[new_realist]

But a heat pump is more than 100% efficient.

[authorityofnil]

I feel this is a bit disingenuous, because using the same logic burning wood is thousands of % effective, or even ∞% if the system only uses convection, making heat pumps seem like a poor choice even when they're perfectly valid.

[vmladenov]

Until the temperature drops below 4 C

[yxhuvud]

Which is why you bore a hole deep enough that it isn't a problem.