Is it hot water or steam? They're not synonymous. Is it controlled by a whole-house or whole-floor thermostat? Is there a thermostat in the valve?

Radiators are pretty much on or off: valve shut or completely open. They're not meant to be somewhere in between.

If the radiator's in a seldom-used room and you shut it off and close the door when you're not in the room, turning it on only when you're going to be there would make sense. If it's in a common area (family room, kitchen, etc.) turn it on and leave it on.

Have you checked out www.heatinghelp.com? That site is a wealth of information on hot water and steam heat.

Lorree

Constant. Radiant heat is great, but doesn't respond quickly to thermostat changes like forced air units. It's pretty futile to try to adjust it unless you're out of the house for a long period of time - say more than 3 days. If you turn it down low, it will take several hours (at least) to get it back up to a comfortable temp, unless you're living in an extremely small space.

Variable. We had hot water heat and I set the boiler at 120 degrees to start in the fall and worked up to 180 if neccessary by January (SW Mich). It is possible to get a thermostat that controls the boiler temp based on the outside temp. The warmer outside the lower the temp on the boiler.

We have hot water heat. It's zoned in our big house so we can really lower temps in those areas of the house we won't be using, or using at night and want it cooler. Due to the age of the house and the difficulty of piping through triple run brick walls, it's not zoned quite the way I would have wanted it, needing to heat some rooms and therefore heating others I wouldn't want heated, but it beats one stat.

Yes, it takes longer to respond to temp changes and doen't have a fast response time. I do adjust the stats occasionally like when the weather is going to be balmy enough to kick off the system entirely and open windows for a couple days to air the house out and take advantage of outside ambient heat. But, I don't wait until it's really cold and uncomfortable in the house to kick it back on. If the thermometer on the stats start to signal the room temps are dropping to below the comfort level and where I'd normally keep the stat, I turn the unit back on, so the rooms don't need hours of the boiler working to produce heat.

Aside from that, I don't monkey with the stats much. This means I likely set the stats a bit lower than someone with forced air heat, so I won't have to be adjusting the stats more than a few degrees up or down. Our system seems to ba able to handle that without running more than usual. Even heat from my cooking or baking can keep the rooms warmer in winter and I use this "waste" heat to crank the stats down a nudge and there is no extra firing of the burners.

But, like said, the shifting up and down of the stat a good amount to save heat when we are away from the house isn't done here unless we plan to be away for days. It's a bit of a different ballgame, but I love hot water heat. It's just so consistant and gentle and there are no periods ever when you get that cold feeling between the burner fires, like you do with forced air. It made me uncomfortable to stay at my parents house with their forced air furnace cycling on and off, because although they were used to the small temp fluctuations and didn't notice it, I did. It was like having hot flashes.

One way of controlling cast iron hot water radiator output is to NOT bleed the radiator completely.
If you leave it partly filled with air you can reduce the heat output.

mine is hot water and it's our first winter here. i'm thinking find a comfort level and keep it constant temp. it sure is warm.

thanks