Hot water runs out after indirect empties

Denniss516

I will do this test and measure pipes !! I did remove the water saver in the shower head as it was a very light spray. Why I am being stubborn and believe I do have an issue is for two reasons. One, I was told a whole family can shower without running out of hot water and 2 which is why I am here in the first place is when the DHW goes cold, the 1" pipes are still very hot and the boiler is not running, which makes sense if the 1" are very hot. Why doesn't those 1' pipes get cooler? Build up on those pipes would insulate which is (to me) the most obvious, but this has been happening since it was new !! When the 45 gal empties, those 1" pipes should cool down and do their job !! They do not feel cooler at all in fact I cant touch them for more than one second when the DHW is cold.

mattmia2

There is only so much heat that can transfer from that coil to the water even when it is new. If you are using water faster than it can transfer heat then you are going to run out of hot water. Someone that is better with thermodynamics than I am could probably figure out if it can transfer the whole ~100,000 bth/hr output of that boiler. It is possible that the controls of the boiler aren't set up right so that it either is not providing hot enough water on a DHW call or it is also allowing heating calls at the same time. I think measuring the temps on the pipes during a big DHW draw is the best way to figure this out. See below.

It is not true that you will have unlimited hot water. It is true that with the right incoming water temp from the city and the right flow from the shower head that a whole family could shower one after the other without running out. If you have a shower head that is say 4 gpm and 35 degree incoming water, neither that 100,000 btu/hr boiler nor the transfer rate of the coil will be able to keep up.

I have the same water heater with a mod con boiler that is about 90,000 btu/hr and my municipal water comes from rivers and is stored in above ground outdoor tanks so it is around 35 degrees in the winter. The water will stagnate in the water heater tank and get much cooler after several minutes. I will get several minutes of around 130 degree water then when it reaches the layer of stagnation and newly heated water, it is around 100 degrees. It is perfectly usable but I have to adjust the valve to use almost straight hot water(if your valve has an anti-scald stop on it, you won't be able to adjust to straight hot water). I also have to adjust the flow of the hot water itself out of the spout to about a half inch column or less.

That being said, I would like you to add some instrumentation so we can see what is going on. A 180 degree and a 150 degree pipe will both feel very hot, so maybe the coil is doing its job but both are so hot you can't tell the difference.

I would like you to get 2 or 4 snap on thermometers like this:
https://www.supplyhouse.com/Mr-PEX-5240748-Strap-On-Pipe-Thermometer-for-3-8-1-5-Pipe-0-248F-Pack-of-2

Connect them to the 1" boiler inlet and outlet connections to the water heater so that we can see what is happening with the water supplied to the coil. You can probably get a better price on them from Amazon or Ebay, just make sure they will measure from about 32 to 200 degrees F. These just snap on to the surface of the pipe with a spring. If you get 4, connect one to the domestic hot water inlet and outlet as well. You can take a video and see what is happening to the various temps during a shower.

I suspect your issue is a combination of things.

bucksnort

You mentioned your boiler is set at 170. You are losing the ability to heat water in the tank vs. if it was 180-190. Even a 10 degree diff in the incoming city water of 10 degrees can affect the recovery rates. There are many tank manuals that show the specs on recovery at different incoming water temps. They also show what the boiler temps need to be in their charts. Why are you running a hot boiler and not cold with the high limit set at 180-190? With out accurate temp readings it's all just guessing. My years working 550 degree pizza ovens have desensitized my feeling of heat. I could hang onto a 180 pipe where my neighbor might flinch at 110.

mattmia2

Oh, one more thing, if the tank is recovering in 15 minutes, the boiler is firing at some point. There may be enough water in the boiler itself that it takes a while for the tank to cool that mass of water enough to cause the burner to fire.

