Water heater installation
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Tankless water heater installation: what it takes, and when it pays
Endless hot water and twenty years of service life are real. So are the larger gas supply, the new venting, the cold inlet temperatures of an Idaho winter and the descaling routine that hard water demands. Here is the whole picture before you buy.
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Get the gas and vent requirements assessed before you buy.
Sized on rise, not gallons
Cold Idaho inlet water changes the maths entirely.
Gas supply matters
Most units need more gas than a tank ever did.
Twenty-year service life
Serviceable parts and a heat exchanger, not a tank.
Descaling included
Hard water means a service valve kit and a routine.
Honest expectations
What is true, what is oversold
True: hot water does not run out. Water is heated as it flows, so a long bath followed by three showers is not a problem. For households where the last person in gets a cold shower, this is the whole argument and it is a good one.
True: it lasts much longer. Twenty years is a reasonable expectation against eight to twelve for a tank, with serviceable components rather than a single vessel that eventually rusts through. The failure mode is a repairable part, not a flood.
True: it saves space. A wall-mounted unit the size of a carry-on suitcase releases a corner of a utility room, a closet or a garage wall.
Partly true: it saves energy. There is no standby loss, and efficiency ratings are genuinely higher. Real savings depend on how much hot water you use, a low-use household saves a modest amount a year, and a high-use household saves more. It is rarely the number that justifies the project on its own.
Oversold: instant hot water. Tankless does not shorten the wait at a distant tap. The water still has to travel the pipe. If that is your complaint, the answer is recirculation, which can be added to either kind of heater.
Oversold: unlimited flow. Endless, yes. Unlimited, no. A unit has a maximum flow at a given temperature rise, and in an Idaho winter that ceiling is lower than the brochure figure. Sizing is the part of this job that gets done badly most often.
Why Idaho sizing is different
A tankless unit is rated at a temperature rise, and rise depends on incoming water temperature. Summer groundwater in the Treasure Valley might arrive near 60°F; in a mountain valley in February it can be down around 40°F. Getting to a 120°F output is a 60-degree rise in one case and an 80-degree rise in the other, and a unit that runs two showers in August may manage only one in January. Any quote that does not mention winter inlet temperature was not sized for this state.
Sized for a January morning, not a brochure.
The infrastructure
What has to change behind the wall
Gas supply capacity
This is the item that decides whether a tankless retrofit is simple or expensive. A tank heater might draw 40,000 BTU per hour; a whole-house tankless commonly wants 150,000 to 199,000. The existing gas line, the meter capacity and every other appliance on the system have to be assessed for that demand. Frequently the branch to the heater has to be upsized, sometimes the run from the meter, and occasionally the meter itself needs the utility’s attention. This is engineering rather than guesswork, pipe sizing follows total demand, length of run and available pressure. See gas line services.
Venting
A tankless unit cannot use the old atmospheric flue. Condensing units vent through sealed plastic or stainless pipe, usually horizontally through a nearby wall, with manufacturer-specified maximum lengths, slope for condensate and clearances from windows, doors, soffits and gas meters. A concentric or two-pipe arrangement brings in combustion air from outside. If the old tank shared a flue with a furnace, abandoning it changes that flue’s sizing, which has to be looked at too.
Condensate
A high-efficiency condensing unit produces acidic condensate, which needs a drain and often neutralisation before discharge. In an unheated space the condensate line itself can freeze, which is an Idaho-specific detail that a careless installation gets wrong.
Water connections and service valves
Isolation valves with service ports are how the unit gets descaled. Skipping the valve kit to save money on installation day makes every future service call more expensive and more invasive.
Electrical
Even gas units need power for controls, ignition and the fan. Whole-house electric tankless is a different proposition entirely: the load is very large, commonly needing multiple high-amperage circuits and a service panel with capacity to spare. In many Idaho houses the panel is the limiting factor and the honest answer is that electric tankless is not practical there.
The number that matters
Flow rate at winter temperature rise
Sizing works from two figures: how many gallons a minute you want to run at once, and how much the unit has to raise the temperature to deliver them.
