13 Best Propane Boiler for Radiant Floor Heat

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Specs are compiled from manufacturer listings and verified buyer reviews and can change over time — please confirm the key details on the product page before buying.

You want warm tile under your bare feet, not a boiler that eats your budget and still leaves the far room cold. The catch with radiant floor heat is that the boiler is only half the system — the other half is how much heat you actually need to push through those loops. This guide walks you through both halves in plain English, so you can pick a unit that fits your square footage, your fuel setup, and your installer’s patience.

This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.

Heat output, fuel type, and venting decide more about your comfort than any badge on the cabinet. Below you’ll find honest picks and the spec math that matters for a propane boiler for radiant floor heat.

Top Picks

Rinnai RX199iN Condensing Smart Sense Tankless Water Heater
Best OverallRinnai RX199iN Condensing Smart Sense Tankless Water Heater4.5+★150+ ratingsOne cabinet that runs your floor loops and your hot showers from the same burner. The number worth circling here is 199,000 BTU — the hourly heat energy this unit can push into water.Check price on Amazon
Rinnai i150SN Condensing Gas Boiler, Whole Home Heater (150K BTU)
Purpose-Built PickRinnai i150SN Condensing Gas Boiler4.0+★The one unit on this list actually labeled a boiler, not a water heater.Check price on Amazon
Rinnai CX199iN SENSEI CX Commercial Tankless Water Heater 199,000 BTU
Best for Big LoadsRinnai CX199iN SENSEI CX Tankless Water Heater4.5+★20+ ratingsA learning pump inside the cabinet that studies when you draw heat. The standout on the CX199iN is Smart-Circ — an internal pump paired with software that watches your usage patterns and then schedules recirculation to match.Check price on Amazon

How To Choose The Best Propane Boiler for Radiant Floor Heat

Radiant floor heat asks the boiler to do something different from a shower heater. It pushes warm water through long loops buried in or under your floor at a lower, steady temperature for hours, rather than blasting a short burst for a faucet. That changes what matters: steady low-end modulation, a heat exchanger built for constant flow, and a control board that talks to zone pumps.

Start with BTU output, then work backward

Heat output is measured in BTUs (British thermal units — the standard unit of heat energy in the US). A 150,000 BTU boiler puts out more heat per hour than a 105,000 BTU unit, and matching that number to your slab area and climate is the first decision. Oversize it and the boiler short-cycles; undersize it and the floor never catches up on the coldest nights.

Condensing or non-condensing

A condensing boiler captures heat from the exhaust gas that a standard unit sends up the flue, which is why condensing models list efficiency figures in the high 90s. That extra step produces acidic condensate, so you need a drain and often a neutralizer — plan for that line before the installer arrives.

Propane, natural gas, or convertible

Some units ship set up for natural gas and need a qualified technician to convert them to liquid propane. Others carry a gas control system that accepts either fuel. Confirm which one you are buying before the crate is opened, because the wrong fuel setup is the single most common reason a new heater will not fire.

The controls and zones you will actually use

Radiant homes usually run several zones — bedrooms, living area, garage — each with its own thermostat and pump. A boiler with multizone control connects those pumps and thermostats directly, so you are not adding a separate control box on the wall. Check the water temperature range too, since floor loops typically want cooler water than a domestic hot water tank.

Side-by-Side Comparison

Model Best For Heat Output Fuel Weight Amazon
Rinnai RX199iN Condensing Smart Sense★ Best Overall Whole-home heat and hot water 199,000 BTU Propane or natural gas 55 lb Amazon
Rinnai i150SN Condensing Gas BoilerPurpose-Built Pick Dedicated multi-zone hydronic heating 150,000 BTU Natural gas (convertible) 68.3 lb Amazon
Rinnai CX199iN SENSEI CX CommercialBest for Big Loads Learning recirculation on demand 199,000 BTU Propane or natural gas 27.2 kg Amazon
Rinnai RXP199iN Condensing Smart Sense Built-in recirculation pump 199,000 BTU Propane or natural gas 58 lb Amazon
Hydronic Radiant Heat Control Panel One-zone distribution, pre-assembled — Works with multi-heat sources 110 lb Amazon
Raypak 014786-156A Propane Pool Heater Large propane water volumes 150,000 BTU Propane 115 lb Amazon
Pentair EC-462024 Natural Gas 125K Small bodies of water 125,000 BTU Natural gas 20 lb Amazon
Pentair EC462025 MasterTemp 125 Propane Small pools up to 15,000 gallons 125,000 BTU Propane 109.8 lb Amazon
Raypak PR106AENC Pool Heater Above-ground pools and spas 105,000 BTU Natural gas 78.8 lb Amazon
Hayward H-Series Propane Pool Heater Inground pools and spas 150,000 BTU Propane 145 lb Amazon
Rinnai EX38DTP Direct Vent Wall Furnace Room-by-room propane heat 36,500 BTU Propane 108 lb Amazon
Bromic Platinum Smart Heat 11000W Outdoor patio warmth 39,800 BTU Natural gas 40 lb Amazon
Kratos 36″ Commercial Radiant Charbroiler Commercial cooking, not heating 105,000 BTU Natural gas (LP convertible) — Amazon

