Wallas Heater Total Confusion

K

Karl

New member
I was just at:
http://www.scanmarineusa.com/wallas_furnaces.html
and I'm left totally confused by Scan Marine's website.

There are totally seperate furnace models for diesel and kerosene fuels...both apparently for marine use, despite only the diesel ones with "Nautic" in the model name.

I was under the impression that the Wallas cooktops/heaters had a pretty wide range of acceptable fuels, so now that I'm looking at the the Wallas' cabin heaters ("furnaces", w/o cooktop), I'm a little surprised that there are two different product lines based upon two similar fuels.

I'm also surprised to see that the Wallas' furnaces seem to have only an exhaust line, and apparently use the cabin space for combustion air-supply.

>>>Unlike other systems, Wallas diesel and kerosene stoves draw combustion air from inside the cabin and exhaust outside the cabin. This feature forces fresh air to be drawn into the cabin area, drying the vessel interior and reducing the effects of mildew.>>>

Their furnaces (as well as their stoves) likewise only seem to have an exhaust port, with combustion air being drawn from within the cabin, rather than from outside.

I hope I'm just being dumb, but I am confused by all these specs.

I have also looked at the specs for the Wabasto and Espar diesel furnaces (both primarily designed for tractor-truck cab heating, but with marine kits) and they both apparently use a dedicated combustion air-intake via a thru-hull.

I would think that combustion air drawn from outside the boat would be vastly superior to relying on cabin "make-up air" to provide that...despite their claim to the contrary...

Am I just being anal and overly-anylytical again?

Hoping for a response from someone with technical industry knowledge, but would also appreciate comments from people with just an opinion...
 
I'm only going to speak on the make-up air issue. Heating a house and heating a boat are two different animals from ventilation standpoint. In a house, it's about limiting the air exchanges per hour and increasing the efficiency of the system as a whole. It's also about retaining the moisture in the house so that you don't need a humidification system.
Many people say that a forced-air furnace system is a "dry heat", and so, that makes a hot water system a "wet heat"? You must remember that you cannot make moisture or destroy moisture, you can only move it from one place to another
What make a forced air system dryer, is that most duct systems are not well designed, installed, and balanced, so that some rooms are at a positive pressure and some at a negative pressure. This causes cold outside air, at a much lower dew point, to be drawn into the negative rooms, and the heat and moisture (higher dew point air) to be expelled through gaps and cracks in the higher pressure rooms in your house.
A 2 story house is even worse, with the chimney effect pulling heated air out the upper level.
The other way to move moisture out of your house is to pull air needed from combustion from the room, and send it up the chimney.
This is why you would want a fresh-air intake duct on your furnace or woodstove.
What does this have to do with boats?
I think the heating needs are much different. With our boats, most of us don't care about the seasonal efficiency of the Wallas. It won't be running all winter.
But what we usually do need is "dry heat". Recirculating in-cabin air is not going to get the windows clear. What we need to do is to bring in the cold, dry air from outside, heat it, and now we have raised the dew point to where the windows won't fog.
C-Dorys are not airtight, so long story short, unless you are heating the boat all season long, you are better off using cabin air for combustion.
 
I was more concerned with oxygen-depletion, and air-quality issues in the cabin in general.

The Wallas recirculates cabin air, it seems, and relyies on cabin air-leaks to supply combustion air...how could that possibly be superior to a ducted source of outside combustion air like the other two manufacturers supply?

Since the exhaust is vented with all three manufacturers' products, condensation and moisture problems would seem to be moot with all of them.
 
The wallas heater draws air from the outside...there are 2 tubes going through the apparent exhaust vent. The outside tube draws in the combustion air while the inner tube exhausts the heater. The tubes are within each other. Ron
 
As Minnow says, the C Dory is not air tight. No problem with the Wallas stove which uses cabin air. If any question in your mind, then open a window a crack. The exhaust is fan forced, thus creating a negative presssure in the cabin, and drawing in outside air. We did have humidity problems when cooking--and thus opened windows to get more dry air inside.

I have had circulating hot water heaters which had a concentric exhaust and air intake. This brought air into the engine room. I did have some concern about CO, because of the proximity to the exhaust, but never did have an alarm. On the other hand--this also had a high powered exhaust fan--and was over 40,000 BTU, so it was putting out a large volume of exhaust.
 
Thanks...that may explain what I'm looking at now, despite what Scan Marine says:

http://www.scanmarineusa.com/Wallas_furnace_1800.pdf

It actually looks like a dual-concentric intake/exhaust...I think it was the Espar that said that intake/exhaust had to be seperated by at least 6 inches...rather than concentric...

It's odd to me that none of these heaters are made in the USA...apparently even truckers need to use foreign-made cab heaters, which with their union affilialtions must really bug the shit out of them...

