(Continued from Part 2.)
Operating the M1941 In Extreme Weather
I’ve found that the M1941 at -30F will provide adequate heat for a cabin that is not insulated and that is no more than 300 square feet in size. It will keep you comfortable and the water in the plumbing flowing if those pipes are exposed to the cabin’s interior.
It will burn 6 to 8 loads of wood every 24 hours at that temperature depending on the type of wood used and how it was processed or split. One load of wood will fill a 6-gallon plastic bucket. Larger rounds of wood should be no longer than 12 inches in length. Kindling can be up to 15 inches in length. I use 5-gallon metal paint buckets to haul this wood in because these can also be used to melt snow on the stove, do the laundry, and heat large amounts of water for cleaning. Metal buckets are multipurpose and nearly indestructible.
A water bowl for the pets that is located on the floor will however freeze solid during the night when the stove is shut down. Before ‘hitting the sack’, heat soak the cabin with a load that is burned hot. When that load is nearly exhausted, fill up the firebox and then shut the stove down for the night. It would be best to set the alarm clock to allow 4 hours of sleep and awaken you so that you can refill the firebox and run the stove hot and until that load is consumed, and then go back to sleep for another 4 hours. When running the stove ‘hot’ during subzero temperatures, watch the stove carefully so that that top or the sides and rear of the stove glow no more than a faint dull red, as seen in a dark room. Choke down the air intake so that the stove will not be run too hot. The stove will last longer, be less likely to fail in a catastrophic way just when it is needed most, and the risk of fire to the structure is greatly reduced.
This is the best way to run any small wood stove. And be sure to clean out the chimney creosote just before the coldest months of the winter. You’ll want the stove pipe to be unrestricted so that the stove draws better and so it can run hotter on the coldest nights. It would also be less likely to cause a chimney fire when the stove is run at high temperatures.
Always run a hot and long fire first thing in the morning, to reduce creosote build-up. This is a good time to prepare breakfast and coffee. And never run more than half a load of bark in the M1941 or any potbelly stove as the bark expands in size and can push open the top lid. This would allow air in from the top and could overheat the stove. That is why there is a latch present next to the lid. Also, shut the flue. as a safety precaution. Use these when burning bark or when shutting down the stove for the night.
If using Larch exclusively, or a more dense wood that contains more BTUs than typical soft woods such as pine, the M1941 stove can hold this fire for 6 to 8 hours. How the firebox is loaded can also lengthen the time the stove will hold a fire. When the stove is unattended, shut the door that controls the airflow and set the latch so that the door will not open. Running any wood stove well requires practice and getting to know the stove and the fuel. It is an art that when mastered will keep occupants warmer. If the cabin is better insulated, the space it can heat during extreme cold weather might be up to 1,000 square feet. If there were no water in the plumbing during an extreme cold weather event, then the heating requirement would be less.
If the temperature were to drop below -30F in a cabin or tent that is not insulated, I would stay up late into the night and keep the stove running and sleep during the day when the temperature is much warmer. If there are many people present then someone should be assigned to ‘fire watch’ day and night or 24/7. If the stove can be run at a constant and higher temperature rather than be shut down at night, a small wood stove such as the M1941 can warm a larger space.
Selecting a M1941 or H-45 Military Heater/Stove
During the selection process that occurred well over a decade ago, I happen to come across the M1941 Military Tent Heater/Stove for only $100 that included shipping, stove pipe, and all accessories needed to burn solid fuels, but not liquid fuels. During the winter, if say in a 5-man Arctic tent or tent of similar size, when using the H45 heater that is often found with all the accessories needed to burn diesel oil, one to two gallons of diesel would be needed to heat the tent during a 24 hour period in intermediate weather temperatures. Because I will not be using diesel for heating, the liquid fuel option is of no interest to me. So I decided to give the M1941 a try and buy one. I did not however have the foresight to purchase several at that price.
Alas, the era of inexpensive and plentiful military surplus items is over. Now the price for a New Old Stock (NOS) M1941 with accessories is now closer to $400, and any cosmoline must be removed before it can be used. The H-45 is closer to $300, yet it does not typically come with a grate. Grates can be purchased for the M1941 on eBay for around $75. Rusty M1941 stoves can be purchased for $100 to $200. But it can be difficult to find an example that comes with all the necessary parts. These have typically been stored outside exposed to many years of weather and the thick rust is unsightly to say the least. And the lid, door, or grate is often missing.
