Could you disconnect 2 radiators for floor finishing? Me: "sure"

Double D

I'm sure the installers were laughing when they connected this radiator. Wait till someone tries removing this one. Left hand thread on bottom of the valve, right hand thread on the radiator side. 3rd floor, No Union.

Steamhead

That was probably installed in the mid to late 19th century. The nipple between the valve and the rad probably has a left-hand thread at the valve end.

Notice that on the right side of the grille on the top, it says the rad was made by the H.B. Smith Co. Not sure if the rad itself is a pipe or column type. Irlbacker & Davis was the installing contractor- in those days, as now, if you buy enough they will put your name on them. I've seen contractors' names on old boilers, but that's the first time I've seen one on a rad.

Steamhead

Found a couple mentions of Irlbacker & Davis:

https://www.buffalorising.com/2012/09/city-living-504-washington-street/

https://www.buffalorising.com/2017/10/95862/

http://www.buffaloplace.com/PopupLeaf/HollingPlace/57

And last but not least, a patent for a beer faucet that was assigned to the owners of that company:

https://patentimages.storage.googleapis.com/2b/12/2d/705a18a884ab61/USRE6394.pdf

Double D

Here is the radiator. You are correct, the nipple has a left hand thread on the valve end. This is the only rad in the house installed this way.
Irlbacker & Davis went out of business roughly one year after this house was built.
Very interesting history. The initial thought was they were the manufacture but it makes sense that they were the installers. I didn't notice the HB Smith name until you pointed it out.

Steamhead

That's a Reed radiator. You'll find a pic of one in Chapter 1 of Lost Art. I'm guessing 1870s, since IIRC there was a financial panic around then, which may have sunk I&D.

How about the other rads in that house? And is that a pipe coming out of the floor to the right of the rad, with a manual air vent on it?

Double D

No other pipe coming out if the floor on the right. The rust stain at the bottom right of the rad is from the old vent leaking before I put the Gorton in last winter.
There are 4 more radiators like the one pictured, 2 Niagara window seat radiators and 5 gold pin floor heat exchangers with ductwork leading to 1st and 2nd floor registers.

Steamhead

The Gold indirect rads were also made by Smith. Niagara sounds like National Radiator Co, these may have been put in later.

Double D

The Gold Pin are the one pictured on page 106 in Dans EDR book. The Niagara rads do appear to be an afterthought. The 2nd floor Niagara never heated in the 30+ years the owners have been there. After moving the rad vent to the opposite side of the supply valve and venting the mains, the radiator worked fine.

Steamhead

Double D said:

The Gold Pin are the one pictured on page 106 in Dans EDR book. The Niagara rads do appear to be an afterthought. The 2nd floor Niagara never heated in the 30+ years the owners have been there. After moving the rad vent to the opposite side of the supply valve and venting the mains, the radiator worked fine.

And now you're their hero!