Thanks for replies!
 
wallas stove top heater use cabin heat. espar, wallas , and other heat only units are designed to use out side heat, but that all depends on the install. case in point my espar heater instructions calls for out side air because it was designed for a truck, which is more air tight. I installed ours to use inside air. Could not think of a reason not to and eliminating one more thru hull seemed a good idea.

boats in this area are moist inside so drawing, heating , and expelling some of that air is a good thing. remember that the air is drawn into two different areas for the cabin heaters. one air flow is used in combustion with fuel and then shot out the exhaust port out side. another air source ( for inside or out depending on your install) is ran thru and heat exchanger and then into the cabin.

So cold air off the floor is being reheated and shoot back into the cabin. more air is being drawn from off the floor and is being use in the combustion chamber and then exhausted out the side of the boat via a thru hull. so far it works great.
 
It vents the exhaust gas outside and draws air from in the cabin. I understand that it could be better if it had a duplexing vent, but they don't - at least mine doesn't. It doesn't seem to matter much as I have a CO alarm and the only time it has ever gone off is with the truck running and the cabin door opened. As others have noted, the way it is designed somewhat dries out the cabin which is a good thing. And truth of the matter, it doesn't even really dry it out enough when it is really wet. Probably nothing would....I just wish the dang things were a little warmer as here in Alaska, things get rather chilly in April and October. Every other month outside of early spring and late fall it is great. Obviously the choice is yours, but they work pretty well for what they are.
 
Maybe for a dedicated Wallas heater, I don't know, but definitely not so for the DU95 cooktop/heater. There is no air intake through-hull, only an exhaust thru-hull. The air intake is inside the cabin, that is why there is a grill in the vertical face under the cooktop.

digger":24r0mvx1 said:
The wallas heater draws air from the outside...there are 2 tubes going through the apparent exhaust vent. The outside tube draws in the combustion air while the inner tube exhausts the heater. The tubes are within each other. Ron
Click to expand...
 
Our brand-spanking new Webasto is DESIGNED to use outside air for combustion, and that is what the installation instructions specify, but Triton Marine INSTALLED it to use inside cabin air for the combustion air. And they have lots of experience installing Webastos, they used to install them in SeaSports. They installed it in the hanging locker aft on the port side and put a grill in the hanging locker door. It would have been very easy to run a fitting from the heater air intake through the cabin bulkhead. Scott said he would do that if I wanted them to. So, can anybody say definitely whether I should have them do that or not?

BTW, I will post pictures of the Webasto install some time over the weekend. I have run it overnight in the driveway, and it got the cabin up to 65 degrees F in this arctic chill we are experiencing, so it should do just fine in more moderate temperatures. It also does indeed sound like a Boeing 747 getting ready for take-off when you are standing outside next to the exhaust port! Sorry guys, we need need to be toasty!
 
I'm extrapolating from my non-marine learnings, but it seems to me that outside combustion air has two advantages:

1. Zero possibility of cabin oxygen-depletion (probably unlikely on most boats anyhow, but, why even risk it? But, with a pilothouse and bulkhead door, it is a conceivable risk).

2. The remote possibility of igniting/exploding any gas or vapor that could ever be present in the cabin area...say from a leaking propane/gasoline/butane/alcohol source (which shouldn't have been in the cabin to begin with!).

Obviously, getting the combustion products vented out is the more important first-step (CO poisioning), but, if the heater or stove is designed for outside combustion air also, why circumvent that feature?
 
Oxygen depletion using the cabin air for burning is NOT an issue since the exhaust goes outside the cabin. As air from the cabin is drawn in to provide oxygen for burning the fuel, a slight vacuum is created in the cabin and fresh air comes in from outside. E.g. the oxygen used for burning the fuel is replenished by suck air in through the multiple air leaks into the cabin. The oxygen levels in the cabin NEVER vary from that of normal outside air. Air comes into the cabine from multiple sources including: the less than perfect seals around all wiring in and out of the cabin, the less than perfect seals around the doors and windows, the drain for the sink, on some boats a hole under the gunwale and through the bulk head, the vent for the bathroom on 25's and Tomcats etc., etc., etc. Oxygen depletion in the cabin IS not a concern.
 
rogerbum":2w4dugoh said:
Oxygen depletion using the cabin air for burning is NOT an issue since the exhaust goes outside the cabin.
Click to expand...

Totally seperate issues, I believe.

Exhaust being vented outside eliminates carbon monoxide issues inside, but does not address inside O2-depletion issues at all.

O2-depletion will probably never be an issue inside a typical pilothouse boat due to available air leakage paths to replentish combustion air, as you mention.

However, there may insufficient incoming air for combustion (and, more importantly, respiration).

If the heating product has made accomodation for outside combustion air, and the installer decides to ignore that, I think that is pretty negligent. There may be no consequences if you have a cabin with lots of air leaks, or, there may just be minor symptoms like fatigue or headache.
 
