Fewer parts, no condensate drain and a lower price. The trade is stainless venting and about ten points of efficiency.
Quick Answer
A non-condensing tankless water heater uses a single heat exchanger, runs at roughly 0.81 to 0.85 UEF, produces no condensate, and vents through Category III stainless. Frisco Tankless Water Heater Pros installs non-condensing units across Frisco, Texas where a short vent run or the absence of a nearby drain makes them the better choice. Call (972) 430-9024.
Overview
A non-condensing tankless water heater does the same job as a condensing one with a simpler machine. Water passes through a single copper heat exchanger over a burner, and the exhaust leaves at 300 to 450 degrees F carrying its residual heat with it. There is no secondary exchanger, no condensate, no neutralizer cartridge, no drain line, and no condensate safety switch to lock the unit out. Fewer components means fewer things to service and fewer things to fail.
The honest trade is efficiency and vent material. Non-condensing units land around 0.81 to 0.85 UEF against 0.93 to 0.96 for condensing. That is a real gap, but it is worth putting a number on rather than reacting to. A typical Frisco household needing about 165 therms of delivered hot water annually burns roughly 200 therms through a non-condensing unit versus about 174 through a condensing one. At North Texas gas prices, that difference lands in the range of 25 to 45 dollars a year.
Because exhaust stays hot, venting must be Category III stainless, typically AL29-4C or 304 stainless, which runs roughly $28 to $60 per installed foot against $6 to $14 for PVC. That single fact drives the entire decision. On a five foot garage sidewall termination the stainless costs almost nothing, and the non-condensing unit is clearly the better value. On a 40 foot run through an attic to a roof penetration, the vent material can cost more than the equipment savings, and condensing wins.
There is a third scenario where non-condensing is simply the practical answer: locations with no drain. Outdoor wall mounts on the side of a home in Newman Village, garage installs on a slab with no floor drain, or detached workshop applications all present the same problem for a condensing unit, which must dispose of roughly half a gallon of acidic liquid per hour. A non-condensing unit sidesteps the issue entirely because it never makes any.
Diagnosis
Symptoms rarely point at a single cause. These are the ones we find most often on North Texas systems.
Cause: Somebody assumed all tankless units vent in plastic. Non-condensing exhaust runs 300 to 450 degrees F, well past PVC's roughly 149 degree service limit.
Fix: We install Category III stainless, either AL29-4C or 304, with sealed joints rated for the temperature and pressure of a fan-assisted appliance.
Cause: Hot exhaust does not make a fan-assisted appliance compatible with atmospheric B-vent. Category III venting is positive pressure and requires sealed, gas-tight joints that B-vent does not provide.
Fix: We install listed Category III vent with locking, sealed connections and correct support, and remove or reline the old flue as the situation requires.
Cause: A 400 degree vent needs meaningful clearance from framing, insulation and finishes. It is not a plastic pipe you can strap to a joist.
Fix: We install to the vent manufacturer's listed clearances, using thimbles and firestops at every penetration.
Cause: With one exchanger doing all the work, scale from Frisco's 8 to 11 grain per gallon supply shows up as lost output faster and more noticeably than on a condensing unit.
Fix: Isolation valve kit at install and annual descaling. On non-condensing units this maintenance is the difference between a 20 year unit and an 8 year one.
Cause: The equipment is less expensive, so it looks like the value pick. On a long vent run the stainless material erases the savings and then some.
Fix: We price both options with actual vent length included, so the comparison reflects the installed cost rather than the sticker on the box.
Process
We measure the exact run to a compliant termination and count elbows, because on a non-condensing unit vent length is the primary cost driver of the entire project.
30 minutes
We price the non-condensing and condensing options with real vent material quantities included, so you see installed cost rather than equipment cost.
Same day
Developed length measured from the meter, branch sized to carry full rated input, and City of Frisco plumbing and mechanical permits pulled.
1 to 3 business days
Old appliance drained, disconnected and hauled off, then the new unit mounted with clearances to combustibles verified for a high-temperature vent.
2 hours
Listed stainless vent assembled with sealed locking joints, supported at required intervals, penetrations firestopped, and the termination set to clearance from openings.
2 to 4 hours
Gas branch connected and pressure tested, isolation valve kit installed, then full-fire manifold pressure verified and temperature rise measured across the exchanger.
