An interesting idea. Maybe make a larger version using larger fatter candles, to last longer? Natural Cures Not Medicine: Heat Your Room For 15 Cents a Day
Here is about all you’d want to know about candles and the heat they produce: http://fire.nist.gov/bfrlpubs/fire05/PDF/f05141.pdf Note that it indicates that the typical candle produces about 77 plus or minus 9 watts of energy. It also notes they burn at an average rate of .105 grams/min with a combustion efficiency of 96-97%. According to Wikipedia the peak temperature in the candle flame is about 1400 deg C. Diatomic nitrogen (N2) in the atmosphere doesn’t start breaking down to react with oxygen to form NOx emissions until combustion temps exceed 1600 deg C so it would seem reasonable to conclude nitrous oxide is not likely to be a significant constituent of the exhaust gases from a burning candle. Consequently, the main constituents of the exhaust are predominately CO2, CO, soot (particulate matter mostly just carbon) and unburned hydrocarbons. The NIST publication states that the production rate for CO to be 0.006 to 0.014 g/g (grams of CO per gram of candle burned). Soot was 0.035 to 0.045 g/g and the total hydrocarbon yield was assumed to be less than 0.005 g/g. Using the median CO production of .01 g/g and the previously mentioned candle burn rate of .105 gram/min this would suggest that a typical candle will contribute about .00105 grams/min of carbon monoxide to the room. To determine if that is dangerous, we look to mass of air in the room and determine the concentration. The mass of air at room temperature is about 1.2 kg/m^3. Using a small room 10’ long x 12’ wide x 8’ high we get a volume of 960 cubic feet which is about 27.2 cubic meters. Multiplying times our density, we get 32.6 kg of air in the room. If the candle burns for 6 hours, it will put .00105 x 60 x 6 = 0.378 grams of CO into the room. For our room with 32.6 kg or air, we add .000378 kg of CO which would yield a concentration of 1.16 e-5 or 11.6 ppm (I think I got all the math right, but someone should double check). From Carbon monoxide poisoning - Wikipedia, the free encyclopedia we see that the average house is some where in the range of .0-5 ppm concentrations of CO. So lets take the middle and say the average is 3ppm. In our room with the candle heater producing 77 watts of heat (not a lot) in 6 hours with no outside air exchange the CO level would get up to about 14.6 ppm. If we needed more heat and were burning three candles the concentration would reach 37.8 ppm which would cause headache and dizziness within 6-8 hours of constant exposure. Of course note that in another 6 hours the concentration would be up to 72 ppm and in a total of 24 hours the concentration would be 142 ppm and after two days holed up in this room with three candles the CO would be about 278 ppm. A headache and loss of judgment would be likely. Of course these numbers are nominal and could easily be lower or higher depending upon the candle, how efficient it is burning, the burn rate, etc. And that would be for the amount of heat produced by three 75 watt light bulbs. A battery operated CO monitor would probably be a very good thing for anyone burning anything for heat and cooking. Be careful. AT ------- Concentration - Symptoms 35 ppm (0.0035%) - Headache and dizziness within 6-8 hours of constant exposure 100 ppm (0.01%) - Slight headache in 2-3 hours 200 ppm (0.02%) - Slight headache within2-3 hours; loss of judgment 400 ppm (0.04%) - Frontal headache within 1-2 hours 800 ppm (0.08%) - Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours 1,600 ppm (0.16%) - Headache, tachycardia, dizziness, and nausea within 20 min; death in less than 2 hours
Using beeswax candles would take care of the soot/smoke issue... tho their upfront cost would outweigh any financial savings you might get from not using a space heater. Making them is on my to-do list when we finally get our hives going, but that's a ways off. However, I'm itching to make one of these and stick it in the cold frame on my aquaponics system. Maybe make a little platform spanning across the sump and set it down there. The plants would welcome the CO2 and the area is a fraction the size of his bedroom. If it could raise the temp 5-10 degrees, it'd be worth what, a few bucks a week?
