The Hotmail Heater, Prepper Bug Out Off the Grid Heat and Hot Water




Introduction: The Hotmail Heater, Prepper Bug Out Off the Grid Heat and Hot Water

About: airplane nut since forever, rower since high school, airplane mechanic since '94, Pastor, father of four

I built a Teardrop trailer in 2011, finding a cheap heat source for of-the-grid camping that is safe is one of those ideas always being kicked around on the best (IMO) website for Tear Drop Trailers (TD)  There is a company that makes a tent heater powered by propane, but a few years ago they stopped making the model that would work the best for tents and TD, instead they now sell a very expensive large capacity one that mostly seems aimed at the military and others with big tents to heat.
    I am an airplane mechanic for a living and small twin engine aircraft are mostly heated using a combustion heater like this one , I figured there has to be a cheap way to make heat for tents and TD's that uses common hardware store items. Then as I was wandering around in the the blue Borg, (though orange is my favorite, we don't have green around where I live)  I think I figured it out.
   My idea is simple, a kerosene lantern, which is used by most of the people in the world, and two mailboxes. the rest is just using physics to get heat to go where we want it and soot to stay out of our lungs.
   While searching for the BTU (heat output) rating of a kerosene lantern I found a site that reports that most people in the world without electricity use kerosene lanterns, and stoves, most of these are not vented to the outdoors, and this causes quite a few lung problems. SO WORK CAREFULLY, SEAL ALL YOUR SEAMS, AND IF IT IS WINDY OUT USE THE 12v FAN FOR POSITIVE PRESSURE SAFTEY.
   One other note, while a candle is a better-than-nothing source of heat, it actually coats the inside of your tent, TD, and lungs with wax as it burns, and anything that burns is using up the oxygen in your tent or TD, every year people don't wake up in their tents due to using candles, lanterns, and stoves to heat. YOU ARE JUST VISITING THIS PLANET, DON'T CUT IT SHORT, PLAN AHEAD AND BE SAFE.
  The figures I found show that a candle puts out 90-100 BTU's (per hour), a human being puts around 250 out (equal to a 100 watt incandescent bulb) and a kerosene lantern puts out 800-3000 BTU's (depending on model and wick width, if a mantel is used, etc.) I am using the cheap oil/kerosene lantern from wallyworld for this which I believe will give me 1000 BTU's input. 
For comparison, my house has a rather small oil boiler rated at 85,000 BTU's, and a pellet boiler rated at 175,000 BTU's, Most homes have 100,000 to 300,000 BTU rated systems. However my TD is about 40 square feet compared to 1,200 sq ft in my house.
   For disaster or emergency use a kerosene lantern is your best bet in most cases for light and now for heat, most wick type lanterns will run on olive, jojoba and just about any type of oil, kerosene or lamp oil may not be around when you need more.

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Step 1: List of Parts and Tools

right now you will need to decide what you want to make....
Do you want a free standing (tent) heater, or a built-in one (TD, TTT (tiny travel trailer), or small caravan)?

Parts to make a tent heater:
-standard size mail box (make sure your lantern fits inside)
-sheet of 1/4" plywood
-adhesive for sticking plywood together
-(2) sink tailpieces (brass not plastic) 
-dryer flex hose, RV sewer hose, or SCAT hose (long enough to reach your tent, 
-12 volt computer fan and power supply (8 D cell batteries in a PVC pipe would work)
-dryer hose duct flange, RV hose flange, which ever you chose. 
-hinges (2)
-1" X ?" board to fit into the base of the mailbox.
-a tube or two of high temp RTV (auto parts store will have this)

