Condensing and non condensing, side by side
Both types heat water only when a tap opens. The difference is in the exhaust. A condensing unit squeezes extra heat out of the flue gas until water vapor condenses, which lets it exhaust through plastic pipe and ties it to a condensate drain. A non condensing unit lets the exhaust leave hot and dry.
| Item | Non condensing | Condensing |
|---|---|---|
| Exhaust temperature | Hot, so it needs a metal vent rated for it | Cooler, plastic vent pipe is typical |
| Condensate drain | None needed | Required, often with a neutralizer |
| Efficiency | Lower rating, still better than most tanks | Higher rating |
| Vent route | Tougher to reroute, higher material cost | Easier to run long or around corners |
| Replacing an older tankless | Often a direct match to the old vent | May need the vent and drain rebuilt |
The vent material and the maximum run length are set by the manufacturer for each model. We follow the installation manual for the exact unit, not a generic rule.
Who a non condensing unit suits
It is a good match when
- You are replacing an older non condensing tankless and the existing vent is in good shape and matches the new model.
- There is no practical way to run a condensate drain from the utility room to a floor drain or sink.
- The vent will go straight out an exterior wall or roof with a short run.
- You want fewer parts that can clog or need annual neutralizer service.
The gas line is the part that surprises people
A tankless heater can ask for far more gas at one moment than a tank burner does. If the line feeding the old tank heater is undersized, the new unit may trip an error or heat weakly when two fixtures run. The line size, the length of run and the regulator all matter.
Before we quote, we check what feeds the heater and whether a bigger line is needed. That scope sits under gas line work and is priced separately so you can see it. If you ever smell gas, leave the building first and call the utility or 911 from a safe distance before calling any plumber.
Morrisville gas service and permits
Enbridge Gas supplies natural gas to Morrisville residents. Its 24/7 line for a gas smell is 1-877-776-2427, or call 911 from a safe distance such as a neighbor's home.
The Town of Morrisville Inspections Department says a water heater swap is generally not permit-required when the energy input is not greater than the original, there is no change in fuel, location, or venting and piping size, and a licensed plumbing contractor does the work. A tankless conversion often changes vent and gas pipe size, so call 919-463-6190 to confirm for your address.
Source: Enbridge Gas North Carolina contact page and Town of Morrisville Residential Inspections page, checked October 2026.
Flow rate and how many fixtures at once
Tankless units are rated by how many gallons per minute they can raise to your set temperature. Cold groundwater is colder in winter, so the same unit delivers less hot water in January than in August. Size for the cold-season number, not the brochure peak.
A shower uses a modest flow, a washing machine and a dishwasher add more, and a second shower at the same time can push past the limit. If your household regularly runs three at once, a larger unit or a second one is on the table.
What the install actually involves
- 01
Verify the vent
We check material, diameter, slope and termination against the manual for the exact model.
- 02
Size the gas supply
We confirm the line, fittings and regulator can deliver the burner input.
- 03
Set isolation valves
A service valve kit lets the unit be flushed later to clear mineral deposits.
- 04
Test everything
We pressure test the gas connection with a leak solution and check temperature at the nearest tap.
If a swap changes your fuel or relocates the unit, it shifts toward a full tankless water heater project with its own permit conversation. We tell you which kind of job it is before work starts.
Maintenance you should expect
Tankless units benefit from an annual flush with the isolation valves, and the inlet screen should be cleaned when flow drops. Cary reports its 2025 tap water as moderately soft, at about 30 mg/L of hardness as calcium carbonate, so scale builds more slowly than in hard-water areas. It still builds, and ignoring the flush leads to errors.
We do not recommend skipping the flush because the water is soft. Soft is not scale-free.
Repair or replace an older tankless unit
An older tankless unit that throws error codes is not always ready for the curb. Scale in the heat exchanger, a clogged inlet screen or a weak gas supply can all cause the same codes, and each has a fix that costs far less than a new unit.
If the heat exchanger leaks or the unit is well past its rated life, replacement makes more sense. A like-for-like non condensing swap is the simplest version, because the vent and gas connections usually stay where they are. See our notes on water heater replacement for how we decide.
Homes on the Durham side of the line
We also dispatch to Durham addresses. The gas utility, permit office and water supplier can differ from what is described here, so check the Durham page before you assume the same contacts apply.
Questions to ask any installer
Get these answered before you sign
- What vent material and run length does the manual require for this exact model?
- Is the gas line size checked and shown as its own line item?
- Who pulls the permit, if one applies?
- Is a service valve kit included for future flushing?
- What is the plan for the old tank or old unit?
Call (919) 944-7281 and describe your vent location and gas meter. We will tell you what the install would really involve.
Questions about this topic
A condensing unit recovers extra heat from the exhaust and drains the resulting water. A non condensing unit vents hotter exhaust through a metal pipe and needs no drain.
Yes, a little. The rating is lower than a condensing unit but usually still beats a standard tank, and the gap matters less in a small household.
No. That is one of its main practical advantages, especially where no drain is close.
Only if the pipe material, diameter and condition match the new model manual. We inspect the vent before reusing any of it.
Often yes. The burner input is much higher than a tank heater, so we check line size and regulator before quoting.
It depends on what changes. Ask the Town of Morrisville Inspections Department at 919-463-6190, and have your licensed plumber describe the fuel, vent and gas pipe changes.