Why tealights & flowerpots will NOT work

Shawna HendersonBy Nova Scotia energy professional and longtime Solar Nova Scotia Member Shawna Henderson:

OK, the time has come to debunk this. People are going to die. They will be cold, asphyxiated or burned to death.

This has been coming across my feed for weeks now, with people gaga over the cheap and amazing heating source. It's not. Four tealights produce about 800 Btu/hr. To put this in perspective, one 100W incandescent bulb produces 340 Btu/hr, 90% of which is heat, so if you are burning two of those bad boys in a room, you are providing 600 or so Btus to to space.

The claim on the video is 15¢/day. However, Presidents Choice 8 hr tealights cost 16¢ each ($8/bag of 50, tax not included). So the cost for 800 Btus of heat = 64¢ + HST for 8 hours. If you were to compare that to burning 2 - 100W and 1 - 50W lightbulb over 8 hours, in Nova Scotia, with electricity charges hovering around $0.13CAD/kWh, you would be shelling out a total of $0.26 + proportion of base charge etc. Not to mention the fact that you would have the non-energy benefit of enough light to read by anywhere in the room.

It’s kind of a moot point since incandescents are now banned in Canada (but that’s another rant for another day).

Let’s look at other claims, or misrepresented/misinterpreted statements:

The flowerpot does not act as a radiant heat source (that’s the candles), nor does it amplify the heat source (that’s impossible), it only acts to concentrate the heat produced by the candles in a very constricted area, before it dissipates to the rest of the cooler air in the room. Not only does the flowerpot add nothing to the available heat, it does not store any of the heat for any appreciable length of time. It is not thermal mass. Clay has a specific heat capacity just slightly higher than air. To get any thermal mass, the clay would have to be much thicker than a flower pot and preferably mortared into a large surface that is buffered on at least one side by another mass that minimizes heat loss to lower air temperatures and colder surfaces.

Let’s look at how the tealight-flowerpot gadget stacks up against a standard-issue radiant-source room heater (to compare apples to apples), because that’s what it’s claiming to replace. Room heaters that work off radiant heat sources, such as oil-filled electric units are cost-effective (and healthier), as mineral oil has a specific heat capacity that is more than 1.5 times that of air. These room heaters use electric elements to heat and circulate mineral oil in a series of fins that then radiate heat to the room via an expanded surface area.

A standard 2kW room heater can provide 10K Btu/hr. To match this amount of heat would require 13 4-candle teapots. That’s 52 candles that last for 8 hours. So let’s do the math. First let’s look at purchase prices and value-for-money:

I bought such a room heater for $80 (+HST) last month at Canadian Tire...that means it’s worth 10 bags of tealights, which will give me heat for 80 hours, and then I have to replenish my supply. Its cold in Nova Scotia for way longer than 80 hours. So lets say I buy 20 bags of tealights in total, which will keep me warm for 160 hours. Still not adequate for winter. Even if I’m willing to put on six sweaters, four pairs of socks, a toque and chop my candle-flower pot heating system in half so that I get 320 heating hours out of it, I’m still nowhere close to adequately providing absolute minimal comfort levels. Now I’ve paid out $160. and I’m not comfortable and I don’t have enough heat for the winter, and I’m subjecting myself to crappy indoor air quality, meaning I have to fill my asthma prescription twice this winter instead of once. Oh wait. I haven’t accounted for the cost of the flower pots. Assuming I don’t have them handy, that will add some more cost and what if I can’t find them in the off season?

Well, let’s say I’ve got the flowerpots on hand so we don’t have to factor them in. But the asthma prescription is $30 a shot.

So I bought the radiant heater for $80. If I use it at it’s full 2kW heating capacity, providing me 10k Btu/hr every hour, I can use it for 423 hours before I hit $110 (the second delivery of 10 bags of 50 candles + my asthma prescription. And I’ve been toasty (possibly overtoasty) for each of 423 of those hours. And I haven’t had a single poor indoor air quality-induced asthma attack or asphyxiated any pet birds or burned down the house.

PS. In the original video, the premise was the heat was provided by one flowerpot thingy (producing 260 Btu/hr) and the computer running (producing 1365 Btu/hr). The flowerpot thingy is not heating the room.

PPS. Regardless of how big your candle is, it will still ONLY PROVIDE 260Btu/hr.