Parts for making a built-in heater (teardrop, tiny trailer or caravan) :
-standard size mailbox (make sure the lantern fits inside with the door shut)
-a bigger mailbox (the little one has to fit inside with the door shut)
-a tube or two of high temp RTV, (any car parts place should have this)
- (2) 1" rigid wiring conduit end piece, (the part that seals the end of the conduit to the wiring )
-or (2) brass sink drain tail pieces (the kind with a rubber grommet, a nut and a flared end that the nut tightens against)
- slide bolt latch
-screws and nuts to mount latch
-(2) dryer or heating duct flanges 
-12v computer fan (same diameter as the duct you use)
-12v power source (a stack of 8 D cell batteries in a PVC pipe will do the trick)
-(4) bolts and nuts (long enough to tie the inner mail box to the outer one in four places)

-drill bits
-hole saws (to match the diameter of the conduit/tailpieces, and dryer/heat ducts.
-screwdrivers, wrenches, pliers

Step 2: Keeping an Eye on Things

-light the kerosene lantern, after the flame settles down, mark the center of the flame on the side of the glass.
-measure the height from the base of the lantern to the mark on the glass
-stand the small mailbox on end, with the door downward and open, measure from the lip of the door up.
-measure and mark the lantern flame mark height onto the side of the smaller mailbox.
(tent heater step)- cut the 1" X ?" board to fit the base of the mail box, 
(tent heater step)- mount the mailbox on the board 
-drill a hole  for the conduit/tailpiece to go into at the mark. this is the way you will be able to check on the flame so aim is important. (for the tent heater you want this hole to go through the 1" X ?" board and the bottom of the mailbox, for the TD heater make this hole in the side of the mailbox.)
-measure the height to top of the glass on the lantern
-mark the side of the inner mailbox just a bit shorter than this measurement (we want to trap heat in the top of the mail box)
-drill another hole at the upper mark (again, through the bottom and board for the tent heater, through the side for the TD heater.
-seal all the seams and holes in the top of the mailbox with high temp RTV and scraps of metal as needed (REMEMBER YOUR LUNGS DEPEND ON THIS PART)


Step 3: A Good Seal Is Important

Tent heater instructions:
-measure the width and length of the mailbox base
-add two inchs (this is a guess) to the width and 2 inches to the length (once again this is a guess) 
-mark these dimensions on the sheet of plywood to make a rectangle and cut it out, this is the base panel.
-lay the mailbox on the base panel so that there is an inch along both sides and two inches on the end that doesn't open.
-trace where the mailbox will sit
-measure the height of the mailbox 
-make two sides for the plywood box that are the same length as the first panel you cut and are both as wide as the dimension from the last step
-make two ends for the box, they need to be the width of the base panel, and the same height as the two long side panels.
-trace the base panel and cut it out, this is the front panel

Step 4: Stick This to That

Tent heater:
-drill a hole to mount your dryer duct, RV sewer, or SCAT tube flanges in the two long sidewalls
-you want one hole near the top and one hole near the bottom.
-mount the 12 fan to the hole that will is closest to the mailbox door. 
-test to see if you can open the mailbox door if it was glued to the back panel, if not  mark and cut slots in the back panel with a hack saw or other thin blade to allow it to open fully.
-glue the base of the mailbox to the base panel where you traced it before
-glue the sides and top panel in place as shown. 
(I think you can figure out how to do this without instructions. to be durable I would use marine epoxy and fiberglass tape, but this is also much more expensive) simple 1"x1" strapping glued to all the edges with construction adhesive or gorilla glue would also work but be slightly heavier.
-run a bead of RTV along the top of the mailbox and glue the front panel in place. you want this to be a close tight fit against the top of the mailbox curve so the airflow has to go over the sealed end of the mailbox as that is the warm end. (see second picture)

Step 5: Put a Lid on It

Tent heater instructions:
-close the mailbox door
-lay the final side piece on the one open end of the wooden box, sand, or plane if needed to get a nice flush fit at all four sides. (a seal of RTV can fill gaps if needed)
-install your hinges so they are on the front panel (you want the box door opening up ward and the mailbox opening downward)
-install the wooden door latch 
-using a stubby screw driver and screw, put a screw in the center of each of the holes in the base of the mailbox.
-remove the screws and drill the correct sized hole for the two sink tailpieces.
-install the tailpieces.

