first all grain tomorrow

I'm using the brew 365 calculator. One silly question. If I follow this calculator to the letter does that include pre heating the mash tun?

I always preheat mine in the winter. I keep my cooler out in the garage and its cold! I put 1 gal of boiling water in there about 45 minutes before I plan on mashing in. I subtract the gallon from whatever volume of strike water I would normally use. What does 365 tell you to do?

For my grain bill with a temperature of 65 degrees it recommends strike water be heated to 165 degrees for a target of 152. This calculator does not mention preheating the mash tun at all.

I would say that you will need to preheat the tun to get 152 with water at 165 degrees. It takes me 168 to get 152 with the grain at about 68 degrees. I always preheat even mid-summer. It is far more important brewing outside during the winter.

^^ this. Unless you are brewing inside and the thermostat is at like 90

If it allows you to input the temperature of your mash tun then it probably takes into account heat loss of strike water I know this is how beersmith works and I hit my mash temp every time even in the winter

I preheat my mash tun as well. The only difference is I dump the preheat water seconds prior to adding my mash water. Then I add my mash water, then the grain (while stirring), get the temp right, close it up cover it with a blanket and a space blanket,and check temp and stir every 15 minutes.

I have a digital thermometer that runs into tun that always displays the mash temp but I also put a glass thermometer in the grain bed too verify the digital temp.

Personally speaking, I always have hot or cold water ready each time I open so that I can add if necessary.

If you are using a Rubbermaid cooler, I suggest insulating the lid. I drop maybe 3 degrees an hour.

"Strike Temperature - Temperature at which to dough-in your mash. This value assumes that your mash tun has been pre-heated."

I cut and pasted this from the Brew 365 calculator page you are referring to, values assume you are pre-heating. I use Beersmith and there is a box you can check to adjust the strike water for my equipment profile.

That said, +1 on the advice from davekippen "put 1 gal of boiling water in there about 45 minutes before I plan on mashing"

I haven't seen anyone mention the preheating technique I use, so I'll go ahead and put it out there. I heat my strike water to about 10 degrees higher than my strike temp and allow it to cool down to strike temp in my mash tun.

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I have a marine 3-day cooler that holds temp really well. I heat my strike water to 170 to hit 152. It was 33 degrees this morning and i hit the temp on the nose. Your best tool is your thermometer, we are all using different rigs at different places. Congrats and welcome to the next level of obsesion