2 to 3 hours
City inspection completed, then we walk you through descaling with the isolation valves and explain what the error codes on this model mean.
45 minutes
Benefits
Cost
| Factor | Effect on price | Range |
|---|---|---|
| Vent length in Category III stainless | The dominant cost variable. At $28 to $60 per installed foot, vent length can outweigh every other line item on the quote. | $150 to $2,400 |
| Unit input rating | Non-condensing units are commonly offered from about 140,000 to 199,900 BTU for residential service. | $300 to $700 equipment delta |
| Termination type | A short horizontal sidewall termination is the least expensive path. A vertical roof termination adds material, flashing and labor. | $200 to $900 |
| Gas branch upsizing | Driven by developed length from the meter, not by whether the unit condenses. | $400 to $1,500 |
| Clearance and firestopping | High-temperature vent requires thimbles and firestops at every penetration through framing. | $100 to $450 |
| Indoor versus outdoor model | An outdoor model needs no vent at all, which removes the largest cost variable from the project entirely. | Saves $300 to $2,000 |
| Scale reduction | With a single heat exchanger carrying the full load, scale control at Frisco hardness is a direct protection of output. | $300 to $2,500 |
| Permit and inspection | Required by the City of Frisco for water heater replacement. | $100 to $300 |
Typical total: $2,400 to $4,300 installed for most Frisco homes. Ranges, not quotes — a firm number needs eyes on the existing installation.
Comparison
| Line item | Non-condensing | Condensing |
|---|---|---|
| Equipment cost | $1,100 to $1,700 | $1,500 to $2,600 |
| Efficiency (UEF) | 0.81 to 0.85 | 0.93 to 0.96 |
| Annual gas input required | Roughly 200 therms | Roughly 174 therms |
| Estimated annual gas cost difference | Baseline | Roughly $25 to $45 less |
| Vent material, 10 foot run | $280 to $600 | $60 to $140 |
| Vent material, 40 foot run | $1,120 to $2,400 | $240 to $560 |
| Condensate handling | None required | $240 to $950 plus annual media |
| 15-year fuel cost difference | Baseline | Roughly $375 to $675 less |
| Best fit | Short vent runs, outdoor mounts, no drain nearby | Long vent runs, high hot water use, drain available |
A non-condensing tankless unit is usually described as roughly 80 to 84 percent efficient, and the number tends to be presented as a shortcoming without explanation. It is not a shortcoming, it is an accounting identity, and the accounting is straightforward enough to do on paper. Once you can see where the energy goes, the decision between condensing and non-condensing stops being a matter of taste.
Start with one therm of natural gas, 100,000 BTU on a higher heating value basis. Two losses account for nearly all of the gap. The first is latent: combustion turns the fuel into carbon dioxide and water vapor, and that vapor carries roughly 9,100 BTU of latent heat out of the vent unless something cools it below its dewpoint. A non-condensing unit deliberately does not, so that nine percent leaves. The second is sensible: the exhaust itself is hot, and hot exhaust is heat you bought and did not use.
| Energy path | Non-condensing at 400F stack | Condensing at 120F stack |
|---|---|---|
| Fuel energy in (HHV) | 100,000 BTU | 100,000 BTU |
| Latent heat leaving as vapor | About 9,100 BTU | About 4,000 BTU after recovery |
| Sensible heat in the exhaust | About 8,400 BTU | About 1,300 BTU |
| Jacket, standby and cycling losses | About 1,500 BTU | About 1,500 BTU |
| Energy delivered to the water | About 81,000 BTU | About 93,200 BTU |
| Resulting thermal efficiency | About 81 percent | About 93 percent |
The sensible figure comes from ordinary mixing arithmetic. Burning a therm with about thirty percent excess air produces roughly 98 pounds of flue gas. Flue gas has a specific heat near 0.26 BTU per pound per degree F, and a 400F stack against a 70F room is a 330F difference. Multiply the three and you get about 8,400 BTU. Run the same calculation on a condensing unit at a 120F stack and the difference collapses to 50F, which is about 1,300 BTU. Nothing about that is proprietary or arguable.