-light the lantern again (you didn't leave it going this whole time did you?!)
-hold the tent heater up in the air with the doors pointing downward
-open both doors
-put the lantern into the mailbox 
-close the mailbox lid
-close and latch the wooden box lid
-put the tent heater down on the box lid, it is the base.
-turn on the 12 volt fan (I expect you to have a basic idea of wiring and switches)
-make sure the fan is blowing into the box
-hook up your hoses to the box and run them to your tent. (I expect you can figure out how to make tent connections.)



The rest of the pictures here are an idea I had to use the "waste" heat from the tent heater to heat a pot of water, I don't know if it would be worth much more than to melt a pot of snow overnight, or if it would even do that. 

Step 6: Built-in Heater Continued Here

set up your door handle so you have a positive secure latch that can't be bumped open by bumping the mailbox, it has to be strong enough to hold the weight of the kerosene lantern and keep it shut no matter what.
-remove the hook from the mailbox door
-flatten the top hook out so it is straight with the top of the mailbox
-install a slide bolt latch on the lid of the mailbox so that the bolt hits the middle of the top hook
-drill a hole in the now flattened top hook so that it keeps the door firmly shut.

Step 7: Making the Heat Collector

-make a board to mount the big mailbox onto and mount it with screws
-mark and drill through the mounting board for the dryer/heat ducts, you want one at the top and one at the bottom (with the mailbox standing on it's mouth)
-slide the small mailbox into the big one just far enough to allow the door to shut 
-orient the small mailbox the way you want it, ensure there is a fairly even airspace around all sides of the small mailbox.
-drill through both mailboxes and install the four bolts so that the inner mail box is secured in place, and not touching the inside of the big mailbox
-match and drill the holes for the rigid conduit/drain tailpieces in the big mailbox (vent/exhaust holes)
-apply sealant around the vent/exhaust holes
-put the conduit/tailpieces in using the securing nuts (MUST SEAL)
-seal around the conduit/tailpiece holes in the side of the large mailbox 

mount the mailbox, with the mouth facing down, against an outside wall
-drill holes through the mounting board and the bottom of the mailbox for the inlet/sight tube, and exhaust tubes
-install drain tailpieces to holes in the mailbox
-rout or oversize the holes in the mounting board to fit the tailpiece nut
-drill holes in the side of the trailer to match the holes in the mounting board
-seal the tailpieces to the mailbox with high temp RTV
-mount the mailbox mounting board to the sidewall of the trailer
-mount the mailbox to the mounting board
 -seal the sidewall of the trailer to the tailpieces to avoid leaks

Step 8: Positive Pressure

-mount the 12 volt fan blowing into the lower heat collector duct, this provides positive pressure in the heat collector, any leaks into the combustion chamber (smaller mailbox) will just blow out the exhaust pipe

This design should work without the fan in a TD, but in windy conditions exhaust may be blown into the heat collector. 

Step 9: Adding Hot Water, and Some Theory

in this picture,
-the blue tank is the water tank
-the red pipe going through it is the upper combustion air pipe, which as heat rises should be the exhaust pipe.
-the red mailbox is the combustion chamber, this is where the lantern goes. The upper end of this mailbox is a heat trap, this is where the heat transfers to the trailer or tent air. don't place this pipe to high in the combustion chamber as you want to hold as much heat as possible.
-the grey pipe is the air inlet pipe and also the way you keep an eye on the flame, 
-the grey mailbox is the heat collector, it doesn't even need to be a mailbox, it can be any metal or wooden box as it will not see that high of an air temp thanks to the constant air circulation through it and into your tent or trailer. I would make it out of wood for a tent heater as then it won't leak that much heat, compared to metal.
-the water tank is filled through a port on the outside of the trailer and there is a valve in the galley for hot water.