Add up realistic simultaneous demand. A modern shower head runs roughly 1.75 to 2.5 gallons per minute. A kitchen faucet is around 1.5. A tub filler can be 4 or more. Two showers at once in a family house is a normal expectation; two showers plus a dishwasher is the design case in some households and irrelevant in others. This is a conversation about how your house actually behaves in the morning.
Then apply the winter rise. With a 40 to 45°F inlet, delivering 120°F water means an 75 to 80-degree rise, and the flow a unit can manage at that rise is meaningfully lower than its headline figure. This is precisely why some tankless installations disappoint in their first winter: they were sized on the brochure number.
The options when demand exceeds one unit. A larger single unit; two units manifolded together for high-demand houses; or a deliberate decision that one shower at a time in January is acceptable. All three are legitimate; being surprised by the third is not.
Minimum flow to fire. Units need a threshold flow to ignite, typically around half a gallon a minute. A trickling tap may not trigger heating, which is normal behaviour rather than a fault.
The cold water sandwich. Turn a tap off and on again quickly and you can get a slug of cool water between two hot ones, because the unit stops and restarts. Modern units with a small buffer tank largely eliminate it, and it is worth knowing about before rather than after.
Ask what the gas line work would actually cost in your house.
Idaho water
Scale is the thing that ends tankless units early
A tankless heat exchanger runs water through narrow passages at high heat, which is the ideal condition for mineral to deposit. In the hard water across much of southern and eastern Idaho, scale is not a possibility to plan around, it is a certainty to schedule for.
What scale does. Reduces flow, reduces efficiency, makes the unit cycle and eventually triggers fault codes and shutdowns. Left long enough it damages the exchanger, which is the most expensive part of the appliance.
Descaling. A circulation pump moves a descaling solution through the exchanger via the service valves for an hour or so. Annually is a sound default in Idaho water; every six months for very hard water or heavy use. It is a routine service, not a repair, and it is the maintenance item most owners are never told about at the point of sale.
Softening or conditioning. A softener ahead of the unit extends its life and protects every fixture and appliance downstream. On a tankless installation in hard water it is close to essential rather than optional. See water softener installation and whole house water filtration.
Filters and screens. The inlet screen wants checking, and on well systems a sediment filter ahead of the unit prevents grit reaching the exchanger. Well properties are common through the western border communities, the mountain valleys and rural eastern Idaho, see well pump and water system service.
Freeze protection. Tankless units hold very little water, which is good, and they have electric freeze protection built in, which only works while the power is on. In a winter outage in a cold garage, an unprotected unit can freeze. Where a unit is installed in unheated space, drain-down provision and insulated lines matter, and in cabins left empty it is a design requirement rather than a nicety. See freeze protection and winterization.
The economics
When it pays, and when a good tank is the better buy
Where the money goes. The unit is a minority of the project on many retrofits. Gas line upsizing, new venting, condensate provision, service valves and the labour of a wall-mounted installation make up the rest. Two houses next door to each other can differ by a factor of two, purely on how far the gas line has to be rebuilt.
The strong cases. New construction and gut remodels, where gas and venting are being run anyway. Houses that genuinely run out of hot water. Properties where the space a tank occupies is worth reclaiming. Owners who intend to stay long enough for a twenty-year appliance to matter. Replacing a tank in a finished basement where a future leak would be expensive.
The weak cases. A modest household on a tight budget whose current tank is adequate. A house where the gas supply would need extensive rebuilding across finished space. A property where nobody will be doing the annual descale, an unmaintained tankless in hard water is a worse outcome than a well-chosen tank. Unheated locations with a real freeze exposure and no drain-down plan.
Payback, honestly. Energy savings alone rarely repay the difference quickly in this region, particularly against cheap natural gas. The case is usually built on capability, service life and space rather than on the utility bill, and we would rather say that plainly than sell a payback figure that does not survive contact with your usage.
The middle options. A high-efficiency tank with a recirculation loop solves the waiting-for-hot-water complaint at much lower cost. A heat pump tank is the cheapest to run of any option on an all-electric property. A well-sized standard tank remains a perfectly good appliance. All three are covered on water heater installation.