That 8,400 BTU of sensible heat has to travel through a pipe, and the pipe has to survive it. This is the entire practical difference between the two designs. A condensing unit's exhaust at 100 to 140F sits comfortably inside the service range of Schedule 40 PVC. A non-condensing unit's exhaust at 300 to 500F is above the service range of every plastic anyone sells, which means metal, and metal that is both corrosion-resistant and gas-tight under positive pressure.
| Vent product | Typical clearance to combustibles | Note |
|---|---|---|
| Single-wall metal connector | 6 inches | The default in NFPA 54 for listed appliances |
| Listed AL29-4C special gas vent | 1 to 3 inches, per the listing | The listing governs, not the general rule |
| Type B double-wall vent | 1 inch | Not permitted on a Category III appliance |
| Penetration through framing | Listed thimble required | Firestopping required at every floor and ceiling |
| Vent support interval | Per the listing, commonly every 3 to 6 feet | Unsupported stainless sags at joints and leaks |
Termination clearances come from the fuel gas code rather than from the vent manufacturer, and they are the same numbers a condensing unit has to meet. A mechanical draft termination must sit at least 4 feet below, 4 feet horizontally from, or 1 foot above any door, operable window or gravity air inlet. It must be at least 12 inches above finished grade. It must be at least 4 feet horizontally from an electric meter, gas meter, regulator or relief vent. Where an appliance over 10,000 BTU terminates adjacent to a public walkway, the termination goes 7 feet above grade.
It is worth being direct: on most Frisco installations we recommend condensing, and the reason is usually vent length rather than efficiency. But there are three situations where a non-condensing unit is the technically better choice, and in those cases specifying condensing to look progressive costs the customer money and creates problems that did not need to exist.
There is no compliant condensate route
A garage wall on a slab with no floor drain, a detached shop, an outdoor mount on the side of the house. A condensing unit in these locations means either a long lateral to a distant drain or a condensate pump, and both are ongoing failure points. A non-condensing unit never produces the liquid, so the problem does not exist to be solved.
An existing masonry chase or short exterior wall path
Where a short vertical stainless liner up an existing chase or a five-foot horizontal run through an adjacent exterior wall reaches a compliant termination, the metal vent costs very little because there is very little of it. The equipment saving is then real and unrecovered by the venting, which is the opposite of the long-run case.
The freeze-exposure profile is bad
An attic or an exposed exterior location gives a condensate line the worst possible conditions: small bore, trickle flow, standing liquid, unconditioned air. Removing the condensate line removes an entire class of winter lockout from the installation. In an attic installation this is a serious argument and it is rarely made.
The hold period is genuinely short
A rental being turned, a house going on the market within a year or two, or an owner who knows they are moving. Fifteen-year fuel savings are not accessible to someone who will not be there for fifteen years, and pretending otherwise is just selling.
The honest counterweight is that a fourth reason gets used far more often than any of these, and it is not a good one: the equipment sticker is lower. On a long vent run the stainless erases that saving and keeps going, which is exactly why the comparison has to be run on installed cost with your measured vent length, not on the price of the box. We would rather lose the smaller sale than install a unit whose vent costs more than the difference.
The efficiency argument gets made in percentages because percentages sound decisive. Put in dollars over a realistic ownership period, and against the other costs the same appliance incurs, it becomes one line item among several rather than the deciding factor. The table below assumes a Frisco household delivering roughly 165 therms of hot water annually, which is a mid-sized family, and it holds vent length constant at a short run so that the comparison is about the equipment rather than the pipe.
| Line item | Non-condensing | Condensing |
|---|---|---|
| Gas input required per year | About 200 therms | About 174 therms |
| Fuel difference per year | Baseline | About 26 therms less |
| Fifteen-year fuel difference | Baseline | Roughly $375 to $675 less |
| Equipment premium | Baseline | $400 to $900 more |
| Vent material, 8 foot run | $225 to $480 | $50 to $115 |
| Condensate handling at install | None | $150 to $700 |
| Neutralizer media, 15 years | None | About $30 per year |
| Annual descaling, 15 years | Identical requirement | Identical requirement |
| Net position over 15 years | Roughly break-even to modestly ahead | Roughly break-even to modestly behind |
The conclusion that table supports is not that condensing is a bad buy. It is that on a short vent run with no easy drain, the fifteen-year difference between the two designs is small enough that it should not drive the decision, and the things that should drive it are vent path, drain availability, termination location and freeze exposure. Flip the vent run to forty feet and the same table swings decisively the other way, because the stainless line item roughly quintuples while the plastic one does not.
