So you're wanting to power a fan with a 5v PSU using a boost converter?

That's pretty much what I'm doing with my solder fume extractor, but I wired it so it can run off of a USB port. 

Boost converters are rather efficient, I wouldn't worry about waste heat (the ones that I'm using are at worst 94% efficient,  the greater the voltage boost, the lower the efficiency), but you can get small heatsinks for it if you are worried. 

Here is the voltage and amperage reading on my fume extractor. 

My wall USB outlets have a bit of voltage ripple, which affects the amperage as well, but that's the average.   5.13v and 0.69a.

Keep in mind that Noctua's spec sheet says that the industrial 3000 RPM 120mm fan draws at max 3a, so I'm more then doubling my amperage draw, so 2.4x is about accurate (and to be expected if you do the math as well).

So as long as you can deal with the extra amperage, you should be fine.  Your wattage should stay roughly the same.  Resistance will more then double though, which may increase heat, but it shouldn't be an issue if you're using reasonable gauge wire.

Here is what I'm using. 

https://www.amazon.com/eBoot-Converter-Voltage-Adjustable-Step-up/dp/B06XWSV89D/ref=mp_s_a_1_5?keywords=MT3608&qid=1560829119&s=gateway&sr=8-5

As well as these to cool it (unessacary, but a cooler chip is always happier)

https://www.amazon.com/gp/aw/d/B07RKHRHJV/ref=ox_sc_act_image_1?smid=A2PL6UUXJC5K5G&psc=1

You can see where I placed it. 

Also, keep in mind that when the capacitors are fully drained (if it has been off for a couple of minutes) then it will draw a significant amount of amps for about a second to fill up the capacitors, it shouldn't be an issue, but some power supplies may trip their over current protection because of it.

Oh, Also, the boost converters come out of the box at maximum boost, which is around 30v if I remember correctly, so definitely adjust it before hooking anything up.  I think it's counterclockwise to lower the voltage, but I honestly don't remember. 

The MT3608 which I already have a handful of are only $1/each so if I burn it out no biggie. It's voltage range is a bit lower and actually looking up stats it claims "Up to 93% efficiency". Kind of makes me wonder if I super chilled it if I could pointlessly make that as high as possible just to see what would happen. Maybe use a Peltier. Could I "overclock" one of these? I have so many ideas now.

Getting back on topic, the charger is USB so I planned on using a USB "breakout board" I guess it could be called. One of these except mine have pins pre-attached.

I did do the math that's how I came to the conclusion of 2.4x if I only have to compensate for a loss of 7% I should only have to add that to the expected current draw. Of course I will want to account for any unexpected overhead but if this is only going to push the charger to about 50% load I don't really have anything to worry about.

I have a whole spool of nickel (or is it tin...) plated copper wire. Solid core. I believe it's ~0.3mm (I'd have to check again). It should be able to handle 350mA (I think...) if not I have a mass of solid core copper Ethernet cable. It's ~0.5-0.6mm. It WILL get the job done. Or I could just double up the tin plated copper wire. Make my own twisted pair.

Well, my boost converters were over 2 dollars a piece, so a 1% drop in max efficiency for less then half the price is pretty good if you ask me.  My biggest concern is the quality of the capacitors actually.  I would imagine that your boost converters probably have more output ripple than mine, but fans tend to not care about that, they are rather robust devices. 

I tend to get USB cables that are fast charge capable and just cut the device end off of it.  The USB cables specifically designed for charging tend to have wires around 22 AWG - 20 AWG, which is generally just fine for higher amperage and resistance draws.

But a USB breakout board should do just fine. 

The more expensive stuff is nickel, the less expensive stuff is tin.  It really doesn't matter when it comes to soldering since the solder makes an airtight seal of sorts.  Copper wiers actually have to be very corroded for it to actually interfere with anything. 

I wouldn't worry too much about the wire that you have.  If it starts to get warm to the touch though, get something lower gauge. 

Behold, my USB powered fan.

Input: 5V

Output: 12V

I wonder if I should make an enclosure and solder in some 5V 7 segment displays. One on the input one on the output so you can watch the voltage levels realtime.

I wouldn't find the displays nessacary, although I do have a couple of LEDs.

The amber LED lights up whenever it's receiving power. 

The teal LED lights up when the power switch is flipped to the "on" position. 

If it's plugged in that is.

My idea with the 7 segment displays is kind of more as a decoration than a debugging tool. I tried wiring in some that run off just two wires and ran into a problem.

The input is fine. 5.15Vish but the output...that display DOES work but when the fan is plugged in the display either doesn't work or flickers 0.00V (you might see its just starting to illuminate in the image). What's interesting is if I touch the exposed circuits in the back it calms down and displays the proper output voltage. I know our bodies carry capacitance and to a very strict extent our skin will conduct so I'm wondering if my body is acting as some sort of capacitor (perhaps the fan is electrically noisy?) Or if I'm acting as a resistor...no idea.

I did order some displays that have a dedicated sense wire which fixes this issue but I need the ones I ordered for another project.

The neutral returning to the input side could also be causing some wonky problems. 

If I were to guess, having the neural there is causing some issues on the return circuit and your body is acting as a neutral wire.

The thing is I tried have both ends on the output went everything was still connected with alligator clips and it behaved the same. For a moment I thought it was behaving normally wired the way you see it but it ended up behaving the same. Weird. I'll probably remove them and wire in a switch. This is just to move air around in my bedroom at night. Don't really need the bright displays they were an idea, one I can probably use in the future.

Lights (especially blue light) tends to keep me up if there's enough of it.

I honestly don't know what's causing the other display to act up.  Perhaps it's defective?  

A PWM knob may come in handy if that's going to be in your room, even though noctua fans are rather quiet. 

No, definitely not defective because I tested both of them on the output and they behave the same once the fan is plugged in. I thought maybe it was a lack of current but that doesn't explain why touching it with my finger makes it behave. I plan to run the fan with a resistor in series to quiet it down. If it's an issue of not enough current maybe this will help.

Thanks for the follow but I should mention most of the stuff I post about is server related things. I do dabble with hobby electronics but I don't frequently talk about them.