TurboMax, eh?

lemesi

I've been slowly researching replacement of my slowly-failing 41-gallon Amtrol BoilerMate, as I described a bit in another thread. A quick refresher- I have an oil-fired Weil-McLain WGO-3 (115,000 BTU). My house is just under 1000 square feet, with convectors on two zones. I hope to add on several-hundred square feet in a few years. Right now I have two full bathrooms (one with a tub), but with the addition I will have an additional full bathroom. I test the (well) water yearly and the numbers are all good except it is quite hard (276 mg/L).

I asked a guy (who seems knowledgeable and I have no reason to doubt) from a mechanical company for his opinion of the best indirect water heater, in terms of efficiency and longevity, and he suggested a couple TurboMax models (23 and 34). I've done a lot of reading about water heaters in the past couple months, but I knew nothing about these "reverse" indirects. What does everybody think of these two models for my situation? They are significantly lower-capacity than the other brands I have been considering. How is this capacity measured? Can they really hold all that water volume just in the coils? The sales guy claims that the TurboMax 34 can handle three showers at once. With the DHW traveling through the coils, is the water hardness a concern for clogging? They also tout the copper heat exchange surface as a selling point, due to efficiency, but wouldn't it be a vulnerability relative to stainless steel?

I've learned from my reading that many people also use reverse indirect water heaters as buffers for space heating. The guy I talked to isn't proposing that. Is there any downside (aside from plumbing cost) to setting it up that way? Should I consider doing this in the interest of decreasing my oil consumption? I've been noticing my boiler cycles this evening. It seems to be coming on for between 20 seconds and 3 minutes every 7-10 minutes or so. Is this considered "short cycling?"

HVACNUT

The 23 will be more than enough. It can actually handle way more than your WGO3 can give, BTU wise.
Be sure to give it priority, pipe the loop in full 1.25, with the correct pump. 
Set tank temperature 10° lower than the boiler limit setting. If the boiler high limit is 180°, then set the tank to 170° with a 10° or 15° diff. It needs a thermostatic mixing valve to temp the domestic hot down to 120°.
And make sure a DOMESTIC RELIEF VALVE is installed. The 30 lb relief valve that comes installed on the Turbo Max is often mistaken for a domestic relief valve. I see it all the time. I used to use a 1-1/4x 3/4x 3/4 sweat tee and a 3/4 female x street right out the top for the domestic relief valve. 

lemesi

@HVACNUT Do you agree with the sales guy's choice to not plumb it as a buffer for the space heating?

Also, what's supposed to be the difference between the 23 and 24 (or 33 and 34, for that matter)? They are both 26 gallons but one seems to have more heat-exchange surface?

HVACNUT

I have no experience using it as a closed loop HX. I might be concerned with pumping through what would normally be the hot and cold, with all the capillaries. 
IMO, for high domestic hot water needs, a reverse indirect is awesome. For a buffer tank, there's other options. 

lemesi

HVACNUT said:

I have no experience using it as a closed loop HX. I might be concerned with pumping through what would normally be the hot and cold, with all the capillaries.

Sorry you just said a bunch of things that I don't understand. Isn't the boiler side always "closed loop?" And what capillaries are you referring to?

heathead

Question what are the standby losses with the water heated in that tank to x degrees. The water outside the coils has to be so hot to heat the water that flows through the coils to heat the domestic water. This heat in the winter is fine because let assume it goes back into the space. In the summer you have to heat up x gallons of water in boiler and now in the tank to x degrees to get hot water. If the boiler was cold start how many gallons of water to heat up before it starts adding heat to tank. Just a thought. I didn't get a triangle tank in tank design because the hotter water was always on the outside. I thought the stand by losses had to be higher because of the higher temperature differential. I am by no means an expert on this just a thought.

lemesi

@heathead I saw somewhere they claim less than 0.5F/hour, which is comparable to others, though who knows what they are assuming for the ambient temperature.

It seems like regardless of whether the DHW or the boiler water is losing temperature, it should be kind of the same at the end of the day in terms of BTUs lost, right? I guess the only thing is people seem to run these reverse tanks hotter (which I guess maybe is necessary to get the heat transfer performance to quickly heat the small volume of water in the coils), which should lead to more loss because it's a greater differential. Maybe that's what you meant, though.

hot_rod

I think the model numbers refers to how many copper coils or loops in the tank either 3 or 4.
Does your system need a buffer tank? Usually with that type of boiler you have enough mass to buffer. Now if you have or will add micro zones , like a single room zone, then the buffer aspect could make sense.

I think the best way to use the tank as DHW and buffer is find a rep or contact Turbomax directly and run your exact plan through their software. The software shows the available DHW under different tank temperatures and deltas as well as DHW flow rates, incoming water temperature, etc. The software is specific to their tank and design.
IF you run on outdoor reset you need to watch tank temperatures and DHW production. Same with mod cons that are on ODR.

