Indirect Water Heaters

The answer is yes it takes more energy to store 60 gallons compared to 32 gallons, all things being equal.

Keep in mind an indirect DHW tank does not have a flue pipe running thru the tank like fossil fueled tanks, so the standby loss of an indirect is much, much lower. Simple heat transfer principles apply.

Again, with a 60 gallon solar tank, you are only heating 30 gallons with the electric element. So you actually have a 30 gallon tank, in electric only mode.

Also electric DHW tanks take much longer to recover compared to fuel fired. Typically they have a 4.5 KW element, so 15,345 BTU/ hr input. gas or oil fired are more like 35,000 BTU/hr or higher + twice the recovery time once you pull them down..

The ONLY time you heat the entire 60 gallons is when you flow into the coil in the bottom from your wood boiler, solar, whatever.

This is the main reason you don't see solar tanks smaller that 60, a few 50 gallon. There is not much DHW available via the electric element only.

We rarely sell a 50 gallon solar tank. Even empty nester couples want more than 25 gallons of DHW.

The general rule of thumb for SDHW sizing has been 20 gallons per person per day.

With low flow faucets and shower heads I feel 20 gallons for the first person, 10 gallons per each additional person is more reasonable rule.
So a family of 4 would be 50 gallons per day DHW required.

In my 40 years of plumbing I have never had a customer complain that I provided too much DHW. But I have under estimated a DHW number of times.

Bob Rohr said:

Keep in mind an indirect DHW tank does not have a flue pipe running thru the tank like fossil fueled tanks,

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No, but alas, the boiler providing the heat does.

velvetfoot said:

No, but alas, the boiler providing the head does.

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Good point.

Typically the boiler only fires on a DHW call for the indirect, at least in the non-heating season, so not the same standby loss as a WH that is maintained at 140F, or whatever.

Bob Rohr said:

Good point.

Typically the boiler only fires on a DHW call for the indirect, at least in the non-heating season, so not the same standby loss as a WH that is maintained at 140F, or whatever.

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Don't think we've heard for sure yet on whether the boiler in question is cold start or not?

On the tank size issue, our electric is 80 gallons and costs in the area of $25-30/mo, so don't think a bigger tank gives that much more operating expense. Sometimes its nice having hot water in reserve.

I have 12 year old 80 gallon Electric water heater. It cost me about $40/month to run it on electric. Its really a non issue since i heat it with wood all year via a side arm HX. I'm considering replacing it with 120 gallon if it ever springs a leak,so i can run my storage temps even lower. It has a rubber lining though so maybe it will last forever ? I heard they are going to outlaw those big tanks for efficiency reasons.

Otis B Driftwood said:

Yes, good point.

I talked to a Heat-Flo rep today. Solar wouldn't make sense price-wise
since I've no intention of solarizing our roof, what with the pitch and wrong
facing direction.

Chloride in the water will corrode stainless steel. A recent test revealed a
reading of ph7.2, which is safe. An older test revealed ph7.5 ( perfect ),
Chloride 12.2 ( EXTREMELY safe as max allowed is 250 ), Sodium 28.7
( HIGH as limit is 28 ), Sulfate 15.7 ( EXTREMELY safe as max allowed
is 250 ). So the flag here is the Sodium level. No softener.

His final analysis: Talk to the installer.

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The reason I am suggesting a solar tank is that it has an electric element back up for non-burn days or months. It's the same tank as an indirect, just with a mid point element.

Over the years I've had my best luck with glass lined steel tanks. Just keep the operating temperature below 180°F, maintain the anode rods and they last a long time. Like your current tank has. Stainless, as you discovered has some water quality limitations. Glass coated steel, really just concerned about excessive thermal shocking.

Good idea talking to a local wholesale supplier, they get a good feel for what type of tank lasts in your area under your water conditions. Or drive by their location and look in their "bone yard" You will get a good idea of warranty returns

Here is a look inside a typical glass tank. The large coils are also glass coated. It's 36 feet of 1-1/2" diameter coil. Very low pressure drop, lots of surface area.
You'll find this same coil in most steel tanks, same manufacturer supplies them.

Hey Bob, what do you think of the life expectancy of my reverse indirect tank (Froling Energy Tank), which is used as a buffer tank and the domestic water goes through a 104' 1.25" corrugated stainless coil in the tank? Buffer side is 108 gal. and dhw side is 11 gal. The tank is steel. My water is not chlorinated and I have a softener for lightly hard water. Thanks.

Not efficient enough. to much standby loss.

Otis B Driftwood said:

Wood: Rubber lined? I see a joke around the corner ...

Seriously, explain, I'm curious. TOO efficient? I can see
such stupid legislation in The '60s, but now? Oh wait –
"stupid legislation" ... hardly an oxymoron.

