Need more consistent domestic hot water
Comments
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@Larry Weingarten Never thought having a bunch of kids as an industrial application, but so be it. 🤣
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
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I love the informative views and experiences of you all wrt water heating. The biggest issue, as some mentioned, is how much water a household needs or wants. A 2 person household when they only do a quick shower a day is a candidate for a simple electric wh.
As far as tankless vs tanks, it seems my customers like tankless better than I do!! For instance, my neighbor with 8 children loves his tankless and that one gets USED. As for maintenance, the simplicity of tanks is appealing to me but then there is anodes and failures also. We have seen a fair number of failures with stainless indirects of various manufacturers. We will not put tankless in if a customers' water is ugly and untreated, so most of them I put in see very little scale/dirt buildup even after several years. If you count the hours runtime on a tankless you typically will find they run but a fraction of a boilers' run time, thus they do last.
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After reading your post a few times has me at a slightly different take.
When you take a shower, is this the place where you notice your problem the most. Think about it. Its important because this could be an issue at the shower only.
You mentioned something about having a replacement coil siting in its box. Replacing one can be a rough undertaking and probably a last resort.
So at this point and hopefully this hasn't been answered yet, but what mixing valve do you have now? What is the one you plan on replacing it with?
Im asking because this and or your shower valve could be your issue. Is the "mixing valve" a "Thermostatic mixing valve?" Or is it a tempering type mixing valve? Answers to these few question should help eliminate a few trouble shooting points.
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and mod cons aren't really made to make 180 degree water. the can do it but not so well
What exactly does this mean? We are not talking about painting a picture. Some people can do it but not so well! We are talking about a boiler. Either it can do it………or it cannot. There is no such position as "not so well".
The mod-cons I have installed go to 180° and hold it just fine. What happens with them is they modulate down as time passes because the coil in the indirect cannot transfer sufficiently once the tank temperature climbs to within 20° of the setpoint. This can result in over 35 minutes to get to a shutdown and allow CH to restart.
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That's similar to the commercials I hear on the radio talking about heating and AC equipment "working hard to keep up"
I'll take an AC unit running continuously over one cycling a lot.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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@mattmia2 said: The recovery rate isn't so great with a mod con because the indirect's coil is sized for 180 degree water from a conventional boiler and mod cons aren't really made to make 180 degree water. the can do it but not so well so if you're using a mod con you should make the indirect bigger.
ModCon boilers are great for Indirect water heaters, the DHW priority on them will produce 180°F to the indirect and the recovery will be just as fast. The fact that it will condense less just means that they go from the 96%+ efficiency to 90%+ efficiency. Still better than the 80 to 85% of a cast iron boiler.
Any boiler that can vent with a plastic vent will always be more efficient that a boiler that must use a metal vent. Show me the science that proves that wrong!
I have installed ModCon boilers on high temperature baseboard heat systems, and for some reason, they always use less fuel compared to the Cast Iron On/Off boilers they replaced. There must be something else that is causing this savings. Just because a condensing boiler that is placed on a low temperature system is more efficient than the same boiler on a high temperature system, does not nullify the savings of outdoor reset and modulation operation. The only difference is a few percentage points on the condensing part of the concept.
Why do some folks believe that the ModCon should only be used for low temperature application? They work just fine at any temperature.
Just this old man's opinion, backed by the science and experience. But you guys can learn from your own experience if you do not want to take my word for it.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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There must be something else that is causing this savings.
There is.
It's called modulation. Most people forget that a mod-con achieves one half of its savings via modulation. You'll see degreed engineers compare the combustion efficiencies between mod-cons and CI and come up with 10%. Their conclusions are always wrong.
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HeatFlo high performance, 100' of coil, tanks are shown down to 120 boiler supply temperature. Although 140 SWT should get the boiler condensing.
If 180° frightens you :)
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
It's like a google search. People want instant answers and instant hot water
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Power vent tank water heaters vent with plastic just because they mix room temp air with the exhaust. As far as I'm aware they're no more efficient when running than a standard tank water heater. Stand by losses are greatly reduced but that's a separate subject.
You can make exhaust temperatures anything you want by mixing cool air with them. Especially when you're using a fan so you don't need any natural draft.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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That is incredible performance.
The tank can perform just about the same with 150°F as it does with 180°F supply. It does fall off a bit at 140°F
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It is what happens to pvc with frequent high temp exhaust that frightens me.
You can't make it anything you want when you're pulling the air through the gas valve(actually a carburetor but heating people wouldn't understand that) and pushing it through the burner. The temp is going to be defined by the design of the burner and hx and the swt and it isn't going to go below the swt.
