Coil versus exchanger tank for baseboard loop

No Coil is needed.

Tried and true hot water loop for base board heating from a steam boiler.

See attachment

Jake

Without an HX, the loop is essentially an open system and needs components designed for an open system, correct?

@jimb245. Is the baseboard above or below the boiler? If above, then use a coil. I have successfully used the other method but the coil is close to foolproof. 

I give up. But don't ask me to install or approve an open system of this type.

seems the elevation to the upper most radiator or fin tube above the water line X .433 put that upper system under a negative pressure, at least when circulator is not running, so then boiling point is determined by that negative pressure?
This vapor pressure graph shows that any condition below the curve, water boils.

Not sure if a steam boiler is considered an open system like the outdoor wood furnaces which have a vent hole in them

There is one minor consideration with systems of the sort being advocated by some here: the pump. If the vacuum is broken in the elevated portion of the system -- and it will be -- then the pump for the system must be chosen to be able to develop enough head to refill the system, not simply to circulate the water around a closed system as we usually do. For example -- the Taco 007e, a rather common pump these days, has a shutoff head of 10 feet. It will not be able to fill the system if the highest point is more than 10 feet above the boiler water line -- i.e. anything but a one story and basement ranch. A pump with a greater shutoff head must be provided. This is unlikely to be the best pump for circulating...

optimist

ethicalpaul said:

If the vacuum is broken in the elevated portion of the system -- and it will be -- then the pump for the system must be chosen to be able to develop enough head to refill the system

In Dan's article I linked above, it explains that you can fill the system with a garden hose if your pump can't do it.

What will break the vacuum (allow air in) to the elevated system? Do you mean like a valve or pipe failure, or something more common?

Pick your poison. First -- and perhaps most important -- remember that it is common for leaks to be selective: that is, they may appear when subject to a vacuum, but not under pressure (even quite high pressure) or vice versa. This makes it much more interesting. However, to directly answer -- the problem could be from a variety of things. Most common would be a valve packing. Another could be a valve seat, such as a bleeder -- but to be fair, those are usually selective the other way: they will leak under pressure, if at all, but nut under a vacuum (one of the more common devils would be a bleeder which isn't (or can't be) quite shut tight). Small leaks in threaded fittings are usually visible and usually aren't selective -- but it takes much less of a leak to cause a loss of prime than it does to cause a puddle on the floor. Many types of fittings which depend on rubber gaskets or o-rings are only intended to really seal one way -- but those are rare in heating and plumbing (nut uncommon, though in hydraulics or fuel supply).

Outright failure of something would be much rarer -- and more obvious.

Typically the piping for that system is type L copper with soldered or brazed joints.

Before the system is put into operation a pressure test is commonly done to assure there are no leaks in the system.

The two ball valves used for a shut off must be at the lowest level of the boiler section. These valves can be shut off at the end of the heating season, this assures that the prime or columb of water does not drain.

Additionally, these valves must be shut off when the boiler is drained for service.

System installed is much cheaper than using heat exchangers and coils.

Jake