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  #51  
Old 03-09-2010
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Quote:
Originally Posted by MedSailor View Post
One more quick propane question regarding the dickinson stoves.
If:
1 gallon of Propane ~= 4.23 lbs ~= 91690 Btus
1 lbs of Propane ~=21,676 Btus
20 lb tank of propane holds approx 4.73 gallons of propane (433,694 BTUs)

Then for the dickinson 9000model if you run it at 5500btu/hr you should only get 78.9 hours of usage (433,694/5500 ~= 78.9) yet the dickinson website claims 140hrs at this rate.

For the high setting of 7500btu they claim 100hrs though 433,694/7500 yields 57.8hrs by my math.

What gives? Surely a pound of propane can't produce more than 22000 btu. So does the stove not run as long as they say, does it not put out quite as many btu as they claim, or am I missing something else? I'm hoping that I'm missing something as I'm actually sold on the idea of a dickenson 9000 for a forepeak heater on my boat if their numbers are indeed correct.

MedSailor
Med,

That's actually pretty interesting -- I'm a bit intrigued. I've never picked apart those numbers like you did. It might be interesting to do the same analysis on their diesel heaters too.

Hopefully some of our physics and engineer types will chime in here and explain this to us. But until they do, and at the risk of being completely wrong in my assumptions, I'll take a common sense stab at it.

As I see this, the figures you cite above are for the BTU output of the propane alone when it combusts. But, there is also an appliance in the equation -- the heater -- which is designed to maximize the return from the heat output of the fuel source. The heater -- made from heavy gauge metal, containing baffles and chambers -- in a sense "stores" and accumulates the heat from the fuel source. This allows a smaller flame, and therefore a lesser amount of fuel, to achieve a higher radiated BTU output from the appliance.

Consider the extreme case where the flame has been extinguished and yet the appliance continues to radiate heat long afterwards. When it's doing that, there is zero propane consumption, and therefore zero BTUs from the flame, yet the appliance is still a viable heat source. In other words, with the flame extinguished, the radiated heat output from the appliance is greater than the amount being generated by instantaneous propane combustion. The same would be true, but to a lesser extent, when the flame is burning.

Not sure if that explanation makes sense, or if it would withstand scrutiny from our scientific community. But another way to think about it might be to question the need for or benefit of the appliance at all. Why bother putting all that effort into designing and constructing the complicated appliance, if the only factor that matters is BTU output of propane when it burns? If according to some immutable law of physics BTU output is BTU output and it makes no matter how BTUs are captured, stored, manipulated, reflected, amplified, why would we bother innovating new heating devices? Why not just have a simple burner with a flame and a chimney to vent it?

Anyway, I'll be interested to hear from folks with a more scientific grounding in this subject matter.
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  #52  
Old 03-09-2010
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Another Option?

Last night I remembered another heating option that is available to boaters. This was mentioned by a Sailnet member in one of those other boat-heater threads that I can't find (d!*# search function!)

I don't have any experience with or direct knowledge of these devices (frankly, it seems almost like black magic to me ), but the member reported good results and they are also used widely in RVs. Maybe worth a look?

THE PLATINUM CAT -- Propane/Natural Gas Catalytic Heaters
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Old 03-09-2010
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Yes, but these will add a lot of moisture to the boat's interior.

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Originally Posted by JohnRPollard View Post
Last night I remembered another heating option that is available to boaters. This was mentioned by a Sailnet member in one of those other boat-heater threads that I can't find (d!*# search function!)

I don't have any experience with or direct knowledge of these devices (frankly, it seems almost like black magic to me ), but the member reported good results and they are also used widely in RVs. Maybe worth a look?

THE PLATINUM CAT -- Propane/Natural Gas Catalytic Heaters
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  #54  
Old 03-09-2010
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heater moisture vented outside?

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Yes, but these will add a lot of moisture to the boat's interior.
website for the heater says the moisture is vented out ... sounds good ... anybody know the costs??
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Exclamation

Somehow, I seriously doubt that they can vent all the combustion by products through a 1.5" hose, especially given the area of the catalyst bed.

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Originally Posted by RonRelyea View Post
website for the heater says the moisture is vented out ... sounds good ... anybody know the costs??
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  #56  
Old 03-10-2010
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As I mentioned elsewhere in this thread, there are quite a few other good threads here on Sailnet concerning cabin heat options. Whereas I spent a fair bit of time describing the advantages of propane as a heat source, some of those other threads contain persuasive and good information about other fuel and heater options.

Unfortunately, the Sailnet search function has been tempermental for quite some time now, and I haven't been able to find them.

That is why I made this thread a prominent "Sticky" -- i.e. so it can easily be retrieved/reviewed in the future. I would like to encourage folks who come across those other threads to post links to them here in this thread.

I posted a couple links earlier, but I'll repeat them here:

Cabin Heater on a Crealock 37

Cabin Heat

Also, here is a thread about a related aspect -- it addresses the concern some sailors might have about taking on water through the chimney of a bulkhead-mounted heater in rough conditions off-shore.

MC1's Solution For Temporarily Capping Off a Chimney When Going Off-Shore
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Am I under the mistaken assumption that diesel is a "dry" heat? As apposed to propane.
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Old 03-10-2010
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Am I under the mistaken assumption that diesel is a "dry" heat? As apposed to propane.
Now you're just messing with me.
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Old 03-11-2010
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Quote:
Originally Posted by JohnRPollard View Post
As I see this, the figures you cite above are for the BTU output of the propane alone when it combusts. But, there is also an appliance in the equation -- the heater -- which is designed to maximize the return from the heat output of the fuel source. The heater -- made from heavy gauge metal, containing baffles and chambers -- in a sense "stores" and accumulates the heat from the fuel source. This allows a smaller flame, and therefore a lesser amount of fuel, to achieve a higher radiated BTU output from the appliance.

Consider the extreme case where the flame has been extinguished and yet the appliance continues to radiate heat long afterwards. When it's doing that, there is zero propane consumption, and therefore zero BTUs from the flame, yet the appliance is still a viable heat source. In other words, with the flame extinguished, the radiated heat output from the appliance is greater than the amount being generated by instantaneous propane combustion. The same would be true, but to a lesser extent, when the flame is burning.

this is not true sorry to burst the bubble, the stove cannot create heat. the propane will waste btu's heating the metal. the metal will store some btu but you need btu to heat it, once warm there is no waste but no heat for free

i still like the idea of wood
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