Step 10: You're All Wet

Parts to make the hot water tank:
-a large pot, 5 gallon bucket, or a water tank (do you want it open topped to keep it clean, or closed) dark in color to keep things from growing.
-copper pipe or tubing (a coil will get even better heat out put, but must always slope upward from the combustion chamber)
-JB weld water weld (special epoxy mix made to seal and even cure underwater, and safe for use in drinking/cooking repairs per the web site)
-drill bit the same size as the pipe.

-mark the bucket where you want the pipe to go in and out. ( a horizontal run through the bottom of the tank would do the most good for heat transfer)
-drill the holes
-push the pipe through and seal the holes with the JBweld 
-fill and check for leaks.

Step 11: Fire Me Up

and now for a little heat:
-light the lantern, let the flame stabilize, adjust it until it is burning correctly.
-open the heat collector door and the combustion chamber door
-insert the lantern into the combustion chamber
-close and securely latch the door with the wing nut
-close the door to the heat collector
-turn on the 12 volt fan
-enjoy a warm tent or trailer. 

this view shows what you will see from the inside of the trailer, the lower duct has your inlet fan, the upper duct should be blowing warm air at you.

I will be building one of these soon, right now I am out of work due to an injury so money is a little tight. If you make this let me know how it goes or if you improve it also, I think a lot of people will be interested.


