Hi, I have a question about the heat accumulator, how is it different from an actual regular heat pipe? It just has a temperature that goes to 1000, so I'm not sure why I would use this? Can it store more heat power somehow?

Yes, it stores more heat energy, so it'll take longer to heat up, and take longer to cool down. It can be used as storage or to balance out peaks in energy draw, somewhat like the electrical accumulator :)

It can also be thought as a bunch of heat pipes on the same square.

Thank you for the confirmation!
I have another question, this time about the heat pump. Does the heat pump lose heat during the transfer? I'm designing a nuclear heat powered furnace stack but my calculations don't match my testing. The heat system loses more heat than it should. (Basically I'm trying to sync a fuel insertion with a number of furnace stack cycles according to how much energy they take so I waste no heat).

The calculation is exactly surprisingly difficult, due to how factorio works. But to avoid it breaking thermodynamics I gave it I think it was a 5% energy loss.

Oh thank God, I'm not going insane then!
I don't mind the heat loss, it's just good to know that my calculations were correct, I'll have to optimize for as few heat pumps as possible then. Thanks!