Slab floor radiant heat might have a leak

[barnowl]

Did one job just like this one.

The lady of the house complained when it was done because she could hear the tic-tick-tick when the fin tube was heating up and expanding.

[Bob10]

From above: 


I don't think a heat pump will work here, as it gets too cold.  Though electric resistance elements would have to be used as backup.  And a heater put in the boiler room, since the water main will freeze if it isn't kept warm.  I did, once, when it went well below zero for a week a few years ago.

If I were you I would look at forced air.  As for cathedral ceilings there is usually an open space between that and the roof out here no idea about where you are.  Good chance you can pull some flex ducting into the area if you have that gap I am talking about

[TDKPE]

. . . no idea about where you are. 

Rochester, NY.  Land of The Long Gray (gallows humor for "normal winter").

[barnowl]

If I were you I would look at forced air.  As for cathedral ceilings there is usually an open space between that and the roof out here no idea about where you are.  Good chance you can pull some flex ducting into the area if you have that gap I am talking about

Only if he wants AC too.

Otherwise, fin tube radiation.

No equipment to buy, install, or wire.

And no ductwork.

[Bob10]

Only if he wants AC too.

Otherwise, fin tube radiation.

No equipment to buy, install, or wire.

And no ductwork.

Forced air no water to freeze

[CLETUS]

Only if he wants AC too.

Otherwise, fin tube radiation.

No equipment to buy, install, or wire.

And no ductwork.

Forced air no water to freeze

Retrofitting for ductwork is generally a PIA in the northern climates unless you have an unfinished basement. I know someone going through this, they are adding a couple mini-splits as an alternative.

[blackhat]

Where to start?  The feed water valve was closed for 2 reasons.  If anything in the boiler room leaked, it would prevent catastrophic flooding and it will let you know if you get an in slab leak as it quits working.  Secondly, it protects the rest of the water system including the city mains from glycol contamination in the event of a reverse flow situation like a broken city main.  Glycol, great stuff but......  at low concentrations, below 30%, it can turn acidic.  Really bad news with old copper.  Annual or more frequent testing and adjustment of fluid chemistry is highly recommended.  Fresh feed water has dissolved oxygen in it.  A tight system, that oxygen will react and caused corrosion but it stops as the oxygen is depleted.  Adding fresh water introduces more oxygen into the system, more corrosion.  The expansion tank is there to maintain constant system pressure as  the fluid is heated and cools.  

I haven't found a Stop leak product that works in hydronics.  A retrofit to baseboard may be your best answer.  Doorways can be problematic.  Return lines can be run in the same cabinet as the fin tube to help get around that.  Plan for air vents in your layout.  Give a shout if you have any questions.

[measure once cut remeasure]

If you really didn't want baseboard, could you pull up whatever flooring is in place.
Then put down the plywood material that has groves cut into it, that radiant pex fits into.
Hardwood or tile over the plywood. This would be more expensive than baseboard.