What it actually looks like to replace an old boiler with a tankless combi unit

Radiant heat is common in older Santa Fe homes, and so are the boilers that run it. A lot of those boilers are twenty, twenty-five years old, still limping along but showing their age: pilot issues, uneven heat across zones, a domestic hot water tank that's rusting from the inside. At some point the question stops being whether to replace the boiler and becomes what to replace it with. One option that comes up often is a tankless combi unit, which handles both the radiant heating loop and the household hot water from a single wall-mounted appliance instead of a boiler plus a separate hot water tank.

What a combi unit actually does

A combi boiler heats water on demand rather than storing it in a tank. When a hot water tap opens, the unit fires and heats water as it flows through, instead of drawing down a stored supply that has to reheat afterward. The same unit also feeds the radiant heating loop that runs through the floor or baseboard. One appliance, two jobs, no separate storage tank taking up floor space in a mechanical closet or basement.

What actually happens during the swap

This is not a same-day appliance swap. It's a real mechanical project, and one of our own customers put it well after we did exactly this on his 22-year-old boiler: he needed a bid on replacing it with an up-to-date tankless combi unit that would heat both his domestic water and run his radiant heating system, and the work involved pulling the old boiler, running new piping, and rewiring the controls, done to the standard of, in his words, a true professional journeyman, with pipes neatly installed and wiring neatly run.

In practice that means a few distinct stages. The old boiler and its associated piping get disconnected and removed. The radiant loop gets inspected and reconnected to the new unit's manifold. Venting gets run to match the new unit's requirements, since a combi unit vents differently than an older atmospheric boiler often did. Controls get rewired so thermostats and zone valves talk to the new equipment correctly. None of that happens in an afternoon, and a contractor who tells you it will is skipping a step somewhere.

What to expect while it's happening

Heat and hot water are both offline for at least part of the job, which is worth planning around, especially in winter. A well-run job sequences the work so the gap is as short as possible, and in cases where the radiant loop is complex or the old piping needs real rework, the project can run a few days rather than one. That's not a sign something went wrong. It's the nature of tying a new appliance into an existing heating loop that was designed around a different piece of equipment decades ago.

• Old boiler and associated piping removed
• Radiant loop inspected, reconnected, and pressure-tested against the new unit
• Venting and controls rewired to match the combi unit's requirements

Why this is worth doing before the boiler fails outright

A boiler that's still limping along gives you the luxury of scheduling the conversion on your own timeline, in shoulder season, rather than in an emergency in January with no heat and no hot water while parts get sourced. If your boiler is old enough that you've started keeping a mental list of what it's done wrong this year, that's usually the sign it's worth getting a real look and a real bid rather than another repair.

We handle these conversions regularly across Santa Fe and Los Alamos counties, and every job comes with a two-year workmanship warranty on top of manufacturer coverage. If you want to know what a conversion would look like for your specific house, call us at (505) 469-1421 and we'll come out for a free in-person estimate within two business days.