Conversions done right, or not at all
Tankless water heater installation, explained by the people who size them
Tankless is excellent technology installed badly more often than any other appliance in a house. The unit is rarely the problem — the gas line, the vent, and the arithmetic behind temperature rise are. Here is how we decide whether to recommend one to you.
Sizing starts with your groundwater, not your bathrooms
A tankless unit does not store hot water; it adds a fixed number of BTUs to whatever water is flowing through it. So the only sizing question that matters is: how many degrees do we have to raise your incoming water, and at what flow rate?
Target 110°F at the shower head. In the Gulf South, winter inlet water sits around 65°F, so you need a 45°F rise. In the Upper Midwest and Northern New England it can drop to 38°F, which is a 72°F rise — 60% more work from the same unit. That single variable is why a model that comfortably serves a four-bathroom house in Houston struggles in a two-bathroom house in Duluth.
We calculate it explicitly: BTU needed equals gallons per minute × temperature rise × 500, divided by the unit's efficiency. Then we compare that to what your gas supply can actually deliver, and we tell you if the two do not meet.
The four things that get skipped on cheap conversions
- Gas line capacity. Half-inch pipe on a long run will not feed a 199k BTU unit. Symptoms are intermittent ignition failure and error codes that a second contractor gets blamed for.
- Condensate handling. Condensing units produce acidic condensate. It needs a routed drain and, where a municipality requires it, a neutralizer cartridge — not a bucket.
- Isolation valves. Without them nobody will ever descale the unit, and a scaled heat exchanger is the number one cause of premature tankless failure.
- Venting material and termination. Category IV stainless or the manufacturer's approved PVC/polypropylene, with clearances from windows and intakes. Reusing an old atmospheric flue is never acceptable.
Good fit
- You currently run out of hot water and would otherwise buy a 75 or 80 gallon tank
- You are staying in the house eight years or more
- The heater sits on an exterior wall or near an easy vent path
- Your gas branch is three-quarter inch, or the run to the meter is short
- Water hardness is moderate, or you already own a softener
- You want the floor space back in a small utility closet
Stick with a tank
- The existing gas line is half-inch on a long run and the utility meter is already maxed
- Winter inlet water is very cold and the household wants three simultaneous showers
- You are on well water with heavy iron or 20+ grains hardness and will not maintain it
- The install is in a finished interior closet with no practical vent or condensate route
- You are selling within a few years
- The budget only covers the unit, not the gas and venting work it needs
What a conversion runs
A straightforward exterior-wall conversion with an adequate gas branch lands between $4,200 and $6,800 installed. Add $600 to $1,800 when the gas line needs upsizing, and $700 to $1,600 for a dedicated recirculation return if you want instant hot water at a far bathroom. Full pricing context sits on the replacement cost page.
One more honest note: if your tank failed this morning and you need hot water tonight, a tankless conversion is not the same-day answer. We can put a quality tank in today and quote the conversion for a planned date — or, if you would rather wait, tell you plainly how long you will be without hot water.
Common tankless questions
Will one tankless unit really run two showers at once?
It depends on your groundwater temperature, not on the marketing. A 199,000 BTU condensing unit at 95% efficiency raises about 5.2 gallons per minute by 70°F. Two low-flow showers pull roughly 3.4 gpm. In Georgia, where winter inlet water is near 60°F, that is easy. In Minnesota at 38°F inlet you need a 72°F rise for a comfortable 110°F shower and the same unit delivers closer to 3.7 gpm — workable for two showers, not for two showers plus a dishwasher.
Do I need a bigger gas line?
Frequently, yes. A tank heater draws 40,000 BTU; a tankless draws up to 199,000. If your existing branch is half-inch pipe running 40 feet from the meter, it cannot deliver that without pressure drop that trips the unit into an error code. We measure the run, count the fittings, and check total connected load of the house before quoting. Sometimes the answer is a three-quarter-inch branch; sometimes it is a meter upgrade with the utility.
Why does the hot water take longer to arrive at the tap?
The unit has to sense flow, ignite, and heat before hot water starts moving — usually two to four seconds — and then that water still has to travel your pipe. People notice it most at a bathroom far from the unit. The fix is a recirculation setup: either a dedicated return line, or a crossover valve at the farthest fixture paired with the unit's built-in pump on a schedule.
How often does a tankless need service?
Descale annually if your water is above roughly 10 grains per gallon of hardness, every two years if it is soft. The service is a 45-minute vinegar or descaler circulation through the isolation valves — which is exactly why we always install isolation valves, even when a spec sheet says optional. Skip descaling long enough and the heat exchanger scales, the flow rate drops, and the manufacturer will point at maintenance records.
Is a tankless worth it if I plan to sell in three years?
Probably not. You will not recover the conversion premium in three years of gas savings, and buyers rarely pay extra for it. Put a good long-warranty tank in and keep the money. Tankless pays off for people staying eight-plus years, or households that genuinely run out of hot water with a tank.
Talk to a real dispatcher
Send us your gas line and we'll tell you the truth about tankless
A photo of the meter, the pipe diameter at the heater, and your city is enough for us to say whether a conversion works at your house or whether your money is better spent elsewhere.