MLT size

So I recently dove into AG brewing! I got a 62qt Coleman extreme. Now the only issue I've run across is that I am doing 5G batches for now...and my tun is nearly 15G. I stepped it up thinking that I might go to 10G once I master the AG thing. What would you suggest to take up air space so that I don't have serious loss of heat during mash? Any suggestions? I just don't want to fluctuat the heat so badly just because I have a big tun.

Some cut foam insulation panels to float on the mash.

When you say float on the mash, do you mean make them steralized and place them on the liquid? Or cut them so they can fit in the top of the MLT?

You are talking about pre-boil so you want it clean but it does not have to be sanitized. Yes float on the mash. You could cover the foam with something since the insulation panels are probably not food grade. Or cut it to fit tight, make a handle on it and slide it right down close to the top of the mash, anything to cut down on headspace.

Perfect! I guess that means another trip to Lowes!

I was curious to this myself. When using a 10 gallon water cooler MLT, should you do the same thing? (5 gallon batches)

I have the 70qt coleman extreme and I dont lose 1° during a hour mash, I think preheating the MLT is a biggy for these large MLT's. Heat up your strike water 5° above what you need, transfer it into the MLT. Crack the lid a little and let the water cool down to your strike temp then add your grain.

If you are really concerned, you can cut a piece of plastic to put around the insulation like a shower cap.

Depending on the inner circumference of the cooler you may be able to use a store plastic bag...the added benefit are the handles (for removing the insulation fro the MLT) and availability.

Just cut a piece of 3/4" foam board so it loosely fits in your cooler. Use a cable tie or something to make a handle.

When I use mine, I wrap it in saran wrap, then sanitize it with star san, just to make sure. I pitch the saran wrap when I am done.

Doing 5 gallon batches in a 10 gallon cooler, I lose less than 1 degree in a 60 minute mash when I use the foam board.

I guess it depends on how big your grain bill is for that 5 gallon beer.... Preheating the tun is a must, I usually heat up at least 1/2 gallon extra and as I'm getting about 5 minutes or so from my target temp in the HLT I'll drain that 1/2 gallon onto the tun and swirl it around, then let it sit 'till the HLT is up to temp, this gets it warmed up some and a final rinse before starting my mash.

I have preheated my 9qt Xtreme cooler using a method similar to bendavanza. I think I will try SporkD2's idea though.

SporkD2 >> Wow, I brewed today and I wanted to thank you for the idea of heating the strike water a few degrees hotter than needed to warm the cooler/mashtun. It was much simpler than what I previously did, and worked like a charm. I nailed the mash temperature.