Product images: Amazon listings

APUS 80,000 BTU Natural Gas Indoor Review

Name: APUS 80,000 BTU Natural Gas Indoor
Brand: APUS
SKU: B0GSYJMSZH

6.7Good · out of 10Not in our top-5 rankings

Written from the listing and 141 buyer reviews, not from our own use · How we rate

The APUS 80,000 BTU Natural Gas Indoor packs up to 3.6 GPM, a 0.81 UEF rating and temperature held within ±1 °F into one indoor gas tankless heater. Rated 6.7/10, it suits a one-bathroom home or a small apartment.

Variants of this model

These 141 buyer reviews (4.4/5) are shared by the 95,000 BTU Natural Gas Indoor and 80,000 BTU Natural Gas Indoor listings, so they speak for the family more than for one size.

APUS 95,000 BTU Propane Indoor · 4.42GPM, Propane, 95000BTU · 7.4/10
APUS 95,000 BTU Natural Gas Indoor · 4.42GPM, Natural Gas, 95000BTU · 6.8/10

Price$249.99Price on Sep 30, 2026 · may have changed

Check the price on Amazon ↗Affiliate link · price and stock on Amazon

Compare side by side ↗

Specifications

Brand	APUS
Category	Gas tankless water heaters
Fuel	Natural gas
Stated mounting location	Indoor
Stated maximum flow	3.6 GPM
Stated gas input	80,000 BTU/h
Stated voltage	120 V
Stated efficiency	0.81 UEF
Temperature hold	±1 °F, per the listing
Freeze protection	Stated in the listing
Buyer reviews	141 · 4.4/5, shared by the APUS listing family (2 variants)
ASIN	B0GSYJMSZH

Full listing title: APUS Natural Gas Tankless Water Heater, 80,000 BTU, 3.6 GPM Indoor

Listing evidence

Fuel	Natural Gas Full listing title
Stated mounting location	Indoor Full listing title
Stated maximum flow	3.6 GPM Full listing title
Stated gas input	80,000 BTU Full listing title
Stated voltage	120 V Listing text

Updated October 2026

Exact listing, ASIN B0GSYJMSZH

Rating from a published formula

Compared with its closest rivals

Two gas tankless heaters on natural gas too, with about the same flow, closest to it on our rating, each with a dated price.

Compare side by side ↗

APUS 80,000 BTU Natural Gas Indoor

6.7Good · out of 10$249.99 Price on Sep 30, 2026 · may have changed

Stated: 3.6 GPM · 80,000 BTU/h · 120 V
141 buyer reviews
Gas tankless water heaters

This product ↑

Vancepic 100,000 BTU Natural Gas Indoor

7.1Good · out of 10$259.99 Price on Sep 30, 2026 · may have changed

Stated: 4.3 GPM · 100,000 BTU/h
Gas tankless water heaters

See the review ↗

Novieex 100,000 BTU Natural Gas Indoor

5.7Fair · out of 10$269.97 Price on Sep 30, 2026 · may have changed

Stated: 4.3 GPM · 100,000 BTU/h · 110 V
45 buyer reviews
Gas tankless water heaters

See the review ↗

Up to 3.6 GPM from an 80,000 BTU burner

That's the maximum flow the listing states, and headline flows are usually quoted at a mild temperature rise. In January the water comes in nearer 42 °F, so a 105 °F shower needs a 63 °F rise and the unit gives you less; the flow chart in the manual shows how much less. At 2 GPM a shower (our calculator's figure), the headline means one shower at a time.

What it has going for it

What changes in the morning shower rush

0.81 UEF. Uniform Energy Factor is the federal efficiency label: the higher it is, the less gas or power goes up the vent instead of into your shower.

±1 °F hold. The burner adjusts as the flow changes, so the shower stays where you set it when somebody opens the kitchen tap. On paper, at least: that is the seller's claim.

One shower at a time, or two?

One at a time: that's what 3.6 GPM is for.

Two at once: not with this one. Look at the bigger units further down this page.

Great for you if…

You need one shower or one sink at a time, not the whole house
A shower that suddenly runs cold drives you mad
It will live in a garage, a cabin or another cold spot

Skip it if…

Two showers often run at once in your house: 3.6 GPM is a one-shower unit
You want the high-efficiency kind: the listing doesn't call it condensing
The far bathroom already waits a minute for hot water: no built-in recirculation is named

What APUS promises

The seller states, word for word, in the APUS 80,000 BTU Natural Gas Indoor listing:

Supplies tankless water heater gas on-demand hot water for a shower, sink and second fixture in a 1–2 person home, apartment or tiny home.
High-precision sensors and smart CPU regulate output within ±1°F of the selected setting, reducing hot/cold swings when another faucet opens.
Oxygen-free copper and demand-matched combustion reduce wasted heat.
20.55 H × 13.27 W × 5.91 D in saves floor space in rentals, renovations and tiny homes; 120 V AC powers controls.
Drain the unit completely below 41°F or during extended non-use to prevent freeze cracking.

