Endless hot water, sized for a Denver winter
Tankless Water Heater Installation in Denver, CO
A tankless unit is only as good as its sizing and its gas supply. We size to January inlet temperatures, not the brochure.
- Navien, Rinnai, Rheem, Noritz, Takagi
- Gas line and venting handled
- Annual descaling plans
- Wall-mount frees up floor space
Tankless water heaters do two things very well in Denver homes: they never run out, and they reclaim the floor space a 50-gallon tank was eating in a small bungalow basement or a Highlands row home. They are also the installation most often done badly, because a tankless swap is not a swap — it is a gas, venting and water-piping project with a heater at the end of it.
The single most common failure we are called to fix is an undersized installation: a unit that performs beautifully in September and disappoints every January. The reason is inlet water temperature.
Why Denver sizing is different
A tankless heater is rated by temperature rise at a given flow. Incoming municipal water in the Denver metro sits in the mid-to-high 50s Fahrenheit in late summer and drops into the low-to-mid 40s by January. To deliver a comfortable 120°F shower, the unit must raise winter water by roughly 75 to 80 degrees — not the 45-degree rise used in the marketing numbers.
| Unit rating | Summer (55°F in, 45° rise) | Winter (43°F in, 77° rise) | What that supports in January |
|---|---|---|---|
| 160,000 BTU | ~7.5 GPM | ~4.3 GPM | One shower plus a sink |
| 180,000 BTU | ~8.4 GPM | ~4.9 GPM | One shower plus a dishwasher |
| 199,000 BTU | ~9.8 GPM | ~5.4 GPM | Two showers, carefully |
| Two linked 199k units | ~19 GPM | ~10.8 GPM | Two showers plus laundry, comfortably |
If someone quotes you a 150,000 BTU unit for a four-bathroom house in Washington Park, ask them what rise they sized it for.
What a tankless conversion actually involves
- Gas supply. A 50-gallon tank burns around 40,000 BTU. A tankless unit demands up to 199,000. Most Denver homes built before 2000 have a half-inch branch at the water heater that must be upsized to three-quarter inch, and in some cases the meter needs review. This is the line item budget quotes leave out.
- Venting. Condensing units vent in PVC or polypropylene through a sidewall; non-condensing units require stainless category III. Either way the old B-vent does not get reused, and the termination must clear windows, doors, soffits and the neighbor's lot line.
- Condensate. Condensing models produce acidic condensate that needs a drain and, in most Denver installations, a neutralizer cartridge before it enters the sanitary line.
- Isolation valves. A proper install includes service valves with hose ports so the unit can be descaled annually without cutting pipe. If they are not in the quote, the installer is not planning to maintain it.
- Electrical. The unit needs a dedicated receptacle — and note that gas tankless heaters do not produce hot water during a power outage.
Scale, descaling, and why it matters more here
Denver Water's snowmelt supply is comparatively soft, which is good news for tankless heat exchangers. But hardness across the metro is not uniform — homes in the south and east suburbs drawing from Denver Basin groundwater run considerably harder, and any hardness at all deposits inside a tankless exchanger because the water is heated rapidly across a very small surface.
Scale shows up as a slow decline in flow rate, temperature swings during a shower, and eventually a flow or overheat error code. An annual descale with a pump and food-grade solution through the isolation valves takes about an hour and restores the exchanger. We include the first year's descale with every tankless installation and offer annual plans after that. If your home is on harder water, a scale inhibitor or softener ahead of the unit pays for itself.
Honest trade-offs
We install a lot of tankless units, and we talk about as many people out of them. Where they win: households that genuinely run out of hot water, homes short on space, owners staying long enough to earn back the premium over an 18–20 year life, and second-home or rental situations where standby loss is wasted.
Where a good tank still wins: modest hot water demand, an electric-only home with no gas at the appliance, a short remaining ownership horizon, or a budget where the difference between a $1,900 tank and a $5,500 conversion is the whole decision. There is also the cold-water sandwich — a brief cool slug when a fixture cycles off and back on — which a small buffer tank or a recirculation loop solves, but which surprises people who were not told about it.
Frequently asked questions
How much does a tankless water heater cost in Denver?
A straightforward installation where gas and venting already suit runs about $3,600–$4,800 installed. A typical conversion from an atmospheric gas tank — including gas line upsizing, new venting, condensate and isolation valves — generally lands between $4,200 and $6,800. Two linked units for a large home run higher.
Does a tankless water heater work at Denver's altitude?
Yes. Most current models are certified for installation well above 5,280 feet; some require an altitude setting change in the control board or a different orifice above a certain elevation, which we handle during commissioning. What altitude does affect is combustion tuning, so the unit should be checked with an analyzer after install.
Do I need a bigger gas line for a tankless heater?
Usually. A tankless unit can demand four to five times the gas of the tank it replaces. Most pre-2000 Denver homes need the branch upsized to three-quarter inch, and the whole run is sized by length and total connected load. We calculate it rather than assume it.
How often does a tankless water heater need descaling?
Annually on the Denver metro's typical water, and more often if your home is on harder groundwater or you run the unit hot. Skipping descaling is the fastest way to void a heat exchanger warranty.
Will a tankless heater work during a power outage?
No. Gas tankless units use electronic ignition, a fan and a control board, so they stop when power does. If outage resilience matters, an atmospheric standing-pilot tank still delivers hot water without electricity.
How long do tankless water heaters last?
Eighteen to twenty years is realistic with annual descaling, and most heat exchangers carry a 12- to 15-year warranty. Without maintenance, expect closer to ten and a heat exchanger claim that gets denied.
Can a tankless unit run two showers at once in winter?
A single 199,000 BTU unit manages two low-flow showers in January if nothing else is running — roughly 5.4 GPM at a 77-degree rise. Add laundry or a third fixture and you want two linked units.
Cold shower this morning? We can be out today.
Tell us what the heater is doing and we will give you a straight answer on the phone — repair, replace, or wait.