Water Heater and Boiler Guide

Hot water is the second-largest energy use in most US homes after heating and cooling, and the water heater is the appliance you only think about when it stops working. This page maps the choices in plain language: gas or electric, tank or tankless, what size, which parts fail, where boilers fit in, and what HVAC MORE does and does not carry.

The quick answer: If your home already has gas and a working flue, a 40- or 50-gallon atmospheric gas tank is the lowest-cost like-for-like replacement; choose a power-vent model if you must vent horizontally through PVC. With no gas, a 50-gallon electric tank with two 240V 4500W elements is simple, reliable and cheap to repair. A condensing tankless gas heater makes sense when you want endless hot water and have a 3/4-inch gas line and a place to vent. Heat pump water heaters are three to four times as efficient as a standard electric tank, though we do not sell them. Boilers heat the house, not the tap water (unless they are combis), and most boiler faults come down to an aquastat, igniter, gas valve or circulator part that we do stock.

Choosing a water heater

• Gas atmospheric tank. Natural-draft burner, metal B-vent flue, standing pilot or electronic ignition. Simplest and cheapest to install where a vertical vent exists.
• Gas power-vent tank. Adds a blower so exhaust can run horizontally through PVC; needs a 120V outlet. Required in many tight modern homes and finished basements.
• Electric tank. Two 240V elements (4500W is the common rating) controlled by two thermostats, on a dedicated 30-amp circuit. No venting and few parts, but the highest operating cost per gallon in most regions.
• Tankless gas. Heats water on demand. Condensing models vent in PVC and need a condensate drain; output is limited by flow rate, so sizing is by gallons per minute at your winter temperature rise. We carry Noritz condensing units.
• Heat pump (hybrid) water heater. Pulls heat from surrounding air into the tank at a UEF of roughly 3 to 4. Needs about 700 cubic feet of air space or ducting, a condensate drain and tolerance for a cooler utility room. The most efficient electric option by far; we do not currently sell them.

Type	Typical UEF	Needs	Best for	At HVAC MORE
Gas atmospheric tank	0.60-0.65	Gas line, vertical metal flue	Like-for-like replacement with a chimney	Yes (40/50 gal)
Gas power-vent tank	0.65-0.70	Gas line, PVC vent, 120V outlet	Basements, no usable chimney	Yes (40/50 gal)
Electric tank	0.90-0.95	240V 30A circuit	All-electric homes, simple repairs	Yes
Condensing tankless gas	0.90-0.96	3/4" gas line, PVC vent, condensate drain	Endless hot water, space saving	Yes (Noritz)
Heat pump water heater	3.0-4.0+	240V (some 120V), 700 cu ft air, drain	Lowest electric operating cost	No

Shop Water Heaters or read Gas vs electric water heaters and the heat pump water heater guide.

Sizing by household

For tanks, the number that matters is the First Hour Rating (FHR) on the yellow EnergyGuide label: how many gallons of hot water the heater delivers in a busy hour, starting full. Compare it to your peak hour (back-to-back showers at about 2 gallons per minute each, plus a dishwasher or laundry load). Rough starting points:

• 1 to 2 people: 30 to 40 gallons
• 2 to 3 people: 40 gallons
• 3 to 4 people: 50 gallons
• 5 or more: 50 to 80 gallons, or tankless

Gas tanks recover faster than electric, so a 40-gallon gas heater often serves a household that would need a 50-gallon electric. For tankless, add up the fixtures you expect to run at once and check the unit's output at a 70°F temperature rise, which northern groundwater demands in winter.

Shop Water Heaters or read Gas vs electric water heaters.

Parts that fail, and what they do

Most water heater "failures" are a $20 to $150 part, not a new tank:

• Heating elements (electric). Screw-in or flange, 240V 4500W is standard; a good element reads about 12 to 13 ohms. Scale and dry-firing kill them.
• Thermostats (electric). Upper and lower, clamped against the tank behind the covers. The upper one carries the high-limit (ECO) red reset button; if it trips repeatedly, find out why before resetting again.
• Thermocouple or igniter (gas). Standing-pilot heaters use a thermocouple that proves the pilot flame; newer and power-vent models use a hot surface or spark igniter with a flame sensor. A pilot that will not stay lit is almost always the thermocouple.
• Gas control valve. The combination thermostat and valve on the front of a gas tank; its status light flashes the fault code listed in the manual.
• T&P relief valve. Opens at 150 psi or 210°F. Constant dripping means it is failing or that house pressure or thermal expansion is too high.
• Anode rod. A sacrificial magnesium or aluminum rod that corrodes so the tank does not. Checking it every few years and replacing it when mostly gone is the best way to extend tank life.
• Dip tube. Delivers cold inlet water to the bottom of the tank. When it cracks you get lukewarm showers and bits of plastic in faucet aerators.

Shop Water Heater Parts, Gas Valves and Igniters and Flame Sensors, or read the water heater heating elements guide.

Boilers in brief

A boiler heats water (or makes steam) for space heating through radiators, baseboard or radiant floor loops. It is a separate appliance from a water heater, in three common residential forms:

• Gas boilers: cast-iron non-condensing units around 80 to 85 percent AFUE, and condensing units in the 90 to 95 percent range that vent in PVC.
• Oil boilers: common across the Northeast where natural gas never arrived. The burner needs a nozzle, electrodes, pump and annual service.
• Combi boilers: a wall-hung condensing boiler that heats both the house and domestic hot water on demand with no storage tank. Space-saving, but hot water output is limited by flow rate like any tankless heater.

HVAC MORE does not sell complete boilers. We stock the parts that keep them running: aquastats and operating controls (including Honeywell), circulator pump parts, hot surface and spark igniters, flame sensors, gas valves, pressure relief valves (30 psi on most residential hydronic boilers), transformers and relays.

Shop Boiler Parts and Thermostats, or read Boilers explained: gas, oil and combi.

Install cost pointers

As of 2026 these are rough, rounded US ranges for a straightforward replacement including labor. They vary a lot by region, permits and how much venting, gas or electrical work is needed, so treat them as estimates only:

• Electric tank, like-for-like: roughly $1,000 to $2,500
• Gas tank, atmospheric: roughly $1,500 to $3,500; power vent adds a few hundred dollars
• Condensing tankless gas: roughly $3,000 to $6,000, more if the gas line must be upsized
• Heat pump water heater: roughly $2,500 to $5,000 before utility or federal incentives
• Boiler replacement: often $6,000 to $12,000 depending on type and piping

Buying the heater yourself and hiring a plumber for the install is a common way to trim the total. Confirm permit, expansion tank and seismic strapping rules with your local code office.

Shop Water Heaters or read Water heater installation cost in the US.

FAQ

How long does a water heater last?

Tank heaters typically last 8 to 12 years for gas and 10 to 15 for electric; tankless units often run 20 years with annual descaling. A fresh anode rod and periodic flushing stretch those numbers.

Gas or electric: which is cheaper to run?

In most of the US, gas costs less per gallon of hot water even though electric tanks have the higher UEF, because gas is cheaper per BTU. A heat pump water heater flips that math.

Can I replace a water heater element myself?

Yes, with the power off at the breaker, the tank drained below the element and a 1-1/2 inch element wrench. Match the voltage and wattage printed on the old element.

Do you sell boilers or heat pump water heaters?

Not today. We sell gas, electric and Noritz tankless water heaters, plus water heater parts and boiler parts.

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Browse Water Heaters, Water Heater Parts and Boiler Parts. If you have a model number and a symptom, contact us and we will help you find the right part.