Brewing beer is a string of steps and processes. Each of these steps has a general set of rules. The aim at the end is to have the best beer you can produce using your setup and your knowledge.
These rules or guidelines come to us from previous brewers' experience and from commercial best practises.
Usually we follow these guidelines, but due to gear or knowledge limitations we can also break the rules, so long as we know the risks.
At every stage we aim to provide the best conditions for the best beer.
So we mash at the right temp, step up to the right rests, look at pH, crush correctly, boil correctly, sanitise, clean etc.
The no chill folks have worked out strict guidelines that must be followed for long term keeping, or your wort will be infected.
Your process of drain hot wort to fermenter, slow chill in a fermenter, no aeration and long lag time does have many problems. You will produce beer, but probably not the best beer.
Hot wort splashing into the fermenter may cause hot side aeration, which means the long term stability of you brew may suffer. The taste deteriorates rapidly. First the hops character fades, then the malt fades.
Slow chill doesn't promote good cold break formation and you may have DMS forming with condensation in the fermenter.
Lack of aeration means poor yeast health.
Long lag means there is a yeast problem. When your brew takes a long time to take off, it is at this stage most vulnerable to infection.
The large headspace in the fermenter is probably the least of your worries. If you use the fermenter to no chill overnight and pitch the next morning, the headspace is not an issue. With no chill where the wort is kept for more than a few days, it is essential that the headspace is zero.
Your beer will probably be fine but any of the above defects may raise it's nasty head. If there are any brew demonstrations in your area, go along and watch what they do and ask why.
