Window IQ · Spec intelligence for architects
How much is your current window spec really costing your client?
For new-build projects. Compare typical North American double & triple-pane windows against LuxHaus European systems across the five metrics that matter: thermal performance, acoustic isolation, solar control, service life, and projected HVAC bill. Adjust for your project, share the numbers with the client.
Step 1 · Project ParametersDefine the Build
Fine-tune window specs
Architects — override any parameter with your project's actual glazing package
Current window (North American spec)
Air leakage around sash and frame adds real heat transfer beyond the U-value. LuxHaus European systems tested to EN 12207 Class 4 are assumed effectively airtight (1.00× baseline).
LuxHaus window (European spec)
NFRC steady-state uses textbook U-value × HDD math. Real-world bills run much higher due to HVAC part-load inefficiency, duct losses, thermostat creep near cold glass, and non-linear infiltration in extreme temperatures. Multiplier auto-sets by climate on region change (cold = 2.0–2.5×, mixed = 1.5×, warm = 1.2×) based on NRCan, NREL, and LBNL retrofit studies. Override anytime.
Step 2 · The Performance GapWhere LuxHaus Moves the Needle
Side by SideFull Specification Delta
| Metric | Current Spec | LuxHaus System | Difference |
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Step 3 · The Long-Term Picture25-Year Outlook
Annual HVAC Bill Savings
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Projected heating & cooling bill reduction for this new build. Compares the full HVAC operating cost at each window spec, holding the rest of the envelope equal.
25-Year HVAC Cost
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vs. $— with current spec
Replacement Cost Avoided (inflated)
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Total 25-Year Advantage
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Combined energy savings + avoided replacement cost over 25 years. Excludes resale value, occupant comfort, and health benefits.
Opportunity costWhat if your client invested the savings instead?
If both savings streams — annual energy savings and the avoided replacement cost — were invested in an S&P 500 index fund at the historical 10% average annual return. Annual savings compound across 25 years; the avoided replacement lump sum compounds from when it would have been spent through year 25.
S&P 500 · 25 yrs · 10%
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Annual savings + avoided replacement, compounded · nominal, pre-tax
How this is calculated (new-build methodology): This calculator projects the whole-home annual heating & cooling bill for a new construction project with each window spec, holding the rest of the envelope equal (code-compliant walls, roof, floor, doors). Step 1 — Direct window physics: Conductive heat transfer (U-value × glazing area × HDD+CDD × 24 hr ÷ 3,412 Btu/kWh, cooling divided by COP 3.5) plus solar heat gain (SHGC × climate-specific solar irradiance from NREL NSRDB × cooling-season days ÷ 3,412 ÷ COP 3.5). This is the NFRC-standard methodology used by ResCheck, REM/Rate, and PHPP. Step 2 — Scale to whole-home HVAC bill: Windows contribute a climate-dependent share of total HVAC load in a new code-compliant home: 55% in subarctic (windows + associated infiltration dominate envelope losses at extreme ΔT), 45% in cold, 37% in mixed, 40% in warm (solar gain through glazing drives cooling). These shares are sourced from NRCan Canadian new-build envelope studies and DOE Building America data. The window-attributable cost is scaled up by dividing by this share to reflect the full HVAC bill. Step 3 — LuxHaus systemic bonus: LuxHaus European windows deliver whole-home HVAC benefits that pure window heat-transfer math cannot capture: (a) airtight EN 12207 Class 4 assembly reduces whole-house infiltration, (b) warm interior glass surfaces eliminate radiant-discomfort thermostat creep (2–4°F setpoint drop), (c) stable envelope enables right-sized HVAC to run at high-efficiency part-load. A climate-dependent systemic discount is applied to the LuxHaus HVAC bill: 10% subarctic, 7% cold, 4% mixed, 5% warm. Modeling method (real-world multiplier): Applied to both specs before the whole-home scaling — auto-set by climate on region change with user override. Options: 1.0× NFRC steady-state (textbook, most conservative); 1.2× warm-climate typical (PNNL AC part-load); 1.5× mixed-climate typical (DOE Building America); 2.0× cold-climate typical (LBNL cold-climate research); 2.5× subarctic electric-heat verified (NRCan retrofit studies). Air infiltration: NA current-window conductive cost is multiplied by an NFRC AL-rating factor (1.05× tight → 1.40× leaky). LuxHaus tested to EN 12207 Class 4 is baseline airtight. Scope: This is the heating and cooling operating bill only. Hot water, lighting, appliances, plug loads, and other electrical use are excluded — those are the same regardless of window spec. Replacement cost = competitor's quoted price × 1.03N, where N is the current spec's lifespan (3% inflation); included in the 25-year total only if N ≤ 25. S&P 500 combines two compounded streams: (a) annual HVAC bill savings invested each year for 25 yrs at 10% nominal (future value of ordinary annuity), plus (b) the inflated replacement lump sum compounded from year N through year 25 at 10%. Architect-tunable ranges: Ug from 2.8 W/m²K (single-pane) to 0.4 W/m²K (top-tier PHI); SHGC from 0.11 to 0.60; STC from 25 to 52+.
Ready to spec LuxHaus on your next project?
Submit your plans and we'll return a free estimate within 5–7 business days. Factory-direct from Germany, Italy & Poland. Passive House suitable. No showrooms, no middlemen.