5C FV temp difference top to bottom. Will it matter?

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morethanworts

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...and a couple of other questions before I resume brewing this week, after years away. Many thanks in advance!

In a test (with water) using a water bath containing an FV full to 4.5 gallons, a submerged aquarium heater (in the water bath) and a probe controlling the heater on/off set to 12C, but no pump, I'm getting a 5C difference from bottom to top. It's a cool fermenting lager I'm planning, hence the 12C.

So, two questions really:

1. Is the 5C so bad that I absolutely should just get a pump?
2. If not, should I

a) set the controller at a temperature that would result in the target figure when I give it a stir (even though the lower depths would be as low as 8.5C, unstirred, in my tests) or
b) set the controller somehow else, perhaps so that the bulk of the lager yeast at the bottom is at least at the best temperature (with the top up to 5C higher)

Two further quickies, if I may...

I don't have a dedicated fridge (yet) for lagering. I have to approach this gently with SWMBO :whistle: . I can make sure it doesn't go below (say) 3C in the shed with a probe controlling a heater, but the average weather here will have it swinging from that up to maybe 10C and slightly beyond by April. Is it likely to develop any real lager notes?

I will be limited to cooling about 15L of wort (from extract) by changing water and ice blocks in the sink, in an 18L stock pot. I know there are many variables, but if anyone could very, very, roughly guestimate how long I may expect it to be before I can get it down to around 15C for pitching, it may mean I can time the brew so it's not 3am when I should be pitching my yeast! SWMBO would love that! :nono: I really have no idea whether it will be 2 hours or 12 hours. I suppose that could be another test to make...
 
I did a lager extract brew in a 15l stockpot and cooled It in the sink. I changed the water a couple of times. It was down to 18C pretty quickly - can't remember exactly but about half an hour.
 

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