Standard vs High-Efficiency vs Combi Boilers Compared
A standard cast-iron boiler is the simplest like-for-like replacement, a high-efficiency condensing boiler uses less gas, and a combination boiler heats the home and supplies hot water from one unit.
| Option | Efficiency | Venting | Hot water | Best for | Utility rebate |
|---|---|---|---|---|---|
| Standard (cast iron) | Typically 80% to 86% AFUE | Chimney or metal flue | Heat only, or paired with a separate water heater | Straight replacements and older radiator systems | None |
| High-efficiency condensing | 95% AFUE and up | PVC venting plus a condensate drain | Heat only, or paired with an indirect water heater | Lower gas bills on hot-water systems | Nicor Gas $350 for 95%+ AFUE |
| Combination (combi) | High-efficiency condensing | PVC venting plus a condensate drain | Heats the home and supplies on-demand hot water | Saving space by replacing the boiler and water heater with one unit | Nicor Gas $500 |
More detail on our boiler installation page.
Rebates you may qualify for
2026 utility programs for Northern Illinois homes. Amounts checked October 2026.
| Program | Equipment | Rebate |
|---|---|---|
| Nicor Gas | Boiler, 95%+ AFUE | $350 |
| Nicor Gas | Combination boiler (heat + hot water) | $500 |
The federal 25C tax credit ended for systems installed after December 31, 2025. Illinois income-qualified HEAR heat pump rebates (up to $8,000) are not available yet as of October 2026, and projects finished before the program opens will not qualify. We confirm the current status on your written quote. ComEd discounts come off your invoice when a ComEd heat pump-trained contractor installs qualifying equipment. Nicor Gas rebates require qualifying equipment and Nicor’s rebate application. Programs can change, so we confirm what your home qualifies for on your written quote. Programs and amounts can change, so confirm current details on the utility sites before you buy. Official details: Nicor Gas rebates · ComEd heat pump discounts.
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