How to Choose a Water Heater

A water heater isn’t one device. It’s a combination of working parts and components that all play a role in the unit’s ability to function properly. Before picking one, you choose between three types, size it to your household’s peak demand, match it to the fuel you’ve got, and round up the fittings and accessories that complete the install. Montana’s cold incoming groundwater changes the math, especially for tankless. Get the sizing wrong and you’ll find out in January, mid-shower.

Here’s how the choices break down.

The Three Types and How to Pick

Three main options sit on the table: storage tank, tankless (on-demand), and heat pump (hybrid). Each trades something.

Storage tank. The workhorse. The most common type holds hot water in a large tank until it’s needed. Lower upfront cost, simpler install. The catch is capacity — when the tank’s drained, you wait for it to recover. Lifespan runs about 10–12 years.

Tankless. Heats water as it flows, so hot water doesn’t run out. Longer service life, 20-plus years. The trade-off is flow rate — there’s a ceiling on how many gallons per minute it can heat at once, and these often need new water and electrical lines run to them.

Heat pump (hybrid). Most efficient of the three. The penalty is air space. These units pull heat from the surrounding air, so they need roughly 700 to 1,000 cubic feet of it, kept somewhere between 40 and 90°F. They lose performance below 40°F. That rules out an unheated Montana garage or basement in winter — exactly when you need the hot water most.

Sizing It Right — Where Most Buyers Go Wrong

Undersizing is the number-one mistake. The sizing method depends on the type.

Storage tanks get sized by First Hour Rating (FHR) — the gallons the unit delivers in the first hour starting with a full tank. Match the FHR to your peak hour of demand, not your daily total. Three back-to-back morning showers can run roughly 66 gallons in that window. That’s the number that matters.

Tankless gets sized by flow rate (GPM) combined with temperature rise. Rise is the gap between incoming water temperature and your target — typically 120°F at the tap. Standard sizing assumes 50°F incoming water for a 70°F rise.

That assumption falls apart in a Montana winter. When incoming groundwater drops near freezing, the required temperature rise climbs, and the unit’s real-world flow rate drops hard. A tankless rated 11 GPM in a mild climate delivers a fraction of that on a cold morning here. Size conservatively. The published flow number is a best-case figure you won’t see in February.

Fuel type also caps tankless output. Gas units handle a 70°F rise at higher flow than electric — electric tankless can choke down to around 2 GPM at the same rise.

Type	Lifespan	Sized By	Hot Water Limit
Storage tank	~10–12 yrs	First Hour Rating	Tank capacity
Tankless	20+ yrs	GPM + temp rise	Flow rate ceiling
Heat pump	Efficiency leader	Capacity + air space	Needs 700–1,000 cu ft, 40–90°F

Fuel Source: Gas, Electric, or Propane

Fuel drives both how complicated the install is and what it costs to run.

Gas heats fast and gas often costs less to run than electricity. Gas water heaters are the most common type — they produce hot water quickly, and gas costs significantly less than electricity. But gas burns, so it vents. The exhaust — flue gas — has to leave the building, and the venting style determines the parts. It’s important to distinguish whether you have a standard atmospheric water heater, power vent water heater, direct vent water heater, or a mobile home water heater, as these different types of models will each have their own unique parts and venting requirements.

A critical point on fuel: natural gas and propane aren’t interchangeable. Although there are two different types of gas that may be used as a fuel source — natural gas and LP/liquefied petroleum — gas water heaters share a variety of parts in common, however parts for a natural gas water heater and parts for a LP water heater are NOT interchangeable. If you’re on propane — and plenty of rural Montana properties are — you order propane parts, full stop.

Electric is the simpler install. An electric water heater offers a safe and reliable alternative to natural gas and LP water heaters. Residential electric water heaters often have fewer parts than natural gas water heaters because there are only two main parts responsible for heating the water. No venting to run. The trade-off is operating cost in most regions, and electric tankless can demand a serious electrical service. Western Building Center carries the parts that keep electric units running — 4500W elements, upper and lower thermostats in both 120V and 240V, and combined thermostat/element kits.

The Parts That Complete the Install

Buyers underestimate what it takes beyond the tank itself. These pieces matter for code and for longevity.