The efficiency on existing baseboard systems comes from not actually running at the design swt most of the time because of outdoor reset, from the much lower standby losses from the much smaller heat exchanger, and lower standby losses by running longer, less frequent cycles because of the odr and modulation.
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you want high performance, high efficiency , continuous DHW?
Size a plate HX to your boilers max. Output
2 gpm with a 77degree rise would take about 110,000 btu/hr boiler
Probably source all the dhw portion on e-bay for 600 bucks or so
Serviceable, replaceable, space saving, and only a tiny thermal expansion tank required
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
I've considered putting one in front of my indirect. The area of the hx in half the problem. The other half is that on a big draw half the tank is gone by the time it senses the tank is colder in the middle, the boiler does its minute or so of pre-purge and flame proving and ramps up the burner and heats the mass of the boiler and water in the system and actually starts transferring heat o the tank. I have thought about adding a button i push that makes a call on the boiler at the tank temp for the swt and opens the dhw zone and turns on the circulator for about 5-10 min to give it a head start before the actual dhw call takes priority. (also not positive the dhw still has priority over the 0-10v bms input on a uft)
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I could never understand how a cold start CI boiler could EVER meet the need of the homeowner in the shoulder seasons and in the summer, if the indirect is maintained at a typical 140°F (unless it was 80 gallon).
If you run a 3 GPM showerhead, you've got less than 13 minutes. The boiler cannot get itself to 180°F in sufficient time before you lose it with the indirect……….considering , as you stated, the indirect might not call for five minutes after the demand begins.
With the direct fired Bock, this never occurs.
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WOW this went sideways…. The OP has a STEAM BOILER. I don't believe 180° is a problem here. Whomever brought up the ModCon boilers is way off topic for this discussion, I was responding to @mattmia2's post about 180° is something a ModCon is not good at. Now that I look at the original problem this has nothing to do with ModCon boilers and everything to do with a domestic hot water problem. As I see it the OP has 2 choices,
- Fix the Tankless Coil Problem
- Get a different water heater.
And since the OP has a WM SGO boiler, that thing is pretty darn efficient and will do nicely with an indirect properly installed.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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is a HX off a steam boiler an option? Move the tankless outside the box. The long warm up the downside?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
@LRCCBJ said: "I could never understand how a cold start CI boiler could EVER meet the need of the homeowner in the shoulder seasons and in the summer, if the indirect is maintained at a typical 140°F (unless it was 80 gallon).
If you run a 3 GPM showerhead, you've got less than 13 minutes. The boiler cannot get itself to 180°F in sufficient time before you lose it with the indirect……….considering , as you stated, the indirect might not call for five minutes after the demand begins.
With the direct fired Bock, this never occurs."
It is funny that you say that "you could never understand …". And I agree with you in some cases. Take for example a customer of mine that used a TACO zone valve for the Indirect. It takes about 1.5 to 2 minutes to set off the indirect thermostat, the the TACO 571 tales about 90 seconds to 2 minutes to open the valve then close the end switch and start the boiler. Now a GV boiler takes another 2 minutes to start the pre purge and ignition cycle until you get a flame in ther 65°F boiler. The flame works pretty fast and heats up to 135°F in about 2 minutes so the tank can start to recover form all that cold water that entering it as the hot water leaves.
So at 3 GPM your 40 gallon tank has used up 24 gallons of hot water before it starts to recover That leaves only about 16 gallons of hot water left while the boiler is getting hotter and hotter to recover all that cold water. I can say from experience that this customer suffered the hot/cold/ hot shower on occasion. I fixed the problem by cutting of 2 minutes of lag time by replacing the Taco 571 with a Honeywell 8043. Just removing that 2 minutes of zone valve delay was enough to solve the problem.
In my own home however I have had an indirect for over 40 years, it is attached to a Buderus boiler with a Riello oil burner, and we have never has a problem with DHW using a 40 gallon indirect. It is amazing how fast that Riello gets that boiler up to 140° so the tank can start the recovery, and the boiler reaches 180° within 4.5 minutes in the summer when there is only the water heater calling. The burner contioues for another 6 to 8 minutrs before it gets to the 190° limit temperature.
So I help this gets your understanding in line with reality
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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It is amazing how fast that Riello gets that boiler up to 140° so the tank can start the recovery, and the boiler reaches 180° within 4.5 minutes in the summer when there is only the water heater calling.
Completely agree with "amazing".
What's the water content of the Buderus?
I presume it is heavily insulated?
Lot of variables in your favor there.
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