Tankless vs Tank Water Heater in Winter: How to Size It Right
Water heaters work hardest in January because the water coming into the house is colder, so a tankless that was fine in July can turn lukewarm when two showers run. Size a tankless by gallons per minute at your winter temperature rise, not by the biggest number on the box. Size a tank by its first-hour rating. A gas tankless often needs a bigger gas line and new venting, which is where quotes jump. Zomg installs tank replacements from $1,075.50 and tankless from $1,615.50.
Why listen to us: Zomg The Handyman crews have done more than 10,000 jobs across all of California since 2009, and every winter the calls change: lights on rooflines in November, cold rooms and dead water heaters in December and January, then leaks, clogged gutters and drafty doors once the storms arrive. This guide is what our installers tell customers before they buy, so the thing you order is the thing that fits your house. Water heater calls peak in winter for a simple reason: an old tank that was barely keeping up fails when the incoming water gets colder.
Quick Comparison
| Pick | Best For | Price Tier |
|---|---|---|
| Best Whole-Home Gas Tankless | Rinnai 199,000 BTU Condensing Tankless (indoor or outdoor model) | Premium tier |
| Best Alternative | Navien NPE-240A2 Condensing Tankless | Premium tier |
| Best Gas Tank | Rheem Performance 40 or 50 Gallon Gas Tank | Mid tier |
| Best Point-of-Use | Electric Point-of-Use Tankless (under a sink) | Value tier |
Our Picks
Why Showers Go Lukewarm in January
A water heater's job is to raise the water temperature from what comes in from the street to what comes out of the tap, usually around 120 degrees. In summer the incoming water is warm; in winter it can be 20 degrees colder, depending on where in California you live, and colder still in the mountains. A tankless heater's flow rate drops as that temperature rise grows. A tank holds the same number of gallons, but each gallon takes longer to reheat.
The quick math installers use for gas tankless: gallons per minute = BTU input x efficiency / (500 x temperature rise). A 199,000 BTU unit at 95 percent efficiency with a 70 degree rise works out to about 5.4 gallons per minute. A shower head uses around 1.8 to 2.5, a kitchen faucet about 1.5 to 2, a washer about 2. Add up what runs at the same time in your house on a cold morning.
Tank or Tankless: The Honest Comparison
| Tank (gas) | Tankless (gas) | |
|---|---|---|
| Hot water | Runs out after the tank empties | Endless, at a limited flow rate |
| Winter behavior | Slower recovery | Lower flow at the tap |
| Space | Floor, closet or garage | On the wall, indoors or outside |
| Install | Usually a straight swap | Often a bigger gas line, new venting, condensate drain |
| Upkeep | Drain sediment yearly | Descale (flush) yearly, especially with hard water |
| Typical life | Shorter | Longer with descaling |
Where Tankless Quotes Jump
- Gas line size. A tank might use 40,000 BTU; a whole-home tankless uses up to 199,000. The half-inch line that fed the old tank often cannot supply that, and the run back to the meter has to be upsized.
- Venting. Tanks vent through a metal flue. Condensing tankless units vent with PVC; non-condensing indoor units need stainless vent. Outdoor units need neither.
- Condensate. Condensing units make acidic water that needs a drain and usually a neutralizer.
- Hard water. Much of California has hard water, and scale is what kills tankless heat exchangers. Ask for isolation (service) valves so it can be flushed every year.
- Permits. Most California cities require a permit to replace a water heater. Tanks must have two seismic straps, and many homes also need an expansion tank.
Buy It, Then Let Zomg Install It
Our crews install what you buy, from Amazon, Costco, Home Depot or Lowe's, anywhere in California. What it costs on our booking page:
- Tank water heater replacement, same type: $1,075.50. New tank install: $1,120.50.
- Tankless water heater installation: $1,615.50. Replacing an existing tankless: $1,525.50.
- Water heater repair visit: $211.50.
- Water heater wrap and pipe insulation: from $121.50.
Prices are from our booking page in November 2026 and are what you pay for the work; the booking page always shows the current price and every option before you confirm.
More: plumbing repair, Rinnai vs Navien, tank vs tankless cost, heat pump water heaters.
Need help with this in California?
Zomg The Handyman installs what you buy, across all of California. Upfront prices, 4.9 rated on Google, same-day slots available.
Book Water Heater Installation →Frequently Asked Questions
Why does my tankless water heater go lukewarm in winter?
The incoming water is colder, so the heater has to raise it more and can deliver fewer gallons per minute at full temperature. Run fewer fixtures at once, or size up to a unit that covers your winter temperature rise.
What size tankless do I need for two bathrooms?
Most two-bathroom homes in California end up with a 180,000 to 199,000 BTU gas unit, which delivers roughly 5 gallons per minute with a 70 degree rise. Add up the fixtures that run at the same time to confirm.
Can I replace a gas tank with a tankless using the same gas line?
Sometimes, but often not. A whole-home tankless can use several times more gas than the tank it replaces. The line size and length back to the meter decide it.
Do water heaters need a permit in California?
Most cities require one for a replacement, and tanks must be strapped for earthquakes. We tell you up front whether your job needs one.
How much does Zomg charge to replace a water heater?
Tank replacement starts at $1,075.50 and tankless installation at $1,615.50 on our booking page.
Our service areas: Plumbing Repair in Los Angeles · Plumbing Repair in San Diego · Plumbing Repair in Irvine
Parts Our Plumbers Recommend With It
Get it installed
