Glowing Inferno vs Heartfire

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Heartfire is a little lighter, cooler than Glowing Inferno.

Can I use Heartfire instead of Glowing Inferno?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Heartfire is a little lighter, cooler than Glowing Inferno.

Can I use Glowing Inferno instead of Heartfire?

The same difference applies the other way round: Glowing Inferno is a little darker, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.