I don't understand the advantages of an indirect

 
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Post by Retro_Origin » Sat. Feb. 04, 2023 9:57 am

I have John Siegelgolfers book on all things hydronic and both he and just about everything else I read says that an indirect for domestic hot water is a very good if not the best option if you already use a boiler. The benefits are said to revolve around not having to maintain high boiler temp as in the case for a tankless coil. This doesn't make sense to me, even with a greatly insulated tank when that temp drops too low for domestic hot water and the boiler has to heat it up, then you have to heat the boiler itself up just to heat the indirect and then after it shuts down that boiler temp is unneeded. So you basically heat up two vessels for the usage of one. Can someone set me straight- what am I missing?


 
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Post by McGiever » Sat. Feb. 04, 2023 2:31 pm

It is all about "recovery time" and just how much HW is needed in what amount of time. Not everybody has the same need so you may be right in your case??

Then there is water quality factors...minerals affect coils. Indirects the scale minerals build-up is on the exterior of the coil/exchanger tubing inside a large vessel whereas in a tankless the scale mineral build-up is confined inside the small bore exchanger tubing causing quicker diminishing performance. So sometimes what works good doesn't work for long...

 
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Post by Lightning » Sat. Feb. 04, 2023 3:04 pm

Is it possible to open up the indirect tank to clean the coils?

 
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Post by StokerDon » Sun. Feb. 05, 2023 9:23 am

Lightning wrote:
Sat. Feb. 04, 2023 3:04 pm
Is it possible to open up the indirect tank to clean the coils?
That is one of the big advantages. You never need to clean the coil. Boiler water circulates through it, not domestic water.

They also tend to be very well insulated. I've had mine starved for heat for a day and a half while doing boiler swaps. The water was still hot when I took a shower. And that's with a cheap Amtrol BoilerMate.

-Don

 
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Post by McGiever » Mon. Feb. 06, 2023 9:50 pm

Lightning wrote:
Sat. Feb. 04, 2023 3:04 pm
Is it possible to open up the indirect tank to clean the coils?
Only way to clean the coil is if the coil assembly can be removed, which some are.

But mineral buildup is not detrimental as the flow is never hindered with progressive external scale buildup, unlike the eventual blockage inside of small bore tubing.

 
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Post by Retro_Origin » Tue. Feb. 07, 2023 12:15 pm

Great info thanks guys!

 
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Post by waytomany?s » Tue. Feb. 07, 2023 3:52 pm

I'm not a boiler guy, but I'm working on it. Can you explain the purpose of the indirect tank? Is it the same as an expansion tank?


 
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Post by McGiever » Tue. Feb. 07, 2023 4:11 pm

waytomany?s wrote:
Tue. Feb. 07, 2023 3:52 pm
I'm not a boiler guy, but I'm working on it. Can you explain the purpose of the indirect tank? Is it the same as an expansion tank?
Nope, it is a hot water heater with storage. A circuit of the closed water system of boiler water is pumped through a immersed coil inside indirect HWH vessel, exchanging boiler heat into the storage vessel's domestic water contents. Naturally there needs to be controls involved in order to start and stop to maintain a storage temperature set point.

 
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Post by waytomany?s » Tue. Feb. 07, 2023 7:03 pm

McGiever wrote:
Tue. Feb. 07, 2023 4:11 pm
Nope, it is a hot water heater with storage. A circuit of the closed water system of boiler water is pumped through a immersed coil inside indirect HWH vessel, exchanging boiler heat into the storage vessel's domestic water contents. Naturally there needs to be controls involved in order to start and stop to maintain a storage temperature set point.
But it's not the same as a dhwh?

 
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Post by SMITTY » Tue. Feb. 07, 2023 10:52 pm

I put an indirect in here in '05 - an Amtrol Boilermate. Hands down BEST hot water improvement EVER. It's amazing. With a tankless coil, any time the hot water faucet is turned on, you're pulling heat out of the boiler - EVERY time. With an indirect, you're STORING heat, and when you open the faucet, it's just coming through the tank, NOT the boiler water. It works AMAZING! I have never once run this thing out of hot water. I've had the oil burner frigg up and quit, and had enough hot water to take a shower before it just started cooling off.

So how it works is, you have the 2 lines (in and out) for the boiler water - basically just another zone with a circulator wired to kick the burner on whenever there's a heat call - and cold water in the bottom, hot water out the top. Just an empty tank with stratified water inside - hot on top, cold on bottom. So as soon as that circ comes on, that heat goes straight up, right into the hot water line to your faucet or shower.

Just yesterday I replaced a few failing 30 year old components on my oil boiler that's tied into my 520 Highboy. 5 hours of work (turned into a *censored*-show - what else is new? :lol: ), boiler EMPTY, ice cold well water filling it up, and I still 127° hot water in the tank! So that's 41 gallons the stoker didn't need to heat from 55° to 165°. When the power goes out just before bed and you don't feel like firing the generator up, you can still take a nice, hot shower (conserving water if you're on a well) and hit the hay. I LOVE that thing!