Detailed Reviews

★ Best Overall

1. Rinnai RX199iN Condensing Smart Sense Tankless Water Heater

Our pick — 4.5+★ from 150+ verified ratings; the strongest balance of quality and price.

11.1 GPMPropane or natural gas

One cabinet that runs your floor loops and your hot showers from the same burner.

The number worth circling here is 199,000 BTU — the hourly heat energy this unit can push into water. That is serious output for a residential wall unit, and for radiant floor heat it means the boiler can bring a cold slab up to temperature and then throttle down instead of running flat out. It ships ready for a 120-volt connection and accepts either propane or natural gas through its Smart Sense gas control, so your fuel decision does not lock you into a single model.

The 11.1 GPM figure is flow rate — gallons per minute of water the unit can heat as it passes through. In a heating loop that pace does not matter the way it does in a shower, but it does mean you can run domestic hot water and floor zones off one box without starving either. At 55 pounds it hangs on a wall without a structural headache, and the listed dimensions of 18.5 inches wide by 30.11 inches high keep it close to a small suitcase footprint.

What wins people over with condensing units in this family is how fast the heat arrives at distant fixtures, and the RX199iN draws the same reaction — warm water at the far end of the house without the old tank’s wait. The efficiency figure stamped on it is 96%. There is a quiet caveat baked into the listing, though: outdoor installs need the RX-OVC vent cap, which is not in the box, and the WiFi control module is a separate purchase too. Factor both into your parts run.

smart recirculation control

  • 199,000 BTU output handles a cold slab and a full hot water load together.
  • Smart Sense gas control accepts propane or natural gas, so fuel choice stays open.
  • 96% efficiency keeps more of each propane gallon inside the loop.
  • Only 55 pounds on the wall, with a suitcase-sized 18.5 x 30.11 inch face.

gas line sizing

  • Outdoor mounting needs the RX-OVC vent cap, sold separately.
  • The Controlr WiFi module is also extra, so app control is not included.
  • Labor warranty requires registration within 90 days, and Rinnai recommends a qualified technician for install.

whole home retrofit: you want one condensing unit to feed both the radiant loops and the household’s hot water, and you like keeping the propane-or-gas option open.

vent termination planning: the vent cap and WiFi module are add-ons, so your parts list is not just the boiler and pipe.

Purpose-Built Pick

2. Rinnai i150SN Condensing Gas Boiler

150,000 BTUMultizone control

The one unit on this list actually labeled a boiler, not a water heater.

Compare the 150,000 BTU output here against the 199,000 BTU of the RX199iN above and you can see the trim: this model asks for less peak output in exchange for control built around heating loops. Its stainless-steel heat exchanger pairs with a modulating wire mesh burner, which is the part that lets the flame ease down to a low, long burn instead of clicking on and off. That slow-and-steady behavior is exactly what a floor slab wants.

The interface is where it earns its place for radiant work. A digital display shows temperature and pressure together, the CH setting (central heat) adjusts between 104°F and 180°F, and domestic hot water runs between 98°F and 140°F. Floor loops generally want the cooler end of that range, and having both ranges on one screen means you are not guessing. Multizone control capability lets thermostats and integrated control pumps wire straight into the boiler cabinet, and a child lock shuts the central heating off with one touch.

