Many older homes in Union County still run on boilers, and plenty of homeowners aren’t sure which kind they have. It matters. Steam and hot water systems work differently, need different maintenance, and show different warning signs.
The good news is that you can usually tell in about 30 seconds. Go down to the basement and look for these four clues.
Clue 1: Look at the gauge
This is the quickest check.
- Steam boiler: The pressure gauge reads very low, usually 0 to 2 PSI when it’s running. The dial often only goes up to 15 or 30 PSI.
- Hot water boiler: You’ll see a combination temperature and pressure gauge. Pressure usually sits around 12 to 25 PSI, and the dial also shows temperature in °F.
Clue 2: Look for a glass tube on the side
A steam boiler has a sight glass. It’s a small glass tube on the side of the boiler that shows the water level, which should be about halfway up.
Hot water boilers are completely full of water, so they don’t need one. No sight glass usually means hot water.
Clue 3: Look for an expansion tank
Hot water systems need an expansion tank. It’s usually a small tank that looks like a propane tank, attached to the piping near the boiler. In older homes it can be a big horizontal tank hanging from the basement ceiling.
You’ll often see a circulator pump on the piping too. Steam systems don’t use either one.
Clue 4: Look at your radiators
Go upstairs and check a radiator.
- Steam: Usually one pipe going into the radiator and a small air vent on the side that hisses as the heat comes on.
- Hot water: Two pipes (one in, one out) and a small bleed valve near the top that you open with a key.
- Baseboard heaters (the long, low metal strips along the wall) almost always mean hot water.
Quick Reference
| What you see | Steam | Hot Water |
|---|---|---|
| Pressure on gauge | 0–2 PSI | 12–25 PSI |
| Sight glass (water level tube) | Yes | No |
| Expansion tank | No | Yes |
| Radiator pipes | Usually 1 | 2 |
| Sounds | Hissing, clanking | Mostly quiet |
Why It Matters
Once you know your system type, you’ll know what’s normal and what isn’t:
- Steam: The water level in the sight glass is important. If it’s empty or completely full, or the pressure goes above a few PSI, call a professional.
- Hot water: If the pressure climbs near 30 PSI or the relief valve drips, something needs attention.
Inspect both types once a year, before winter starts.
Still Not Sure? We’ll Take a Look.
Continental Plumbers has worked on steam and hot water boilers across Union County for more than 40 years. If you’re not sure what you have, or something doesn’t look right, one of our licensed technicians can check it, explain how your system works, and get it ready for winter.
📞 Call (973) 900-0430 or Book Your Boiler Check
Your Neighbor Plumber — We Live Here Too. NJ License #9142.
