Collection: On Demand Water Heaters & Boilers

Electric Thermolec boilers need no venting or gas line, making them simpler to install and a common choice for smaller spaces or off-grid-adjacent setups. Gas and propane Lochinvar boilers cost more upfront but handle larger heating loads more efficiently and are the standard choice for whole-house systems or larger square footage.

Sizing depends on your square footage, climate, insulation, and whether the boiler is also supplying domestic hot water. As a rough guide, smaller homes or single zones often work with 3–9kW electric units, while larger homes typically need 15kW+ electric or a gas boiler in the 80K–150K BTU range. Use the sizing guide linked above for a more precise number, or contact our team with your square footage.

Flow rate depends on how many fixtures might run hot water at the same time — a shower, a sink, a dishwasher, etc. Use our Gallons Per Minute calculator to estimate your household's peak demand, then match it against a boiler's rated GPM output — this matters most if you're also using the unit for domestic hot water through a combi model.

Gas and propane units heat water faster and handle higher continuous demand, which matters more in larger homes or colder climates where recovery time counts. Electric units cost less to install since there's no venting or gas line, run quieter, and are simpler for a DIYer to handle, but they're generally better suited to smaller loads. If you're deciding between the two, your square footage and how many fixtures run at once are the deciding factors — not just budget.

A standard boiler only heats water for your radiant floor system. A combi boiler does that plus supplies domestic hot water for sinks and showers, so you don't need a separate water heater. All our 110K BTU and up gas models are combi units; the 80K BTU model is boiler-only.

We don't recommend it. Gas and propane boilers involve gas line connections and venting that should be handled by a licensed or experienced professional. Electric Thermolec boilers are more DIY-friendly since they skip gas lines and venting entirely.

If you are buying a HUG Tank, the matching fitting kit comes complimentary with your boiler. If you are using your own boiler, then you will have to talk to a sales tech if a brand fitting kit is not available.

Yes — every item listed (and a nice handful of unlisted water heaters) are available for domestic use. Just order online or reach out to sales to see what kind of deal you can secure.

We sell very few of them because the HUG Hydronics system is a closed loop system that should work well if you start with filtered water. If you are installing for domestic use; some manufacturers require a filter to maintain the warranty on tankless units — check your specific boiler's documentation, or ask us before you install.

Most standard installs don't need it — the upgrade kit is for boilers that need a higher flow rate or specialized setups like geothermal. For custom flow setups or unique applications, connect with our engineering team — ask for Ryan.