Recirculation. If the real complaint is a long wait at a far bathroom, a recirculation loop or a dedicated return is the fix, and it can be designed into either a tank or a tankless installation.
Hard water? Descaling and softening belong in the plan.
How it runs
From assessment to endless hot water
The assessment is most of the value here, half the honest answers to "should I go tankless" are no.
1. Assess gas, vent and demand
Total gas demand and existing pipe capacity calculated, vent route and terminations checked, condensate drain identified, electrical supply confirmed, and simultaneous hot water demand established with you.
2. Size for a winter morning
Flow requirement set against the coldest realistic inlet temperature for your area, then a unit chosen, or two manifolded, with the limits stated in writing so there are no surprises in January.
3. Install, commission, teach
Gas and venting brought up to the unit’s requirements, service valve kit fitted, condensate handled, unit commissioned and gas pressure verified under load, permitted and inspected, then shown to you along with the descaling routine.
Coverage
Tankless work across Idaho
The plumber installs and services tankless units statewide, and the local answer differs: straightforward retrofits in newer Treasure Valley construction with modern gas service, tougher gas capacity questions in older housing in Boise, Pocatello and Coeur d’Alene, and cold inlet temperatures through the mountain valleys and eastern high country that push sizing up a step.
Questions
Tankless water heater questions
The unit is often less than half the project. What moves the total is gas line capacity, venting and condensate provision, a retrofit next to an adequately sized gas line and an easy exterior wall is a fraction of one that needs a new gas run across a finished basement.
Ask for the quote itemised: unit, gas work, venting, condensate, service valves, permit. That is the only way two tankless quotes can be compared honestly.
Correct, with a limit on rate rather than volume. It will heat water for as long as you draw it, but only up to its maximum flow at the current temperature rise.
Exceed that, two high-flow showers and a dishwasher on a cold January morning with an undersized unit, and the output temperature drops. Which is why sizing at winter inlet temperature is the whole game.
Very often, yes. A whole-house tankless commonly needs three to five times the gas input of the tank it replaces, and the existing branch was sized for the tank.
The assessment covers the branch, the run from the meter, the meter capacity and every other gas appliance in the house. Sometimes only the last few feet change; sometimes it is a substantial gas project, and you should know which before committing.
Annually is a sensible default across most of southern and eastern Idaho. Every six months where water is very hard or usage is heavy. Softened water can stretch it further.
It is a scheduled service taking about an hour through the isolation valves. Skipping it in hard water is the most reliable way to shorten the life of an expensive appliance.
A short slug of cooler water arriving between hot water, caused by the unit shutting down and re-firing when a tap is closed and quickly reopened.
Modern units with a small internal buffer tank largely eliminate it. On units without one it is a minor characteristic rather than a fault, most noticeable in showers where the mixer gets adjusted repeatedly.
Yes, with the freeze question answered honestly. Units have built-in electric freeze protection, and it only works while the unit has power, a winter outage in an unheated garage is exactly the scenario that damages one.
For seasonal properties we want a drain-down provision, insulated and correctly routed lines, and a condensate path that will not freeze. Where a cabin sits unheated for months, that design work is essential rather than optional.
For a single fixture or a remote sink, yes, and it works well. For whole-house hot water in Idaho, usually not.
The electrical load is very large, generally needing multiple high-amperage circuits and panel capacity most existing houses do not have, and the cold winter inlet makes the required load worse. On an all-electric property a heat pump tank is nearly always the better answer.
Twenty years is a fair expectation with descaling, against eight to twelve for a tank. The heat exchanger is the core, and igniters, fans, flow sensors and control boards are serviceable parts.
Stick to mainstream brands with parts availability and factory support, and keep the installation paperwork, warranty terms on heat exchangers are long but they generally depend on evidence of correct installation and maintenance.
Not sure tankless is right? We will tell you if it is not.
The whole picture before you commit
Real sizing, real gas and venting costs, and a straight answer on whether tankless is right for your house. Call any hour, anywhere in Idaho.
(833) 472-2088