You forgot the H2O that is produced by the Hydrogen in the Wax being burned at the same time as the Carbon.... Hydrogen is a significant part of ANY HYDROCarbon compound... I mean really, a Significant PART...... ......
I made two this evening! Supposed to be the same low tonight and tomorrow night so I'll check the temp in the coldframe first thing in the morning. Going to put one under each growbed tomorrow night and see if it's noticeably warmer Monday morning.
Update on it... so far unimpressed. I set one up in the garage last night, put one votive candle under it at 2 am and went to bed. This morning around 8:30am it was warm to the touch, but certainly not hot. Put 2 more candles under it and went to watch last week's Walking Dead on Project Free TV. Just checked it @10:15 am using a digital meat thermometer. Lying on top of the pot the reading climbed up to 113F. (the 212 is the default "goal temperature") Sitting just an inch away on top of one of the pavers the pot rests on, it dropped to 73 within a minute or so... and it stayed there when dangled around in the air well away from the pots. Holding my hands a half a foot away I feel zero heat coming off of it. It is currently 57F outside, 68F in the garage. So I dunno... perhaps under the growbeds in that enclosed space the heat will radiate enough to help but for a room heater? Not buying it. Granted when I took the pots off to blow out the candles, I found that two of them had gone out, but even so I don't see this doing much beyond making a nice hand warmer. I'll still put them under the beds tonight and see. Low is supposed to be 37 tonight.
Love the math, Airtime. A human body produces about 150 watts of energy, about twice that of a candle. So, imagine a couple of naked people (your choice) sitting in your greenhouse trying to keep it warm... Ya, I've seen this little candle heater all over the interWebz, never saw where anyone said it heated enough to matter. I did find this neat-o wax stove tho... Correctly called a G-Micro PSL Wax Gasifier A fun read. if nothing else, it shows that it will boil two cups of water in about 20 min, rather then 8 min for alcohol or 6 min for an Esbit tab. None of which put out enough heat for any kind of space... That said, I still have a couple of candle lanterns because they work for what little light I need outdoors at camp. Have fun.
BTUs in, and BTUs out.... It is ALWAYS in the Math.... If your candle puts out X BTUs and your room has Y Cubic Ft of Air @ Z Degrees, and it takes W BTUs to raise 1 cubic Ft of that Air 1 Degree F. One can calculate how many Candles need to be burning, for how many hours, to raise the Air Temp in said Room so many Degrees F. This does NOT take into account that the Room Walls allow some of those BTUs to escape to the outside. The "Rule of thumb" for this is, If you are planning on a candle as your heat source, you had better have a WHOLE BUNCH of them, or a Really SMALL Room, PERIOD. ..... YMMV.....
I think a better way to heat and save money would be to make/buy/acquire a good steel stove and then make your own biomass bricks out of newspapers, magazines, wood chips and sawdust. Basically, use anything combustible and non-toxic, break it down and soak it in water. Then, press it into compact bricks for fuel. Or course, ventilation is always important, as well as fire safety. Alternatively, you can make a very cheap and simple briquette compactor out of a caulk gun and a little handy-work, for smaller ventures...
I will give it credit for being a great hand warmer. You can lay your cold hands directly on the flower pot and the warmth just soaks in, which is nice. I ended up setting one on my desk because my hands get really cold when I'm on the computer. I tend to have candles burning in the house all the time anyway so what's one more? As far as all the YT videos of people swearing it keeps their room warm, I'm calling BS on it.
I know, from a friend of mine who has worked with the homeless, that they will use a metal coffee can (or #10 can) with a small candle (tea light or similar) inside, as a personal heater. Just sit "indian style), with the can down in your lap, and you can pretty much hug your body around it, to capture all the heat it's generating. I've also heard that if your vehicle is stranded in the snow, you can generate enough heat to survive by burning a candle inside the vehicle. That being said, how exactly is a small candle (or even 4 of them) supposed to heat a MUCH larger room?? Like has been said already, BTU's are BTU's, and a candle flame only puts out a certain amount of BTU's.......doubtful, enough to heat a room.
