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Central Ohio water and plumbing

Hot water for a Central Ohio shower: the heater, the cold that comes in, and the winter

Two things decide whether a Central Ohio shower runs out of hot water: how much the heater can deliver in the hour it is asked to, and how cold the water is when it arrives at the house. The federal government publishes a sizing method for the first. For the second it offers a national default and nothing for any particular place, and no agency was found publishing a temperature for the cold water reaching a Columbus tap in any month. This page gives the Department of Energy's method as it was written, the NOAA and Geological Survey figures that stand nearest to the missing one, the federal efficiency standards as they stood in September 2026, and what Ohio's plumbing and energy codes ask of a water heater, its relief line and a recirculation loop. The one piece of arithmetic here that is an inference says so in the sentence.

Last updated September 2026 · Federal sizing guidance was read from archived copies; the code sections, standards and climate normals were read September 2026 · No prices on this page; the Estimate Builder carries those · Part of the knowledge base

The two things that decide it

A shower's hot water is settled by two numbers, only one of them printed on the appliance: how much hot water the heater delivers in the hour a household uses it, and how cold the water is when it arrives. The second moves with a Central Ohio winter and the first does not. It is also this page's honest limit: no agency was found publishing a temperature for cold water arriving at a Columbus tap, in any month.

The cold water that comes in

NOAA's 1991 to 2020 climate normals put the mean annual temperature at the Columbus airport weather station at 53.5 degrees Fahrenheit and the January mean at 29.6 degrees, each being a 30-year average by NOAA's definition of a normal. Those are air temperatures read at a weather station, not water.

Water in the ground is far steadier than air, and the agency statement relating the two is old. The United States Geological Survey wrote in 1925, in Water-Supply Paper 520-F, that the temperature of water in the ground is in general about the same as the mean annual air temperature of the place, and that water 30 to 60 feet down runs 2 to 3 degrees above it. That is a century-old paper, printed with its date because no modern agency restatement of the relation was found. The water supply page carries the Geological Survey's monthly Hoover Reservoir readings, which measure a reservoir and not a tap.

Sizing a tank: the first hour rating

The Department of Energy's Energy Saver guidance, read here from an Internet Archive snapshot of July 2026 because energy.gov no longer serves those pages, sized a storage water heater by its first hour rating: the number of gallons of hot water the heater can supply per hour, starting with a tank full of hot water. It told readers to look for a first hour rating that at least matches the household's peak hour demand, defined as the highest energy use during a single one-hour period for the home. That is a busiest-hour method rather than a gallons-in-the-tank method.

That removal was measured on September 5, 2026: the address redirects away and every water heater page under it returns not found. One live federal rule still carries the number. The labeling rule of the Federal Trade Commission, at 16 CFR 305.17, requires a storage water heater's capacity to be shown as both its rated storage volume and its first hour rating, and sorts first hour ratings into four bands: fewer than 18 gallons, 18 to 50.9, 51 to 74.9, and 75 gallons or more.

Sizing a tankless heater: a flow at a temperature rise

A tankless heater is different arithmetic: the Department of Energy's guidance rated it by the maximum temperature rise possible at a given flow rate, so its output is two numbers and not one: how many gallons a minute, and how far it can lift them. Its worked example shows the inlet doing the deciding: it told readers to assume that the incoming water temperature is 50 degrees Fahrenheit unless they knew otherwise. With water arriving at 50 and a 120 degree target, the example needed a temperature rise of 70 degrees, and the department said a rise that size is typically possible at 5 gallons per minute through a gas-fired demand water heater and 2 gallons per minute through an electric one. It counted a shower head at 2.5 gallons a minute when adding up what would run at once, as does the Environmental Protection Agency's ENERGY STAR program, which lists shower and bathtub together at that figure.

Now the inference, labeled as one. Fifty degrees is a national default, not a figure for any place; set against the NOAA and Geological Survey findings above, water entering a Central Ohio house in winter is likely colder, meaning a larger required rise and a smaller flow from the same heater. That is an inference from the department's method applied to NOAA's normals, not a measured inlet temperature.

What the federal standards require, and what Congress changed

The efficiency levels in force now were set in an April 2010 Department of Energy rule, with compliance required for units manufactured on or after April 16, 2015; the trade's phrase, the 2015 standard, names a compliance date and not a rule year. Under the standards at 10 CFR 430.32, electric storage water heaters above 55 gallons and up to 120 gallons are already held to a level only a heat pump can reach.