When my tank is acting as above, the burner in my boiler is firing at full output the whole time, so even at 160 degree boiler water set point with 90,000 btu/hr of boiler capacity and 35 degree incoming water, the coil is transferring all of the energy that the boiler can produce, in fact the water never gets to 160 with the boiler adding that much heat.

bucksnort

Here's your manual. Page 6-7.
https://images.homedepot-static.com/catalog/pdfImages/9a/9a5ef352-5447-450c-8e1c-e87b84ad293c.pdf
They don't say what incoming temps they are testing at as other companies have in their specs. 35 degree incoming water vs. 50. The specs are showing a boiler with 50% more BTU's than yours with the same tank. We don't know what your
1: incoming water temps are.
2: what your in and out temps are from and back to your boiler
3: Your GPM of your showerhead. Could be anywhere form a firehouse Kohler body spray to a mega mizer shower head.
what might you need?
1: larger storage tank.
2: tempering tank for incoming cold water to warm up from 35 degrees? What is your incoming water temps?
3: smaller showerhead?
4: setting your boiler to say 190. Cheap as in free and easy. Why not start there until you get your temp gauges/meters? Eliminate one aspect at a time
We can replace a lot of things and not solve anything until you are broke. You replaced a auqaset that probably was fine.
The only way to solve the puzzle is for factual figures on everything.
If all the numbers all don't fly you aren't flying to the moon.

Denniss516

Ok, that product is reasonably priced, not available in many places, I will check my plumbing supply next few days. Thank you again

Ahead

45 gallons doesn't mean you have 45 gallons of hot water. Tank might be 40 gallons (subtract displacement by coils). At 2.5gpm demand (max per IPC these days) that's 16 minutes of hot water. But, WAIT! As you pull out hot water you're pulling in COLD water, in which case you're NOT getting 16 minutes of that high temp hot water that you're thinking you're supposed to get; you're getting maybe 8 minutes or so and then it's starting to drop fairly quickly as in-rushing cold water becomes an ever-increasing proportion of the volume (the point in the shower at which one cranks the cold valve down and twists the hot valve as though that's going to produce higher temps).

The boiler can switch on (is there a delay built in somewhere here?) but it's going to take a bit before that cold water infiltration can be neutralized (heated sufficiently). Being a 45 gallon tank I'd think that it might not have all that much coil surface (and, again, the flow through) to take advantage of the BTUs being pumped from the boiler.

Wife and I tend to take sub-ten-minute showers: probably closer to the 7 minute mark. Standard 50 gallon electric water heater tank. Pushing much more and we'll start to sense a waning in temps.

As suggested, take the area heating out of the equation. Boiler should then be focused only on DHW. If you run out before 40 / GPM of shower head minutes then there's a problem in the system. If you're about on the mark then it's a demand/expectation issue: adjust use or adjust tank size. Maybe set the DHW service request to come at a higher temp?

Also, recovery time... Maybe calculate what it should be and check against reality.

I've played around with numbers for a 20.5k BTU (electric) boiler for area heating (16.7k BTU) and DHW using an indirect water heating tank. Thanks to all the information in these forums I was able to figure it to be possible. BUT, it would only be possible IF our demand was the same as it currently is (with our standard electric water heater).

Jamie Hall

Some fundamental thermodynamics here, as a giggle check.

Incoming water at 40 degrees F. Domestic use temperature at the shower head or whatever at 110 degrees F. Now assuming that we can get all 100,000 BTUh output from your boiler into the incoming water (you can't, but just for the moment), that is an absolute maximum flow rate of 2.9 gallons per minute.

Salesmen and brochures can claim otherwise, but the physics doesn't lie.

Your 15 minute recovery figure, which works out to 104,000 BTUh, matches your boiler input pretty closely, so it would appear that things are running pretty well.

If the heat transfer to the incoming water is less than optimal, or the flow in the tank is such that not all of the tank contents are uniformly heated, your maximum flow rate will be less than that.

"Unlimited hot water" in salesman speak means that if you run the water at a flow less than that you will never run out of hot water. They don't bother to mention that maximum flow -- it would spoil their pitch.

Dave T_2

I would want the boiler to run to 190 (or even 200 if it solves issue) when my indirect hot water tank called for heat. You will get more hot water production from 190 vs 170. SuperStor ratings are based on 180 and 200. Try that easy adjustment to see if it solves problem. If you can install a shower head that uses less gpm water flow the hot water will last longer and be consumed slower. If nothing else is broken, you can run the tank at a higher temperature, up to 160, and have a plumber install a tempering valve at the tank.

JUGHNE

Did the homeowner ever try the isolation test to prevent water from flowing thru part of the heating loops???

SteveBrady

Did this problem ever get fixed? I have the exact same equipment and system and exact same problem!

Erin Holohan Haskell

@SteveBrady, welcome to Heating Help! I recommend you start a new discussion so that your questions don't get lost at the bottom of an old thread.