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i was surprised to find a rubber liner when I changed a heating element.

velvetfoot said:

Hey Bob, what do you think of the life expectancy of my reverse indirect tank (Froling Energy Tank), which is used as a buffer tank and the domestic water goes through a 104' 1.25" corrugated stainless coil in the tank? Buffer side is 108 gal. and dhw side is 11 gal. The tank is steel. My water is not chlorinated and I have a softener for lightly hard water. Thanks.



View attachment 156433

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I like the concept of reverse indirect. I have used a number of the Ergomax and TurboMax. They got crazy expensive with a hundred pounds of copper tube inside them, however. The corrugated stainless HX make sense, same reason Tom uses SS in his Solartechnic tanks now. Less $$, encourages turbulent flow, easy to shape.

You do need to run them fairly hot to get the rated performance on the DHW side. So not great if you want to pull the tank temperature way down for radiant or with ODR controls.

Ideal for a separator/ DHW tank right along side the boiler.

Otis B Driftwood said:

Bob: Again, you're all kinds of awesome. Thanks for giving
your precious time to this Olde Farte.

Would you mind explaining what's going on in that setup you
posted of the glass tanks? I'm guessing what we're seeing is
a backup tank on the right? It's the Frankenberry of HWHs ...

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These pics were a couple ideas I had for drawback solar. With the dual coil I was trying to allow the upper coil to be the drainback "air space" so I did not need an additional drawback tank. It worked well as long as the collector loop volume was low. It also had a prototype Grundfos Alpha as the DB pump.

The other pic shows using a typical off the shelf steel compression tank, slightly modified, as the DB tank.

The cut aways are just sample tanks that we take to various trade shows to demonstrate the tank features.

Bob Rohr said:

I think the State of Montana recently dropped the double wall HX requirement, maybe others States will follow. Thanks for carrying the torch

Manufacturers hate building double walled HXers. Performance, corrosion, cost, leak path, all sorts of challenges.

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EXACTLY

Don't forget the 1007 at the tub filler. To many engineers at the code table and not enough "working" plumbers...

Here in Minnesota the old plumbing code required double-wall, unless you were in the union and could/would jump through ridiculous technical hoops to meet the exception clause.

We also gave Amtrol a monopoly on indirects for since they were first made. Disgraceful!

Finally the State has run out of money for their own code and accepted the UPC, but before accepting they tried to sneak in a mandatory RPZ at the meter of every residential application, effectively killing indirects and combi boilers and water heaters forever.

I presented the case for this class of appliances and heat exchangers noting the related EPA study and the UPC is now accepted with single wall (non-toxic) clause and all.

Rock on Hot Rod!

BadgerBoilerMN said:

they tried to sneak in a mandatory RPZ at the meter of every residential application, effectively killing indirects and combi boilers and water heaters forever.

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Care to explain more?

TS

Back to the question first posed........
Triangle Tube = Vile McLain. Stay away based on our experience.
Same goes for the newer low price version of indirect currently marketed by Heat Transfer Products. Their Super Store Stainless tank/coil was-is good.

Viessmann is in a class by themselves for both quality and price on their 300 series tanks.
Buderus indirects truly suck. I think we have replaced every single one we have installed.
Have not used Bradford White ever since their fiasco with the combination water heater/heating unit came and went. Very poor support back then on that product so....seeyah!

The Lochinvar Squire has been our go to indirect for the last several years and they have provided very good performance and done so with zero problems so far. We've installed all sizes up to 119 gallon. No issues whatsoever.

http://www.lochinvar.com/products/default.aspx?type=productline&lineid=50

Otis B Driftwood said:

Well, that was interesting. Guy came by this AM.
Nice, caught something in our setup and confirmed
our boiler is cold startup. He recommended Vaughn's
stone-lined tanks. Whatever.

Buuut ... he had no idea what reverse indirects were.
There went my "informational interview".

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The main thing to watch with reverse indirect is their performance at various tank temperatures. Generally their output is rated with a fairly high tank temperature. Ergomax used to be rated at 190F tank temperatures.

The Vaughn tanks last a long time and have plenty of thermal mass, but I'm not a fan of finned copper coil style HX. Hard water can really limit their output.

My Froling Energy Tank indirect has performed well for us even down to 135; not sure about 'rated' though. We got it mostly for the buffer tank aspect of it for use with the pellet boiler. It extends the run time of the oil boiler too when that is running, so I thought that was a good idea as well. Downside is keeping 120 gallons warm all the time and the cost of the tank.

Bob,
is there any difference (in your experience) between the hard water scaling problem with finned exchanger tubing if it is made of copper or copper/nickel alloy?

A Vaughn tank might be a great solution. If you are concerned about internal HX, then use a standard tank without one and use an external plate hx. They do last a very long time.
They are heavy as hell. They were my motivation to make modular tanks. I could not handle them by myself when starting out.