Alliance indirect performance with smaller boilers?

Replacing a stand alone WH, want to go with an Indirect.

The alliance SL indirect water heaters list their required inputs as 99K BTU's for the 35 gallon model, and 110K for the 50 gal model. Does anyone know how much the performance would be decreased when using an Alpine 80? For full burn its listed capacity is 72K...
As a non-engineer, I would only guess the alliance would be about 73% of its rated capacity, but perhapse someone here could shed more light on that.

I have two full bathrooms, washing machine, dishwasher. The bathrooms both have full size bathtubs (one is a jacuzzi tub which is a little larger) and one has a seperate shower with a multihead unit thats probably good for 5-7gpm if its all on full force. I have two adults and two young kids living here, but around the holidays, I frequently add two more adults to the house.

I was wondering if the 35gal alliance would be enough, or if I should spring for the extra money and size for the 50 gal. Logic says go bigger, but if I only need the 27 gal, then the 35 would be one size up, not the 50.

Could I get enough performance from the 35 if I kept the temperature a little high and installed a mixing valve?


I tried to contact US Boiler with this question, but they will only speak to licensed plumbers apparently... Even an email was responded to "please direct any question to your local contractor" And every licensed plumber I contacted doesnt have any idea, and won't take the time to call US Boiler unless I sign a contract with them. I cant blame them for that, but I also want to know what I need instead of the normal rply of "when in doubt get a larger one..."

So I come here hoping someone has already inquired and got an answer... Plumbers?

I was waiting for one of the pros to respond...but, since you haven't had a hit for awhile, here's my thoughts.

The boiler has a larger output than many standalone tanks, so getting the water in the tank hot enough isn't an issue, it's about how long it takes and the first hour recovery rates. The spec sheet is only valid on the time and flow when you have at least their specified heat input to the tank. Because the boiler's burner is larger than that in a typical standalone tank, you can often go smaller. But, when trying to fill a large tub at max speed and a smaller boiler, you will not get the first hour volumes in the spec sheet, so larger may be required. This all assumes you put the IWH on a priority zone so it can get the full output of the boiler (and typically, it would also fire to what may be a higher temp than when space heating).

I have no experience with that brand IWH, so can't comment on how good or bad it is. I have a big 6' air tub, and ended up with a 50-gallon IWH. I can take essentially an endless shower because of the recovery rate, or fill the tub up without issues. Other than initial costs, a good indirect WH can have very low standby losses - some of the better ones are rated at less than 1/4-degree per hour and have a lifetime warranty against leaking.

How big is your boiler that keeps the endless hot water flowing, and what temp do you keep the IWH tank set to? For the showers I am not too concerned with going with the smaller 35 gal unit, but filling the big tub would deplete that and then some unless I had a mixing valve and the tank at 150 degrees... But even that is hard to figure out what amount of hot water flow I would get.

35 gals at 150* through a mixing valve with 45* cold water yields how many gallons at 120*??? i havent been able to find a formula to figure that out...?

Well, consider that you'll never get all of the volume of any tank dumped quickly- figure maybe 75-80% of it. Yes, once the temp starts to drop in the tank the boiler will come on, but that can only raise what's coming in so much if the flow is at max. WHen your flow rate is smaller, like when taking a shower rather than having the flow at max to fill the tub, then, the size of the boiler becomes a bigger factor. FWIW, most IWH are kept nominally around 140-degrees - higher and your standby losses start to get bigger and you're better off (IMHO) with a bigger tank at lower temps.

Mixing the two to get 120-degree water will produce about 38g, if you use 75% of that 35g tank, then the temp will start to drop until it gets to nearly all cold since it won't be able to heat the incoming water very much - basically, you might get 5gpm, so maybe 7-minutes of hot at full flow, if I did my algebra correctly.

The 8th grade algebra problems aside, nobody uses 120F water for bathing or showering. Typical showering temps are 104-108F, while tub-fill temps might need to be as high as 110F for cast iron tubs. Dishwashers and clothes washers can use 120F water, but compared to any indirect tank size those draws are but a sip, not a barrel.

But even at 105F you're not going to be filling a spa-sized tub with 35 gallon tank, even if you keep the tank at 180F.

The ALP-80 can handle a 2.5 gpm shower with a 60F rise (45F-in 105F-out) pretty much 24/365, but not much more than that. For gusher-showers you can roughly double that forever-flow with a drainwater heat exchanger if you can fit in a big enough one, which may be worth it in your case. But it does nothing for tub-filling performance:



Generally speaking, if you size the tank for the largest tub you have to fill the rest will be OK, but if you want to run 10 back-to-back showers @ 5gpm with the ALP-80 as the heat source, add a drainwater heat recovery heat exchanger. To get a big enough boost you'll nee 4" x 48", 3" x 60" or bigger (both fatter and longer is always better) but it has to fit in a vertical drain space- horizontal installation doesn't work.

Dana, thanks for checking in. I wish I had the space and location for a drain heat xchanger, but my house has the drain going to one side of the house and the water main and boiler on the other side. It would be a 30'+ run each way, and even at that, the amount of drain pipe I could get an exchanger around wouldnt be that much.

So I guess the 50 gallon tank is my best bet.

I thankyou both for the insight and clarity!!

Just to be clear, the drainwater heat exchanger replaces a section of drain pipe. They're made out of a section of copper drain pipe with a tight slinky of flat-sided potable piping around them. The distance between the heat exchanger and water heater doesn't affect performance significantly, but it's easier to install when they happen to be close to one another.