How many years the stove might have been exposed to the elements? The degree of corrosion might be severe enough to have rusted away the sheet metal. Structural damage may have occurred and the sheet metal could be too thin as it may have been corroded severely and the service life of the stove greatly shortened. This is a valid concern, yet I have not found an old rusty M1941 that would not clean up well. Nor have I found one structurally damaged to the point where it would not be serviceable even after a decade of weathering. When sanding away the rust, inspect it all, closely. Look for deep pitting that if deep enough could be burned though prematurely after only a few years in service especially if these spots occur on the lower part that is closest to where the fire will burn. If spots of deep pitting are found, they can be repaired by quickly laying down a bead of weld around the pitted area and then filling in over it.
The metal on these stoves is tough. I am currently restoring an M1941 for a neighbor. This stove was extremely rusty, yet there was only some light pitting on the top surface and one small yet deeper spot of pitting on the side and to rear near the pipe collar. I’ll probably hit this spot with the stick welder today. There is a risk that the welder will burn a small hole in the stove wall. A small piece of plate would fix that, if it occurred. This stove was stored outside for at least a decade, yet it is still serviceable as it was found, even as rusty as it was. Amazing. The cosomline did the job it was designed to do and protected the stove. When the restoration is complete it will look better than the stoves advertised for sale for $400 or more, and it would be better than what is typically offered for sale, these days. All the cosmoline has been removed and a durable flat black finish will make it presentable.
This particular stove was manufactured in 1950. It was purchased on eBay. The price including shipping was right at $100, delivered. This is one of many backup stoves. Unfortunately, the seller did not include the lid. I would not buy again from any seller who will not accept returns. In this case the seller hid behind the conditions of the sale to obscure his fraudulent activity from eBay, and would not supply the missing lid. When buying these stoves from an eBay vendor, buyer beware. For these and other reasons, such as missing parts, I would avoid any vendor who will not accept returns. As a rule, I will no longer buy from any eBay vendor that does not accept returns, unless I can afford to lose part or all of the value of the item purchased. Bottom line: For those who can not modify, repair, or refinish wood stoves, it would be wise to pay the prevailing retail price of military surplus outlets for the best example that one can afford.
Fortunately, I was already using a cast iron frying pan as the lid on another stove. So I will use this on the new stove until I can weld a handle on a metal plate that fits the opening. It has only been used a few times, first for the purpose of burning off the cosmoline, then for curing the new paint and a few more times to test to see if the effort to make the stove ‘air tight’ enough to hold a fire for at least 8 hours. In all three tests, the stove performed as expected.
The cosmoline was burned off and it was sanded to bare metal, and then painted with a high-temperature Rustoleum brand paint. This brand of paint is tough, scratch-resistant, and bonds well to bare metal. This makes the stove presentable and protects it from rusting. Before painting, the two halves were welded together from the inside making it safer to operate and to make the stove ‘airtight’.
The stove halves of course do not have to be welded together and the stove can be used perfectly well as the U.S. Army prescribes. It is a much more compact stove if the two halves can be nested together, for transport. The height of the stove including the pipe collar is 20 inches when assembled. The diameter is 18-1/2 inches. When the top and bottom halves are nested together for transport, the height is only 12 inches.
The stove can use a variety of solid fuels which can include sawdust from a wood mill, or forest duff that includes pine cones and twigs that can be piled up with a rake and burned. I can get mountains of free sawdust from the local lumber mill without charge. It burns long and well if it is dry. Because of the heavy grate, it will burn coal as well. Coal would be ideal, if I could get any.
Modifications and Operation of the M1941/H-45 Stove
The flush-fit metal door on the lower half of the stove works well enough to control the burn rate almost to the point that a fire might be put out. Once the inside temperature of the cabin is comfortable simply close the door and the stove will maintain a steady and low-level heat production. The photo at right shows this metal door that serves two purposes. One to remove ash, and second, for controlling the amount of air and thus burn rate by opening or closing the door. As an important operational note that concerns safety, I’ve made it a habit that when this stove should be unattended, that this door is fully closed and the latch is in place to secure the door in the closed position.
