Steam vs hot water radiator heat in North Jersey homes

How to tell whether you have steam or hot water heat

Start at the boiler. A few minutes in the basement will usually settle it.

• A steam boiler has a sight glass: a small glass tube on the side showing the water level, which sits partway up. A hot-water boiler is filled completely and has no sight glass.
• A steam boiler's pressure gauge reads in very low numbers, usually 0 to 3 psi when running. A hot-water boiler's gauge typically reads somewhere around 12 to 25 psi and usually shows temperature as well.
• A hot-water system has a circulator pump on the piping and an expansion tank, often a small metal tank hanging near the boiler. Steam systems need neither.

Then look at a radiator. A radiator with a single pipe and a small metal air vent on the side, often shaped like a bullet, is one-pipe steam. A radiator with two pipes and a small bleed screw at the top is almost always hot water. Two pipes with no bleed screw can be two-pipe steam, which has a trap where the second pipe leaves the radiator.

How steam heat works

A steam boiler boils water. The steam rises through the pipes, pushes the air out of each radiator through its vent, condenses back into water inside the radiator as it gives up its heat, and runs back down to the boiler. Nothing pumps it; it relies on heat, gravity and the pitch of the pipes.

That simplicity is why steam systems from a century ago still work. It is also why small things matter: a vent that will not let air out, or a pipe that has lost its slope, is enough to leave a radiator cold.

Common steam heat problems

• One radiator stays cold. Usually a clogged air vent, or a radiator valve left partly open. On one-pipe steam the valve must be fully open or fully closed; halfway traps water in the radiator.
• Banging or hammering pipes. Usually water sitting in a pipe that has lost its pitch, or a radiator tilted the wrong way, so steam slams into trapped water.
• Water spitting from a vent. Often a sign the boiler is running at too high a pressure, or that the water level is too high.
• The boiler short-cycles or the far rooms never warm up. Often the pressure control set too high. Residential steam usually needs only a pound or two of pressure; more pushes steam through slower, not faster.
• Uneven heat between floors. Usually venting: main vents in the basement that have failed, or radiator vents that are all the same size when the far radiators need faster ones.

None of these needs a new boiler. Most are a morning's work.

How hot water heat works

A hot-water boiler heats water without boiling it, and a circulator pump pushes that water through the pipes and radiators in a closed loop. Because the loop is sealed and pressurised, it also needs an expansion tank to absorb the water's growth as it heats, and a relief valve as a safety.

Hot water can be zoned easily, holds an even temperature, and runs quietly. It is also what high-efficiency condensing boilers are designed for.

Common hot water heat problems

• Radiators warm at the bottom and cold at the top. Air trapped in the radiator; bleed it at the screw until water comes out.
• Gurgling in the pipes. Air in the system, often after work has been done or the system has been drained.
• The relief valve drips, or pressure climbs high when the boiler heats. Usually a waterlogged expansion tank.
• Hot boiler, cold house. Usually the circulator pump, or a zone valve that is not opening.

Simple maintenance for each system

A little attention at the start of each heating season prevents most mid-winter calls.

• Steam: check the water level in the sight glass regularly while the heat is on. It should sit roughly halfway. If you are adding water often, or the glass looks dirty and the level bounces, have the boiler looked at.
• Steam: the low-water cut-off needs periodic flushing, as the boiler manufacturer describes. On many boilers it is a valve you open for a few seconds into a bucket. If you are not sure how, ask on the next service visit.
• Hot water: check the pressure gauge with the boiler cold. If it has dropped well below its usual reading, the system is losing water somewhere.
• Hot water: bleed any radiators that are cold at the top before the first cold week, not during it.
• Both: have the boiler serviced once a year, before the season starts.

Should you convert steam to hot water?

It can be done, and in some houses it makes sense. But it is a much bigger job than swapping the boiler. The old steam piping and radiators have to be checked to make sure they can hold the higher pressure of a hot-water system, the pipe sizes have to suit circulating water, and leaks that never mattered on steam suddenly do.

For most homes with a working steam system, the better money is spent making the steam system run properly: fixing the venting, the pitch, the pressure setting and the water level. A well-tuned steam system is quiet, even and reliable.

Which is better?

Neither, in the abstract. Hot water is easier to zone and pairs with the most efficient boilers. Steam is simpler, very durable and heats quickly. The best system for your house is usually the one already in it, working properly.

What matters more than the type is who works on it. Steam systems in particular are often misunderstood, and a lot of the noisy, uneven steam heat in older North Jersey homes comes from previous repairs done as if it were hot water.