Tankless units never run out of hot water, but cold winter inlet water cuts how much they can deliver at once. Here is the math, the hidden installation costs, and when tankless actually pays.
Get Connected Or call now: (401) 324-9590Tankless can be worth it in Rhode Island, but not for everyone. It tends to make sense for small to mid-size households that want endless hot water, are tight on floor space, or are getting a gas rebate and already have adequate gas piping. It tends to disappoint when winter inlet water is very cold, the household runs several showers at once, or the home needs new gas piping and venting. The savings are real but modest, and they take years to pay back the extra cost.
A tankless unit has a fixed heating power. The more you have to raise the water temperature (the "temperature rise"), the less water it can heat per minute. The temperature rise is your hot water set point minus the incoming cold water temperature. The Consumer Product Safety Commission recommends 120 degrees Fahrenheit, according to a Plumbing & Mechanical magazine sizing guide, and winter groundwater temperature tracks the average winter air temperature where you live. Rheem notes that in the north, inlet water can dip into the 30s and 40s, which calls for larger BTU input.
| Cold inlet water | Temperature rise to 120 F | Max flow of hot water |
|---|---|---|
| 70 F (summer) | 50 F | about 7.2 GPM |
| 60 F | 60 F | about 6.0 GPM |
| 50 F | 70 F | about 5.1 GPM |
| 40 F (cold winter) | 80 F | about 4.5 GPM |
| 35 F | 85 F | about 4.2 GPM |
Compare that with demand. A standard showerhead uses up to 2.5 gallons per minute (the 1992 federal maximum; WaterSense models use 2.0 or less). Rheem's sizing page gives the same 2.5 figure. Two showers running together can ask for 4 to 5 GPM of hot water, though a shower mixes in cold water so the heater delivers less than the full flow. Add a dishwasher or a washing machine and a unit that is fine in summer can run out of capacity in winter. The result is not a cold shower, it is weak flow or a temperature that fades.
How to use this. We do not have a measured winter inlet temperature for your address, and it varies across Rhode Island. The best check is to run your cold tap in January and measure it with a thermometer, then size the unit to the coldest number you see. Ask your plumber for the manufacturer's flow chart for that specific model at that temperature rise. Larger households sometimes need two units.
This is the one that surprises people. A typical tank draws about 40,000 BTU per hour. A tankless can draw 140,000 to 200,000 BTU or more, which Rheem calls one of the largest single appliances on a typical gas system. According to Rheem's gas piping guide, the gas piping typically has to be upgraded for a tankless unit. A 199,900 BTU unit on a 20 foot branch needed 1-inch pipe in its example, and a common household meter and regulator rated at 250 cubic feet per hour can end up undersized once the tankless is added to a furnace or boiler and a dryer. Your gas utility can advise on a meter or regulator upgrade. Ask your plumber to size the pipe, not assume the old half-inch line will do.
Gas tankless units have venting requirements set by the manufacturer, and they are often different from a simple tank. Ask which vent material the unit requires and whether the old chimney can be reused. Cost guides put gas venting setup at $300 to $1,000, and a power-vent configuration at $600 to $1,100 more. Older Rhode Island homes with a masonry chimney or tight basement runs are more likely to need a new vent path.
Cost guides list tankless labor at 4 to 6 hours versus 1 to 3 hours for a tank. Tankless units also need periodic flushing or descaling of the heat exchanger. Noritz describes the process as circulating vinegar or a descaling solution through the unit with a small pump, and says units on hard water without a softener need it periodically based on the manual. Water that is already soft needs it less, but follow your model's maintenance schedule. Ask your plumber to install isolation valves so flushing is easy.
Using our worked estimate from the electric vs gas guide (60 gallons per day, about $2.09 per therm from EIA's 2024 Rhode Island average), a gas tank at 0.64 UEF costs about $417 a year to run and a tankless at 0.87 UEF about $307. That is roughly $110 a year in savings.
Savings depend on use. Households that use very little hot water see smaller dollar savings, and large households see the flow problem first. Treat the numbers as an example you can redo with your own bills.
| Tankless is a good fit if... | Stick with a tank if... |
|---|---|
| You have 1 to 3 people and moderate hot water use | You have a big household with showers running at once |
| Your gas piping and meter already have capacity | The home needs new gas line, meter, or regulator work |
| You want to free up floor space | The cheapest reliable replacement is the goal |
| You plan to stay long enough for the payback | You may sell or move within 5 to 8 years |
| You will keep up with flushing | You would not remember to descale it |
If your home is all-electric, tankless electric units and heat pump water heaters are different decisions with different costs. Start with the electric vs gas guide, and see typical prices in the cost guide.
RI Water Heaters is a referral service. We do not install water heaters. We connect you with a local Rhode Island plumber who can check your gas line, venting, and winter water temperature before you commit.
Yes, but with a lower maximum flow. The colder the incoming water, the more the unit has to heat it, so the gallons per minute it can deliver drop. A 199,000 BTU unit in our math delivers about 7.2 GPM from 70 degree water but only about 4.5 GPM from 40 degree water. Size it for your coldest winter water, not summer.
Often, yes. Rheem says tankless units draw 140,000 to 200,000 BTU or more, and that gas piping typically has to be upgraded compared with a tank. The meter and regulator may also need to be checked. Ask your plumber to size the gas line before you buy.
In our example the energy savings are about $110 a year against a price premium of roughly $950, so about 8.6 years, or about 3.8 years if you receive the $600 Rhode Island Energy rebate on an ENERGY STAR model. Extra gas line or venting work lengthens it.
Yes. The heat exchanger needs periodic flushing or descaling, especially on hard water without a softener, following the manufacturer's schedule. Isolation valves make it easier. The manual for your unit has the exact schedule.
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Figures on this page come from the sources below. Prices and program terms change, so confirm with the program or a plumber's written quote before you decide.