Want this priced for your specific Frisco home? Talk to a tankless specialist at (972) 430-9024.
No, it is a different trade-off. It runs at roughly 0.81 to 0.85 UEF instead of 0.93 to 0.96, which costs a typical Frisco household on the order of 25 to 45 dollars a year in gas. In exchange you pay $400 to $900 less for the equipment, skip condensate routing entirely, and have one fewer heat exchanger and one fewer safety switch to service. On a short vent run or an outdoor mount with no nearby drain, it is often the smarter installed-cost decision.
Because the exhaust leaves at 300 to 450 degrees F, far above what plastic can handle. PVC is rated to roughly 149 degrees and CPVC to about 194. Non-condensing units require Category III vent, typically AL29-4C or 304 stainless, which is rated near 480 degrees and uses sealed locking joints because a fan-assisted appliance vents under positive pressure. Standard galvanized B-vent is also not acceptable, since it is designed for atmospheric appliances with gravity draft and non-sealed joints.
Roughly when the vent run exceeds about 15 to 20 feet. Category III stainless costs $28 to $60 per installed foot while PVC runs $6 to $14, so every additional foot widens the gap by 20 to 45 dollars. At 40 feet the vent material difference is often $900 to $1,800, which comfortably exceeds the equipment premium and then keeps paying through fifteen years of fuel savings. We price both ways with your actual measured vent run before you decide.
Yes, and outdoor models are one of the best uses for the non-condensing design because they need no vent at all, which removes the biggest cost variable. There is also no condensate to route, which matters when there is no drain on that side of the house. The trade is freeze protection: outdoor units rely on internal heaters that only work while the unit has power, so the water lines feeding it need insulation and a plan for extended outages.
A little less, but not on the part that matters most. There is no neutralizer media to replace and no condensate trap or line to keep clear, which saves a small amount of annual service. The descaling requirement is identical and arguably more important, because a single heat exchanger carries the entire load. At Frisco's 8 to 11 grains per gallon, an annual flush through the isolation valves is what determines whether the unit reaches its design life.
Slightly, at the same BTU input rating, because less of the fuel energy ends up in the water. A 199,900 BTU non-condensing unit delivers roughly 6.0 GPM at a 55 degree winter rise where a condensing unit of the same input delivers about 6.9. In practice manufacturers offer both across a similar range of ratings, so we size to your demand and then choose the type. Capacity comes from the model you pick, not from the condensing decision alone.
Related
System Type
A second heat exchanger pulls latent heat out of the exhaust. That is what lets a condensing unit vent in plastic pipe and hit the mid-nineties on efficiency.
Installation
The BTU rating on the box is meaningless if the pipe feeding it cannot deliver the gas. We size the fuel first.
Components
Tankless units vent under positive pressure. That single fact rules out every B-vent flue in Frisco and decides which unit can go where.
System Type
No vent system, no combustion air calculation, no interior space consumed. The one thing that has to be planned properly is freeze protection.
Installation
Properly sized, permitted and vented on-demand hot water for Frisco homes — from Starwood estates to Frisco Lakes patio homes.
Maintenance
Frisco water runs 8-11 grains per gallon. Calcium goes exactly where it does the most damage: the hottest surface in your heat exchanger.
Background reading
Longer explanations of the tradeoffs behind this work, written for homeowners rather than trade readers.
Buying Guide · 11 min read
The efficiency gap is about ten points of UEF. The venting cost gap can be a thousand dollars in the other direction. Which one wins depends entirely on where the unit is going.
Water Quality · 11 min read
Scale does not build evenly. It builds on the hottest metal in the system, which is the one surface a tankless water heater cannot afford to insulate. Here is the mechanism, the timeline and the fix.
Buying Guide · 10 min read
Tankless is not automatically the right answer. Here is the comparison with the inconvenient parts left in, including the three situations where a storage tank is still the better buy.
Coverage
We take non-condensing tankless water heater installation calls throughout Collin County and Denton County. These are a few of the areas covered.
See every Frisco neighborhood and surrounding city we cover.
Call (972) 430-9024 and speak to someone who works on tankless systems every day. Open 24 hours a day, 7 days a week.
Open 24 hours a day, 7 days a week
Available 24/7
Frisco, TX Tankless Pros