The 30-Ton Rooftop Nobody Could Read

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The call

This one's a church — New Friendship Baptist Church, on East Eager Street in Baltimore. The congregation goes back to 1933, and the building sits in the Old East Baltimore Historic District. They called about the heat and air, so I went up to see what was running the place.

What's up top is a big gas/electric package unit — heat and cooling all in one cabinet, sitting on the roof. Off to the side there's a second package unit and a clean view of the city skyline. Classic commercial setup: put the whole machine on the roof, run the duct down into the building, keep it out of the way.

Thirty tons of old iron

This is a 30-ton unit. For anybody not in the trade: a "ton" of cooling is 12,000 BTU per hour, so 30 tons is 360,000 BTU/hr of cooling capacity — roughly the load you'd put on a building this size. Gas-fired heat on one side, electric cooling on the other, packaged together.

It's a combination cooling and heating unit, and it has clearly been up there a long time. The cabinet's weathered, the panels are sun-baked, and somewhere along the way somebody went over the whole thing with paint.

A 30-ton machine that's been up there long enough to lose its own name.

The plate I couldn't read — and I'm not going to pretend otherwise

Here's the honest part, and it matters. I wanted a model and serial number off this unit. I went looking. There isn't one left to read.

What's actually legible up there is a service sticker — a phone number, 661-7937, left by whatever contractor was maintaining it. That's a service company, not the manufacturer. And there's a CSA ratings placard that's been painted over — you can make out "Combination Cooling and Heating Unit" and the line telling you to "refer to the manufacturer's nameplate," but the actual nameplate with the model and serial isn't there to refer to.

So I'm not going to slap a brand on this unit that I can't read off the metal. I checked it hard, frame by frame. The verifiable facts are: 30 tons, gas/electric, combination package unit, very old. The brand and model are gone. When I tell you what something is, it's because I can read it or measure it — not because it sounds good.

So how do you spec a unit you can't read?

This is the real lesson, and it comes up more than you'd think on old commercial jobs. When the nameplate is gone, you don't guess — you measure and you reason:

• Physical size and tonnage: the cabinet dimensions and the existing curb tell you the footprint and the rough capacity class. Thirty tons is thirty tons whether or not you can read the sticker.
• The curb and the duct openings: these dictate what a replacement has to mate to. A new unit either matches the curb or it gets a curb adapter.
• Gas and electrical service: what's feeding it now sets the envelope for what can replace it.
• The building load: you don't inherit the old sizing blind — you confirm it against the actual space.

The missing nameplate doesn't stop the job. It just means the work is in the field measurements, not in copying a number off a tag.

Next: what was hiding in the basement

The rooftop was the reason for the call. But the better story was downstairs — a whole second system the rooftop unit had nothing to do with, tucked away in the mechanical room. That's Part 2.

Read Part 2: The Hidden Split System →

Sources & honest notes: Church history and location from the Old East Baltimore Historic District; tonnage-to-BTU conversion is standard (1 ton = 12,000 BTU/hr per the U.S. Department of Energy); equipment listing/safety placards from CSA Group. I've kept this to what the footage and the metal actually support: it's a 30-ton gas/electric combination package unit, and the manufacturer nameplate is painted over and not legible — so I'm naming no brand on this one.

About the author: Gregory Frazier is a heavy commercial HVAC estimator working Maryland, Pennsylvania, Delaware, Virginia and Florida for 25+ years. Read his story →