Not sure how to quantify exactly how much heat you'll lose, but here's what I would expect:
1) if you are doing a recirculation mash, you'll lose more heat in the process
2) if you don't insulate your MT in some way (reflectix, blankets, etc) you'll lose heat faster.
3) if you ambient temp is cooler, you'll lose a good amount of heat as well in both scenarios.
If you recirculate your mash, you can direct fire you MT manually to make up for the heat loss. Otherwise, bundle that MT up in 4-5 blankets. Regardless, watch your temps closely.