That's the seller talking, not us. No listing tells you how it copes with 42 °F water at 6:45 in the morning.

APUS 80,000 BTU Natural Gas Indoor, view 3

Gas, venting and what's in the box

What the APUS 80,000 BTU Natural Gas Indoor listing names:

Up to 3.6 GPM
80,000 BTU/h input
Natural gas
Indoor mounting
0.81 UEF
±1 °F temperature hold claimed
Freeze protection named

For the APUS 80,000 BTU Natural Gas Indoor, the installation manual settles the venting, the gas line and the clearances.

APUS 80,000 BTU Natural Gas Indoor, view 4

Price and cost per GPM of stated flow

$249.99 Price on Sep 30, 2026 · may have changed

At the price on Sep 30, 2026, each GPM of stated maximum flow works out at about $69.44 (price ÷ stated GPM, our arithmetic). That puts it in the cheaper third of the 45 indoor gas tankless heaters we have a price and a stated flow for.

The heater is often the smaller half of the bill: the venting, a gas line that may need upsizing and a licensed installer's day come on top.

The button opens the exact listing (ASIN B0GSYJMSZH), where today's price, stock and seller apply. Sizes and variants of the same family often sit at different prices.

APUS 80,000 BTU Natural Gas Indoor, view 5

A better fit for your house?

Two showers and the dishwasher at once? The ThermoMate CZ422LP Propane Indoor (7.8/10) states up to 5 GPM.

On propane, not natural gas? The Novieex 100,000 BTU Propane Indoor (7.2/10) runs on propane.

The far bathroom takes ages to run hot? The Rinnai REP199eN Smart-Circ (7.3/10) has built-in recirculation, per its listing.

Our take

The verdict

The APUS 80,000 BTU Natural Gas Indoor earns its place with up to 3.6 GPM and a 0.81 UEF rating. 141 buyers give it 4.4/5, which is a solid sign. The catch with this APUS indoor gas tankless heater: no word on the warranty. We'd pick it if you need one shower or one sink at a time, not the whole house; otherwise, put it next to the APUS 140,000 BTU Natural Gas Indoor first.

Check the price on Amazon ↗Affiliate link · price and stock on AmazonAll gas tankless water heaters →

Living with it

Install day

Old tank out, unit on the wall, vent through the wall or the roof. Plan the gas line for 80,000 BTU/h; a licensed pro handles it, and often a permit.

The first shower

Hot water arrives after the cold already in the pipes, then stays (within ±1 °F, per the listing). A trickle from a bathroom tap may not light the burner; open it a bit more.

The first winter

January water comes in colder, so the same unit gives fewer GPM. Stagger the showers if you sized it tight.

Once a year

Flush the heat exchanger with a pump and a descaler (the service valves make it an hour's job), and clean the inlet filter. Our flushing and descaling guide has the checklist.

What buyers say

Buyers give it 4.4/5, a strong record, above our ranked picks' 4.3 average. 141 reviews is a fair sample, enough for the average to mean something. The same reviews appear on both variants of the APUS family, so they describe the family rather than this exact variant.

The numbers

Buyer rating: 4.4/5
Reviews: 141
Ranked picks' average: 4.3/5

The one thing we'd check first

Before you order the APUS 80,000 BTU Natural Gas Indoor, check your gas line: 80,000 BTU/h is a lot of gas at once, so ask your plumber whether the existing line can feed it.

Before you buy

Your winter flow

3.6 GPM is the headline. In a northern January the water comes in near 42 °F, so a 105 °F shower needs a 63 °F rise and the real flow drops. Our flow-rate calculator runs the numbers for your house.

Vent and gas line

Ask the plumber to check the gas line size and the meter against the heater's input, and to quote the vent route at the same visit. Our install cost guide shows what that usually adds.

The warranty terms

Read what it requires: a licensed install, the gas type and regular flushing are the usual conditions.

Flushing

Hard water scales the heat exchanger. Service valves on the water lines turn the yearly flush into an hour with a bucket and a pump; our flushing and descaling guide shows the routine.