Start with safety. The temperature and pressure (T&P) relief valve is non-negotiable. The T&P valve allows pressure to escape from the tank when temperature and pressure levels get too high. Below it hangs the discharge pipe. The overflow pipe is a piece of copper or flex line that hangs down from the T&P relief valve on the exterior of the tank, providing an outlet for excess pressure to escape if temperature and pressure levels get too high. A drain pan underneath catches leaks and relief-valve discharge, directing water away from the unit. The stock list here includes a T&P relief valve and a 25-inch round drain pan.

For connections, three-quarter-inch is the standard size. Flexible braided supply lines do the connecting, and they come in the configurations you’ll actually need: 3/4 FIP x FIP in 12, 15, and 24-inch lengths, 3/4 FIP x MIP at 18 inches, a version with a built-in ball valve, and a 1-inch FIP to 3/4 FIP adapter line for stepping down. On a typical hookup, a flex hose runs from the tank to a threaded ball valve, with a brass compression-to-thread adapter tying back into the existing copper. Stacking multiple compression rings on the heater is worth avoiding — keep it to one per line where you can.

Gas units bring their own fittings. The list covers gas ball valves in 1/2 and 3/4-inch FIP, plus stainless gas supply connectors in 36 and 48-inch lengths. Thermocouples — the safety device on the pilot assembly — are stocked in 24 and 36-inch copper.

For tankless, a service valve kit pulls the connections together. A tankless water heater service valve kit has everything needed to connect a tankless installation, all in one place. These kits include both a hot and cold water valve along with an additional recirculation valve, with a captive nut and washer on the appliance connection that won’t kink or misalign — and an integrated drain valve that reduces the number of components needed to install the appliance. Typical specs run 3/4-inch FIP, rated 40° to 180°F at up to 125 PSI.

One more on closed systems: where a check valve or pressure-reducing valve isolates the house from the main, you need an expansion tank to absorb the pressure spike when water heats and expands. Skip it on a closed system and you’ll be cycling that T&P valve constantly.

Maintenance That Doubles the Life

Two simple habits decide whether a tank dies young or outlives its warranty.

First, the anode rod. Since tanks are made of metal, they all corrode over time as a result of natural minerals in the water — despite a protective glass lining. A sacrificial anode rod inside the water heater absorbs corrosive material so that the rod corrodes instead of the tank. The three most common types are aluminum, zinc, and magnesium. It’s a consumable — when it’s spent, replace it before the tank starts eating itself.

Second, flush the tank. Sediment settling to the bottom is the number-one cause of premature failure. Regular flushing clears it out.

Do both, and the payoff is real. Regular flushing of the tank and periodic anode replacements will mean your heater stands a good chance of far outliving its warranty, instead of becoming a consumable due for replacement in six to fifteen years.

Frequently Asked Questions

Why does my tankless heater feel weaker in winter? Because cold incoming water forces a bigger temperature rise. Standard tankless sizing assumes 50°F incoming water for a 70°F rise to a 120°F target. When Montana groundwater drops toward freezing in winter, the unit has to work harder to hit the same target temperature, and its real flow rate falls. A heater rated 11 GPM in a mild climate delivers far less on a cold morning. Size conservatively for the worst case, not the brochure number.

Can I put a heat pump water heater in my garage? Only if that garage stays warm. Heat pump units pull heat from surrounding air and need roughly 700 to 1,000 cubic feet of it, held between 40 and 90°F. They perform poorly below 40°F. An unheated Montana garage or basement in winter is exactly the wrong spot — they lose efficiency right when demand peaks.

Are natural gas and propane water heater parts the same? No. While gas water heaters share many common parts, components for natural gas and LP/propane units are not interchangeable. Confirm your fuel before ordering any gas-side part. The same goes for venting — standard atmospheric, power vent, direct vent, and mobile home models each carry their own parts and venting requirements.

What size storage tank do I need? Size by First Hour Rating, not tank gallons alone. The FHR is how many gallons the unit delivers in the first hour starting full. Match it to your peak hour of use — for example, three morning showers running close together can demand around 66 gallons in that window. That peak figure, not your daily total, is what prevents cold showers.

What’s the most common reason a water heater fails early? Sediment buildup in the tank. It settles to the bottom and shortens the unit’s life. Regular flushing prevents it, and replacing the sacrificial anode rod on schedule protects the tank wall from corrosion. Those two tasks alone can push a properly maintained tank well past its warranty period.

Do I need an expansion tank? On a closed plumbing system — one with a check valve or pressure-reducing valve at the main — yes. As water heats and expands it has nowhere to go, and the pressure spikes. An expansion tank absorbs that, protecting the T&P valve and the tank itself from constant stress.