Using a temp gun

[Bogertophis]

We bought a pretty good one and are relatively close BUT if my screen holes are relatively small, by the time I am taking off the screen and shoot, won't the temps be very different?

Your question makes me wonder how cold your house (or room) is, & if that's the case, I'd assume that your screen is also covered to keep in the warmth? If so, I can see where you'd lose some heat as far as measuring the ambient temperature in the enclosure, but (as previously answered) certainly not most of the heat where the heat source actually is. (hot stove is a good analogy)