An(heater) - boom, boom

Reminds me of another joke

Little boy says to Dad - where did I come from?

Dad squirms, starts talking about the birds & the bees, stutters a bit, muddles about daddy giving mummy a seed to put in her belly, stops exhausted

Boy looks stunned; replies - oh, Fred across the road came from Shropshire

What do you call a lady with a frog on her head? - Lily