The Rinnai I-Series Plus combi boilers are the products in this selection designed to provide both home heating and domestic hot water. The 120,000-BTU model is a middle-capacity option, the 90,000-BTU model is the lower-capacity choice, and the 150,000-BTU model offers the highest listed capacity. The other listings are tankless water heaters, not home-heating boilers, so they should not be treated as direct boiler replacements. Confirm fuel type, heating load, installation requirements, and local code before choosing.
| Product | Best suited for | Key distinction |
|---|---|---|
| Rinnai 150K-BTU combi boiler | Buyers comparing the highest listed boiler capacity | Space heating and hot water; 96% AFUE listed |
| Rinnai 120K-BTU combi boiler | Buyers considering a mid-capacity combi unit | Space heating and hot water; 96% AFUE listed |
| Rinnai 90K-BTU combi boiler | Buyers considering the lowest listed boiler capacity | Space heating and hot water; 96% AFUE listed |
| QERPRE 85K-BTU tankless heater | Buyers seeking domestic hot water only | Natural gas tankless water heater; not a space-heating boiler |
| APUS propane tankless heater | Propane users seeking domestic hot water only | Propane appliance; not a natural gas boiler |
Rinnai I-Series Plus 150K-BTU Combi Boiler
Best for: Buyers comparing combi boilers who need to evaluate the highest listed heating capacity among the three Rinnai boiler options here. The product is described as providing home heating and hot water in one appliance, which can appeal to households considering a combined system rather than separate equipment.
The listing specifies a 150,000-BTU capacity, a 96% AFUE rating, and Smart Sense Gas Valve technology. AFUE is the listing’s stated annual fuel utilization efficiency figure; it is useful for comparing listed efficiency, but it does not determine whether the appliance is correctly sized for a particular home.
Why it was selected: It is explicitly presented as a condensing combi heat boiler and includes both space-heating and hot-water functions. Its larger capacity makes it a distinct comparison point against the 90K- and 120K-BTU versions.
Limitation: The listing describes natural gas or propane operation, so verify the exact fuel configuration and installation requirements with the manufacturer and a qualified installer. Do not select capacity based on square footage alone; a heating-load calculation is important.
Rinnai I-Series Plus 120K-BTU Combi Boiler
Best for: Homeowners comparing a mid-capacity combi boiler option for space heating and domestic hot water. Its 120,000-BTU rating falls between the 90K and 150K versions in this selection, making it useful for comparing capacity tiers—not a substitute for calculating a home’s actual heating load.
The product description lists a 96% AFUE rating and Smart Sense Gas Valve technology. It is also described as combining hot-water supply and home heating in one appliance. That combination may be relevant when planning a system that serves both functions, but the listing does not provide enough information to determine hot-water output under a specific household’s simultaneous demand.
Why it was selected: It is one of the three listed Rinnai products explicitly identified as a condensing combi heat boiler. The 120K-BTU model offers a clear capacity comparison for buyers who do not want to compare only the lowest and highest listed options.
Limitation: Confirm whether the exact unit is configured for the home’s fuel source. The listed efficiency and capacity do not establish that it will fit a particular hydronic system or meet local installation rules.
Rinnai I-Series Plus 90K-BTU Combi Boiler
Best for: Buyers evaluating the lowest listed boiler capacity in this group. The 90,000-BTU rating makes it the lower-capacity comparison among the three Rinnai combi models, but it should not be assumed suitable for a smaller home without a professional heat-loss assessment.
The listing describes this unit as providing home heating and hot water, with a stated 96% AFUE rating and Smart Sense Gas Valve technology. Those features distinguish it from the water-heater-only products in this roundup. A combi system’s suitability depends on both the building’s heating demand and the household’s hot-water needs.
Why it was selected: It is a boiler product with a combined heating and hot-water function, and it gives buyers a lower listed capacity to compare against the 120K and 150K models.
Limitation: The product description mentions natural gas or propane. Verify the appliance’s specific fuel configuration, venting, and system requirements before purchase. A lower BTU rating is not automatically more efficient or better sized for every home.
QERPRE 85K-BTU Natural Gas Tankless Heater
Best for: Buyers seeking a natural gas tankless water heater for domestic hot water, rather than a boiler for whole-home space heating. The listing specifies 85,000 BTU and up to 3.6 gallons per minute, with use described for two to three water points. Those figures may help buyers compare hot-water options, but they do not make this a boiler.
The listed features include a self-modulating temperature system, a stated temperature stability of ±1°F, and three modes: four-season, kitchen, and bathtub. These are water-heating functions. The product description does not identify hydronic space-heating service, so buyers replacing a home boiler should not assume it can serve that purpose.
Why it was selected: It is the only clearly identified natural gas tankless water heater in the supplied non-boiler options, making it relevant to readers comparing domestic hot-water equipment alongside a boiler search.
Limitation: This is not a direct substitute for a natural gas home boiler. Confirm the intended application, gas and venting requirements, and local code before purchase.
APUS 95K-BTU Propane Tankless Heater
Best for: Propane users comparing tankless domestic hot-water equipment for multiple fixtures. This product is included as an adjacent option, not as a natural gas home boiler. Its listing identifies propane fuel, a 95,000-BTU capacity, and a maximum flow rate of 4.42 GPM.
