We're in the process of remodeling our bathroom are expanding its size by capturing a few feet from a walk in closet. By doing so, we're going to be intersecting a baseboard radiator that runs on the outside wall about 4 feet of the 3 feet we want to capture. I'd prefer not to have to alter the hydronic system, so my questions are as follows: can I remove the radiator cover/reflector, wrap the pipe and fins in insulation and then build the wall over/around it? I would then build the tub platform over the then-insulated radiator in what will be the new bathroom. We intend to install radiant floor heating under the tile, so I'm not concerned about the overall heat situation in the to-be larger bathroom. Boiler system is a loop system, with the entire 2nd floor on one zone, furnace cut-out temp is set at 160 degrees in the winter.
Any thoughts/advice is appreciated.
A fin-tube baseboard is a convector, not a radiator. A boiler isn't a furnace- it's a boiler.
The amount of work it takes to strip a convector and build a wall around it is more than the amount of work it takes cut it out replace it with piping (routed out of the way of the wall construction.)
160F is above the operating temperature of gypsum wallboard.
160F is above the operating temp for radiant under tile. (Or maybe you're going low-voltage electric?)
Insulated or not the enclosed 160F fin-tube under the tub is going to heat up the tub- possibly above the operating temp if fiberglass & plastic, or above skin-damage temp if steel or cast-iron. Stripping the fins and insulating the bare pipe to at least R6 would be a step in the right direction, but no guarantee. Sheet metal as a heat-spreader place between the fin-tube & tub (in contact with neither) may still be necessary to avoid hot-spots on the tub.
160F is probably higher than is necessary to deliver the heat in a baseboard system, and you can save ~3% in fuel use for every 10F you can drop the temp. (The temp of the water returning to the boiler still needs to be 140F or above if it's oil-fired, or above 130F if gas-fired, but that can be "fixed" with some near-boiler plumbing if need be to protect the boiler yet still deliver the heat at lower temps.)
True baseboard radiator (the cast-iron type) is a far more comfortable way of getting heat into a room than fin-tube convectors at any room setpoint or heating water temp.