Step 12: The Benefits of a Plywood Tent

this doesn't have much to do with building a heater, however it is about heat...
   A teardrop (TD) is the best way to travel for cheap and light. The original design seems to have been worked out by men traveling around looking for work during the great depression. A TD provides shelter as you have an enclosed insulated bed, and a food prep area. Unlike a tent there is no set up and take down, you hop in and go to sleep, you get up , shut the door, walk around to the back, open the galley and there is your kitchen.
  Many people use them to travel, as they are light and small so they barely change your gas mileage, and being always set up, if you get tired you just pull off somewhere safe and  go to sleep. The original TD's were 4 feet wide, the size of most of those cheap trailers  you can get today to use as your starting point. Most of the trailers built today are 5' wide, the width of a queen size bed, which is an easy size to build on a 4' wide trailer, and also can be towed by almost any car without extra towing mirrors.
  If you require a machine to sleep or other medical equipment that kept you from tent camping, a TD with extra batteries could be the answer. Most basic TD's have a car battery built in, to allow a few lights and fans kept on a battery tender when at home and connected to the Tow Vehicles alternator while towing, and even a solar panel to keep it fully charged. LED lights and small fans don't put much drain on a battery at all, and some of us (including me) have those solar powered lights on and in the TD, which would put no drain on the main battery. some TD's also have AM/FM/XM/TV it all depends on what you want, and how much you want to leave behind.
    Many people use TD's today for off-roading, 4-wheeling, dry (no hook ups) camping, and as a base camp for mountain biking, hiking, boating, or hunting. Built correctly TD's have crawled all through the outback in OZ, and done just about every trail in north america a jeep can, as well as travel every road made in the whole world. Unlike an expedition trailer, roof tent or regular old tent on the ground, your set up and take down are almost nothing, you can avoid having to fold and later dry a wet tent, and you don't have to worry about touching the walls in the rain or heavy dew. A well insulated TD should take no more than body heat to keep warm in normal temps, and even in the dead of winter you can sleep in one in comfort with a small addition of heat. Good insulation will also make your TD easy to keep cool in the sun using a swamp cooler, or ice water bath air conditioner  .   Another bonus, many parks and campgrounds are not allowing soft side (tent) camping due to bears,  a TD counts as a camper so you can still visit places like the Grand Canyon campgrounds without a big trailer or camper.
-Some off road TD's and TTT (tiny travel trailers)
    As a TD can be as light and small as you want there are designs out there for motor cycle TD's for one or two, the "normal" size being for two people, a few designs fitting 4 , all the way up to my own TD (can it really be called one if it is this big ?) for 6 people called the "long long Teardrop" (second picture, it really isn't that big, 5' wide 4' high, 20' long, normal being 5' wide X 8-10' long), as long as you build light weight any car will be able to tow a two person TD, as most of them weigh less than 1,000 pounds, some as little as 200 lbs. If you build one, BUILD LIGHT! most people build their first TD like a tank and then make or plan a second one that weighs much less.
    There are a few TD manufacturers in the world  
and a few kit makers  
but today most TD's are home built has a great set of plans, has plenty of free plans with designers and builders who will help you if you ask nicely
My favorite website for information on TD's is , is another page of free designs
    So if you have basic carpentry or wood working skills and can read or look a lots of pictures, YOU can build one also. In fact you would be surprised at the number of women who have built their own trailers, and love to use them, even by themselves. Part of this is because TD's can be pushed around by hand easily, as they are so light and small, so even if you can't back a trailer up to save your life, all you have to do is unhitch and push it where you want it to go.
   If you are a doomsday, bug out, prepper, or just live in a place where you may need to evacuate for hurricanes, earth quakes, wild fires, and floods, a TD would be ideal. You can keep it stocked and ready to go in the garage or backyard, with a bin or two of canned/dried  food and water, a 12 volt car battery plugged into a battery tender, all your camping gear and towels, and a last minute "don't forget" check list. This should keep the last second scrambling to a minimum, and avoid anything important being forgotten. With your own trailer, even if the highways are jammed and it takes you way longer than you thought to get away, you already have your bed ready to sleep in, food ready to eat, and a home away from home until you can get back. Motels and hotels will all  be full, but campgrounds and state, and national parks are usually not as likely to be full in an emergency, and in a pinch a rest stop, or just a wide spot on a dirt road will do.
  Living in a TD may seem kind of cramped but there are people who have lived in them for years. The first thing to think of is that a TD is a plywood tent, add on a side tent if you want a place to stand up, or check out other peoples ideas. One guy I have seen pictures of has a removable hatch in the bottom of his bed, he can stand, inside his trailer, with his feet on the hatch on the ground. Many people put dropped sections in the floor for under-bed storage, and even the ability to make a table inside that you and some friends could eat, talk and play games at, in cold rainy weather.
  Most TDers carry an awning, a side tent or two, from elaborate tents that hook onto the side of the TD, to those 4' X4' shower tents that allow you a place to stand to change, a private spot for a porta-potty, and even a quick camping shower with a hanging bag shower or garden sprayer type. The nice thing about them is that you have plenty of space carry them in, roll up the sleeping bags and pillows, put them out of the way and your bed area becomes a huge storage spot for all the extra chairs, awnings, and other stuff you need for camping.
  Unlike big RV's who pull into a campground, set up the camper and then aren't seen again, TDers are more like Tent trailer campers, they set up and then sit and camp and even cook outside, which is the reason most people leave home, to get away from it all and enjoy the great outdoors.
   Another option for a home away from home on the cheap, a cargo trailer, a cargo trailer also will work, just add a few vents and a window or two, depending on how much stealth you want, add a bed and shelves, camping gear and go. Cargo trailers are heavier though and will usually require a larger heavier vehicle, and will cause a drop in gas mileage, but no where near what a "normal" travel trailer does.

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    13 Discussions


    3 years ago

    Thanks so much for this post. Any updates or real-world use?

    I plan to modify this using a small $15 kerosene stove burner (about 8" wide x 8" tall) inside a small stock pot, vented in & out through the window of my camping van. This will eliminate the need & complication of the forced air fan & should be quieter & keep all the radiant heat inside. I'll set it on an insulated "air-bake" cookie sheet and fit the base of the stove into a piece of 2" foam board to keep it secure inside the pot. Might even put a mica window in the side to check the flame while burning. Of course, I'll try to take time to post my results. Thanks again!



