hot water heaters

Unknown

the tank on the right is only a storage tank. It has no elements or burner.

It is just for storing recirculated water, which tempers the cold feeding the water heater.

The shower habits of college students taught me that.

Noel

I almost missed you yesterday at NEFI. You were in disguise, I was looking for a lobsta suit.

duffy

hot water heaters

got a question is it better or more effecient to install 2 40 gal hwh or a single 75 gal hwh.new construction 4000 sf home.the home owner was asking me this today.if you go with 2 40 gal hwh's do you pipe them in parallel(equal hot water draw from both) or pipe in series and stagger the supply temps.I'm leaning toward pipeing in parellel and valving in such a way if one fails you could close valves and run off one till other is replaced.will need to install recic lines also as master bath is quite a distance from mechanical room.any comment or opinions appreciated.

Heatermon

I get asked this question all the time.

And always answer it with "Why do you want to heat hot water anyway. If it's already hot just use it."

But seriously, either way, you will need a 4" flue vent, so there is no difference there, except for the tee if you go with 2 heaters. Same goes for the gas (no difference either way) as you will still be under 100,000 b.t.u. either way. Water on the other hand could be interesting. A typical 75 gallon will have 1.0" inlet and outlet with the 40&50 gallon models with 3/4". So, if you run the smaller heaters in series, you will lessen the maximum flow as compared to one 75 gallon. So, now the question really is the difference in efficiency between (2) 40 gallons and (1) 75 gallon. The 40 or 50 gallon models will be around a .62 energy factor and the 75 will be at .49. The cost difference between (2) 40's and (1) 75 will be very little, so all in all, if I had the room, I would install (2) 40 or 50 gallon models (in parallel with isolation valving as you suggested) so that they would have redundancy, ease of replacement, and easier to find (commodities) products. I always ask the homeowner how he would feel if he had to wait 4 or 5 days (think long holliday weekend) to have hot water if the one 75 gallon went out and depending on his answer, do whatever the hell I want :-) Just kidding, give the guy what he thinks is best. Personally I like redundancy if space permits. Good luck with your project.

Heatermon

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Al Letellier

water heaters

What's heating the house? Are you using indirects or direct fired units? With today's high tech stuff, why would you install a direct fired unit. A boiler and an indirect may be more expensive, but much more efficient and almost always will have a longer life and warranty. What about a point of use heater if you're going direct fired. Much more efficient, they have variable inputs and can produce a LOT of hot water on demand. Rinnai amongst others make great units.

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[Deleted User]

Not just parallel...

but REVERSE RETURN parallel. That's the way the pros do it. You want both water heaters to see the coldest inlet temperature they can.

Series is not a good way to do things. Simple, yes, but correct, no.

Another common mistake is parallel direct returns. They look cool, but if you think like water (wet, lazy and dumb) you'll see that there is a "path of least and great resistance, and water, being lazy will follow the path of least resistance. Not exactly what you want.

I agree with the tankles idea. If there is no critical dump load in the near system, I'd skip the tank and go tankless. Takagi Mobious comes to mind.. So many heaters, so little time...

ME

Mike T., Swampeast MO

Series water heaters

Hey Mark, what are the objections? I'm probably prejudiced by this college town but see water heaters in series quite often and they provide nearly endless hot water for protracted moderate use periods (say two different showers used in rapid succession).

hot_rod

I've used series also

typically in vacation homes. It allows you to turn down, or off, the first tank at low load periods. I have found with parall if one tank fails you get an odd mix of hot and cold as it draws from the hot and cold tank.

hot rod

[Deleted User]

Why not in series...

In theory, a water heater is a water heater and shouldn't care whether the water entering is 40 degress or 100 degrees. In practice, it does make a difference as it pertains to efficiency. It also has a lot to do with the life exppectancy of the appliances. In every case of series water heater I've seen, the #1 unit looks about 10 time older than the #2 unit. With a little closer scrutiny, the flue gas passage ways of #1 show a MAJOR sign of on going sustained condensation, which equates to shorter life expectancy of the # 1 heater. With the load spread equally between two units in parallel, each heater sees 1/2 the flow potential, thereby limiting the exposure to condensate by approximatley half also.

Granted, nothing is perfect, but it just makes more sense to me to pipe them in parallel than it does in series. Both heaters "see" equal loading, and contribute equally as well.

One of my teaching associates wants to set up a test stand and test these two thoeries side by side up in the lab at RRCC. We just never seem to be able to make our schedules meet on the same level at the same time.

Yes HR, you are corrrect, if one of them goes down, you get a lot of luke warm water, but if in series, and the # 2 goes down, you also get a lot of luke warm water. The # 2 unit becomes a fat spot in the line full of luke warm water. I've experienced more complaints from series heaters than I have paralleled.

JMHE

ME

Here's a good way to over come dump load capacity with a limited flue capacity. (Thanks Noel!)

Brad_3

I believe that two 40 gal tanks would have MUCH more surface area to lose heat than a single 75 would they not?

ScottMP

I am SO confused ?

Marc,

You say you like tanks piped in parallel, and then draw tanks piped in series and say this a good way to overcome dunp loads ? The only difference I see is a re-circ line.

Whats the difference here ?

Scott



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duffy

hwh

thanks for the input,will most likely pipe in parallel,have done it this way in the past and most owners like the option of still having dhw if one heater fails.mark are you saying i should not pipe the recirc line also in parellel and just into one tank or did i misunderstand you.will explain all the diff to home owner and let him decide thanks for the help

ScottMP

I would think

That the size of the flue passage way and the vent connector for a 75 gal. heater would increase the degree loss due to draft, after the burner has shut down.

??

Scott

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[Deleted User]

Bring the circ return

back into the cold inlet so it sees both tanks.

ME

[Deleted User]

What

Noel said lobsta man. The drawing was presented to show an option for taking care of occasional dump loads with regular small individual (shower) loads.

Sorry for the cornfusion.

ME