Water heaters
What size water heater do I actually need?
The short answer is that gallons matter less than people think, and first hour rating matters more.
This comes up at the counter most weeks, usually from someone whose heater has just failed and who wants to know whether to put the same thing back. Sometimes that is right. Often it is not.
Start with how many people, not how many bathrooms
Bathroom count is the rule of thumb everyone quotes, but bathrooms do not use hot water. People do. A four bathroom house with two occupants uses less hot water than a two bathroom house with five.
As a rough starting point for a tank:
| Household | Typical tank |
|---|---|
| 1 to 2 people | 30 to 40 gallon |
| 3 to 4 people | 40 to 50 gallon |
| 5 or more | 50 to 75 gallon, or two units |
Treat that as a starting point, not an answer. A household of two who both shower at 6am puts more strain on a heater than a household of four who spread out through the morning.
First hour rating is the number to look at
Every tank has a first hour rating, or FHR. It is how much hot water the unit can deliver in one hour starting from full, and it accounts for both what is stored and how fast the unit reheats. It is printed on the yellow energy label.
A 40 gallon gas heater often delivers more hot water in the first hour than a 50 gallon electric, because gas recovers faster. Two units with the same gallon rating are not equivalent.
To work out roughly what you need, add up your busiest hour. A shower runs around 10 to 20 gallons, a dishwasher about 6, a load of washing about 7. Total that up and compare it to the FHR.
When tankless makes sense, and when it does not
Tankless heats on demand, so you do not run out. That is the appeal and it is real. Two things to know before you commit.
- Gas tankless usually needs a larger gas line and its own venting. That is where the cost lands, not the unit.
- Output is rated in flow, not gallons stored. A unit that handles one shower comfortably may struggle with two at once in a cold month.
- In North Texas, incoming water is warmer than in northern states, which works in tankless's favour. Sizing still needs doing properly.
Tankless suits a household that runs out of hot water, wants the floor space back, or is building new. It is a harder case for a straight swap in a house where the existing tank was fine.
The thing most people skip
Hard water. North Texas water is hard, and scale builds up inside a tank and on tankless heat exchangers. A heater sized correctly but left on untreated water will still underperform and fail early.
If you are replacing a heater that died young, it is worth asking why before putting the same thing back in the same spot.
What we would tell you at the counter
Bring the model number off the old unit, tell us how many people are in the house and whether you ever run out, and we will tell you if the same size is right. We stock Bradford White and American tank heaters and Rinnai tankless, so there is no reason for us to steer you toward one over the other.
Call the counter on 972-242-7900, text your model number to 469-521-9293, or see what we stock. Need someone to fit it? We list plumbers who buy from us.