Pat wrote:
"To the OP, heat is not electromagnetic radiation."

Physics books disagree with Pat. Henry Semat, Ph.D. wrote on page 327 of
"Fundamentals of Physics":
"The transfer of heat by the process of radiation need not involve the
use of material media. An outstanding example is radiation of energy
from the sun to the earth: by far the greatest part of space between
these two bodies is a very good vacuum. The fadiant energy consists of
electromagnetic waves which travel with the speed of light, about
186,000 miles per second."

Best regards, Richard Harrison, KB5WZI