At 68.3 pounds it is heavier than the RX199iN’s 55 pounds, and at 10.9 inches deep it sits closer to the wall than the CX199iN’s 15-inch depth — a real advantage in a utility closet. Rinnai states a 12-year residential heat exchanger warranty, but the spec sheet’s parts and labor terms read shorter, so confirm registered terms with your installer. There is no customer review data on this listing to lean on, which makes the spec sheet and your technician’s sizing judgment the whole story here.

combi boiler pairing: a genuine hydronic boiler with a stainless exchanger, modulating burner, and 104°F-to-180°F central heat range gives a radiant system the low, even water temperature it was designed around.

wall clearance needs: the listing shows this model under a natural gas label, so ask your installer about the propane conversion path and finalize the warranty registration details in writing.

radiant floor loops: a homeowner building a dedicated multi-zone hydronic system who wants boiler-specific controls rather than a repurposed water heater.

licensed install required: the fuel configuration and warranty paperwork need confirming before install, since propane use depends on the conversion your technician performs.

Best for Big Loads

3. Rinnai CX199iN SENSEI CX Tankless Water Heater

199,000 BTUSmart-Circ recirculation

A learning pump inside the cabinet that studies when you draw heat.

The standout on the CX199iN is Smart-Circ — an internal pump paired with software that watches your usage patterns and then schedules recirculation to match. In a radiant setup, that means the loop water can be kept warm ahead of demand instead of waiting for a thermostat call. It shares the 199,000 BTU output of the RX199iN, and the 11.1 GPM flow rate edges the RX199iN’s listed 11 GPM by a hair on paper. It also runs on propane or natural gas through the same Smart Sense control.

The commercial framing is not decoration. Its heat exchanger warranty runs 8 years or 12,000 hours, an hours-based cap that matters in long, steady floor-heating cycles. It weighs 27.2 kg, and its 15-inch depth makes it the deepest of the Rinnai trio here, so measure the closet before it ships.

Owners upgrading from old equipment report efficiency climbing from 82% to 98% and faster hot water at remote faucets. The taller cabinet meant plumbing changes on that install, and the unit is picky about setup: it needs electricity to ignite, and one buyer in a new build had a unit that never produced hot water from day one and described a rough support experience with pressure checks and long holds. Treat professional commissioning as mandatory rather than optional.

restaurant hot water: you want the recirculation intelligence and the longer commercial hours warranty, and you have the wall depth for a 15-inch cabinet.

descaling schedule: it needs a power feed to fire, and a competent installer is what separates a smooth start from a frustrating one.

Recirculation Pick

4. Rinnai RXP199iN Condensing Smart Sense Tankless Water Heater

Built-in recirculation199,000 BTU

The version that keeps water moving so the far bathroom stops making you wait.

Its 11 GPM flow rate and 199,000 BTU output sit alongside a built-in recirculation pump — the piece that pushes warm water through the line before you turn the tap. In a house with long pipe runs, that recirculation is the difference between heat in seconds and heat after a wait. The 96% efficiency figure and the propane-or-natural-gas Smart Sense control round out the core spec sheet, and at 58 pounds it is three pounds heavier than the RX199iN.

Quality is the trait that carries this model’s reputation, and the heating speed backs it up — fast hot water at the faucet and even temperature room to room. The flip side is real: a share of buyers report units that did not work at all, and the Rinnai Central app draws consistent complaints as glitchy and awkward outside Apple devices. Recirculation still takes a little time even with the pump and a bypass valve, so do not expect instant heat at every tap.

One practical note that applies to any propane tankless: it needs electricity to ignite, so a power outage means no heat unless you add a battery backup. The install cost also runs higher than a tank swap, and the warranty on this family requires installation by a Rinnai-authorized pro. Confirm that in writing before you book anyone.

high demand homes: recirculation is the feature you want and you have a long pipe run to the back of the house.

freeze protection: your installer needs to be Rinnai-authorized for the warranty, and the app is best treated as a setup tool only.

Panel Pick

5. Hydronic Radiant Heat Control Panel 1 Zone

1 zonePre-assembled

Not the boiler — the distribution brain that makes a one-zone floor loop behave.

Here is the piece most buyers forget. A boiler makes hot water; a distribution panel decides where it goes and at what mix. This one arrives pre-assembled for a single zone, which removes the biggest source of radiant install errors: hand-building pump-and-mixing assemblies on site. It works with multi-heat-source setups, so you can pair it with a boiler and a second heat source rather than being locked to one fuel path.