The H-45 would be the better choice as its firebox is larger and subsequently produces about 25 percent more heat in the same footprint. It is a tad taller while the other dimensions are pretty much the same. I’ve increased the BTU output of the M1941 stove with the use of 6-inch pipe instead of the 4-inch pipe that came with the stove. Its BTU rating was established using 4-inch pipe that is too restrictive unless it is used as a tent stove that exits the exhaust with a straight and shorter length of 4 inch pipe that is no longer than 11 feet high.
In addition, a 4-inch stove pipe allows creosote to quickly accumulate and further reducing the inside diameter of an already a restrictive pipe. As a further impedance to the potential to produce heat, installing these stoves with one or more 90-degree elbows slows the velocity of the airflow of any pipe system and slows the stove’s ability to take in fresh air needed to create a hotter fire. The better a stoves ‘breathes’ — the better it can intake fresh air — the more heat that can be produced. Using stove pipe that is 6 inches in diameter (with a step-up adapter sleeve) is the ideal choice even though the stove was designed for 4inch stove pipe.
Increasing the diameter of the stove pipe and elevating the pipe to a point above the roof peak creates a better draw that will increase the velocity of exhaust gases and allow the stove to produce more heat as a cross wind from any direction will pass over the opening of the pipe and draw air through the pipe in the same manner that a carburetor on a motor creates a ‘venturi effect’ and draws gasoline from the bowl of the carburetor into the intake and mixes with the air in the correct proportions.
As the fire inside heats up, the velocity of the incoming air increases and the fire has created its own air current and flow that sustains a hot fire. If the exhaust pipe, that is the stove pipe, is too restrictive, the fire can’t achieve a sufficient airflow to produce as much heat as it could otherwise make. There is a strong correlation between the cubic feet of air that can be brought into the firebox and the BTUs of heat produced. A stove designed with 4-inch chimney pipe in mind is the minimum practical size for any wood stove that I would consider. If the stove was not manufactured to use at least 4-inch pipe, that I would look further.
The M1941/H45 as a Practical Cook Stove
The M1941 and H45 both have a 9-inch opening for loading wood. That is ideal for fitting the common 9 inch in diameter bottom of the typical cast iron skillet. And some pots can also fit snugly inside this opening reducing the chance of fumes of the stove from escaping. The M1941 functions quite well as an efficient wood cook stove. Even if the vessel such as a large coffee pot or pot with a bottom that is larger than 9 inches in diameter, these can be positioned over this opening and the food or liquids inside will more quickly be heated by the coals of the fire.
Small and lighter portable wood stoves were hauled across the county in covered wagons because they were important to the lives of the pioneers. Some of these stoves were of the potbelly design that lent itself to burning both coal and wood, or coal exclusively. The side-loading kind is intended for wood. Cast iron stoves were popular. Modern metallurgy and rolled steel were not yet available.
Cooking on a wood stove with less wood and heat was facilitated by a round plate that could be removed and a pot or pan lowered down into the hole or placed directly over the hole exposed it directly to the radiant heat produced by glowing coals. This method made these stoves more efficient because less time, fuel, and heat were needed, to cook.
Heat is transferred by via convection, conduction, or by radiation, or any combination thereof. A wood stove that more quickly and more efficiently transfers heat to a cook pot or pan transfers heat by both conduction and radiation. Setting a cook pot on top of a solid stovetop only heats the pot via conduction and as the only mechanism, the stove must be burning hotter and longer and use more wood to cook the meal or to heat water. It takes a great deal of heat to boil water, regardless. This means more wood than is otherwise necessary must be burned.
When cutting wood by hand, this translates into more work during an era when most labor-saving devices known today might not exist and manual labor will be required from sun up to sun down to perform essential tasks and make improvements to a farm, and to tend the livestock and a large garden. Because the M1941/H-45 model stoves are light enough to be picked up with one hand, during the warm months, it is easy to move this stove outside to provide a “summer kitchen” cooking or canning.
(To be continued tomorrow, in Part 4.)