How it compares

How the APUS 80,000 BTU Natural Gas Indoor stacks up against the closest alternative, the APUS 140,000 BTU Natural Gas Indoor.

Criterion	APUS 80,000 BTU Natural Gas Indoor	APUS 140,000 BTU Natural Gas Indoor
Our rating	6.7/10	6.7/10
Max flow	3.6 GPM	6.8 GPM
Gas input	80,000 BTU/h	140,000 BTU/h
Buyer reviews	141 · 4.4/5	102 · 4.0/5

Both score 6.7/10. The APUS 140,000 BTU Natural Gas Indoor adds more flow (6.8 GPM) and a bigger burner (140,000 BTU/h), while the APUS 80,000 BTU Natural Gas Indoor brings a higher buyer rating (4.4/5).

Compare side by side ↗See the APUS 140,000 BTU Natural Gas Indoor review →

The score in detail

How we rated it

Our score: 6.7/10

Buyer rating (45%)

39.6 / 45

4.4/5 average

Review volume (35%)

20.4 / 35

141 buyer reviews, shared by 2 variants

Documented specifications (20%)

7.4 / 20

37/100 listing documentation score

Our rating is an evidence index on a 0–10 scale. It is not a buyer star rating, and we have not used the product ourselves.

Buyer rating (45%): the captured average of the review pool shown on both variants of the APUS listing family, damped when there are fewer than 50 reviews.
Review volume (35%): more reviews mean more reliable evidence, on a logarithmic scale up to 5,000 reviews.
Documented specifications (20%): how completely the exact listing documents the attributes that matter.

Our editors then look at how it compares with the other heaters we rate. A commission is never an input to the rating. Read the full methodology.

Read the methodology →

Frequently asked questions

Is the APUS 80,000 BTU Natural Gas Indoor any good?

We rate it 6.7/10 (good). It is based on 141 buyer reviews averaging 4.4/5, shared by the APUS listing family (2 variants) and the specifications stated in the listing.

How much hot water can the APUS 80,000 BTU Natural Gas Indoor deliver?

The listing states a maximum flow of 3.6 GPM and a gas input of 80,000 BTU/h on 120 V. The headline flow is a mild-weather number: with cold winter water coming in, the same unit gives you less. Read the maker's flow chart at your winter rise, or let our flow-rate calculator do the sums.

Can the APUS 80,000 BTU Natural Gas Indoor be installed indoors?

Yes, the listing says indoor mounting. That means a vent route to the outside, combustion air and a gas line sized for the unit, all as the maker and your local code require. A licensed plumber or gas fitter sorts that out.

Are the reviews specific to the APUS 80,000 BTU Natural Gas Indoor?

No. The same review pool appears on every variant of the APUS listing family: 141 reviews averaging 4.4/5 on the APUS 95,000 BTU Natural Gas Indoor and APUS 80,000 BTU Natural Gas Indoor. The count therefore describes the family, not this exact variant, and in our rankings the family takes a single slot.

What do you get with the APUS 80,000 BTU Natural Gas Indoor?

Its listing states up to 3.6 GPM, a 0.81 UEF rating, temperature held within ±1 °F and freeze protection. These are the seller's figures, not our measurements: how steady the temperature is in your shower and how it copes with your winter water can't be read from a listing.

What should I check before ordering the APUS 80,000 BTU Natural Gas Indoor?

Your winter flow: 3.6 GPM is the headline. In a northern January the water comes in near 42 °F, so a 105 °F shower needs a 63 °F rise and the real flow drops. Our flow-rate calculator runs the numbers for your house. Vent and gas line: ask the plumber to check the gas line size and the meter against the heater's input, and to quote the vent route at the same visit. Our install cost guide shows what that usually adds. The warranty terms: read what it requires: a licensed install, the gas type and regular flushing are the usual conditions. Flushing: hard water scales the heat exchanger. Service valves on the water lines turn the yearly flush into an hour with a bucket and a pump; our flushing and descaling guide shows the routine.

Where can I buy the APUS 80,000 BTU Natural Gas Indoor?

We link to the exact listing on Amazon, where today's price, stock and seller apply. It is an affiliate link, and it has no effect on the rating.

Have you used the APUS 80,000 BTU Natural Gas Indoor yourselves?

No, we haven't used it ourselves. Everything on this page comes from its listing and 141 buyer reviews, read line by line and weighed with our published formula.

Gas tankless water heaters ↗All APUS products Comparison tool All product reviews