The panel measures 44 by 33.5 by 9.5 inches and weighs 110 pounds, so it is a wall-mounted unit that needs planning, not a shelf item. Packaging reports are glowing — strong cardboard strapped to a wooden pallet, arriving without dents. The company’s communication gets the same reaction, with delivery coordination handled proactively. One practical sizing detail worth pinning to the fridge: this is a 1-inch to 3/4-inch system, while most boilers are 1 1/2-inch and most manifolds distribute at 1 inch, so verify your piping sizes match before ordering.

Assembly quality and parts selection are the other recurring theme — owners mention the components are well chosen and expect a long service life. It does carry a premium tag for what is essentially plumbing hardware, and one buyer who needed a different heating direction found the return process smooth. If you are a confident DIYer or a pro who wants a repeatable install, this shortens the job considerably.

simple loop setups: a single-zone radiant build where you want the mixing and pumping solved before the installer arrives.

extra zone cost: the 1-inch to 3/4-inch sizing has to line up with your boiler and manifold connections, so measure first.

Propane Volume Pick

6. Raypak 014786-156A Propane Gas Pool Heater 150K BTU

150,000 BTUPropane

A powerful propane burner for large water volumes, with a durability question mark.

At 150,000 BTU and 115 pounds, this is a big cast of heat aimed at a body of water, not a floor loop. If you are heating a large volume indirectly — a buffer tank, a spa, a big open loop — the raw output is there. The honest part: durability shows up as a concern in the feedback, with reports of breakdowns within a couple of months of use sitting alongside buyers who say it works wonderfully. Value opinions split the same way, with operating cost called expensive by several.

Reliability lands as a mixed read rather than a strength, and the right way to use that is as a fit guide. Buy it where you have service access and a warranty plan you trust, and think twice if you need a unit that runs unattended for years. The 32 by 30 by 16 inch footprint also needs real space.

What it does well is heat water aggressively when it is working, and the simpler control scheme means fewer electronics to fail. The 115-pound cabinet is not a one-person lift onto a pad, so plan the delivery and placement before it lands on your driveway.

mid size pools: you need strong propane output for a large water volume and you have a service plan in place.

vent clearance rules: durability feedback is genuinely split, so buy it where a return or warranty claim is easy to pursue.

Compact Pool Pick

7. Pentair EC-462024 Natural Gas 125K Heater

125,000 BTU82% efficiency

Small-water specialist with fast pre-mixed combustion and a light 20-pound body.

Pre-mixed combustion is the headline here — it blends gas and air before ignition for an ultra-fast ramp to heat. With 125,000 BTU and a 1-1/2 inch plumbing connection, Pentair targets smaller bodies of water: aboveground pools, spas, and inground pools up to 15,000 gallons. At 82% efficiency it is quoted as highest in class, and its 20 pounds makes it the lightest unit in this group.

Reliability is the mixed note, with some units running flawlessly and others stopping within days of install. Durability feedback skews toward breaks within a few months, and repurchase regret appears among buyer concerns. That pattern points to fit and support rather than a universal flaw: it suits a small pool owner who wants fast heat-up and has a dealer or service contact nearby.

The digital display and controller keep operation simple. If your plan is a large radiant slab, this is the wrong tool — the 15,000-gallon ceiling tells you it is sized for water volume, not floor loops. For a spa or a modest aboveground pool, the fast pre-mixed heat-up is the real payoff.

smaller gallons: you are heating a spa or a small pool and want quick heat without a heavy lift.

bypass valve install: the 15,000-gallon size ceiling means this is not a radiant floor boiler.

Small-Pool Propane

8. Pentair EC462025 MasterTemp 125 Propane Gas Heater

Propane125,000 BTU

The propane twin of the 125K Pentair, sized for pools up to 15,000 gallons.

Same 125,000 BTU output and 82% efficiency as the natural gas version above, but this one runs on propane and carries a heavier 109.8-pound frame. The 1-1/2 inch plumbing connection and pre-mixed combustion for fast heat-up make it a straightforward small-pool heater: aboveground pools, spas, and inground pools up to 15,000 gallons. One buyer ran it off 40-pound and 60-pound tanks with a low-pressure regulator and found it worked well for nudging the pool a few degrees warmer in May.

