Had a leak in our 50 gal garage water heater last night, so replacement is happening. And the in house unit is probably on a ticking clock too, so we're just going for it on both. We've got gas units, and the garage unit just serves laundry and kitchen, and the back unit is for the bathrooms. We rarely run any two things at the same time, but the master bath is a fairly long run from the heater. Takes between 60-90 seconds for hot water to arrive at the shower, if that matters.

Garage unit is 50 gal / 39k BTU - seems like overkill for just laundry and dishwasher
Back unit is 50 gal / 40k BTU

Lowe's and Home Depot are both running some sales for Labor Day with ~15% savings, so wondering if we should just make the switch.

I'd love to research this and really understand what I'm getting into, but time is of the essence.

Any quick advice? I'm in North Dallas if anyone has a recommendation

Short answer based on my situation/research. For a tankless gas unit, you need to make sure you have enough gas supply. I have a 1/2" supply line to my water heaters, and while that doesn't tell you everything about how much demand it can support, I'm pretty sure I could only get away with a high efficiency unit. The high efficiency units have very corrosive exhaust, so normal galvanized vent pipe won't do (I think they actually recommend PVC since the exhaust gas is relatively cold.). In my case, the heater is in the middle of the house, so re-routing the exhaust wasn't a serious option and I ended going back with a traditional tanked unit.

I think your shower is the high demand item which typically requires a bigger unit - you may be able to go smaller, just need to look at the GPM ratings of those appliances and go from there.

I probably would have done it if I could have. Good luck.

Thanks for the input.

We have pretty hard water here, and from what I've just read, a whole home filter is recommended in any case. If it's another pile of money to install that, I won't bother since we likely won't be here forever.

The reason PVC is needed is due to the moisture. In an 80% heater, there is enough heat going up the vent pipe to prevent condensation. In a 90% (high efficiency), there is not enough heat going up the vent pipe and you will get condensation in the pipe. This will rust out a metal vent pipe.

For the house unit you're looking at needing a 3/4" gas supply line. Many models require a double-wall vent pipe, that can't be done with PVC and silicone condensate drain line. You also need to make sure it has a place to drain to in the event of an emergency, and is easy to flush. That typically requires additional fittings.

Here's the setup I installed several years ago:

Always in new house designs, demand WHs are popular.
Post Feb Texas freeze, some are adding a backup tank WH for at least one minor bath.

What happens to tankless water heater when power goes out?
"Tankless water heaters - even gas fired - also have a direct electric ignition that uses 120v power that lights the burners as hot water is needed. If the power is out, the ignition system will not operate"

Remember the TEXAS Feb power out freeze


If it were me wanting no hassles
replace both with tank WHs that someone designs capacity as a better fit to serve.

tgivaughn said:

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What happens to tankless water heater when power goes out?
"Tankless water heaters - even gas fired - also have a direct electric ignition that uses 120v power that lights the burners as hot water is needed. If the power is out, the ignition system will not operate"

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Power inverter and extension cord run to the car.

Another good point about the power. You may not have an outlet near your existing tank heater and will have to get one installed for the tankless.

Thanks all. Feedback was pretty much as I expected. Keeping it simple and sticking with tanks

I'm not saying it isn't important to plan on what-if, but the state wide power outage was rather unusual. Hot water also wasn't the major necessity in my mind but I also didn't have my power go out, so different perspective.


We replaced a tank heater with tankless Rheem High efficiency. Paid $1100 for the Rheem and got $650 back from Texas Gas. We were lucky in not having to move gas lines very far.

It's an annoyance in having separate water tanks and paths...plus the space to have them somewhere.