3/8s would way to small to keep the intake heated. I would think the Cold fuel would kill any heat the 3/8s would give. I wouldn't go no less then 1/2 Bu t5/8s would be the better seeing that a heat core runs 3/4 or 5/8s lines. And i beleive it's 3/4 in 5/8s out.
God doesn't like ugly.