Heat exchanger failures are part of the picture, though — one reviewer noted a leak within weeks that filled the unit with water. A separate report describes a unit that would not ignite and showed an “eng” error code the installer could not clear. Wiring clarity is a legitimate gripe too: the instructions leave the 230-volt versus 115-volt connections unclear, so have your electrician confirm the supply before connecting.

The bright side is the operating experience when it runs — the 12×24 pool owner describes easy operation and solid heat, and a returning buyer had good results with an earlier MasterTemp. For a small propane-heated pool, this is a real option if you have a Pentair service contact nearby.

off grid pools: you are running a small propane pool and want fast pre-mixed heat from a familiar pool brand.

tank sizing math: have the electrical supply and warranty path confirmed, since the wiring notes are unclear and some units ship with ignition problems.

Above-Ground Value

9. Raypak PR106AENC 105,000 BTU Natural Gas Pool Heater

105,000 BTUCopper fin-tube exchanger

Polymer headers keep rust stains off the surface, and the copper does the rest.

The polymer headers are a small detail with a visible payoff: no rust stains creeping across your pool or spa finish. Inside, the heat exchanger is made from a single piece of extruded copper — an all-copper-fin-tube design that handles heat transfer without the seams of welded assemblies. At 105,000 BTU and 78.8 pounds, this sits in the modest-output range for above-ground pools and spas at elevations of 0 to 4,999 feet.

Raypak claims uninterrupted heating through falling leaves, wind, downdrafts, sleet, and snow, with no fans needed to fight drafting. Quality earns the clean read, while reliability is the mixed one — some units work fine for years and others will not stay running. Value opinions split along the same line. Use that as a support-plan question rather than a blanket warning.

For an above-ground setup with a short plumbing run, the low-output copper design is a sensible fit, and the 30 by 27 by 16 inch body leaves room on a pad. If your goal is a heated pool that runs season after season with minimal fuss, budget for a service relationship.

spa sized loads: you are heating an above-ground pool or spa at moderate elevation and want a copper exchanger.

cold climate limits: reliability is a coin flip in the feedback, so plan for service access.

Pool Volume Pick

10. Hayward H-Series Propane Gas Pool Heater 150,000 BTU

150,000 BTUIn-ground pools to 450 sq ft

Fast water-side heat with a front panel you can actually service yourself.

Radiant or not, this is the strongest water-heating pick on the list for output and control. The 150,000 BTU propane burner covers in-ground pools and spas up to 450 square feet, and the front control panel with a digital LED display shows water temperature and runs self-diagnostics. Left-or-right connection routing on water, gas, and electric gives your installer real flexibility in tight pool pads.

Functionality is what people notice first — it works from day one and often kicks on only a couple of times a day to hold temperature. That duty cycle is the energy-saving angle, since the heater trims circulation-pump run time. One 10x10x4 plunge spa owner timed it at roughly 1°F per 10 minutes, versus 1°F per hour for a heat pump. Quality and installation feedback divide, though, with some units arriving defective and install effort ranging from easy to considerable.

The low-end efficiency rating is the honest limitation, and one buyer flagged it as the weakest point versus other heaters. If your pool is larger than the 450 sq ft ceiling, look at the bigger H-Series sizes instead. At 145 pounds it needs a solid pad and two people.

family pools: in-ground pool and spa owners who want fast propane heat and a serviceable front panel.

warranty paperwork: efficiency sits at the low end and the 450 sq ft coverage means large pools need a bigger model.

Room Heat Pick

11. Rinnai EX38DTP Direct Vent Wall Furnace 36,500 BTU Propane

36,500 BTUPropane, 1,600 sq ft

A propane wall heater that warms one zone without a boiler or a duct run.

If your radiant project is really one cold room — a basement, a converted garage, an addition over a crawl space — a 36,500 BTU direct vent wall furnace may be the simpler answer than running new hydronic loops. It heats up to 1,600 square feet, mounts on the wall at 15 by 18 by 30 inches, and pulls just 0.98 amps to run its controls and blower. The beige cabinet is designed to stay cool to the touch for households with kids.

Heating method is forced air with a radiant element, so it warms the room air fast rather than storing heat in a slab. Modulating technology trims the flame to match demand instead of blasting on and off, which is where the energy savings come from. A programmable thermostat lets you set temperatures per schedule and can tie into Wi-Fi-enabled systems. Self-diagnostic electronics report faults on their own.

