1 large, 1 small water heaters - which 1 first?

[John Kogel]

The 40 gallon (US Gals.) Electric water heater is nearly new. House guests are expected for prolonged stays. I suggest a 10 gallon tank could be mounted on a shelf (sturdy shelf) above.

For max efficiency, does the small tank serve as a pre-heater? Or does it go in as a downstream super heater, with the larger tank turned down as a pre-heater?

Note: these are older folk, no 30 minute showers expected. They want a minimum cost for an average hot water supply for 3-4 people.

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[Marc]

Are the KW specs the same for all three elements?

Marc

[John Kogel]

Let's say they are.

[Chad Fabry]

The wattage of the elements isn't a factor. A calorie is a calorie.

[Marc]

Assuming this is your house (and knowing that you and I share an affinity for experimenting), I'd plumb the 10 gallon to receive cold water first with the 40 gallon receiving water from the 10 gallon.

In like manner, and to avoid running another water heater branch circuit, I'd replace the lower thermostat on the 40 gallon with one identical to the upper thermostat and wire the 10 gallon to this lower thermostat. That way, all three heating elements are wired in identical fashion to that of the 40 gallon with the twist that there are now three elements between two tanks. The 10 gallon is the first to get power when first powered up. After it's satisfied, the lower element on the 40 gets its turn. Finally, the upper element gets its turn and all is hot hot hot.

Don't call me if the hot water pressure in the shower is dismal.

Chad's right if you do it my cockamamie way.

Marc

[John Kogel]

Chad, the goal is to heat water just enough but not too much. []

Heating 50 or 60 gallons of water and keeping it hot day and night is a waste of energy, no?

So, Marc, are you saying if only a bit of hand washing takes place, only the small upper tank is actively heating? Ice cold water enters there. But we want hot from the downstream tank, not 50 gallons always hot.

I like that idea, and the wiring advantage is a big saving in copper.

But the water in the downstream 40 gallon tank is going to be cooling off while the system is dormant. The box could be stuffed with insulation.

[Jim Katen]

. . . . They want a minimum cost for an average hot water supply for 3-4 people . . .

The existing electric 40-gallon water heater *is* an average hot water supply for 3-4 people.

[mjr6550]

. . . . They want a minimum cost for an average hot water supply for 3-4 people . . .

The existing electric 40-gallon water heater *is* an average hot water supply for 3-4 people.

Only if they are French.

[kurt]

Only if they are French.

Really.

I don't know as if they'd have any appreciable savings from dinking around with 10 gallon "primer" tanks. Maybe, but I doubt it.

If they were short with a 40 gallon tank, and I think they will be, they should just spring for another 40, set it up in series or parallel as one believes, and when house guests arrive, turn on the 2nd water heater.

A 10 gallon unit is well on the way to the cost of a new 40 gallon unit, and the installation costs are about the same; why not spend a little extra dough and get a real tank and turn it on and off as necessary?

[John Kogel]

Only if they are French.

Really.

I don't know as if they'd have any appreciable savings from dinking around with 10 gallon "primer" tanks. Maybe, but I doubt it.

If they were short with a 40 gallon tank, and I think they will be, they should just spring for another 40, set it up in series or parallel as one believes, and when house guests arrive, turn on the 2nd water heater.

A 10 gallon unit is well on the way to the cost of a new 40 gallon unit, and the installation costs are about the same; why not spend a little extra dough and get a real tank and turn it on and off as necessary?

There are space restrictions. A second 40 gallon won't fit in there.

Anyway, using a guideline of 12 gallons of hot water per person (HGTV), 40 is adequate for 3 folks but not four, while 60 is good for 5, too much for 4.

Price wise, no doubt the standard 40 US gal tank can be had for the best price, and the 10 gal is almost the same price, but will waste less power.

So using the 10 in series with the 40, I suggest that the 40 gal could preheat the water to 95 or 100 degrees F and then the 10 could be set to 120. A smaller amount of water is kept stored at the higher temp that way.

[Jim Katen]

. . . . They want a minimum cost for an average hot water supply for 3-4 people . . .

The existing electric 40-gallon water heater *is* an average hot water supply for 3-4 people.

Only if they are French.

We're talking Canada. Isn't that the same thing?

[Jim Katen]

So using the 10 in series with the 40, I suggest that the 40 gal could preheat the water to 95 or 100 degrees F and then the 10 could be set to 120. A smaller amount of water is kept stored at the higher temp that way.

I think you're attributing too much value to standby losses. They're nearly insignificant with modern water heaters. The last study I read on the subject showed the average total value of standby losses over a 1-year period to be about $50 (US).

And if the water heater is in the conditioned space during the cold months, the "losses" just offset your heating costs.

