I tend to use duals in everything that will accept them, and some things that won't (I may be the only person who ever put a dual build in a Kayfun). I like dualies as it lets you use smaller diameter wire (heats faster and uses less watts) and more wraps for more surface area and shorter ramp time on less watts. I judge this more efficient. You are (if I remember) a MTL girl, though, so efficiency is not your main interest, really, in a lower watt regime. Duals, in my experience, give more cloud for the same watts as they have bigger surface area provided you size the wire right. This may or may not be important to you. I also find building duals in a topper intended for them makes better use of the air, and the block outs most toppers use to allow single coils don't work well, but that's minor compared to getting a good vape. You vape all day every day, but you only rebuild occasionally.
The "heat flux thing" is your next step, so fasten your seat belt and be prepared to re-read it a couple of times. This is one of the great reasons Steam Engine is such a useful tool; it enables you to know where you want to set the watts, and how your coil set will perform before you build it. While it is generally true more watts = more vapor, it is more accurate to say what makes vapor is thermal energy flowing from the coil surface in contact with wet wick. Heat on dry wick burns your cotton; heat not applied to wick can't make vapor. The abbreviation I gave above, read in English, is "milliwatts per square millimeter of coil surface." That tells you how much power your coil is pumping out. Read in conjunction with the total watts the machine makes, it give you a clue about how much surface area the coil has by dividing. All other things being equal: two coils fired at the same watts, the larger surface area coil will be cooler and make less power per mm² than the smaller; and two coils with equal surface, the more watts will be hotter and make more power per mm² than the lower power coil.
So bring up Steam Engine to the "Coil Wrapping" page. Set it up for 26ga Kanthal A1 round wire (I am assuming that's the only wire you have, and it will do for an example), dual coils, a target resistance of .5Ω, a mandrel size of 3mm and a coil leg length of 5mm. Over to the right in the Results box, you can see you will need two 7/6 wrap coils. Note the number in parenthesis behind that figure is .93Ω. This is the resistance of each one of the coils as individuals, and that means you won't get exactly .5Ω for the total build, but rather half of .93, which is .465Ω. That's not bad-- it might be within the limit of your ability to measure it-- but it isn't exactly what we want, so let's play with the mandrel size. Raise it to 3.5mm and you will see the 7/6 coil comes out to 1.05Ω, and the pair will total .525Ω. Closer, but still not exact. So we try it at 2.5mm and get a 9/8 wrap, also for 1.05Ω. We're probably not going to get much closer, so pick which one you want to use (I would go with the 7/6 on 3.5). One key thing to note is, so long as the resistance doesn't change, the length of the wire, and therefore the surface area of the coil, also does not change. Thus the 9/8-2.5 and the 7/6-3.5 have the same surface area and will make the same heat flux, while the 7/6-3 will have slightly less surface, and be slightly hotter than the other two. Note also, the bigger the mandrel, the more wick it will take to fill the center of the coil, a thing to remember if you're having juice transport problems and getting dry hits. FWIW, I like to make my coils between 5-10 wraps and the largest mandrel I can cram into the build deck, consistent with the wrap count.
On to heat flux. In the Results box, two lines below the number of wraps, is a line headed "Heat Flux." There's a clicky-box where you can adjust the watts you set on the machine, and off to the right there's that annoying mW/mm² thingy again. The background of that number shades through the spectrum (backwards, actually) with blue being cold, red being hot and green the sweet spot. The background gets noticeably green between 100-200 mW/mm². That's actually a measure of the power streaming from the coil surface, but it's also an excellent indication of how hot the vape will be: the bigger the number, the hotter the vapor coming off the coil. I personally find I like vape between 80-180 on that scale. You may find you like something else. It doesn't matter in the absolute sense, save you will find some juices respond better to different temperature regimes. What's important is knowing what you like, so you can duplicate the heat flux no matter what kind of build you attempt. Assuming you are set up for 26ga, 3mm, 7/6 wrap, you'll see the green starting at 23 watts for 102mW/mm², and it starts shading yellow-green at 47 watts for 208mW/mm². That's where you set your mod wattage to keep that coil set "in the green." Now, go back and change the wire size to 28ga and look at what happens to the heat flux. Whoa! 47 watts is way up in the red at 417, and the new coil set wants to be a 5/4 wrap. That set doesn't get into the green until you back off to 12-23 watts! Now, my friend, you know why I stock a variety of wire sizes and types, and keep a selection of mandrels handy
I know what heat flux I like, and my preferred wattage range, and I build my coils to match it. I told you, months ago, Steam Engine was a handy friend to make
As to how long it took me... the right answer is forever plus 3 days, but it was different for me. For one thing, my background is engineering and I already understood Ohm's Law and math did not scare me before I started building. For another, I did not then have the advantage of Steam Engine, or the resources of this board at my beck and call, precisely because I never even imagined either one existed. Another big difference is, back in the stone age, when mods were carved out of rock and we wound coils out of plant fiber and animal sinew, there were no high power regulated mods available at all. The best you could get was 15 watts, and no coils lower than 1.5Ω. That's why I started building and went to mech mods; I needed more than 15 watts could give me, and the only way to get there was go mech, and build subohm.
So, it was a trial. It took me weeks to build a coil that would actually vape, and I had to go down to the vape shop and pay a pimple-faced kid to teach me how to wick it. And I figured out my resistance the old fashioned way: by calculating the circumference of the drill bit I used as a mandrel, times the wraps, and multiplied the total wire length by the resistance factor. (I might also mention tank availability was a great deal more limited; I never liked the Kayfuns much because they don't breathe freely enough, so I found the Fogger and stuck with it for 3 years). Once I got a build that worked, I never varied it at all for years; just kept building the same thing over and over because it worked. When you're a mekkie total resistance, and thus amp loading, is a lot more important than heat flux, and the vape varies with battery charge anyway, so I never gave heat flux a though.
Then I found this board, got introduced to Steam Engine, and things began to hum
