Extreme Heat Guide
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Getting off on the right foot
Dealing with extreme heat is similar to dealing with extreme cold, except with coolers as opposed to heaters. As your colony crashlands (this guide assumes the standard Crashlanded scenario), you'll quickly want to equip everybody and get straight to work with structures. As tropical rainforests can handily push 60C and some Arid Shrublands can even get into the mid-high 60's during heatwaves, you'll want to get a bedroom setup to tackle this as soon as possible.
First of all, you're either going to want to initially put everybody into a barrack, or connect everybody's bedrooms together using vents. Gather plenty of steel and components around the map, as you're going to need them for solar generators, wind turbines, batteries and coolers. You'll also want to consider setting up growing zones for food - rice and corn will do nicely for a relative stream of low amounts of food, and occasional bursts of high amounts of food. You'll also want to build a room (ideally 7x7) for research or at least place a research bench to get passive coolers going.
Planning for success
At this point, you should have a very basic setup and you'll soon need to start producing meals. As with any other climate, you'll want to make a butcher table and Stove of some sort, and bill as appropriate so they'll actually be utilised. You will definitely want to consider an electricity farm also a freezer to start freezing ingredients to stop them from spoiling. As the Extreme Cold guide mentions, you'll want to build something along the lines of a 7x7 room with a centered door to start with, but leave room for expansion as your colony grows. Because you'll be dealing with Heat Waves typically within the next 7 or so in-game days after landing, you'll want to build 4 coolers and set them at -5C to compensate for warm air going in when colonists move in and out.
As for the electricity farm, you'll probably want to build 2 solar panels and 3 batteries to start, as coolers consume more power than heaters when under load (200W vs 175W). It may not be the worst of ideas to consider a nutrient paste dispenser too (but only for emergencies), as all local animals will migrate during heatwaves and crops will slow down or even cease to grow if it gets hot enough. Although nutrient paste meals give a -3 moodlet for '[Eating an] Awful Meal,' they give 0.9 nutrition (the same as a fine meal), and also only require 5 ingredients to make. You should also have researched passive coolers at this point so when the heat waves do come, you can simply stick a few in the barracks that your colonists share, or put one in connected bedrooms for every 2 rooms (assuming 4x4 bedrooms), and connect them with vents for each column or row.
It is possible, in unmodded game, to generate maps where temperatures do not drop below 40 °C (104 °F) and routinely exceed 100 °C (212 °F) during heat waves. On those maps, there are no animals (except thrumbos), plants don't grow outside (they may gain few "ticks" of growth in winter, but that's it), temperature in coldest winter is enough to kill humans through heat stroke and trade caravans do not arrive (ever).
The first thing that needs to be done is creating a cooler. It can be tiny (just enough for colonists to sleep in), but it is mandatory for survival. The very next thing is rushing hydroponics basin research, but doing so while conserving wood (you still need that butchering table and stonecutting table). While the research is in progress, find sources of steel and prepare that energy surplus you will need for hydroponics.
Despite the hardships, raiders will still arrive. They will get heat stroke (they never seem to bring dusters) but unless your base is a fortress, they have enough time to destroy your life support system (electricity and coolers) and down your colonists, even during one of the 100 °C (212 °F) heat waves. Their existence is, however, vital for your survival - until you put up hydroponics, human flesh nutrient paste is the only semi-reliable source of food this map will have. Constant cannibalism and paste diet means you should expect to deal with breaks - don't give your colonists melee weapons during downtime.
As soon as you amass a significant amount of textiles, you should make dusters, cowboy hats, and tribalwear. They provide protection during Solar Flares, outdoor construction projects and prolonged fights (you can wear down human raiders with heat alone if you can lock them down somehow). Textiles that provide the most heat insulation should be prioritized - in the extreme desert, this is typically camelhide from dromedaries, and to a lesser extent, guinea pig fur from guinea pigs. A combination of these three items, made of camelhide and in normal quality, will prevent heatstroke up to a temperature of 81.6 °C (178.9 °F) which makes surviving heatwaves significantly easier, even in the most extreme environments.
Micromanage your hydroponics farm to avoid emptying batteries. Plants can survive few days without light or in extreme heat, but die in moments if the hydro tray loses power. Note that you can control your coolers without a colonist having to flick them - if your freezer is empty or contains only rice/berries, consider turning off the coolers by setting their temperature very high.
Other tips moving forward
(This section for anything else of note)