Pipes knocking all over - BHW system

[garlandnh1]

Hi, we just bought a house with baseboard hot water, run off of a gas furnace. The system is under 20 years old. Not sure if that helps. Since the heat has been on, there is a knocking of the pipes. It's not in one place, we hear it in different rooms and of different intensity, louder when the heating first kicks in. We have two thermostats in the house, and are under the impression that it happens in the upstairs zone (the alternative to that is that the upstairs furnace does nothing, but it is definitely related to upstairs) - but the knocking happens on both the second and first floors.

Anyone have this happen or have any ideas? Thanks!

[Andrew]

Welcome to the world of hydronic heat!
The knocking is the expansion and contraction of the pipes and rads as they heat and cool. While it is annoying, it shouldn't be dangerous. You might try to rub some graphite on the inside of the pipe hangers to allow the pipes to move more quietly.
Happy Holidays :)