Heating and hot water in one compact, wall-hung unit. Expert combi boiler replacement and installation across Nassau and Suffolk County since 1979.
A combi (combination) boiler provides both home heating and on-demand domestic hot water in a single compact unit. When you open a hot water tap, the combi boiler switches from heating mode to instantly heat water directly from the mains, eliminating the need for a separate water heater or hot water storage tank. This makes combi boilers an attractive option for smaller Long Island homes, condos, and apartments where space is limited and hot water demand is moderate.
Combi boilers are extremely popular in Europe where they account for the majority of residential boiler installations. On Long Island, they are growing in popularity as homeowners discover the space savings and simplicity of replacing both an aging boiler and water heater with a single unit. Modern combi boilers achieve 95-98% AFUE, making them among the most efficient heating appliances available. They are gas-fired, wall-mounted, and about the size of a kitchen cabinet.
However, combi boilers are not the right fit for every home. Because they heat domestic hot water on demand, they have a limited flow rate, typically 3 to 5 gallons per minute. This is sufficient for one or two simultaneous hot water uses (one shower plus one faucet, for example) but not for larger homes where three or four bathrooms may be running at the same time. We help you determine whether a combi boiler is the right choice for your specific hot water demand and home size.
Understanding the trade-offs between a combi boiler and a traditional boiler paired with a separate water heater (or indirect tank) is essential for making the right decision.
| Feature | Combi Boiler | Boiler + Indirect Tank | Boiler + Water Heater |
|---|---|---|---|
| Equipment Count | 1 unit | 2 units (boiler + indirect tank) | 2 units (boiler + water heater) |
| Installed Cost | $8,500 – $9,800 | $9,200 – $11,600 | $6,500 – $14,000 |
| Space Required | Wall-mounted (minimal) | Floor space for indirect tank | Floor space for water heater |
| Hot Water Delivery | On-demand (3 – 5 GPM) | Stored (40 – 80 gallons) | Stored (40 – 50 gallons) |
| Simultaneous Use | 1 – 2 fixtures | 3 – 4+ fixtures | 2 – 3 fixtures |
| Best Home Size | 1 – 2 bathrooms | 2 – 4+ bathrooms | 2 – 3 bathrooms |
| Efficiency | 95 – 98% AFUE | 80 – 98% AFUE | 80 – 98% AFUE (boiler), 60 – 96% (WH) |
| Maintenance | 1 unit to service | 2 units to service | 2 units to service |
If your existing boiler and water heater are both nearing the end of their lifespan, a combi boiler can be more cost-effective than replacing both units separately. For a full comparison of all boiler types, see our boiler types comparison guide.
Your home has 1 to 2 bathrooms with moderate hot water demand.
You want to eliminate a separate water heater and free up basement or utility room space.
Your current boiler and water heater are both aging and due for replacement.
You prefer the simplicity of one unit to install, maintain, and eventually replace.
You have access to natural gas (combi boilers are gas-only on the residential market).
Your home has 3 or more bathrooms with frequent simultaneous hot water use.
You have a large soaking tub or whirlpool that requires a high volume of hot water at once.
Your home is larger than 2,500 square feet with high heating demand.
You need the hot water recovery rate that a stored tank system provides for a large family.
You rely on oil heat (residential combi boilers are not available for oil-fired applications).
| Brand | Installed Price | AFUE | DHW Flow Rate | Highlights |
|---|---|---|---|---|
| Navien | $8,400 – $9,500 | 95% | 4.0 GPM | NCB series. Most popular combi on LI. WiFi-enabled. Compact. |
| Bosch | $8,400 – $9,800 | 95% | 3.4 – 4.5 GPM | Greenstar Combi. Quiet operation. German engineering. |
| Weil-McLain | $8,400 – $9,500 | 95% | 3.5 – 4.2 GPM | ECO Tec Combi. Stainless steel heat exchanger. Reliable. |
| Burnham | $8,800 – $9,800 | 95% | 3.5 GPM | Alpine Combi. Well-known in Northeast market. |
| Buderus | $8,200 – $9,500 | 95% | 3.7 GPM | GB142 Combi. Premium. Excellent build quality. |
All prices shown are equipment only. Total installed cost depends on model selection, gas line sizing, and venting requirements. For a full cost breakdown, see our boiler replacement cost guide.
A combi boiler eliminates both a separate water heater and the hot water storage tank, freeing up significant utility room or basement space. In smaller Long Island homes, condos, and mother-daughter setups, this space savings can be substantial.
Typical space freed: A floor-standing boiler occupies roughly 6 to 10 square feet. A water heater adds another 4 to 6 square feet. A wall-hung combi boiler takes zero floor space and mounts in an area roughly 18 inches wide by 28 inches deep.
Combi boilers vent through PVC pipe directly through an exterior wall (direct vent), which means they do not require a chimney. This gives additional flexibility in placement and can be especially beneficial when the existing chimney is deteriorating and would otherwise need repair.
Sizing for both heating and domestic hot water demand based on your home and fixture count.
Removal of the existing boiler and water heater (if switching to combi).
Gas line sizing verification. PVC direct-vent installation through exterior wall.
Required mechanical permit and post-installation building department inspection.
Heating supply/return, domestic cold water inlet, and hot water outlet connections.
Combustion analysis, heating zone testing, DHW flow rate testing, and homeowner walkthrough.
Combi boilers typically last 12 to 15 years, slightly shorter than traditional boiler-only units because they work harder (handling both heating and hot water year-round). Signs that replacement is approaching include declining hot water output or temperature fluctuations, error codes appearing on the digital display, ignition failures or frequent pilot issues, rising fuel bills despite similar usage, and a unit age of 12 years or more. For a detailed guide on replacement timing, see 10 signs it is time to replace your boiler or use our repair vs. replace decision guide.
Every combi boiler project begins with a free in-home assessment. We evaluate your heating load, count your fixtures, test your water pressure, and determine whether a combi boiler is the right fit. If it is not, we recommend the best alternative. Call (631) 860-6681 or schedule online.
Schedule a free in-home assessment. We will evaluate whether a combi boiler is the right fit and provide a detailed written estimate with no obligation.