A second table is scheduled. The department published amended standards for consumer water heaters on May 6, 2024, effective July 5, 2024, with compliance required on and after May 6, 2029. In that table the exempt small class is an electric storage water heater of at least 20 gallons and not more than 35 gallons effective volume, in the very small or low draw patterns. Both thresholds are true of different tables: 55 gallons is what is on sale now, 35 gallons is what the 2029 table would do.

Congress then disapproved a water heater rule, and it was not that one. A joint resolution originating in the House of Representatives became Public Law 119-6 on May 9, 2025, and what it nullified was the department's rule on consumer gas-fired instantaneous water heaters, submitted in December 2024. It did not name the May 2024 rule covering storage water heaters, and as of the electronic Code of Federal Regulations' currency date of September 3, 2026, the 2029 standards for electric storage water heaters were still in the code. That is a reading taken on one date.

What Ohio's residential energy code asks of hot water

Hot water in a house is governed here by the energy chapter of the Residential Code of Ohio, rule 4101:8-11-01, effective July 1, 2019, built on the 2018 International Energy Conservation Code named in Ohio's referenced standards rule. That chapter's Table 1101.7 puts Franklin, Delaware, Licking, Fairfield, Madison, Union and Pickaway counties all in climate zone 5A. How recently that chapter arrived in Ohio's code, next to the older mechanical and fuel gas rules it sits beside, is on the heating page.

Ohio's section 1103.5.1.1 requires a heated water circulation system to have a circulation pump, and states that gravity and thermosyphon circulation systems shall be prohibited. The controls must start the pump based on the identification of a demand for hot water, and shut it off automatically when the water in the loop is at temperature and there is no demand. Section 1103.5.2 adds that where a demand recirculation system returns water through the cold water piping, the controls must hold that water to not greater than 104 degrees Fahrenheit, the code's answer to the complaint that a loop makes the cold tap run warm.

Ohio's plumbing code sends a reader here for pipe insulation: its own section on insulation of piping was rewritten to point at chapter 11 of the Residential Code of Ohio. Section 1103.5.3 states that insulation with an R-value of not less than R-3 shall be applied to hot water piping in seven listed cases, among them piping three-quarters of an inch and larger, and piping outside the conditioned space. The seventh case is the supply and return piping of recirculation systems other than demand recirculation systems.

What the Ohio Plumbing Code asks of the water heater itself

Ohio adopts the plumbing code by reference and amends it separately, and for water heaters that amendment is short: its rule for chapter 5, effective October 15, 2025, touches only sections 501.1, 501.5, and 504.7, which it replaces in its entirety. Everything else is the incorporated model text, unchanged in Ohio.

Ohio's replacement for section 504.7 calls for a pan under a water heater where leaking from the tank will cause damage, and names what the pan may be made of: galvanized steel or aluminum not less than 0.0236 inch thick, plastic not less than 0.036 inch, or other approved materials. Whether the model's pan-drain subsections survive that replacement is unsettled between the two places a person reads this code: Ohio's rule carries no drain requirement in its replacement text, and the commercial rendering of the Ohio edition still shows those subsections beneath it. That is a legal question this page cannot settle, so it prints Ohio's text and stops.

Ohio's unamended sections shape a project more. Section 504.4 requires a storage water heater operating above atmospheric pressure to have an approved, self-closing pressure relief valve and temperature relief valve, or a combination of the two; 504.4 and 504.5 cap that device's temperature setting at 210 degrees Fahrenheit and its pressure setting at the manufacturer's rated working pressure or 150 pounds per square inch, whichever is less. Those are limits on the relief device, not a setting for the water.

Ohio's section 504.6 governs where that discharge pipe ends, in fourteen numbered requirements: through an air gap in the same room as the water heater, where the building occupants can readily observe it. Item 12 says the pipe shall not have valves or tee fittings, which is the item a shut-off added in the field breaks. Section 607.3 separately requires a thermal expansion control device where the cold water supply to a storage water heater has passed a check valve, a pressure reducing valve or a backflow preventer, because each of those turns the heater into a closed system.

What temperature, and who says so

Two federal agencies give advice here, answering different questions, and this page does not adjudicate between them. The Consumer Product Safety Commission, in its publication Avoiding Tap Water Scalds, urges all users to lower their water heaters to 120 degrees Fahrenheit.

The Centers for Disease Control and Prevention is addressing a different hazard, and says Legionella may grow at temperatures as low as 68 degrees Fahrenheit. For building water systems, its control toolkit says to store hot water at temperatures above 140 degrees and to ensure hot water in circulation does not fall below 120. Its answer to holding both at once is a thermostatic mixing valve as close as possible to the fixture.

