Answering the most common buyer question: which hot water tank burner assembly is right for your water heater model and fuel type. This guide highlights five solid options, from A. O. Smith to Rheem, and explains who each product is best for. Use this to compare compatibility, installation scope, and safety considerations. The selections cover natural gas and liquid propane configurations, various burner sizes, and kit components designed to simplify replacement for common residential heaters.
| Product | Brand | Best For |
|---|---|---|
| AO Smith 100112342 – K, FINAL BURNER ASSY, NAT, 16″, #37 ORIFICE | A. O. Smith | Natural gas, 16″ burner, standardized orifice |
| AO Smith 100094001 – K, FINAL BURNER ASSY, NAT | A. O. Smith | Natural gas, direct replacement for common NAT models |
| Rheem SP45034 Burner Assembly Kit | Rheem | Gas-fired, safety ignitor/pilot assembly, OEM parts |
| Rheem SP43285 Burner Assembly – 40 in. Kit | Rheem | 40″ burner kit, larger replacement for extended assemblies |
| Rheem SP43282 Burner Assembly – 16 in. Kit | Rheem | 16″ burner kit, standard residential sizes |
| Rheem AM40277-1 Water Heater Burner Assembly | Rheem | General burner assembly replacement |
| AO Smith 100112347 – K, FINAL BURNER ASSY, LP, 16″, #51 ORIFICE | A. O. Smith | Liquid propane, 16″ burner with LP orifice |
AO Smith 100112342 — K Final Burner Assembly
The K Final Burner Assembly for NAT gas on a 16″ burner with a #37 orifice is designed for standard natural gas replacements. This part is best for residential natural-gas water heaters that require a direct-fit, factory-style burner. It is a straightforward swap for compatible AO Smith NAT models and supports typical ignition and flame generation for reliable hot water performance. Caution: verify the 16″ burner length and orifice size matches your existing unit to avoid improper flame geometry.
AO Smith 100094001 — NAT Final Burner Assembly
This NAT final burner assembly serves as a direct replacement for natural-gas water heaters that need a ready-to-install burner with standard NAT configuration. It’s best for homeowners replacing an aging burner in a typical AO Smith NAT model. Reason to choose: compatibility with common natural-gas appliances and avoidance of mismatched orifice sizes. Limitation: ensure the unit’s burner length and diameter align with your tank’s burner compartment.
Rheem SP45034 Burner Assembly Kit
The SP45034 Kit from Rheem includes the ignition and safety components needed to replace the burner and pilot assembly for compatibility with many Rheem water heaters. It’s best for buyers who want a complete OEM-style kit that covers igniter and safety features together. Choose this if you’re focused on restoring proper pilot ignition and flame safety in one package. Caution: confirm that your heater’s model matches the kit’s compatibility notes by serial number to avoid incompatibilities.
Rheem SP43285 Burner Assembly — 40 in. Kit
This 40-inch burner assembly kit is designed for larger replacement projects or heaters that accommodate extended burner chambers. Best for homes with high-demand hot water needs or certain Rheem models requiring longer burner assemblies. It includes all OEM parts to replace the burner assembly and assists in maintaining efficient heat generation. Limitation: longer kits may not fit compact or space-limited furnace closets.
Rheem SP43282 Burner Assembly — 16 in. Kit
The 16-inch Rheem burner kit is a standard residential option for 16″ burner compartments. Best for typical gas-fired water heaters that require a straightforward, mid-size burner replacement. It’s a safer pick if your model matches the 16″ chamber and the corresponding valve and ignitor setup. Caution: confirm the precise model and serial compatibility, as not all 16″ kits fit every Rheem NAT or LP heater.
Rheem AM40277-1 Water Heater Burner Assembly
The AM40277-1 is a general burner assembly replacement from Rheem, intended for standard gas-fired water heaters. This option is best for buyers seeking a common, no-frills burner replacement that aligns with many Rheem models. Consider this when the focus is restoring core burner functionality without additional ignitor or safety kit components. Limitation: verify model compatibility and ensure the unit supports your heater’s gas type and venting configuration.
AO Smith 100112347 — LP Final Burner Assembly
This LP burner assembly is designed for natural gas-to-LP configurations, with a 16″ burner and a #51 orifice. Best for propane-fueled replacements on AO Smith units needing an LP-specific burner. Choose this if your heater uses LP gas and the orifice size matches #51. Caution: incorrect LP orifice or length can affect flame stability and efficiency.
Buying Guide
What should you check before buying a burner assembly?
- Fuel type: NAT or LP. Match the burner and orifice to your fuel source.
- Burner length and chamber fit: ensure the kit length (16″, 40″, etc.) matches your heater’s burner compartment.
- Orifice size: confirm that the #37 or #51 orifice aligns with your heater model and gas pressure.
- Ignition and safety: decide whether you need a full ignition/pilot assembly kit or a simple burner only.
- Model compatibility: verify serial numbers and model numbers against the replacement part’s notes.
- OEM vs aftermarket: OEM replacement parts typically maintain exact fit and function for your brand.
Frequently Asked Questions
- What is a burner assembly responsible for in a water heater?
It generates the flame to heat water by burning the gas supplied to the unit. - How do I know if a burner kit fits my model?
Check your water heater’s model and serial number, then compare with kit compatibility notes. - Is it safer to replace the entire burner kit or just the burner?
If ignition and safety components are worn, a full kit with ignitor and safety features is advisable. - Can I mix NAT and LP parts?
No. NAT and LP configurations use different orifices and gas pressure settings; use the correct configuration. - Do I need professional installation?
Replacing a burner involves gas connections; consider professional service if uncertain about safety. - Will these parts affect warranty?
Replacement parts sourced from OEM listings typically align with manufacturer guidelines; check warranty terms for your unit.
Buying Considerations at a Glance
- Best for NAT gas: AO Smith 100112342 and 100094001 replacements.
- Best for LP gas: AO Smith 100112347 final burner assembly.
- Best all-around OEM kit: Rheem SP45034 for integrated ignition and safety features.
- Longer replacement kits: Rheem SP43285 suits larger burner chambers; ensure compatibility.
- Standard 16″ replacements: Rheem SP43282 and AO Smith NAT/LP 16″ options fit common residential heaters.