Ventilating combustion byproducts in water heaters I'm designing a system which will heat up water by burning natural gas which is commonly available. I would like to have a slow flame because water will need to reach $\mathrm{70^\circ C}$ and stay there. Having in mind that even weak winds can extinguish the flame as well as the system will be put together with other objects and systems in a tight space I decided it would be a good idea to build a chamber around the flame nozzle thats directly attached to the water container. I will build a small opening in the chamber to which I will attach a tube which will feed atmospheric air into the chamber through some kind of a filter (probably a piece of cloth) to keep it clean. I read that the byproducts of burning natural gas are $\ce{CO2}$ and water vapor which raises 2 questions:


Do I have to worry about humidity increasing in the chamber and eventually water forming on the inside, in extreme conditions water in the system can be as low as $\mathrm{-20^\circ C}$ (I call it water but it will be actually antifreeze)
Do I have to worry about the chamber filling up with $\ce{CO2}$ and eventually putting the flame out which will then be unable to be lit again. Is there anything I can do such that the byproduct will exit the chamber naturally without me having to do any work for it. 


Edit:

So far from the comments it was made clear that it would be better to use a condensing boiler design efficiency wise, however due to construction complications that I'd like to avoid I'll stick with only the hot half of the design in question where the water will pass through a tubing inside the chamber where it will be heated, instead of applying heat to the container directly. There will be an exhaust that will utilize natural convection to expel the exhaust gasses in addition to the inlet.
Rather than design something that offers danger of overheating, carbon monoxide poisoning, gas and over-pressure explosion, etc., why not use an off-the-shelf "instant" tankless water heater, available from sources such as Home Depot, Amazon or Lowes?

Find one certified for your area. Making your own is a tankless task!