I'd remove standby losses from the calculation entirely.

[David Meiland]

Before I added a 10 I would rewire the 40 for simultaneous firing of both elements. You're adding another wire anyway, so try that first, it might be enough.

[Tom Raymond]

If you have room to add a 10 you have room to go to an 80. Upsize one tank and sell the old one on craigslist.

[kurt]

Yeah, or that. Or, wiring it so both elements fire at the same time.

The 10 gallon mini primer doesn't make much sense in my view. I'm always interested in experiments and results, but it just seems like dinking around to me.

[David Meiland]

Actually, do the both-elements-firing deal, add a tempering valve so you can run it at 145 and temper down to 120, you're probably all set, watching basketball and drinking beer by 1 PM.

[John Kogel]

Before I added a 10 I would rewire the 40 for simultaneous firing of both elements. You're adding another wire anyway, so try that first, it might be enough.

That requires adding one 20 amp circuit, right?

I could switch that element back to normal operation when extra heat isn't needed.

Sounds about right, thanks, David.

Thanks, Jim. I pictured heat loss but you are right, the tank gives off heat into the laundry room.

BTW, the French won Quebec only. They have been threatening separation ever since but we need them for a buffer to keep the Yanks out. []

French on cereal boxes is a small price to pay.

Just kidding, not politix. []

[Denray]

When we're camping we feel great after splitting a 5 gal solar water shower bag. Are all 4 people lined up at the door to take showers? Get a six pack of beer in there to thin them out and figure a way to cut the flow way down on the shower head. Make it easy to stop flow while soaping up instead of just letting the hot water fly. Kind of like letting the water run while brushing your teeth. My wife likes to have Niagara Falls coming down when using our home shower.

I apologize for the above statement.

[mlparham]

When we're camping we feel great after splitting a 5 gal solar water shower bag. Are all 4 people lined up at the door to take showers? Get a six pack of beer in there to thin them out and figure a way to cut the flow way down on the shower head. Make it easy to stop flow while soaping up instead of just letting the hot water fly. Kind of like letting the water run while brushing your teeth. My wife likes to have Niagara Falls coming down when using our home shower.

I apologize for the above statement.

It's called a sailor's shower. Shut the water off when you soap up then turn the wate on to rinse.

[fyrmnk]

Put in a tankless and sell the old 40. Still wouldn't trade mine after 6 years it's been in

[mlparham]

I like the idea of adding a tempering valve at your cold water heater. You can then turn the temperature up on your cold water heater when you have guests but you will still receive only a safe, 120 degree water output. This modification will likely add as much hot water capacity as adding a small electric water heater.

Once your guests have finally departed simply turn the temperature down on your cold water heater.

[Marc]

Before I added a 10 I would rewire the 40 for simultaneous firing of both elements. You're adding another wire anyway, so try that first, it might be enough.

That requires adding one 20 amp circuit, right?

30 A, 2 pole. Just like clothes dryers.

Marc

[John Kogel]

I like the idea of adding a tempering valve at your cold water heater. You can then turn the temperature up on your cold water heater when you have guests but you will still receive only a safe, 120 degree water output. This modification will likely add as much hot water capacity as adding a small electric water heater.

Once your guests have finally departed simply turn the temperature down on your cold water heater.

You mean modifying the lower element on the existing tank, right? But only one element comes on at a time. That will be the simplest, cheapest and quickest.

[John Kogel]

Before I added a 10 I would rewire the 40 for simultaneous firing of both elements. You're adding another wire anyway, so try that first, it might be enough.

That requires adding one 20 amp circuit, right?

30 A, 2 pole. Just like clothes dryers.

Marc

I just took a look at it, 3000 W elements, max 18.75 amps on a 20 amp circuit.

And here's the best part. The tank is actually 40 Imperial gallons, 48 US gallons. I should have checked the label closer with a light and a mirror. Some home inspector, sheesh. []

[John Kogel]

When we're camping we feel great after splitting a 5 gal solar water shower bag. Are all 4 people lined up at the door to take showers? Get a six pack of beer in there to thin them out and figure a way to cut the flow way down on the shower head. Make it easy to stop flow while soaping up instead of just letting the hot water fly. Kind of like letting the water run while brushing your teeth. My wife likes to have Niagara Falls coming down when using our home shower.

I apologize for the above statement.

Low-flow shower heads, good idea for everybody.

Then I think the big wasters of water are the washers, clothes and dishes. But the times can be staggered for those.

Yes, we used to heat water in a bucket on the campfire. That's a possibility too. Big metal tub and a wash board.

So in conclusion, now that I have a 48 US gallon tank, since we like the shower head we got, I propose doing nothing at all. []