Hey all, we just moved into a prewar studio in Inwood. First real cold snap and the radiator is absolutely cranking. It’s one of those old painted valves near the floor, and I can’t tell if I should turn it or if that’s a call-the-super thing. I don’t want to be the new tenant who floods the place or makes the whole line bang. Is there a renter trick, or do I just leave it and crack a window? The window route feels dumb given how much heat we’re getting.

firstwinter, depends what kind of system. If it’s a steam radiator, that valve is not a dial—usually you keep it all the way open or all the way closed. Half turning it can trap water and cause banging. If it’s too hot, open a window before you start wrenching painted metal. If the valve is frozen or painted shut, def call the super. If it’s a newer two-pipe with a thermostat, you have more room to adjust.

GreenwichVillage_G, wait, so even if I turn mine just a little bit to slow it down, that’s bad? I’ve been doing that in my Bed-Stuy place for weeks and now there’s a knocking sound that comes and goes. I figured it was air in the pipe. Should I put it back all the way open and leave it? Also, do you have the hissing air vent thing on the side? Mine hisses for like ten minutes then stops.

new_in_brooklyn, that knocking is probably water hammer from half-opening the valve. Steam gets in, condenses, can’t drain back, and the next push of steam slams the water around. Put it back fully open. If it still knocks, tell the super so they can check the pitch or the trap. The hissing is the air vent; that’s normal if it stops. If it spits water or never stops, swap the vent.

EastHarlem_E, I thought you were supposed to bleed radiators with a little key? My brother in Co-op City has baseboard heat and we opened a tiny valve to let air out. I tried looking for something similar on my prewar radiator but it's just a big valve and a small chrome thing near the floor. Maybe I shouldn’t touch that. I’ve been using a towel on the roaring pipe but that feels sketchy.

Thanks for the warning, GreenwichVillage_G. Okay, so I did the exact thing you shouldn’t do—turned it halfway to try to make it less like a sauna. Now it clanks at 5 a.m. like someone hit the pipe with a hammer. I turned it back full open, but the knocking is still there. Should I call the super and admit I touched it, or will that just annoy them? Also thanks for the tip about the air vent; mine just hisses and stops, no water.

firstwinter, just tell the super it’s banging. You don’t have to write a confession. But if you leave a half-turn on there, they’ll find it anyway. In a one-pipe building, the fix might be as simple as opening the valve all the way and checking that the radiator leans back toward the pipe. If it’s still banging after that, it’s above the newbie pay grade.

EastHarlem_E, I put mine back to fully open and the knocking mostly went away, so thanks. One thing I still don't get: if the radiator is too hot and I can't really throttle it, do people in these old buildings just keep windows cracked all winter? That seems expensive but I guess the landlord pays. Also, is it normal for the floor under the valve to get warm? Mine does, maybe that's the pipe.

new_in_brooklyn, crack a window is literally the classic steam heat move. The old systems were designed around fresh air, so don’t feel bad. If you want to be cute about it, put a small fan by the window to move the hot air through the room. Warm floor near the valve is usually the riser doing its job, not a leak. But if it’s wet or smells like steam, call it in. DykerNewbie, no radiator key—that’s for hot water baseboards, not steam.

EastHarlem_E, okay so no radiator key. Got it. I tried opening the valve all the way with a rag around it, and now the giant clang I had is gone. I still feel like my apartment is about 80, but I’m just going to open the window a crack. Do you need to leave the valve open even if you’re away for a few days? Or can you close it without messing up the line?

Update: super came by, took one look at the valve and said it was already slightly off the full-open position, probably from me. He turned it back, checked the tilt, and the knocking stopped. He said in this building the valves are either full open or full closed, no middle. So I’m joining the window-crack club. Thanks everyone—this thread saved me from a much more embarrassing maintenance ticket.