Lone Tree sits at roughly 5,900 feet, and gas-fired appliances, tankless water heaters included, are derated for combustion efficiency at that elevation. A unit rated for a certain flow rate and temperature rise at sea level won't perform the same here unless it's sized, or the installation is adjusted, with altitude accounted for.
Tankless units also give back real square footage, which matters in a finished basement where every mechanical closet is space that could otherwise be living area. The tradeoff is that they're less forgiving of hard water scale on the heat exchanger than a standard tank, so a properly sized system with a maintenance plan matters more with tankless than it does with tank.
Retrofitting an existing home for tankless sometimes means upsizing the gas line, since tankless units generally draw more BTU at peak demand than the tank they're replacing. We check the existing gas supply capacity as part of every tankless quote so there are no surprises once installation is underway.
Altitude and hard water change the math here
Front Range water supplies, drawn from a mix of mountain runoff and groundwater sources depending on the district, run moderately to very hard in most of the metro area. Scale builds on a tankless heat exchanger faster than it builds in a large tank, which is why manufacturers specify a descaling interval and most warranties require it to stay in effect.
Signs a tankless unit needs service:
Sizing it right the first time
| Consideration | Why it matters at this elevation |
|---|---|
| Altitude derating | Gas-fired units lose combustion efficiency above 2,000 feet; sizing must account for it, not just household demand |
| Venting | Correct vent length and diameter for the model, verified against manufacturer altitude tables |
| Descaling interval | Hard water shortens the safe interval between flushes compared to manufacturer defaults for soft-water regions |
The venting detail installers skip
Installation follows the manufacturer's altitude-adjusted specifications along with the gas and venting requirements in the plumbing and fuel gas codes adopted in Colorado. Skipping the altitude adjustment is a common source of underperforming tankless installs, not a defect in the unit itself.