Even 48" x 4" delivers better than 50% energy return @ 2.5gpm and over 45% @ 5gpm (and I'd be taking some pretty tepid showers without it! )

You'll probably need at least a 50 gallon tank to have anything left over after filling the Jacuzzi anyway, and even bigger wouldn't hurt.

The problem comes with getting a long enough vertical drop without T's and other lines coming in. I dont have even 36" without having to cut and reroute all the drain lines....

I think with the 50 gallon and it wired as a priority on the boiler I should be in good shape. My main thought was wondering if I could get away with the 35 and fill a tub then take a shower by using a mixing valve and keeping the tank at a higher temp. That seems like a no-go so I will just get the 50 with a mixing valve to keep the tank above the 140* bacterial killing level.

NYresq said:

I think with the 50 gallon and it wired as a priority on the boiler I should be in good shape.

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Watch out for that priority controller thing, my house was getting cold! It was because the tank was was retrofit on the existing manifold set up with 3/4 not 1". My solution was to take it off priority and install a zone valve with basically a zero constriction port like a ball valve, unlike the typical Honeywell. Got much better flow and recovery without having to totally rebuild the manifolds to 1".

Those drain heat recovery coils do come dear, I just priced a 2" at $600! That's a lot of showers for the 3 members of my family on the line that's easy to do (other shower is on 4" cast iron). And won't it not help at all for baths or laundry? The water drains after the tank has already refilled. Food for thought.

Fortunately my boiler is piped with all 1" pipe. I hear what you are saying with the house going cold, I will probably set the priority for a 30 minute run. My house is tight enough that even on the coldest day a 30 minute run without heat won't drop the temps in the house more than a couple degrees. My radiant floors stay warm for a while without any flow. The alliance tank has 3/4" male taps for the coil, but I will be running all 1" for the feed and return to maximize the flow with 1" sweat x 3/4 female couplings at the tank. They specify 6gpm flow for the tank, then build it with 3/4" fittings which just barely make it to 6gpm on their best day...

Belmondo said:

Watch out for that priority controller thing, my house was getting cold! It was because the tank was was retrofit on the existing manifold set up with 3/4 not 1". My solution was to take it off priority and install a zone valve with basically a zero constriction port like a ball valve, unlike the typical Honeywell. Got much better flow and recovery without having to totally rebuild the manifolds to 1".

Those drain heat recovery coils do come dear, I just priced a 2" at $600! That's a lot of showers for the 3 members of my family on the line that's easy to do (other shower is on 4" cast iron). And won't it not help at all for baths or laundry? The water drains after the tank has already refilled. Food for thought.

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You can get a 4" x 48" from EFI for less than that if you open an account with them (which you can do via phone if you have a credit card.)

NYresq said:

They specify 6gpm flow for the tank, then build it with 3/4" fittings which just barely make it to 6gpm on their best day...

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That is odd. My 35 gal Triangle Tube has 1" ports.

Yea, I can only think they did it to increase velocity through the coil at the expense of volume??

Just a follow up, I Installed the alliance 50 gallon, wired up as a priority direct to the Alpine 80. When it calls for heat, it disregards the ODR and fires up to 185* (or tries to, I havent seen it get above 175 even after a few minutes at full burn) with priority so the heat loop circulators turn off. I have the tank set to 150* with a 15 degree drop and a mixing valve set to about 120*. After a long shower with the kitchen sink running and a load in the washing machine, it takes less than 5 minutes to get back up to temperature and shut off. I am pretty impressed with the output of the Alpine 80 combined with the alliance 50 gallon.

The system works great, and I havent been able to outrun the hot water yet. With the washing machine running, the wife doing dishes and a 20 minute shower with the multiple head 6gpm shower, I havent had any dip in the temp of the water.

For those wondering, I piped the heating loop with 1" copper from the circ to the 1"sweat x 3/4" female adaptor on the tank (coil is only 3/4" male thread on the top of the tank) I used a Grundfos 26-99 three speed circ (on the lo setting) and it matched up perfectly, no noise, plenty of flow (Alliance manual said it requires 6gpm through the coil) and it matches the boiler loop circulator, so flow to the tank matches the flow through the boiler to make the most effiicent use of it. (head is about the same for primary and secondary loops)

If anyone is in a similar situation of having a boiler that doesn't match the specs of "required BTU's" for a IWH, I have found that being close enough worked for me.The alliance 50 gallon would need a 150K Alpine to meet the required specs, which would be more than double what I needed for heating my house. Size the boiler to the house, not to a IWH. My DHW loop kicks on only if I take an extended shower and it hasn't run for over 8 hours. I have washed a sink full of dishes and not had it come on, and if we are away, it fires once every other day to maintain temp. I could set the drop for a 25 or 30 degree swing and have it run even less, or turn down the temp if we are going away for an extended period and have it not run for days.

I had thoughts of going with a stand alone water heater and glad I didn't. The mod/cons don't like being shut off in the summer, and the IWH doesnt have heat going up the chimney. A 40K 75% efficent water heater compared to an 80K at 85-95% efficent boiler is no contest as to who will make more heat for less money and do it faster. The upfront cost is more, but with the rebates it qualified for, combined with the savings in gas use, I think the difference in upfront cost will pay for itself in three years or less.