We're currently a family of five with no hot water-saving fixtures and the single 50 US gallon/180 litre gas water heater is sufficient. A while back, with six of us, two 75 US gallon electric units were inadequate.

Here's a calculator to help you decide.

Are the two WHs in separate locations, adjacent to different bathrooms, to provide faster hot water to the bathrooms?

They are installed in the garage next to each other and not as separate systems. Lots of piping is connected between the two and there appears to be just one output. Here's a photo:

Local codes may require two heaters for that number of bedroom/baths.

Anything's possible. But have you actually come across thatother than for multi-family dwellings?

Looks like they are plumbed in parallel, with the ability for one to be isolated or not used. Keep them both but consider a heat pump water heater when it's time for replacement. Since they appear to be atmospherically vented (ugh) be extra careful with air sealing between garage and house.

When you say they're "atmospherically vented" are you referring to the inwardly-angled metal vent pipes at the top of the photo? If so, those join to a single vent pipe which terminates outside the home somewhere.

A high efficiency condensing model, let alone two of them, would have been more economical over the long run. Atmospherically-vented antiques are not used in most new homes here. And there are many rebate/grant programmes across Canada to prod homeowners to upgrade existing systems.

So am I correct that this is major overkill to have 2 of these beasts?

No idea if this is overkill, but I'm curious- did you have clear plans for this space? If so, do you show two of the water heaters? If not- why did the extra come in?

Best to clarify with all relevant pros involved in your project, before doing anything.

Just a BTW, but tankless water heaters are very cost/energy efficient. LOVE mine.

Do you have geothermal heat/air by any chance? That looks very close to the set-up we have to take advantage of the hot water produced in our geothermal lines (or something like that).

So am I correct that this is major overkill to have 2 of these beasts?

Check the calculator above and keep in mind peak load for your family. Say, if all five showers are running at once as everyone's off to school and work and the dishwasher(s), and washer are all running as well.

If you have a basement, why are they in the garage?

Rrah...we had geothermal in the house we just sold but our two tanks were electric.

Not sure either pan drain is going to do much good, especially the vertical one on the right! :-)

The orange tube tells me the one on the right is questionable.

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Mark, what are you saying about the orange tube? What's questionable and why does the orange tube indicate this?

I live in Georgia. Given the number of baths and kitchens, kitchenettes and jetted bathtubs a home of this size, two large, standard hot water heaters are considered necessary. Nat Gas is the cheapest form of energy in the area. A gas home is considered an upgrade from an all electric home. It will probably cost you $50 per month for your two water heaters. The orange flex line is your gas line. Yes, you will be keeping 150 gallons of water hot at any one time.

While this isn't the most financially efficient use of your hot water dollar, it is standard to the area. To change to geothermal will be cost prohibitive. Natural gas on demand heaters may require extensive movement of plumbing and venting, but are more efficient. You would have to consult a plumber to make that determination.

You do have the option of having some "modifications" made to the system after you close. You can get a plumber to take one off line. You need to talk to the builder.

I was alluding to the tube in the form of a question mark. Every once a while I take a break from my work and make a totally useless but highly observant comment.

This installed in the garage?

Make sure they are raised.

IRC P2801.6 Water heaters installed in garages. Water heaters having an ignition source shall be elevated such that the source of ignition is not less than 18 inches (457 mm) above the garage floor.

Number of water heaters is not a big deal, you can shut one off; turn water valve off and turn gas off. And may be drain

Mark, Just a guess, but I think the tubes connected to the tray are designed to be turned down to allow drainage if needed. They are perhaps overlong for their intended purpose.

I am talking about the orange flexible gas line, not the (off) white PVC drain pipes.

IMO....you should have gotten a 'on demand' hot water heater. Then you don't pay to heat water 24/7. It only costs a few hundred bucks more than a regular hot water heater but you would save 1000's of bucks over time.

Re: higher-tech / less-crappy heaters, this isn't a custom build and customizing the water heater wasn't one of the options allowed. Also the builder mentioned that the extra heater was a screwup and they are fixing it now. To everyone who replied, thank you!

Mallory, it seems that it's in everyone's best interests to keep the extra heater. You can always shut one off and you have a free backup, so long as it was free. The labor to remove it, should be motivation for the builder to leave it for you.

It's got a vent sure, but it's still an atmospherically vented appliance that puts indoor air quality at risk. They really need to make those things illegal. You probably have little control in keeping your garage air separate from your house air at this point but it's something to be aware of. You could possibly do more to seal the mud sill of attached walls and be aware of the need to keep the garage-to-house door closed and keep the weather stripping fresh.

For readers and posters perpetuating the myth that tankless (on-demand) water heaters save money, scientific studies have found otherwise. Heat pump water heaters are where it's at, especially in hot, humid climates or even cold climates when basements and tall crawlspaces are involved.

Two 75 gallon gas-fired hot water heaters seems like overkill for most family's needs. You might try isolating one heater and see if it is sufficient for your needs. If so, you can drain the other heater and have an installed spare. I agree with Mark Bischak that the shape of the orange gas lines calls into question the installation as does the orientation of the drain lines from the two pans.

My house has 2 75 gal gas water heaters plus a small electric for the kitchen. In California on natural gas the 2 large ones cost $35-40 per month to run. That is for both. There is no possible justification for tankless. Even if it was free, they don't save enough to cover the maintenance and increased replacement cost.

We have two 50-gallon natural gas fired tanks in our 2900 sq ft ranch with 3.1 baths. We had one tank fail after twelve years -- still had hot water until it could be replaced. One of my *favorite* things in the whole house is the electric circulator pump -- hot water in three seconds at every hot water tap in the house!

Our tanks are in our basement -- along with two two-stage gas furnaces with flow-through humidifiers and air cleaners. An igniter failed on one furnace, but the house stayed tolerably warm with the other until repair was made. (Belt and suspenders?)

With all those bathrooms it might be smart to keep both.