Steam Heat and Heating Q&A

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Dear NH,

I've been searching the web and couldn't find much on the topic of steam heat radiators. I live in New jersey and just bought a house that is over 60 years old. All the radiators are working but one. The unit in questions was converted several years ago to a baseboard steam radiator. There is no warmth in the unit at all. Family advice was to "bleed the unit". I have never lived in a house with radiators before so I am completely unfamiliar with the process of "bleeding". Also I can't seem to locate a "bleed" bolt. any idea?

MY from South Plainfield, NJ

I haven't even seen a steam radiator since my first home, a hundred year-old two-bedroom shack I bought in 1973. I fondly remember the banging and clanging of the rapidly expanding iron pipes as the boiler did its work. On my first night there, I slept on the sofa. I didn't have a bed yet! When the heat went on, I thought the place was haunted!

Steam radiators do not need to be "bled". Bleeding is done in hot water systems to allow trapped air to escape. There is no air trapped in steam radiators... it is blown out by the steam!

Steam radiators have a valve that allows steam to escape at a controlled rate so that the radiator can heat up. If this valve is clogged with mineral deposits or stuck shut, no steam can enter the radiator, so it doesn't heat up! These valves can be unclogged sometimes, but you would be better off getting a replacement. You should be able to find the valve under the end cover of the radiator. Most plumbing supply houses sell generic replacements.

Another possible problem is that the house has settled causing the pipe leading to the radiator to no longer slope downward towards the boiler. If this has occurred, the condensation within the radiator that would normally flow back to the boiler is instead pooling in the pipe. This can block the movement of steam to the radiator, or cause a very noisy hammering as pressurized steam bursts through this water "dam".

The easy solution is to raise the radiator, if possible on wood blocks to restore the downward slope. The more difficult solution, and sometimes the only option, is to do some major league plumbing OR think about an alternative heating system such as electrical or propane.

Dear NH,

Could you give a small explanation of steam heat ? My girlfriend heats her home with a steam furnace. She has a 7 room house, and what we are wondering about is the noise that comes from the valves on the radiators. Not all 7 rooms give off this annoying hissing sound when the furnace is running, right now 3 of the rooms hiss like crazy .. We have changed the valves, that seems to work for a while and then either the same room or another room will start the hissing sounds ... Is this hissing sound a normal function ? And if it is, then why don't all the radiators give off that noise ?



Residential steam heating systems typically incorporate a single pipe that leads from the boiler to each radiator. When the water boils, the steam rises into the radiators to heat them. When the steam reaches the cooler radiators, it condenses to water and drains down the pipes back to the boiler, where it is reheated.

The pressure release valves are designed to keep the steam moving throughout the system. The "hissing" is a normal function and, generally speaking, the more steam that is released, the quicker the radiator heats up. Since the escaping steam adds moisture to the air in the cooler months, it should be accepted as a positive, not negative, quality of steam systems... even though having lived with a steam system for ten years I sympathize that the noise at times can be irritating!

You didn't mention whether all the radiators had pressure release valves. If the non-hissing radiators don't have them, that would explain the lack of hissing. If they do, the valves may be malfunctioning. Generally speaking, the adjustment and/or size of the pressure valves affects how much hissing each radiator produces. Radiators on upper floors and radiators that are further from the boiler are adjusted to release more steam to compensate for the increased condensation due to the distance from the boiler. Since these distant radiators take longer to heat up, they also take longer to begin hissing.

If you haven't, you should have a plumber or HVAC service person check over the furnace to be sure everything is working as it should. Sometimes minor adjustments can have a major impact of the efficiency of the system AND your comfort level.

However, as mentioned earlier, a certain amount of hissing is normal and does not in and of itself indicate any problems... except annoyance.