Indirect Output

Jim_109

How much hot water can I expect, both first hour and continuous with the major brands of 40 gallon indirects? Buderus, Triangle and Super Store are a few examples.

Much of the literature I have read rate the indirects using boilers with 100 plus BTU/HR. However, I am looking at boilers with a DOE heating capacity of 74,000 BTU/HR and a net rating of 64,000 BTU/HR.

During the non-heating season if use hot water for two showers in the morning, how often can I expect a 3 -pass oil fired boiler to fire during the day assuming an indirect with a 1/2 per hour stand by loss?

We are two adults in the home. THANKS!!!!!!!!!!!!

lee_7

Is this boiler just for indirect or also for home heating?

Mike T., Swampeast MO

Your last question is by far the simplest. Presuming 1/2 degree F per hour drop in temperature per hour and a plus/minus 5F control setpoint it would take ten hours before a fully heated tank required a "recharge". Of course this presumes no parasitic loss due to unintended gravity circulaton and no intentional loss due recirculation (gravity or forced). In other words, if everyone left for 9 hours or so in a typical work day the boiler would not fire until you came home and produced a considerable load (e.g. more than preparing a typical evening meal). BTW, the 1/2 degree per hour drop with modern indirects [seems] valid and verified here unless in a cold (say <55F) basement and even then it won't grow too much unless the basement is extremely cool or you have an unusually high indirect storage temperature to compensate for lack of storage volume...

Here I said the answer was "simple" but as you can see there are still a number of qualifications...

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Your question regarding first hour and continuous production however is MUCH more complicated. Why? Unlike stand-alone water heaters, indirects are tied to the <I>entire system. Temperature and flow through the heat exchanger in the indirect as well as the available energy from the boiler have to be considered. And guess what? All of these are inter-related and cannot be separated from one another! Even "available energy from the boiler" is not as simple as it may sound as there are different boiler control strategies that vary from "any excess not needed for space heating to EVERYTHING to the indirect" and sometimes things in between...

To make matters even worse, it's not at all uncommon (as you've seen) for indirects to be rated in one or two fixed set of conditions that may or may not apply to any given situation. While I believe it safe to assume that some components of such are linear and can be interpolated with reasonable accuracy, it's impossible to separate such given the ratings I've seen for most indirects.

Indirects are essentially unheard of in my area of the country. Where the ARE common and from what I hear here at "The Wall" they are one of the MAJOR culprits behind GREATLY oversized boilers.

All else the same, an indirect of higher volume will have a higher "first hour" rating. All else the same the "continuous" rating will be affected only by the heat transfer ability of the heat exchanger in the indirect. Unfortunatelyy the "all else the same" conditions rarely exist in a complete system yet the ratings of many indirects don't allow you to compute reasonably accurate values when the other conditions are changing as well.

All this said, any decent 40-gallon indirect drive by a boiler of the size you stated should not have any problem delivering sufficient hot water for your purposes in any reasonable condition as long as it has full priority--e.g. the boiler supplies either the indirect or space heating.

Tom Hopkins

If

you're talking about a Buderus G115/21 boiler it can be fired @ .75 if needed giving a DOE of 90K.I've Installed many of these and have never had a Ins DHW complaint. Use a mixing valve and keep the tank @160, eliminates any Legionella concern and functionally increases the size of the tank by 50%.Still need more DHW? Increase the size of the Indirect to satisfy the load instead of oversizing the boiler.
The Logamatic can be programmed to ignore DHW calls overnite although not during day I believe.

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greg_28

Indirect Output

R O'B,
Yes, my logamatic (OR) is programmed not to make Hot water in the evening. It can also be programmed to always make hot water. However, the max temp of the indirect is 140 degrees on the Logamatic settings. I also had to upfire to .75 gph for a few reasons. the Stack temps were way too low with baffles in, and DHW needed more btu's. BTW, I have a 30 gal buderus indirect to a 115/21. In hindsight I should have gotten a 40 gal, but I am happy with the performance of the 115/21 & 30gal.

D107

you upfired 25%

that's quite alot; I think Buderus specifies only 10% upfiring without special factory tech assistance...We had that slight problem with the stack temps and other burner issues. Solved it by increasing pump pressure only from 145 to 155 which only slightly raised firing rate from 84 to 87K btu. We have 5" stainless steel lined, insulated chimney. This is with .5 nozzle, air gate 2.25. Also added Tiger Loop.

David

clammy

baffles and by pass plates

Greg instead of up firing your buderus take another look at the i&o manual for your boiler i believe that there is a small by pass plate that can be chipped to provide a bypass from the combustion chamber to your final pass to help raise the stack temp if it still remain low after removing the baffles ,i believe that the removal of a piece of this by pass plate as discussed in the i&O instruction would also let you re install the baffles with a very mimuin lose of eff.Peace and good luck clammy ps i have a few G115 /21 with st150 tanks and have done as Mr.o,brain has suggested and have no complaints about lack of domestic hw

greg_28

My baffles are in and firing a .60 "B" @ 175psi. Stack temp is 375 gross. Just did a brush and vac and everything was behaving nicely. No soot, just some grey dust. Had a problem with high vacuum in 1/4 inch oil line last year, caused 2 lockouts, but took care of that and it is purring along fine. Guess it was crappy oil. How were you able to set indirect to higher that 140? the logamatics documentation says max is 140. Thx

clammy

aqua stat

I used a taco sr503 circ relay with a mech aquastat that had a adjustable differental setting so i set the differental at 30 and my tank at 160 and my mixing valve at 120 tons of hot water espically with the st150 tank and the one boiler set up was only a munchkin t50 2 1/2 baths and one was acustom shower with body sprays and a rain fall shower head peace and good luck clammy

Kevin G_3

Super-Stor SSU-45 ratings

The first hour rating for the Superstor SSU-45 for the reduced input is as follows. All this information can be found on Heat Transfers web site.
Based on 60,000 BTUH's reduced boiler input
A) less than 90 sec.for boiler to heat up to tempature.
more than 90 sec. " " """.
A) 138 first hour rating
99 first hour rating
Heating coil flow required is 10 GPM @ 7.9' of head
Pump for indirect required for first hour rating. Taco 0010 or Equiv. Check flow charts to size properly.
Piping to the tank coil must be 1" Not 3/4"
The information for the tanks is in the I/O manual. Pump sizing graph is in the munchkin manual.
I recommend to all the contactors I deal with to run there tanks at 140 degree's and install a quality tempering valve for a larger first hour rating and also a more constant temperature supply.

The boiler will cycle for domestic load based on 1/2 degree per hour and and 7 degree set point differential about every 14 hours without and water consuption. boiler on at 133 degree's of at 140.
Kevin Gabelmann

Glenn Sossin_2