I grew up with a POS tankless coil that failed in 1978. My parents didn't replace it until 2001, long after I'd been out on my own! My parents knew how to suffer to save a buck! :D

Only problem I ever had in 18 years with the Boilermate was the electronics (SURPRISE! ;) ). There was a relay inside designed to switch if the magic box received anything besides 120v. It can run on 24v <s>or 220v also</s>. Problem is, when that relay fails, it switches to 220v, so you don't have enough juice to keep the magic box happy, and it wigs out. I happened to stumble upon a post buried DEEP in the recesses of the internet, where an electrical engineer explained step-by-step how to rid your life of this stupid relay. I followed his instructions and desoldered the relay and a little capacitor, and soldered 2 jumpers in the appropriate holes, and voila! Saved me $200 just like that! I could've kissed that guy, LOL! :clap:

Been working great for the past 10 years. The relay only lasted 8.

EDIT: It was only 120v or 24v. So it would default to 24v upon relay failure, and cook other components, like that cap. Can see on the board where it got REAL hot! My memory sucks, lol.
Amtrol Smart Control.jpeg
.JPEG | 389.3KB | Amtrol Smart Control.jpeg
Amtrol Smart control unit repair.jpeg
.JPEG | 441.6KB | Amtrol Smart control unit repair.jpeg
Last edited by SMITTY on Tue. Feb. 07, 2023 11:04 pm, edited 2 times in total.

 
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Post by SMITTY » Tue. Feb. 07, 2023 10:59 pm

Here's a cutaway to better understand:
Screenshot 2023-02-07 at 10.59.11 PM.png
.PNG | 1.2MB | Screenshot 2023-02-07 at 10.59.11 PM.png
Indirect fired hot water tank.jpeg
.JPEG | 118.7KB | Indirect fired hot water tank.jpeg

 
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Post by Retro_Origin » Wed. Feb. 08, 2023 8:14 pm

Great post smitty! Seems the advantages are more about buffer allowance than fuel consumption although even that I could be wrong on. I don't like the idea of having a whole separate unit to plumb in, take up space, maintenance, and pay for- not saying it doesn't work for people but for me with a family of four we are fine without. I'm surprised you need one with the highboy- isn't that monstrous?

 
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Post by Retro_Origin » Wed. Mar. 06, 2024 7:02 pm

So I've been doing research and a lot of thinking, I think I finally get it.

A tankless coil has to heat up water from ground temp, to usable temp. Say incoming 55 degrees and boiler water is 160 - it takes a lot of BTU to pull that temp up to 120 for hot water usage. So the indirect STORES potable water at 140ish, which means when you tap off water for hot water usage, it's stored above usable temp allowing it to last a lot longer than what a tankless coil system of the same water capacity could last, for modern low volume boilers I can see this being GREAT, plus the fact that the indirect is insulated so well.

But strictly from a coal standpoint, how are you guys doing it? To me it seems like the large volume stokers would be fairly useless tied into an indirect because in between heat calls your fire would go out, unless you have a timer which is surely going to force the fire to bleed the heat into boiler and now you have TWO vessels that are held at 140 or above temperature.

This is mainly from a curiosity standpoint, not something I would probably implement... but with my KA6 it could pretty much just run on the timer all day in the summer and supply all needed hot water without getting an 'actual heat call'.

Am I wrong in saying there aren't many (if any) stoker boilers that could even hold a temperature like 120-140 thru the summer without either going out or overheating? It just seems like unless they shed the heat or are set higher than that the timer cycle will either be too short and it will go out, or too long and the boiler will be 150ish or more.

Furthermore many of you have reported between 10-15 lbs of coal per day in a tankless coil situation. I can't imagine getting lower than that and keeping the fire alive.

Thoughts?

 
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Post by nepacoal » Wed. Mar. 06, 2024 7:36 pm

My kaa-4 runs all summer and stays between 205 and 215. I have it set for 51s on and 10m off. Once it warms up in the spring and I turn the thermostat down, I adjust the feed rate down slightly from my full bore winter setting so it doesn't dump. I also reduce the LL to 150 and have never seen it drop below the LL and trigger a stoker call. It just idles and provides two adults with all the hot water we need all summer. We burn between 12 and 13 lbs per day. Had one outfire in 2017 caused by excess flyash in the breech area and horizontal stovepipe connected to the boiler. I clean the stovepipe once in the spring now and have never had another outfire.

 
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Post by StokerDon » Sun. Mar. 10, 2024 10:40 am

Retro_Origin wrote:
Sat. Feb. 04, 2023 9:57 am
The benefits are said to revolve around not having to maintain high boiler temp as in the case for a tankless coil. This doesn't make sense to me, even with a greatly insulated tank when that temp drops too low for domestic hot water and the boiler has to heat it up, then you have to heat the boiler itself up just to heat the indirect and then after it shuts down that boiler temp is unneeded.
The cost saving for a coal boiler indirect really only happens in the Winter when your keeping the boiler hot for heating purposes. If you can run your boiler at a lower operating temperature and still satisfy your heating needs the boiler will use less fuel. Standby boiler losses go up and down with boiler low limit setpoint temperature.

You typically set the indirect to 110 to 125 degrees. Your boiler can heat the indirect easily with 150 degree water. The indirect also eliminates DHW temperature fluctuations related to boiler temperature.

Using an indirect also opens up the possibility of heating DHW from other sources like solar.

-Don


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