    Reply 3 years ago

    Bought the parts, and never got around to trying it out. I don't have a need to camp in cold weather the way i would have when I first had the idea.
    I would love to hear how it works out for you.


    4 years ago on Step 12

    interesting concept I do like the idea. I have a couple of duel mantel "Coleman" type lanterns vs the wick type you used. These babies put off tons of light and heat. We even cooked hot dogs over the hot air coming out the top. Granted not fast but it did work. There is also a "tent heater" someone makes.... or did, and right now I can not tell you who it is / was. but in certain places the drive in theaters would rent you one to keep your car warm in the winter months while you watched your movie. They had a large "wick" area of sorts it just glowed with not real open flame. and you def. had to have the window open. But I have one like it as well but your idea of a box to vent the fumes out is brilliant and would make things much safer, Thanks for the idea.

    Hope you recover soon, it is no fun being out of work with and injury.



    4 years ago on Introduction

    Conceptual or not, I think this is a brilliant idea and welcome Instructables that are filled with detailed instructions for an idea that should work, even if not tested. I am considering constructing something based on this idea. If I do it, I will definitely post share images and tips. Thank you!


    5 years ago on Introduction

    Warning for kerosine lamps in general:

    There are various grades of fuel oil sold as "kerosine"

    Some of these May have flash points as low as 100F. If this is used in a wick type lamp it is likely to result in a runaway condition weth huge flames that can be very unsafe.

    Proper lamp oil has a flash point around 140F, and is what the lamps are meant to burn.

    If the container label leaves any doubt, search online for th MSDS for the product, and that will list the flash point.


    Reply 5 years ago on Introduction

    In addition to your comment, gumby, I can attest to the poor quality of some of 'made in China' kero lamps. Having two of them explode in normal outdoor use has put me off them forever, now.


    5 years ago on Introduction

    I have my Mr. Heater that provides more heat than I could ever need from a propane source and a couple of D-Cell batteries for the internal fan. It has a tip-over and oxygen depletion sensor, so it's not going to cause any problems.


    6 years ago on Introduction

    This virtual heater should keep me virtually warm in my virtual world. I could probably use the real lantern and tape measure. Do you have a picture of the finished product?


    Reply 6 years ago on Introduction

    I came up with this as the answer to a problem I don't have. I camp at campgrounds with 110V, and have a tiny heater that is more than enough. I also don't camp in the winter.
    Back when i built my tear I was planning on staying in it year round a few nights a week. That has never happened.
    How to have heat off the grid comes up often on TnTTT, I made this i'ble as a possible answer.
    I have all the parts sitting in my workshop, but boat building and teardrop modifying has taken up all my free time :( , right now I'm in wood splitting and stacking for the winter mode. I may get to building this and trying it out this winter, but make no promises


    7 years ago on Introduction

    Look in the wood stove/fireplace supplies at the local hardware and try to find the fire barrier/fire stop spray in foam. There are several different ratings for this as well as the RTV silicone sealants. If you wet you fingers (spit on them!) you can use them to get a really nice smooth finish on the RTV.


    7 years ago on Introduction

    Looks good on LCD. Now go out and build one. If it works I am sure it will be a huge hit. Can't wait to see the prototype.


    7 years ago on Introduction

    the outer box wouldn't be that hot, at least I don't think it would be hot enough to melt plastic.
    I labeled some of the pictures, hope that helps.


    7 years ago on Introduction

    Some labeling of the parts/sections, flow directions in the diagrams would be nice.
    Also I wouldn't use the foil faced bubble wrap.
    (Plastic, melty, burn, poisonous gas, bad, very bad.)
    Hit up the plumping section of you hardware store for water heater exhaust insulation. It's made to handle the heat and is rather fire proof/resistant. Or even the regular household insulation section, looking specifically for fire rated.