Whole house gas tankless
A.O. Smith ATI-540P-N 199K BTU Specifications
Researched from the DOE test procedures, NFPA 54 and NEC code tables, and manufacturer specifications. Updated .
Quick answer
This page collects what is actually published about the A.O. Smith ATI-540P-N 199K BTU and shows what those figures produce, computed rather than transcribed. Anything the listing does not publish is not filled in with an estimate.
One caution about the flow figure. The listing title states 10 gallons per minute with no temperature rise attached. Flow and rise trade against each other directly, so a flow figure without a rise is not a specification. The table below shows what the published input rating actually produces across the range.
Published specifications
Everything here is taken from the listing or the manufacturer, and nothing is inferred.
| Specification | Value |
|---|---|
| Fuel | Natural gas |
| Btu Input | 199000 |
| Max Flow Gpm | 10 |
| Condensing | Yes |
| Mounting | Indoor |
Published standard Source: Manufacturer listing data. A specification not listed here is one this listing does not publish. Check the installation manual for the full data plate.
Flow across the temperature rise range
Computed from the published input rating with the energy relation, so these figures cannot disagree with the calculators on this site.
| Temperature rise | Flow | Inlet needed for a 120 F outlet |
|---|---|---|
| 35 F | 10.6 GPM | 85 F |
| 45 F | 8.2 GPM | 75 F |
| 60 F | 6.2 GPM | 60 F |
| 70 F | 5.3 GPM | 50 F |
| 80 F | 4.6 GPM | 40 F |
| 90 F | 4.1 GPM | 30 F |
Published standard Source: Energy relation applied to the published 199,000 BTU input at an assumed 93 percent thermal efficiency. These are computed from the published input rating, not taken from the manufacturer curve. The installation manual curve is the authority and accounts for modulation.
What gas line it needs
At 199,000 BTU per hour this draws about 193 cubic feet of natural gas per hour. Over a 40 foot run the NFPA 54 low pressure table calls for 1 inch Schedule 40 pipe.
Check your own run length on the gas line page for the nearest input worked through in full. Gas line upsizing is routinely the largest single line in a tankless quote and the one most often missed from an estimate.
How it sits against the rest of its category
There is a full review of the A.O. Smith ATI-540P-N 199K BTU covering who it suits and who should not buy it.
Other whole house gas tankless in this catalog: Rheem RTG 7.0 GPM Natural Gas Indoor, Rheem RTG 8.4 GPM Natural Gas Outdoor, Rheem RTG 7.0 GPM Propane Outdoor, Rheem RTGH 6.8 GPM Natural Gas Indoor.
Compare them on input rating and on the figures the manufacturer actually publishes rather than on the headline number in the listing title, which in this category is frequently a maximum measured under conditions the listing never states.
Other whole house gas tankless
Rheem RTG 7.0 GPM Natural Gas Indoor
$653.77A 160,000 BTU non-condensing indoor unit, which is the cheapest way into a real brand-name gas tankless with a dealer parts channel behind it.
Best for: A one or two bathroom house in a warm inlet climate
Check price on Amazon
Rheem RTG 8.4 GPM Natural Gas Outdoor
$964.10An outdoor unit needs no flue at all, which removes the single most expensive and most dangerous part of a tankless retrofit in a climate that never freezes hard.
Best for: Warm climate retrofits where running a vent is the problem
Check price on Amazon
Rheem RTG 7.0 GPM Propane Outdoor
$770.17The propane version of the same outdoor chassis. Propane and natural gas units are not interchangeable and are not field convertible on this line.
Best for: Propane properties with no natural gas service
Check price on AmazonFrequently asked questions
- What are the specifications of the A.O. Smith ATI-540P-N 199K BTU?
- The listing publishes fuel, btu input, max flow gpm, condensing and related figures, shown in full in the table on this page. Anything not shown is something the listing does not publish, and this page does not estimate it.
- Does the A.O. Smith ATI-540P-N 199K BTU really deliver 10 gallons per minute?
- At some temperature rise, yes, and the listing does not say which one. Flow and rise trade against each other directly: the same unit that makes a given flow at a 35 F rise makes roughly half of it at a 70 F rise. Take the flow curve from the installation manual and read it at your own inlet temperature rather than trusting the headline figure.
- What gas line does the A.O. Smith ATI-540P-N 199K BTU need?
- About 193 cubic feet per hour, which over a 40 foot run calls for 1 inch Schedule 40 pipe under the NFPA 54 low pressure table. Fittings add equivalent length this does not account for, and other gas appliances share the meter, so a gas fitter sizes the whole system.
- Is this page based on hands-on testing?
- No, and we never claim otherwise. Everything here is compiled from the manufacturer listing, published specifications and the energy relations that turn those specifications into flow and recovery figures. We do not test products in person. Where a figure is not published, this page says so rather than estimating it.
- Are the prices on this page current?
- They come from verified catalog data at the time the page was built, and prices in this category move often. Treat any price shown as a guide and check the listing itself before deciding. Availability moves even faster than price does on water heater accessories in particular.
Gas and flue work belongs to a licensed plumber or gas fitter. An undersized gas line starves a burner, and a starved burner produces carbon monoxide. Backdrafting on an atmospheric vent is real, it is invisible, and it kills. Nothing on this page is a substitute for the sizing done by the person who signs the permit, and a working carbon monoxide alarm belongs on every floor of a house with a gas appliance.