Scope of work
A new-construction custom home on a 14-acre parcel up Bridger Canyon Road, at 5,240 feet elevation, built by Heritage Builders MT to drawings by Pearson Design Group. Two stories of timber-frame over a full basement; primary suite and guest suite on the first floor, three additional bedrooms on the second; a 2,400 sf great room with a south-facing window wall; mudroom with snow-melt mat below the bench; primary and guest baths with hydronic towel warmers; a 730 sf front-approach driveway and walkway with glycol snowmelt.
Headwaters scope: complete hydronic heating system, snowmelt at the front approach, mechanical room piping and equipment, ventilation routing for the boiler vent, condensate handling, commissioning, binder leave-behind. Excluded from Headwaters scope: forced-air ventilation (ERV by separate contractor), domestic hot water (indirect tank sized and installed by Headwaters but DHW distribution and fixtures by general plumbing), wood-stove install, snowmelt at the rear deck (declined by owner).
System summary
Heating load at the 99% design temperature of –14°F: 148,000 BTUH per Manual J calculation against the as-built envelope (R-30 walls, R-49 attic, U-0.28 glazing, ACH50 of 1.4 measured by blower-door 2024-10-30). Snowmelt load: 730 sf × 145 BTU/sf = 105,850 BTUH at the slab. Total peak combined load (rare): approximately 254,000 BTUH; we never see both peaks at once and the operating profile holds the plant comfortably within its 155,000 BTUH input across the typical heating-season hour.
Distribution: 12 manifolds — 10 Caleffi 663 (6-port and 8-port) for the heating zones, 2 Uponor ProPEX (4-port and 6-port) for the snowmelt and a smaller secondary loop in the upstairs east bedroom run. 38 loops total across the manifolds, each between 180 and 280 feet of ½″ PEX-a. Two Taco 00-VR ECM circulators on Δp control for the primary and secondary heating loops; one Taco 0011-F4 cast-iron circulator for the snowmelt at 32 gpm design flow.
The manifold map
The mechanical room is in the northwest corner of the basement, 12 feet by 18 feet, with a poured slab and an east-facing service door for boiler access. The manifolds break out as follows:
| ID | Location | Ports | Loops used | Serves | Δt design |
|---|---|---|---|---|---|
| M-1 | Mech room E wall | 6 | 5 | Primary bath slab · WIC slab | 20°F |
| M-2 | Mech room E wall | 6 | 6 | Primary bedroom slab | 22°F |
| M-3 | Mech room S wall | 8 | 7 | Great room slab | 18°F |
| M-4 | Mech room S wall | 6 | 4 | Kitchen slab · pantry slab | 20°F |
| M-5 | Mech room W wall | 6 | 4 | Mudroom slab · entry slab | 20°F |
| M-6 | Mech room W wall | 4 | 3 | Guest suite slab | 22°F |
| M-7 | Upstairs E hallway closet | 6 | 3 | BR-2 + BR-3 staple-up | 25°F |
| M-8 | Upstairs W hallway closet | 4 | 3 | BR-4 staple-up · bonus rm | 25°F |
| M-9 | Upstairs E hallway closet | 4 | 2 | Upstairs bath slab | 22°F |
| M-10 | Basement S wall | 4 | 1 | Wine cellar (TRV-only) | 25°F |
| SM-1 | Mech room N wall | 4 | 2 | Snowmelt · driveway approach | 18°F |
| SM-2 | Mech room N wall | 4 | 3 | Snowmelt · front walk · steps | 18°F |
The mechanical room layout
Commissioning record · 2024-11-12
Outside temperature on commissioning day: –4°F at 07:14 MT (system start), falling to –14°F at sunset. Building enclosed, drywall complete, finish flooring complete on first floor, second-floor finish flooring in progress in the bonus room only. The system was filled with city water, glycol added to the snowmelt loop only via the brazed-plate isolation, total system pressure 18 psi cold.
Boiler started at minimum firing rate (15,500 BTUH); combustion tested with Testo 320 at 25%, 50%, 75%, 100%; CO < 12 ppm air-free at all rates; CO₂ 9.1–9.4%; O₂ 4.6–5.1%; stack temperature 110–118°F at 25%, 138–146°F at 100%. Outdoor-reset curve set: 130°F supply at 0°F outside, 105°F supply at 50°F outside, return-water protection floor 95°F. All twelve manifolds purged loop-by-loop using the integral purge valves; Δt at each manifold measured at the trunk against the loop average; actuator presets adjusted on loops where the as-purged Δt exceeded the design Δt by more than 3°F. Snowmelt loop pressurized to 100 psi cold, glycol concentration verified at 32% via Reichert refractometer.
Building brought to setpoint over six hours; final reading at 17:42 MT showed primary bedroom at 70.2°F setpoint, great room at 69.8°F setpoint, mudroom slab surface at 78°F (target 76–80°F), snowmelt slab idling at 32.5°F surface (target idle 32–34°F), boiler firing at 36% (54,000 BTUH).
Credits
Engineer of record · Iris Cottonwood. Loop layout · Iris Cottonwood + Marlowe Krenn. Manifold install + tubing pull · Kel Begay + Marlowe Krenn. Boiler set + venting · Lars Treadway + Kel Begay. Snowmelt slab prep + tubing · Kel Begay (lead) + Marlowe Krenn. Commissioning · Wendell Pratt (commissioning engineer) + Iris Cottonwood. Binder · Halla Bjørndal. Signed off by Lars W. Treadway, MT Master Plumber #PLM-MR-04217, 2024-11-12.
Service since commissioning
Three service events to date:
- 2025-01-22 03:15 MT · outside –22°F — Service call: loop C-6, primary bath slab, reading 8°F below setpoint. Diagnosis: seized actuator on manifold M-2. Replacement actuator (Caleffi Z-One) installed from truck stock at 03:54; system recommissioned at 04:50; loop returned to setpoint by 07:00. See daybook entry.
- 2025-04-10 14:00 MT · outside 41°F — Scheduled annual service: combustion analysis (no drift); condensate neutralizer media replaced; expansion tank pre-charge verified at 12 psi (no change); glycol refractometer reading on snowmelt loop at 31.8% (within tolerance); igniter cleaned; flame-sensor inspected (no carbonization). Service sheet added to binder.
- 2025-10-17 11:20 MT · outside 49°F — Pre-season check requested by homeowner: nothing out of spec; outdoor sensor reading verified within 0.4°F of NIST-traceable reference; system enabled for heating season.
Read across
Read the radiant floor scope and the snowmelt scope for the design assumptions; the manifold sheet in the atlas for the Caleffi 663 and Uponor ProPEX product details; the January cold-snap entry for the field-call story; and the crew credits for the people named above.