Six hands, one shop, fourteen winters on Griffin Drive.

I · Origin · the 2011 winter

Lars W. Treadway opened the shop in the second bay of a single-story commercial strip on East Griffin Drive in November 2011, one week before the first cold snap of that season. He had spent the previous eleven years as a journeyman plumber in Helena and then Bozeman, the last three of those on hydronic crews that retrofitted ski-town houses up the Bridger Canyon and out toward Big Sky. He had concluded two things from that work. First, that the houses being built in Gallatin Valley deserved better hydronic systems than they were getting, because the loads were being misread and the controls were being left at factory defaults. Second, that the way to fix that was to do one trade well, write every install down, and never sell anything that the binder couldn't justify.

The shop's first job was a two-zone radiant retrofit in a 1972 ranch off Sourdough Road, commissioned 2011-12-14 with the outside thermometer at –7°F. The job book opens on that page. Fourteen heating seasons later, we are still in the same bay, with two installation trucks on the lot, a commissioning kit on a rolling cart, and the same single bookkeeping system Lars set up — pen on the daily page, transcribed to the binder at the end of every week.

II · Why radiant, in this climate

Southwest Montana lives in IECC climate zone 6B across most of the valley floors and 7B at the higher elevations. The 99% design temperature in Bozeman is approximately –10°F; design temperatures in Big Sky, West Yellowstone, and Cooke City run colder. The heating season starts in earnest mid-October and extends past Mother's Day in the higher elevations. Heating degree-day accumulation at the Bozeman station, base 65°F, runs around 7,800 HDD in a normal year per NOAA's Climate at a Glance.

Hydronic radiant suits this climate for three reasons. First, the load is dominated by envelope losses with a relatively flat duty cycle — radiant systems with outdoor-reset controls modulate against that envelope load far more accurately than forced-air systems modulating against a thermostat set-point. Second, the comfort distribution from a warm floor matches the way southwest Montana houses are actually used in winter: long evenings on the floor in front of a window, mudrooms with snow-soaked boots, primary baths that double as dressing rooms before dawn. Third, the houses being built here at the scale we work on have the budget and the architectural ambition to do the system once and do it correctly, with concrete-slab pours that accommodate the tubing on the first try, not as an afterthought.

We are not zealots about radiant. There are buildings — especially small single-zone outbuildings, guest casitas under 600 sf, or pre-1900s additions where the floor cannot be opened up — where a properly-sized panel radiator or a low-temperature baseboard run off the same mod-con plant makes more sense than a radiant slab. We are happy to design those, and you'll find them in the towel-warmer and baseboard scope.

III · Load first, equipment last

Every system we design starts with a Manual J load calculation against the actual envelope — assembly by assembly, infiltration measured rather than assumed, glazing area and U-value pulled from window submittals, internal gains assigned per ACCA Manual J 8th edition. We do the Manual J in Wrightsoft Right-Suite Universal; the file is delivered to the homeowner with the submittal. Manual D follows where there is forced-air involvement (rare for us), Manual S sizes the boiler, Manual T sizes the terminal units — slabs, panel radiators, baseboards — against the supply water temperature curve we have committed to.

This sequence matters because most of the radiant systems we are called on to rehabilitate were sized backward: the boiler was specified at twice the actual load, the manifolds were specified to the boiler's flow rate rather than the slab's heat-output capacity, the loops were drawn from a generic 12″ on-center template rather than against the room's actual heat loss. The result is a boiler that short-cycles, manifolds that don't balance, and a floor that runs hot at the kitchen island and lukewarm at the windowed reading nook.

We size to the load. Then we pick equipment that can modulate down to about 25% of the design load — almost always a sealed-combustion mod-con boiler, AFUE ≥ 95%, with a published 5:1 or higher turndown ratio. Lochinvar Knight, Triangle Tube Prestige, and Viessmann Vitodens are the three plants we install most often. The picks are not loyalty — they are because their turndown, venting, and control protocols match the way we want the system to run.

IV · The binder we leave behind

Every commissioned system gets a three-ring binder, printed at a local copy shop on Tabloid stock, indexed by tab. The binder contains: the cover sheet with system summary; the Manual J/S/T calculations; the as-built manifold map and loop schedule; the boiler submittal with model number and serial; the venting diagram; the outdoor-reset curve set on commissioning day with the outside temperature stamped; the commissioning checklist initialled by the responsible technician; the warranty registrations; the maintenance schedule; the on-call instructions. The binder lives in the mechanical room. The digital twin lives on this site under the homeowner's job-book entry.