The standards body behind that building guidance draws its own line. ASHRAE writes in the scope of its Legionella standard, ANSI/ASHRAE Standard 188, that the standard does not include single-family residential buildings, applying instead to commercial, institutional, multiunit residential and industrial ones. Whatever a tank is set to, the temperature at the shower is decided again at the valve, by a limit stop inside it, and what that stop is sits on the valves page.

Fifty feet, and what a loop does to it

The Ohio Plumbing Code limits the developed length of hot or tempered water piping, from the source of hot water to the fixtures it serves, to 50 feet, measured along the pipe rather than across the room; the supply pipes page sets that rule out. The same section's second sentence explains recirculation: recirculating system piping and heat-traced piping shall be considered to be sources of hot or tempered water. A loop, in the code's eyes, relocates the source, so the fifty feet is measured from wherever the loop reaches, which is the code's own reason why a distant bathroom gets a loop rather than a bigger heater. Ohio rewrote the next section, 607.2.1, to require an automatic circulating pump or heat trace to be arranged so that it can be conveniently turned off, automatically or manually, when the hot water system is not in operation.

The Environmental Protection Agency's WaterSense specification, a voluntary label for a new home rather than a code, agrees and goes further: it also counts a recirculation loop as a hot water source, and requires such a system to be demand-initiated rather than solely timer-based or temperature-based. That is what demand-controlled means in the agencies' language: nothing circulates until somebody asks for hot water.

A heat pump water heater in an Ohio basement

A heat pump water heater moves heat rather than making it, and both federal programs attach the same condition to where it goes: the Department of Energy and ENERGY STAR each say it needs at least 1,000 cubic feet of air space around it, in a space that stays between 40 and 90 degrees Fahrenheit year round. A closet is usually not 1,000 cubic feet; a basement usually is.

The department is plain about the cold month, in its own words: such a heater will not operate efficiently in a cold space, since these units tend to cool the space they are in, and does better where there is waste heat, such as a furnace room. ENERGY STAR adds a sentence the department's page does not carry: in hot humid weather it can help cool and dehumidify the space it is installed in.

TypeHow the sources size itWhat the sources say about the winter inletThe federal standard that governs it
Storage tankFirst hour rating matched to the household's peak hour, in the Department of Energy's method. The Federal Trade Commission's rule requires both storage volume and first hour rating on the label.Nothing; the rating is in gallons and the method does not ask for an inlet temperature.The April 2010 rule, compliance required for units made on or after April 16, 2015; a second table applies from May 6, 2029.
Tankless, gas or electricThe maximum temperature rise possible at a given flow rate, so two numbers. The department's example: a 70 degree rise at 5 gallons a minute on gas, 2 on electric.Assume 50 degrees unless you know otherwise, the department said; a cooler inlet reduces the temperature at the most distant faucet. A colder inlet here is an inference.Public Law 119-6, of May 9, 2025, nullified the December 2024 rule on consumer gas-fired instantaneous water heaters.
Heat pumpA space condition rather than a sizing number, from both programs: at least 1,000 cubic feet of air space, in a room between 40 and 90 degrees Fahrenheit year round.Nothing about the incoming water. The department's caution is about the room's air: it will not operate efficiently in a cold space.Electric storage above 55 and up to 120 gallons already sits at heat pump levels; the 2029 table leaves only 20 to 35 gallon units outside them.

What it means when a tub becomes a shower

Nothing at the water heater changes because a bathtub leaves and a shower takes its place: ENERGY STAR's sizing guidance lists shower and bathtub on the same line, at 2.5 gallons a minute. What changes the arithmetic is an outlet that can run at the same time as another: a second shower head, a hand sprayer alongside a fixed head, body sprays. Each is another 2.5 gallons a minute when adding up what runs together, and on a tankless heater more flow at the same rise is what the rating limits. Fittings are on the valves page; the pipe feeding them is on the supply pipes page.

The short version. The Department of Energy rated a tank by its first hour rating matched to the household's busiest hour, and a tankless heater by its flow at a given temperature rise, assuming water arriving at 50 degrees. NOAA puts the Columbus annual mean at 53.5 degrees of air and January at 29.6, and a 1925 Geological Survey paper ties shallow ground water to the mean annual air temperature, so a colder winter inlet here is an inference. Ohio's codes decide the rest: a loop that starts on demand and shuts itself off, insulation at R-3, a relief line with no valve, and a pan where a leak would do harm.

Sources

Every figure, date and quotation on this page comes from one of these documents, read on the date given. Where two of them disagree, the page says so.