Karl, I don't think you're thinking about this the right way. From where does the exhaust gas come? It's a combination of the inside air + the fuel. So, when the stove draw air in from the cabin, all the air that was there (oxygen, nitrogen etc) passes into the combustion chamber and out the exhaust. It's not as if the oxygen is being sucked out of the air in the cabin. None of air that is pulled in for combustion is returned to the cabin. On a Wallas, the heat is generated by circulating cabin air over the ceramic cook top (which is sealed from the combustion chamber. So in the end, the air that is used for combustion and exhausted to the outside, is really no different than having an exhaust fan in a bathroom. When you turn on the fan, oxygen in the house (or head in a boat) is not depleted. Fresh air is drawn in from outside. If the boat was super tightly sealed, the only consequence would be a slight negative pressure inside the boat since the fan can't generate a vacuum great enough to cause any problem at all. Even a huge fan running at high speed wouldn't deplete the cabin air to any level that was worrisome to human health,
 
Well, I see his point, up to a point.

But, it would also seem that the percent O2 in the room could decrease despite venting combustion products outdoors, but that probably implies that a partial vacuum is being created in the room.

If there is zero oxygen depletion, why do the cabin heater makers provide outdoor combustion air in the first place?

Is it done solely to seal the combustion chamber from the room and thus prevent ignition of any flamables within the room?

Or, maybe due to the possibility of backdrafting whereby the combustion products get sucked back out the air intake under certain conditions (like an exhaust fan running, or vacuum created via Bernoulli principal while boat is moving forward at speed)?

Anyhow, my main point is that if a seperate intake port was thoughtfully provided by the heater manufacture, it should be plumbed to take in outside air.
 
Karl":otu4duhe said:
<stuff clipped>
If there is zero oxygen depletion, why do the cabin heater makers provide outdoor combustion air in the first place?

Is it done solely to seal the combustion chamber from the room and thus prevent ignition of any flamables within the room?
<more stuff clipped>
Click to expand...

The primary reason for providing outdoor air for combustion is that then one isn't sucking cold air inside through the slight partial vacuum that's created. E.g. all the air inside is simply recirculated over the heater. In a tight house or other compartment where there's very little air exchange (intentionally) this might make sense. However, in a small compartment (like a boat or an RV) where there's a fair amount of humans breathing moisture into the air, it's a good idea to have a fair amount of exchange with the outside air.
 
Karl,

Just because something has a provision for something does not mean it is best to use it no matter what. I believe we have to consider the usage too. I hear you on your theory of O2 depletion, but it really isn't possible as whatever air is taken out, is replaced with air that has O2. The odds of any boat being so well sealed that the stove of furnace consumes all O2 is unrealistic. It become even more unlikely, more like impossible, when one considers that the stove is vented outside since now it is not sealed........ Even that little dinky hole can move an enourmous amount of cubic feet of air in a hour.

However, no matter what descriptor we use unlikely, impossible, ect....if it makes you more comfortable to use a duplexing vent, and the stove is set up for it, by all means use it. In all likelyhood none of this matters anyway. The amount of drying the stove creates is just as minimal as the amount of O2 it consumes. Either way, I really doubt there is difference, except maybe in your piece of mind which is all that matters.
 
To take oxygen depleation to an extreme--as we breath air (about 20% oxygen) we exhale products of oxygen consumption--mostly CO2 and water. There is enough "venting" in cars, boats, houses etc to allow the oxygen level to reman constant and vent exhaled CO2. It is entirely possible that the people in the boat are using more oxygen than the stove is. Now sealed space, such as a Submarine--this is entirely different. Oxygen has to be replaced and CO2 scrubbed.
 
I tried to clarify the carbon monoxide issue a year or so ago and I knew the mythology was so ingrained it was pointless. But the issue of carbon monoxide poisoning is so important, I will make one more stab at it. Here is the message: "Venting" is NOT to remove carbon monoxide from the immediate atmosphere (home, cabin, etc.). The ENTIRE purpose of "venting" with carbon based combustion, for safety, is to maintain a level of oxygen to prevent carbon monoxide from forming! Carbon monoxide will ONLY form when (1) a carbon fuel is oxidized (at a high enough temperature) and (2) when the level of oxygen is low enough such that some of the carbon oxidizes to carbon monoxide (one oxygen atom) instead of carbon dioxide (two oxygen atoms). In practice, it is essentially a moot point since any air you vent will be replaced by "good air" unless you are reducing the air pressure which won't happen in your boat or home. Oxygen depletion leading to carbon monoxide formation is why oxygen sensors are used by some as a safety measure. However, my experience as a lab chemist with such sensors is not entirely reassuring, I certainly won't bet my life on them.

So, please refer to "venting" when the purpose is to remove something such as water vapor, odors, or carbon dioxide which can displace oxygen. You can also vent a "stuffy" room such as a room with a lot of people in it giving off carbon dioxide, moisture and odors and that is a good thing but you won't be venting carbon monoxide in that case. If you are venting carbon monoxide you have gone past a place you should be. With an air source, such as an open window, you are "replenishing" oxygen to prevent the formation of carbon monoxide.

Steve in Olympia
 
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