Add heating tower from space age as standalone, the tech require chemical science pack, it's a natural upgrade to boiler, it's a nice middle tech between boiler and nuclear if you exclude solar, require space age DLC as its use graphics and code from the DLC.

Current Cost

heating_tower_tech.prerequisites = { "chemical-science-pack" }
heating_tower_tech.unit = {
  count = 250,
  ingredients = {
    { "automation-science-pack", 1 },
    { "logistic-science-pack",   1 },
    { "chemical-science-pack",   1 }
  },
  time = 60,
}