Turning down radiators

MacBosnia

Maybe this is a stupid question, but is there another way to turn down radiator heat besides the central furnace/thermostat?  I have 3 floors in my house and about 15 radiators.  The heat in the house is controlled by a thermostat on the 1st floor.  Of course I can turn down the central thermostat, but then the whole house is cooler.  I've tried closing the knob a little on individual radiators to turn down the heat, but that doesn't seem to be cooling them down (maybe just lessens the water in the radiators?)  Am I missing something?  

Brad White

Water flow rate is a lousy way to control temperature

Those valves you are dealing with are manual valves typically designed to be fully open or fully closed.  If your system is an older gravity HW system (converted now with a pump or not), the flow velocity is pretty low and the rate surprisingly high sometimes. But cutting the flow in half, if you were to use those valves (and no, you should not), would still get you 90 percent of heat output. Not a linear response.



Long term, I would put thermostatic radiator valves (TRV's) on all of your radiators and let them enjoy some high-limit control authority.



In the meantime, the only advice I can give is to reduce the top floor output by dropping the water level somewhat down the radiator column. This will ONLY work if your radiators are supplied and returned across the bottom, of course. It is a trial and error approach and will not affect the lower floors.



In the way of explanation, I can offer some common experience. Older houses often have their attics insulated as the first "low hanging fruit:" of energy improvement. Thus upper floor radiators are suddenly over-sized compared to their original heat loss.  Even if you insulate the walls, the lower floors tend to be where air leaks in, so your lower floor may well be cooler than any higher floor.