Background
The homeowner had owned the cabin since June 2022. The cabin had been built in 2018 by a Bozeman general contractor and the hydronic system installed by a hydronics subcontractor whose identity the homeowner asked us to withhold from the public daybook entry. For three winters running, the smallest bedroom in the cabin — a 132 sf room on the north side with a single 32″ × 60″ double-pane window — had been reading 4–6°F below the homeowner's setpoint at the wall thermostat. The owners had set the bedroom's wall thermostat to 70°F and watched the displayed temperature drift to 64°F on cold nights, while the rest of the cabin held setpoint within 1°F.
The owners called us in March 2025 after being unable to reach the installing contractor. They had read about us in a Bozeman Daily Chronicle piece on local trades, asked at the front desk at Copytrade for the company that does the binders, and called the shop directly. We quoted the audit fee at $3,180; the homeowner signed the audit agreement; we scheduled the visit for the first dry day in April after the road up Bridger Canyon was reliably ice-free.
What we found
Three findings, ranked by priority.
Finding 1 · Outdoor-reset curve at factory defaults
The Tekmar 274 boiler control had its outdoor-reset curve at the factory defaults — supply 180°F at 0°F outside, 140°F at 60°F outside. For a radiant slab system in a tight 2018 building envelope, those supply temperatures are 30–40°F higher than needed at design and 25–35°F higher than needed at typical operating conditions, which means the boiler runs in non-condensing mode for most of the heating season and the system never benefits from the mod-con plant's efficiency. The boiler had been firing for seven winters at an effective AFUE more like 87% than 95%, which the homeowner's utility-bill history corroborated.
The fix is the same fix we make on every audit where this finding appears: reset the curve to a residential-slab curve matched to the building's envelope. We set 125°F supply at 0°F outside, 95°F supply at 50°F outside, return-water minimum 95°F. The change is two screen presses on the Tekmar 274; the savings, if the homeowner's pre-audit baseline is reliable, will be approximately 18–22% reduction in annual gas consumption.
Finding 2 · BR-3 actuator preset too low
The bedroom complaint resolved against the loop schedule at the M-3 manifold. The Caleffi 663 manifold has built-in micrometric balance valves and built-in flow meters; the bedroom's loop (M-3 port 4, ~190 ft long) was reading a flow rate of 0.31 gpm against a design flow of 0.42 gpm. The neighboring living-room loop (M-3 port 1, ~220 ft long) was reading 0.51 gpm against a design flow of 0.46 gpm. The actuator preset on M-3 ports 1 and 4 were set to the same default, but the loops are different lengths and the longer loop needs the larger balance-valve opening to achieve its design flow.
The fix: open the balance valve on port 4 by 1.5 turns, close port 1 by 0.5 turns. Re-measure at the manifold. Flow on port 4 stepped from 0.31 to 0.46 gpm; flow on port 1 stepped from 0.51 to 0.44 gpm. Re-measure 45 minutes later (allowing the slab to come up): bedroom thermostat reading 70.2°F at 70.0°F setpoint, living room 70.0°F at 70.0°F setpoint. The bedroom complaint should be resolved.
Finding 3 · Cracked auto-air-vent on M-2
Visual inspection of all four manifolds during the audit identified a hairline crack on the auto-air-vent body on the M-2 manifold's return header. The vent had been weeping a small amount of water onto the catch pan below — about 1–2 drops per day at this season, more in deep cold. The pan was about 30% full. This is not an emergency but it is a service item; the auto-vent will eventually fail more dramatically and the homeowner will get a wet floor.
We did not have a replacement Caleffi 558 in the truck (we keep stock of the manifold itself but not the individual auto-vent). The recommendation is for the installing contractor to replace under their workmanship warranty; failing that, we will come back with the part at the homeowner's request for a separate trip charge of $480.
The deliverable
Two weeks after the visit (delivered 2025-05-02), we returned a three-ring binder to the homeowner containing: a one-page executive summary; the three findings as written above; the as-found and as-left data tables; printout of the Tekmar 274 reset-curve change with before/after screen captures; the manufacturer's literature for the Caleffi 558 auto-vent; and a one-page PDF summary the homeowner could hand to the installing contractor. The same PDF was emailed to the homeowner so they could forward it directly.
Follow-up
The homeowner reported back via email on 2026-02-08, after the cabin had been through one complete heating season since the audit: bedroom holding setpoint consistently, gas consumption down approximately 19% against the prior winter (winter-vs-winter HDD-normalized via NOAA data), auto-vent replaced by the installing contractor under warranty in October 2025. The audit was successful; the long relationship with the original contractor is intact; we have not been back to the cabin and don't expect to be.
Read across
Read the commissioning & loop balancing scope for the audit framework, the manifold sheet for what we measured at, and the about page chapter IV for the binder philosophy.