At 108 pounds it is a two-person wall mount, and the direct vent means you need an exterior wall for the flue. The listing states a 10-year heat exchanger warranty, 5-year parts, and 2-year labor. This is a space heater, not a boiler — do not expect it to feed water loops, because it does not move water at all.

garage heating: heating one room or zone where running water loops is impractical or too costly.

wall cutout size: you want warm floors, because this one heats air and needs an exterior wall for venting.

Outdoor Pick

12. Bromic Platinum Smart Heat 11000W Gas Patio Heater

39,800 BTU215 sq ft coverage

Infrared warmth aimed at people, not air, for the patio you want to keep using.

This one earns its spot on a list like this because radiant heat is exactly what it does — the 11,000 watt burner puts out 39,800 BTU and concentrates warmth onto people and objects across up to 215 square feet. A tinted ceramic glass fascia spreads the heat evenly while dialing down the glare, so a cold evening on the terrace turns comfortable in a short window. It is natural gas only and rated for outdoor use, with a 110-volt, roughly 2-amp draw for the controls.

Mounting is flexible: wall or ceiling, with a minimum 96-inch clearance for both, and an adjustable directional bracket aims the heat where you want it. Smart control compatibility (hardware sold separately) adds remote on/off and a master remote for setting output. The stainless-steel body is built to sit outside in weather.

The honest boundary is the “outdoor only” rating — this is not a floor-heating device and cannot be brought indoors to warm a basement. At 40 pounds it needs proper anchoring overhead, and at 15.6 by 29.75 by 15 inches it is a substantial fixture. If you are heating a covered patio, this does the job a boiler cannot.

covered patios: you have a covered patio and want targeted warmth without heating the whole outdoors.

gas line distance: outdoor-only rating, natural gas fuel, and separate smart controls mean it solves patio comfort, not interior floors.

Kitchen Pick (Not Heat)

13. Kratos 36″ Gas Radiant Charbroiler

Three burnersStainless steel

Yes, it says radiant — but this one cooks burgers, it does not warm floors.

You will see the word “radiant” in this listing and it deserves a straight explanation. This is a commercial 36-inch charbroiler with three independent burners running on natural gas that a qualified technician can field-convert to liquid propane. The radiant element here is a cooking surface that glows under cast iron grates, delivering 105,000 BTU of cooking heat — nothing to do with hydronic floor loops.

It earns a mention because buyers searching for radiant propane heat occasionally land on it, and that mistake is expensive. Built for commercial kitchens, it pairs with a custom 16-gauge stainless steel open-base stand for supply storage, and the heavy-duty cast iron grates are removable for cleaning. A grease management system and dual-zone cooking are part of the design.

If you run a diner, food truck, or restaurant kitchen that needs volume cooking, this is a sound piece of equipment with a 3/4 inch gas connection and a field-conversion path to propane. If you want warm tile in a bathroom, close this tab and go back to the Rinnai i150SN.

commercial kitchens: commercial cooking where three burners and a stainless stand earn their footprint.

hood vent needed: home heating, since it is a cooking appliance with no water loop and no hydronic function.

Know the Specs

BTU Output and Slab Sizing

BTU (British thermal unit) is the standard measure of heat energy, and the output figure tells you how much heat the unit can deliver per hour. A 150,000 BTU boiler moves more heat than a 105,000 BTU one, and matching that number to your loop length and slab area is the first check. Oversized units cycle harshly; undersized ones fall behind on cold nights.

Condensing Efficiency

A condensing boiler recaptures heat from the exhaust that a standard unit sends up the flue, which is why these units list efficiency figures in the high 90s. That extra step creates acidic condensate, so budget for a drain line and often a neutralizer. Efficiency matters most for radiant heat because the boiler runs many low, long cycles instead of short bursts.

Heat Exchanger Material

The heat exchanger is the metal part that separates flame from water. Stainless steel appears in several picks here and copper in others,dominates the pool heaters, where copper’s heat transfer is the priority. Stainless suits long, steady hydronic cycles; copper suits fast water heating. Neither is universally better — it depends on what the unit has to do all day.

Flow Rate and Loop Demand

Flow rate is measured in GPM, or gallons per minute — how much water the unit can heat as it passes through. In a radiant loop this figure matters less than in a shower, because floor loops move water slowly. It becomes important when one unit also supplies domestic hot water, since you do not want taps competing with the floor for output.