Common questions

How cold is the water coming into a Columbus house in the winter?

No agency was found publishing a temperature for water arriving at a Columbus tap, in any month, and none is given here. What exists is nearby rather than exact. NOAA's 1991 to 2020 climate normals put the mean annual air temperature at the Columbus airport station at 53.5 degrees Fahrenheit and the January mean at 29.6 degrees. The United States Geological Survey wrote in 1925 that the temperature of water in the ground is in general about the same as the mean annual air temperature of the place. Reading those together points to a colder inlet in January than the 50 degree national default, but that is an inference and not a measurement.

What size water heater does a Central Ohio house need for a walk-in shower?

The federal method does not answer that with a tank size. The Department of Energy sized a storage water heater by its first hour rating, the gallons of hot water it can supply in an hour starting from a full tank, and told readers to look for a rating that at least matches the household's peak hour demand, meaning its busiest single hour. The Federal Trade Commission's labeling rule requires both the rated storage volume and the first hour rating to be shown, and sorts ratings into four bands: fewer than 18 gallons, 18 to 50.9, 51 to 74.9, and 75 or more. The number depends on the household, not on the shower alone.

Does a tankless water heater keep up in an Ohio winter?

That depends on the flow it is asked for and how cold the water arrives, because a tankless heater is rated by the maximum temperature rise possible at a given flow rate. The Department of Energy's guidance, now read from an archived copy, told readers to assume incoming water at 50 degrees Fahrenheit unless they knew otherwise, and said a 70 degree rise is typically possible at 5 gallons a minute through a gas-fired unit and 2 gallons a minute through an electric one. NOAA's Columbus January air normal is 29.6 degrees, so a colder inlet here, a larger rise and a smaller flow is an inference rather than a published figure.

Does Ohio require a drain pan under a water heater?

Ohio replaced the model code's drain pan section, 504.7, in its entirety, effective October 15, 2025. Its own text calls for a pan where leaking from the tank will cause damage, and names the materials: galvanized steel or aluminum not less than 0.0236 inch thick, plastic not less than 0.036 inch, or other approved materials. Whether the model's pan-drain subsections survive that replacement is unsettled between the state's rule, whose replacement text carries no drain requirement, and the commercial rendering of the Ohio code, which still shows them. The building department covering an address is the one that answers it.

What does the Ohio code require of a hot water recirculation loop?

Two codes reach it. The energy chapter of the Residential Code of Ohio, at section 1103.5.1.1, requires a circulation pump, prohibits gravity and thermosyphon circulation, and requires the controls to start the pump on an identified demand for hot water and shut it off automatically when the loop is at temperature and nothing is calling for it. Section 1103.5.2 holds water returned through the cold water piping to not greater than 104 degrees Fahrenheit. The Ohio Plumbing Code adds, at its rewritten section 607.2.1, that the pump or heat trace be arranged so it can conveniently be turned off when the hot water system is not in operation.

Why would a Central Ohio bathroom need a recirculation loop at all?

Because of a distance limit. The Ohio Plumbing Code holds the developed length of hot or tempered water piping, from the source of hot water to the fixtures it serves, to 50 feet, measured along the pipe rather than across the room. The second sentence of that same section says recirculating system piping and heat-traced piping shall be considered to be sources of hot or tempered water. In the code's own terms a loop is not a comfort upgrade; it relocates the source, and the fifty feet is then measured from wherever the loop reaches. That is why a distant bathroom gets a loop rather than a larger heater.

Do the federal agencies agree on what temperature a water heater should be set to?

They are answering different questions, and this page does not choose between them. The Consumer Product Safety Commission urges all users to lower their water heaters to 120 degrees Fahrenheit. The Centers for Disease Control and Prevention, writing about building water systems, says to store hot water above 140 degrees, to keep hot water in circulation from falling below 120, and to fit a thermostatic mixing valve as close as possible to the fixture. ASHRAE states in the scope of its Legionella standard that the standard does not include single-family residential buildings, which is worth knowing before applying building guidance to a house.

What does a heat pump water heater need in an Ohio basement?

Room and warmth. The Department of Energy and ENERGY STAR both say a heat pump water heater needs at least 1,000 cubic feet of air space around it, in a space that stays between 40 and 90 degrees Fahrenheit year round, which describes a basement far more often than a closet. The department adds that such a heater will not operate efficiently in a cold space, since these units tend to cool the space they are in, and that it does better where there is waste heat, naming a furnace room. ENERGY STAR, not the department, adds that in hot humid weather it can help cool and dehumidify the space.

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