Bleed your radiators
Annual · typically October
Why it matters
Air works its way into hot-water heating systems every year — it's just what water does when it's heated and cooled a few hundred times. The air rises to the high points, which are the tops of your radiators, and a radiator with an air pocket is cold on top and warm on the bottom: it's heating at half strength while the boiler pays full price.
First, know which system you have. Hot-water radiators have two smallish pipes and a little bleed valve at the top corner — they bleed. Steam radiators (common in pre-war houses) have one fat pipe and a bullet-shaped air vent that hisses; they do NOT bleed, and opening things on a steam system mid-season is how you get scalded. This card is for the hot-water kind.
What skipping it costs
$100–$400
A radiator that's half air is half a radiator. You compensate by nudging the thermostat, the boiler runs longer to heat the same rooms, and you quietly burn an extra $100–$400 in fuel over a winter — to heat air pockets.
Two ways to get it done
Do it yourself
You'll need: Radiator key (~$2 at any hardware store), Small cup or rag.
Do this with the system ON and warm, one radiator at a time, starting closest to the boiler:
- Feel the radiator. Warm bottom, cool top = air. Uniformly warm = skip it, it's fine.
- Put the key on the bleed valve (top corner), hold the cup under it, and open a quarter turn. You'll hear the hiss.
- Wait out the hiss and the sputter. The moment you get a steady dribble of water, close it. That's the whole job.
- Work through the house — upstairs radiators collect the most air.
- When you're done, glance at the boiler's pressure gauge. Bleeding drops pressure slightly; most systems have an auto-fill valve that brings it back to ~12–15 psi on its own. If yours reads low, mention it at your annual service.
The gurgling sound in your pipes at night? That's the air you just released. Enjoy the silence.
Hire it out
$90–$160National fair range — local labor moves this number.
There's no honest standalone service here — it's a two-minute job per radiator. If a radiator won't warm up even after bleeding, or a bleed valve is seized or snapped off, THAT's a visit ($90–$160 as part of a service call), and it's worth folding into the annual boiler service rather than paying a separate trip charge.
The thing to watch for is system confusion: a tech who starts "bleeding" a one-pipe steam system either isn't paying attention or doesn't know heating. Steam problems (banging pipes, spitting vents) are real and fixable — but the fix is pitch and vents, not a bleed key.
Ask the tech
- Is this a hot-water system or steam? Show me how you can tell.
- If you're here anyway — check the boiler pressure after bleeding, did the makeup water bring it back to spec?
Red flags you're being upsold
- A service call sold JUST to bleed radiators on a hot-water system — this is genuinely a two-minute job per radiator with a $2 key.
- Anyone 'bleeding' a one-pipe steam system. Steam radiators don't bleed — if a tech doesn't know that, end the visit.
The call
DIY, absolutely — it's a $2 key and a cup. The one exception: if you have steam radiators (one big pipe, a hissing air vent), put the key down; that's a different system and it doesn't bleed.