Most DIY radiant systems (including Radiantec's cookie-cutter designs) based on tankless water heaters are insanely over pumped and over-fired resulting in excessive cycling. With low thermal mass radiation such as staple-ups or WarmBoard etc cycling is going to be worse than with a radiant slab or radiators that have some water volume to work with.
The first order of business is to get a handle on the design heat load. It's possible to measure the heat load reasonably accurately using wintertime fill-ups and weather data between fill-ups on your existing hot air system using
the methods outlined here. (Take a free trial subscription to read the details.) If you are willing to share your fill-up dates and amount, thermostat settings, and a ZIP code I can run that napkin math on the forum here. You can use Bangor's 99% temperature bin of -2F as the design temp, or maybe -5F, but not any colder than that (yes, I know it gets quite a bit colder than that, but less than 1% of the hours in a year.) Upsizing the output of the system by more than 20% from the load at the 99% design temp leads to more cycling and lower efficiency, for essentially a zero uptick in comfort.
A typical reasonably tight 1150 foot 2x4/R13 house with clear glass double-panes over a 1150' full basement (not a walk-out), with NO foundation insulation will come in around 25-30,000 BTU/hr, or as low as 20,000 BTU/hr if the basement walls are tight and fully insulated. A tight 2x6/R19 with low-E windows and an insulated basement would come in under 20,000 BTU/hr. But run your fuel use numbers (wintertime use only) against heating degree-days as a sanity check. If you are on a regular fill-up service that stamps a "K-factor" on the billing slips, a few wintertime K-factors is enough information to put firm bounds on the potential heat load.
I'll wait for the load numbers rather than chase down any number of potential dead-end paths.