The features include a stated 95°F–140°F temperature setting range, a 120V specification, anti-freeze functionality, and an LED touchscreen. The description also states a 0.66-GPM low-flow start and up to 98% thermal efficiency, alongside a UEF of 0.81. These are listing claims for a water heater and should not be compared directly with a boiler’s AFUE rating.
Why it was selected: It provides a useful contrast for buyers considering fuel type and hot-water-only equipment. The listing describes simultaneous demand for multiple fixtures, but does not describe space-heating service.
Limitation: This is a propane water heater, not a natural gas boiler. Avoid it if the requirement is a natural-gas-fired appliance that heats a home’s hydronic system.
Buying Guide: How to Choose a Natural Gas Home Boiler
Start by separating boilers from tankless water heaters. A boiler heats a home through a heating system such as radiators or another hydronic distribution setup. A tankless water heater supplies domestic hot water at taps and showers. A combi boiler is designed to provide both functions, while a water-heater-only listing should not be assumed to heat living spaces.
Does the appliance need to heat the home, hot water, or both?
Write down the system’s required jobs before comparing product specifications. If the appliance must heat rooms through an existing hydronic system, look for a product explicitly described as a boiler and verify compatibility with that system. If the requirement is only showers, sinks, or other domestic hot water, a tankless water heater may be relevant. If one appliance must do both, compare combi boilers and confirm their hot-water capacity for expected use.
How should you compare boiler capacity?
The listed Rinnai options span 90,000, 120,000, and 150,000 BTU. These figures provide a simple capacity comparison, but they are not enough to establish the right size for a house. A qualified professional can calculate heating load using building characteristics, local climate, insulation, windows, and other factors. Oversizing or undersizing should not be addressed by guessing from floor area alone.
For a combi boiler, ask about both space-heating output and domestic hot-water performance. The supplied product descriptions give BTU ratings but do not provide all the information needed to assess hot-water delivery under a home’s peak demand. Check the full manufacturer specifications and installation documentation.
What does AFUE tell you?
AFUE is a seasonal efficiency measure used for furnaces and boilers. The Rinnai listings state 96% AFUE, which can be used as a starting point when comparing the stated efficiency of those models. It does not predict a household’s exact utility bill or establish whether a unit is the right size. Installation, controls, maintenance, weather, and household use also affect real-world energy consumption.
Do not compare AFUE directly with the APUS listing’s thermal-efficiency or UEF figures as if they were interchangeable. The APUS product is a propane tankless water heater, and its listing supplies different measures for a different appliance type.
Is the fuel type correct for your home?
Confirm whether the exact model is configured for natural gas or propane before ordering. The Rinnai descriptions mention both fuels, but the listing details supplied here do not establish the configuration of each unit. The QERPRE listing identifies natural gas, while the APUS listing identifies propane. Fuel availability, appliance setup, gas connections, and local requirements all matter.
Never treat a propane model as a natural gas model without manufacturer-approved conversion information and qualified installation. Ask the installer to verify the appliance’s fuel specification and the home’s gas supply before work begins.
What installation details should you check?
Boiler installation can involve venting, condensate handling, water connections, gas supply, electrical power, controls, and integration with existing heating equipment. The product features provided here do not answer every installation question. Ask a qualified installer to review the complete manual, the site conditions, and applicable local codes before purchasing.
Also confirm whether the appliance is intended for indoor installation and whether its connection requirements match the planned location. A product page’s headline features are not a substitute for installation instructions or a professional site assessment.
When does a combi boiler make sense?
A combi boiler may be worth considering when one appliance is intended to serve both space heating and domestic hot water. It can reduce the need to plan around separate appliances, but whether that arrangement is suitable depends on the house, heating system, and simultaneous hot-water demand. Compare the Rinnai models by capacity and verify the details that are not included in the supplied feature summaries.
If the existing home has separate heating and water-heating equipment, ask an installer to compare a combi replacement with retaining or replacing separate systems. The best choice depends on system design, installation needs, and the household’s usage—not just the number of appliances.
Frequently Asked Questions
Which product in this list is a natural gas home boiler?
The Rinnai I-Series Plus 90K-, 120K-, and 150K-BTU products are described as condensing combi heat boilers. Their listings mention natural gas or propane, so verify the specific fuel configuration before purchase.
Can a tankless water heater replace a home boiler?
Not necessarily. A tankless water heater supplies domestic hot water, while a home boiler provides space heating. The QERPRE and APUS listings describe water heaters, not hydronic space-heating boilers.
Which Rinnai model has the lowest listed capacity?
The Rinnai I-Series Plus 90K-BTU combi boiler has the lowest stated capacity among the three Rinnai models in this selection. A heating-load calculation is still needed to determine whether it suits a particular home.
Do these listings confirm natural gas compatibility for every Rinnai model?
No. The descriptions mention natural gas or propane but do not establish the exact configuration for each listing. Confirm the fuel type for the specific unit with the seller, manufacturer documentation, or installer.
Is the APUS tankless heater a natural gas option?
No. The supplied product name identifies it as a propane tankless water heater. It is not a natural gas home boiler and is included only as an adjacent hot-water comparison.
What should a homeowner do before selecting a boiler size?
Have a qualified professional assess the home’s heating load and review the existing heating system, fuel supply, and installation requirements. The BTU rating alone is not enough to establish a suitable model.