Common Questions

Can a tankless water heater run radiant floor heat?
Yes, many installers pair a condensing tankless unit with a mixing valve and a distribution panel so the cooler loop water gets blended down to the right temperature. The trick is that floor loops want steady low-temperature water, and not every water heater modulates well at that low end. Always confirm with your installer that the specific model is rated for the loop temperature and flow your system uses.
How many BTUs do I need for my radiant floor area?
There is no single number, because heat loss depends on your slab insulation, window quality, ceiling height, and local climate. The safe path is a heat-load calculation done by your installer, which gives you the real BTU target instead of a guess. Then pick a boiler that can cover that load and modulate down below it, so it does not short-cycle on mild days.
What is the difference between the Rinnai i150SN and the Rinnai RX199iN?
The i150SN is built as a hydronic boiler with a stainless-steel heat exchanger, a modulating wire mesh burner, and multizone control that connects thermostats and pumps directly. The RX199iN is a condensing tankless water heater with 199,000 BTU and a 96% efficiency figure that also handles domestic hot water. For a dedicated floor-heating system, the boiler-specific controls on the i150SN are the more natural fit.
Can a natural gas boiler be converted to propane?
Often yes, but only by a qualified technician using the manufacturer’s conversion kit, and only on models the maker lists as convertible. Some units here already accept both fuels through a built-in gas control system, which removes that step entirely. Never field-convert a gas appliance yourself — the wrong orifice or regulator setting is a safety issue, not just a performance one.
Do I need a distribution panel with a radiant boiler?
If your system has more than one zone, or if the boiler output temperature is hotter than your loops should see, a distribution panel handles the mixing and pumping. A pre-assembled panel saves the time and labor of building those assemblies on site. Check the pipe sizing first — the panel here is a 1-inch to 3/4-inch system, while many boilers use 1 1/2-inch connections.
Why does a condensing boiler need a drain?
Capturing heat from the exhaust produces condensation, and that liquid is acidic enough to need a neutralizer before it goes into household plumbing on many systems. Budget for the condensate line and neutralizer as part of the install, not as an afterthought. Skipping it can void the warranty on some units.
Will a propane boiler work during a power outage?
Most propane tankless and condensing units need electricity to ignite and run their controls, so a power cut means no heat unless you add battery backup. A few buyers of the Rinnai tankless models add a backup unit for exactly this reason. If outage resilience matters, ask your installer about a backup supply sized for the ignition and pump draw.
How often does a radiant floor boiler need servicing?
Annual servicing is the common recommendation — a technician checks the burner, the heat exchanger, the pressure and temperature readings, and the condensate path. Hard water areas also benefit from flushing, and several Rinnai models include a Quick Flush feature to simplify that job. Skipping service is one of the fastest ways to shorten a heat exchanger’s life.
Is a pool heater the same as a radiant floor boiler?
No. Pool heaters like the Hayward H-Series or the Raypak units are built to heat a large volume of pool water fast, with plumbing connections sized for pool circulation. A radiant boiler heats a closed loop of water at lower, steadier temperatures for hours. They look similar on a spec sheet but are engineered for opposite duty cycles.
What temperature should radiant floor water run at?
Slab systems typically run at the cooler end of a boiler’s central-heat range, which is why the Rinnai i150SN’s 104°F to 180°F adjustment band is useful — you can dial the water down where the floor wants it. Your installer sets the exact target based on slab thickness, floor covering, and outdoor design temperature. Do not simply copy someone else’s setting.

The Bottom Line

For most radiant floor projects, the propane boiler for radiant floor heat winner is the Rinnai RX199iN, because 199,000 BTU of condensing output with a 96% efficiency figure and a propane-or-natural-gas gas control covers both your loops and your hot water without locking you into one fuel. If you want controls built specifically around heating zones — a 104°F to 180°F central heat band, multizone wiring, and a stainless-steel exchanger — the Rinnai i150SN is the more purpose-built machine. And if your radiant project is really one stubborn cold room, the Rinnai EX38DTP wall furnace delivers 36,500 BTU of propane heat across 1,600 square feet without a single water loop.

One practical nudge before you buy: size the boiler with a real heat-load calculation and have a qualified technician commission it, because the fuel conversion and venting details are where these installs succeed or fail. Do that, and the choice between these picks becomes simple.

How we choose

We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.

Sources

Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of October 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.

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