"Stormin Mormon" wrote in
:

Lets say you're in apartment building with a lot of units. You're in
the first apartment. You want the room colder, so you open the
window. The room now has colder air, so there is greater delta T from
the room to the radiator. The radiator loses heat faster, and cools to
a lower temp (lower room temp) so the next guy gets colder water. And,
the water going back to the heating plant is colder, also. So they use
more fuel. See? Opening windows does at least two bad things. One of
which is to cool the water that the later apartments need.

This assumes there is 1 continous loop. Highly unlikely, don't you
think? Probably the loops are for individual units, from a main central
loop. So your return (colder) water does NOT have to heat someone else's
unit. But the same reasoning for covering the radiator rather than
opening a window still holds - total heat loss is less, and so operation
is more economical.

--
Best regards
Han
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