There is no tank or indirect that isn't prone to hard water scaling. It either is inside or outside the coils I had one instance where the reverse indirect scaled over the orifice plate where the DHW connection is made. The plate is a limiter of sorts to prevent excessive DHW flows.

The tank was a buffer on a waste oil boiler so it would run up around 190F at times. Those high temperatures combined with 12 gpg hardness really causes a lot of mineral precipitation and scaling on the copper coils. In less than a year the hot water flow dropped to a trickle. So there may be some maintenance if you have hard water. Use a union at that connection to get access to the limiter plate.

https://www.pmmag.com/articles/101984-john-siegenthaler-a-synergistic-system

lemesi

hot_rod said:

if you have or will add micro zones , like a single room zone, then the buffer aspect could make sense.

Now that I think about it, that's probably why I get some shortish cycles. I only have two zones, but one is a single convector in a breezeway that isn't very energy efficient. We keep that thermostat set relatively low but I guess that is probably hurting our efficiency quite a bit.

hot_rod said:

There is no tank or indirect that isn't prone to hard water scaling. It either is inside or outside the coils

This makes sense. The other indirect I am considering is the SuperStor Ultra Max (or maybe SuperStor Pro), in which the coil flexes, which they claim reduces scaling. That seems like an intriguing idea that likely has merit.

I think overall this discussion has me leaning toward the SuperStor and away from the TurboMax. It seems like the higher water temperatures generally stored in the TurboMax are likely to increase scale as well as heat loss. And having the scale buildup inside as opposed to on the outside of the coils has a real potential to cause DHW to stop flowing, as opposed to just reduced performance. The TurboMax does seem like cool technology, but it strikes me as too much uncertainty about a more complicated piece of technology. Even their manual states that it should be checked for scale monthly, which there is no way I'm going to do. My current BoilerMate likely has lots of scale, but it's had zero maintenance in its 20 year (or whatever) life and is still going (with slightly reduced performance). It seems to me that the SuperStor is fundamentally the same technology as that and I should expect adding stainless steel and some other design improvements will give me a long trouble free life, especially if I actually do maintain it properly. With the TurboMax I'm just not so sure. If I were planning to use it to increase the efficiency of my space heating, then maybe that tradeoff could be worth it. But if my goal is just to get hot water, I don't see much reason to take all these risks of added problems.

hot_rod

Sometimes it's better to "fix" your water instead of trying to buy a tank that can deals with hard water. None can.
Is a water softener an option, you can get them adjusted so they are not softening down to 0 or a few grains. There are other salt free technologies now like TAC, but I do not know how they effect tank scaling.

Have your water tested, a good lab test not a water softener salesman test Chlorides is a very important number with stainless steel tanks. Warranty is void from day one if any of the specs are out, ph, hardness, chlorides.

Of all the tanks I have installed, removed, cut open, warrantied, etc I have had the best luck with the enameled steel tanks with a smooth coil. They handle all water conditions, nothing sticks to the coils, the coils are usually 1-1/4" so they can handle a lot of input.

If your water quality allow stainless go with a smooth coil. I like the HeatFlo for large diameter smooth coil ss tanks. i think some of the HTP are also smooth coil.

Next to water quality, high temperature operation can really shorten the life of any tank, lots of thermal stress. 140°F should be sufficient to kill bacteria and provide enough DHW. Size the tank so you do not have to crank it way up.

Here are examples of Viessmann and HTP water quality spec.

lemesi

@hot_rod We have well water and we get it professionally tested yearly. Last year we splurged and got all sorts of extra tests. Literally our only problem is the hardness. We do have a whole house filter, but have never wanted to get a water softener. It is definitely hard but we haven't had anything fail up to this point that we could point to hardness as the cause. We've had our dishwasher, for example, for a few years and it works fine. Our current BoilerMate must be about 15-20 years old with zero maintenance. I grew up in a house with soft water and I hate it. I guess I never realized when I was young, but now when I go back showering is just awful. I suppose I could consider setting it to be a bit less aggressive, but that's something I haven't researched. Also I guess I was never a fan of the whole ordeal of lugging bags of salt down the steps, and the health implications of that.

Tell me more about the smooth coil aspect. HTP markets their higher-end tanks as being better *because of* the corrugated coil, saying it has more heat exchange surface, and they further claim that it flexes to reduce scale. You're not the first person I've seen who prefers the smooth coil, however, so is there some science on this?

flat_twin

The corrugated coil may offer more surface but it also makes it easier for mineral scale to build up. I did a lot of homework and chose a Bock Sidekick 40 gal indirect. The coil is smooth 1.5" diameter. Recovery time with 70k btu, 160 degree supply temp is about 12 minutes.

https://www.bockwaterheaters.com/40skindirect.html