Vent mains fast, radiators slow

ben_18

I get vent mains fast, but why "radiators slowly"?

nicholas bonham-carter

The largest volume of air which must be pushed out by the steam is in the pipes. The main vents, which handle this air escape must be large enough to provide as little resistance as possible. The steam will then fill all the pipes first before starting to rise to all the radiators simultaneously.
Slow radiator vents will provide a slightly higher resistance to the escaping air, and therefore the radiators will fill after the pipes.--NBC

KC_Jones

1. If you vent them too fast you can more easily overheat the space. This is about control.
2. If you vent them too quickly and have rads connected at the top and bottom they can short circuit more easily.

ben_18

So in theory if you vented all of the radiators equally fast you would get even heating.
@KC_Jones what do you mean by short circuit?

KC_Jones

The steam will rush to the end, skip most of the sections and close the vent. Essentially reducing output. If you vent them really fast you can equally overheat the entire house. Remember just because steam stops doesn't mean that heating stops. Those rads stay hot for a while.

Johnson_Rod

KC_Jones said:

The steam will rush to the end, skip most of the sections and close the vent. Essentially reducing output. If you vent them really fast you can equally overheat the entire house.

Couldn't it be the exact opposite too? Assuming you're trying to overcome a big difference in current temp vs. thermostat setting. Closing those rad vents too quick will increase chance of shortening the cycle from pressure before thermostat is satisfied.

KC_Jones

If you short circuit and can't get the whole rad hot, you could run the risk of not heating the house. It depends on what type of radiators you have and how they react. I have steam only rads in my house so the short circuiting isn't an issue.