The binder is not paperwork. It is the diagnostic instrument we use when the system stops behaving — at 11 p.m. on a Sunday in January, with the homeowner saying the office over the garage is reading 64°F. Open the binder, find the manifold serving the office, walk to it, read the actuator state and the supply/return Δt, set the actuator preset, write the change on the page. The binder is what makes the trade legible to the homeowner ten years after we install the system, and to the technician we hand the call to in 2035.

V · Why we pick the brands we pick

Manifolds: Caleffi 663 and 668 series for the primary heating manifolds; Uponor ProPEX manifolds where the tubing run is long and the homeowner has elected PEX-a. Viega for the manifold-to-trunk fittings in stainless. Tubing: Uponor AquaPEX or REHAU RAUPEX, both PEX-a, both with the cross-link expansion behavior that makes a kink recoverable with a heat gun rather than a cut and a fitting.

Boilers: as named above. Circulators: Taco 00-VR or Grundfos Alpha2, both ECM, both Δp-controlled. Controls: Tekmar 256 or 274 for outdoor-reset and snowmelt; Honeywell Home RedLink for residential thermostats where the homeowner already lives inside that ecosystem. Mixing valves: Caleffi Mixcal 521 for the manifold-level mix; Tekmar 356 where injection mixing is the right answer.

None of the brands above pay us to specify their parts. They earn the spec by being good at the job, by having a U.S. distribution network we can buy from on a same-day basis (we order through F.W. Webb on the Bozeman branch), and by publishing submittals and IO manuals that are unambiguous. We deviate from these picks on the rare occasion that the project demands it — for example, when a homeowner specifies a German cast-iron panel radiator from Runtal because the architect drew it into the elevation. We then design the system to make that radiator perform correctly at our chosen supply water temperature.

VI · Snowmelt, honestly

Driveway and walkway snowmelt is the most-asked, second-most-expensive scope we install, and the one where homeowners get the most surprising news. The first surprise is that 100 BTU per square foot is the minimum design load for southwest Montana, and 130–150 BTU/sf is what we actually specify for driveways at the elevations we work on. The second surprise is that the snowmelt plant must be at least as big as the house heating plant, and is almost always larger. The third surprise is that running it costs money in BTU and electricity per snow event, which is not trivial over a heating season.

We design snowmelt to ASHRAE Handbook Applications Chapter 51 (Snow Melting and Freeze Protection), which gives wind-corrected load tables for U.S. cities. We size for class III idling-on melt — the system is on at idle through the heating season and ramps up at the first detection of snow on the slab. We use mixed propylene glycol at 30–40% concentration; the loop has its own circulator, sensor pair (slab + outdoor), and a Tekmar 654 snow-melt control. The plant is either a dedicated mod-con boiler or a shared boiler with hydraulic separation, depending on the homeowner's budget and the load profile.

We will tell you when snowmelt is the wrong answer. For a 30-foot walkway from the garage to the front door, an under-roof heated mat from WarmlyYours or Warmup on its own line is often the correct scope, and we will refer you to an electrical contractor who can do that work. We do not install electric snowmelt.

VII · What we read at the shop

The reading shelf above the workbench: Modern Hydronic Heating by John Siegenthaler (Cengage, 3rd ed., 2011) — the standard reference, dog-eared past the index. Dan Holohan's Pumping Away and The Lost Art of Steam Heating for the rehab work. The current and last four issues of Caleffi Idronics, every issue of which is free and which we recommend to architects who want to understand what we are doing. The ASHRAE Handbook: HVAC Systems & Equipment, and Applications. Plumbing & Mechanical magazine (pmmag.com), which we read for the labor-market and code-trend reporting more than the product reviews.

We are members of the Radiant Professionals Alliance (membership #2614, active since 2015) and the Plumbing-Heating-Cooling Contractors Association. We are licensed by the Montana Board of Plumbers (Master Plumber: PLM-MR-04217, Lars W. Treadway; Hydronic-Specialty Endorsement: HYD-22-1004) and bonded to the state's required threshold.

VIII · What we promise · what we don't

We promise to design from a real load calculation, to install to the design, to commission against the actual outside temperature on commissioning day, to leave the binder, and to answer the phone for the systems we built — at 11 p.m. on a Sunday in January, at 03:15 on a Tuesday morning in February, at any other hour the system asks for attention. We promise to publish what we do, to credit the people who do the work, and to write the bad days down with the same precision as the good ones.

We don't promise to be the cheapest hydronics shop in the valley — we are not. We don't promise to deliver in eight weeks for a system that needs sixteen weeks to be designed, sourced, installed, and commissioned correctly. We don't promise to install a brand the homeowner picked from a catalog if we don't trust it to perform at –20°F in February. We will say no to those things, kindly, in writing.

Read the scope next, or the job book if you want the proof, or the colophon for every reference cited above with verifiable links.