or house side) rather than a roof top. When run in an exposed location (in the cabin with you) they have no effect on oxygen content at all.

Your comments about burning oxygen from the cabin lead me to believe that you did not understand my earlier explanations. An exposed flame burner can and will rob the cabin of oxygen by burning the air and leaving the resulting combustion process gases in the room, lowering the net percentage of oxygen in the room as they burn. This is a bad combination, making it more and more difficult to breathe and in the case of propane, adding huge quantities of water to the cabin air.

Wallas forced air products that do not use the duplex (coaxial) exhaust system include the 40D furnace, 85D stove, 86D oven, 87D stove/oven, 88DU stove and 800 stove all take combustion air from the cabin, burn it and sent 100% of that air out the exhaust pipe overboard. There is no exhaust left in the cabin and new air finds its way back into the cabin, replenishing the oxygen supply and generally drying the cabin. These devices actually IMPROVE the oxygen content in the cabin air more than their coaxial design cousins described above do, replenishing stale air with new air from outside.

It is important to keep in mind that combustion air and makeup air are completely different considerations. If you take any of our ducted furnaces (1800, 2400, 30D, 40D) and feed them makeup air from both outdoor and inside (return) air, then any of them can work to replenish oxygen in the room, by slightly pressurizing the cabin with outside air. This is typically what we shoot for with new installations.
Thank you.
Doug McElroy
SCAN MARINE EQUIPMENT
2144 Westlake Avenue N., Suite D
Seattle, WA 98109 USA
Phone: 206-285-3675
Toll Free: 1-888-606-6665
Fax: 206-285-9532
Mobile: 206-755-2368
www.scanmarineusa.com

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I'll have to reply back, but my question is ... if air can get into the combustion chamber and into the cabin, then how do you prevent fumes (however small an amount it may be) from getting into the cabin ???
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Old 23-03-2010, 10:24   #55
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I'll have to reply back, but my question is ... if air can get into the combustion chamber and into the cabin, then how do you prevent fumes (however small an amount it may be) from getting into the cabin ???
By keeping positive pressure in the cabin. I.e., making sure the dorades are pointed into the wind, be sure to close the companionway all the way if you have a dodger, and if necessary (during a storm) turn on the air intake fan for the combustion unit.

It's all about pressure. You have be mindful, that's all. At anchor air is usually flowing over the boat. That air flow can be harnessed to create negative and positive cabin pressure. So long as you are aware what does which, the issue resolves.

P.S. I'm glad he confirmed my statements about the need to remove stale cabin air. I thinks that's more important than you realize, especially if drying out the cabin is an issue (think wet clothes or cooking with propane).
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Old 23-03-2010, 11:14   #56
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Apart from the fact that I have no dorades, if it's freezing cold outside why would you want to open up anything just to maintain cabin pressure? Why not just vent directly into and out of the fire? Besides, wind changes direction and you will inevitably lose a high, positive cabin pressure at some point. Trust me, one nasty back-wind of fumes and you will be opening up everything to be able to breathe !!

I understand that you can use the venting of a heater or oven/stove to vent fresh air into the cabin, but my concern is that you then open up the possibility of venting fumes into the cabin. I think fresh air circulation in a cabin can be done with different venting - something that can be closed off when it's freezing cold while you're heating up the air in the cabin. I do get that a balance with air heating (burning fuel) and natural draft are benefits of using ventilation with the heating system, but the down side of potentially getting fumes into the cabin make me think that a separate ventilation system (forced air, natural air flow, etc.) would be safer (safer as in no fumes into the cabin).

This kind of system would be much dryer and hotter than the non-pressurized alcohol unit (Origo 6000) that I'm considering buying as my oven/stove gimbaled device. Alcohol doesn't burn as hot and puts out moisture. If this turns out to be a closed combustion system, then I guess I'll need to weigh diesel/kerosene heat for cooking vs. heat in summer (and flex venting and the angle I need where the oven/stove is, etc.). It may still make sense to go with the diesel/kerosene closed combustion system for the heater and stick to the Origo for cooking.
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Old 23-03-2010, 11:58   #57
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why would you want to open up anything just to maintain cabin pressure? .
Because it works. Is that an adequate answer? It is for me.

1. I carry 99 gallons of diesel. So it's a dependable fuel source for heating on my boat.

2. My system is dead simple and therefore nearly bullet proof. That's important to me.

3. I remain warm and dry.

4. I don't get fumes in the cabin. The unit I have now was installed to address the fumes-in-the cabin problem. I've spent nearly every other weekend on the boat this winter and never had a hint of back draft. Winds up to 30 knots minimum, prolly more. I don't really check that kind of thing any more. It's sort of ho hum by now.

4. I never said it's the only way. To each his own.
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Old 23-03-2010, 13:17   #58
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How do you stay warm opening up a hatch when it's sub-zero weather outside? You were concerned about cooling the exhaust vent with the coaxial flue design, but opening a hatch would be much worse, right?
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Old 23-03-2010, 14:55   #59
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How do you stay warm opening up a hatch when it's sub-zero weather outside? You were concerned about cooling the exhaust vent with the coaxial flue design, but opening a hatch would be much worse, right?
Sub-zero F or C? Big difference.

First, I don't open hatches. I have two dorades, plus a solar driven fan vent. All it takes is one opening equal in area to the exhaust stack, preferably on the upwind side of the boat, or else the dorades pointed into the wind.

My prior boat had no dorades. It was based out of Seward Alaska. We were usually the first boat out in the spring. Not unusual for there to be 10 feet of snow still on the ground. Sub-freezing night temperatures. Low 40s during the day. Had a propane catalatic heater, non-coaxial fan driven exhaust to the outside. I would crack open the V-berth hatch about an inch, and that worked fine. Plenty warm; boat totally uninsulated fiberglass. This was with wife and two small kids (2 and 5). Nobody complained about being cold, so it's not a case of me being tough. (I'm actually a certified wuss, which is why I insist on bombproof heating--totally operable without electrical juice, which I didn't have in Alaska and that always bothered me.)

Second, I now have a steel boat with foam insulation so I'm better insulated than most production boats. I think that helps.

Third, the coldest I have used current heater is about 20 degrees F, and it took awhile for the boat to warm up but eventually got very comfortable.

Fourth, I don't know if this is irrelevent or not, but my stack is about 22 inches above the cabin top. I have a staysail stay which keeps the jib sheets off the stack so the sheets don't melt. Without the staysail stay, I think I would have to have a much shorter stack to protect the sheets.

All I know is that it works well enough for me, but then I am now in the PNW where winters are admittedly mild.

But in any case, I have real questions about whether the coaxial design is any more efficient, especially once you take into considertion the desire to vent breathing air. If the cabin is damp for any reason, my heater sucks out the dampness which is very much welcomed. Prior boat and heater was also just as effective at drying out the interior.

OTOH, I've never used coaxial so I really don't know.
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Old 23-03-2010, 15:06   #60
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Maybe I should clarify that I've never operated a heater at night while sleeping. We have good sleeping bags and rely on them instead of the heater while sleeping. I'm conservative about somethings and this is one of them. I like to be sure I wake up in the morning.

In the same vein, we turn off the propane stove at the tank valve after the meal is over. So I'm admittedly goofy in my approach to some issues. As I said before, to each his own.
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