Hoffman 1A vs Gorton C: CFM compared

The Hoffman 1A is an adjustable radiator vent: a dial from 1 to 6 changes the orifice, so the same valve can be slow or (relatively) quick. On a one-pipe job it is the most common thing already hanging on the radiator when someone starts chasing a cold room.

“Hoffman 1A vs Gorton C” is therefore rarely a shopping question. It is “my upstairs rad is late — is a C actually faster than what is on there now?” The honest answer needs three things: the published capacity of both valves, proof the mains are not the real bottleneck, and the EDR plus runout volume that sets the required rate.

1. Is the vent dead, clogged, or the pitch wrong? A vent that has failed shut passes nothing, and no letter on the box fixes that. A radiator pitched back toward the valve holds water and spits. Rule both out before you spend money — a stuck 1A masquerades as an undersized 1A every winter.
2. Are the main vents undersized? Until the main is clear, every radiator on it is waiting for air that has nowhere to go, and the far end waits longest. This is the single most common reason one upstairs radiator “needs a bigger vent.” Size the mains in the main vent sizer and check the count against how many Gorton #2s you actually need.
3. Only then, size the orifice. Required CFM = (radiator + runout cu ft) ÷ target minutes. Pick the smallest published vent that meets that rate at your ounce column, then step up for geography if the room is far or cold. A 1A already at 6 that still misses the rate is the textbook case for a C.

Gorton D is 0.33 / 0.54 / 0.70 CFM — faster than C, and Gorton places it “where a large amount of air must be vented.” That is a specific condition, not a default. Skip the D when:

• C already meets the required rate. Buying extra capacity you do not need just moves the imbalance to a different room.
• The mains are still the bottleneck. A D on a starved main is a louder version of the same problem — and fast venting into a wet main invites hammer.
• It is the thermostat's room. Never. That radiator is the building's sensor; fill it first and the boiler shuts down while the rest of the house is still cold.

Noise is the other tell. A big orifice on a rad that does not need it whistles and spits more than a correctly sized one, and the complaint call costs more than the vent.

Time it, do not guess. Before you touch anything, fire the boiler from cold and write down the order in which radiators start to heat, plus the clock time the late one goes hot end to end. That baseline is what tells you whether the new vent did anything.

After the swap, fire from cold again and repeat. A 1A at 6 replaced by a C should visibly move the late radiator up the order. If it does not, the restriction is upstream — go back to the main vents, the supply valve, or the pitch. Two radiators that now race each other mean you moved the imbalance rather than fixing it; step the newly-fast one back down.