barometric damper?

if you have more draft than the boiler spec calls for, then yes it would be a good choice.

Yes.

A Dwyer Model 25 Mark II is a good one.

(Not 100% sure I got that 100% right - that's from a poor-at-times memory).

At the risk of hijacking the thread a little, do units with closed-loop stack temperature control, e.g., Fröling, require a barometric damper?

How would that compare with a digital model, assuming you would only use it to dial in the barometric damper and occasional other readings?
http://www.amazon.com/Dwyer-Series-...UTF8&qid=1403095193&sr=8-9&keywords=manometer

That digital meter has a 40" range. Recommended drafts for boilers are about 1/20". I don't think you could count on the accuracy of the meter to give you a measurement that would mean anything useful.

Chimney draft meters are pretty sensitive devices. They measure too narrow a range to be useful for much else.

I think you can order these right from Dwyer. They can be a little cumbersome to work with due to handling the fluid and having to level the gauge before use but they are cheap and highly accurate. Check out the model MarkII 25. Looks like it lists for $34 and will do exactly what you need.

http://www.dwyer-inst.com/market/hvac/Product/Pressure/Manometers/Stationary/SeriesMarkII

I use this one.

It's cheap enough so you can just mount it permanently near the boiler(s). Even 3" is high though; I suppose that's the lowest range of the Dwyers?

That's the same one I have & was trying to recommend. Mine has been permanently mounted since September 2012. Simple & reliable, and seems to be quite accurate too. Took just a little bit of fiddling, and a little bit of spilled red stuff, to get it zeroed the first time but I haven't touched it since. When burning in the winter I'm pretty steady right at 0.1".

My manometer probe is about 6" from the back of my boiler, then my barometric damper is a couple feet downstream of that, followed right away by a cleanout T that sends things up out my chimney - except for a bit of ash that doesn't make it up & out & therefore settles in the bottom of the cleanout.

The draft probe needs to go in between the baro and the stove. Preferably in the middle of a straight run of pipe

I only put it there because it was a after thought and i would hav had to buy more high $$$ pipe to make it work. That being said it works great where it is and it stays very clean.

Did not put one in..works fine