What Should The High Boiler Temp Be Set To For Heating DHW During Summer Months?

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  #41  
Old 05-10-11, 05:25 AM
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How many gallons was your old Bock and how many BTU's was the burner?
It was a model 32E which had a 32 gallon capacity and a 104,000 BTU burner.
 
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  #42  
Old 05-10-11, 05:37 AM
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With that information, I can tell you that the higher BTU output of your old Bock would have made for shorter burn times, but that doesn't mean you were using less fuel.
 
  #43  
Old 05-10-11, 06:22 AM
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drooplug said
With that information, I can tell you that the higher BTU output of your old Bock would have made for shorter burn times, but that doesn't mean you were using less fuel.
I understand that the Bock may not have used less fuel as was previously described by NJ Trooper.

My biggest concern is how often the indirect calls for heat. Right now, it is calling for heat and turning the burner on every 2 1/2 - 3 hours when there's absolutely no usage of hot water in the house anywhere. So it runs 8-10 times a day. My 30 year old Bock that this indirect replaced ran 3-4 times a day.
 
  #44  
Old 05-10-11, 07:39 AM
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If you understand that your new setup uses less fuel, then why are you concerned with the number of times it runs during the day?
 
  #45  
Old 05-10-11, 01:49 PM
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drooplug asked

If you understand that your new setup uses less fuel, then why are you concerned with the number of times it runs during the day?
My old stand alone Bock was 79%-80% efficient and my new Buderus is suppose to be 86.7% so from that standpoint the new one uses less fuel assuming everything else is the same. However, my old Bock only ran for 10-15 minutes 3-4 times a day to heat hot water when there was no hot water demand (sitting idle). Right now with the Buderus Boiler and Buderus indirect, under the same circumstances, the indirect is calling for heat 8-10+ times a day.

Granted it uses a little less fuel each time it runs (80% efficiency compared to 86.7% efficiency). However, the indirect is calling for heat 2 or 2 1/2 times more often so my total fuel usage to maintain hot water at the aquastat set point (125) when there's no hot water demand is consuming much more fuel.

The 6 % improvement in efficiency doesn't come close to offsetting the 250 % increase in burner run time.

If I'm looking at this wrong, please let me know.
 
  #46  
Old 05-10-11, 02:24 PM
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Well. We don't how equal or unequal things are. The differential on the indirect may not be the same as the differential on your Bock. You also have to take into consideration that the output of your boiler is less than the output of your Bock. Even if both units had the same efficiency, your boiler has roughly 85% of the output as your Bock did. Trying to figure how much fuel you are saving based soley on how many times the burner fires is not going to be accurate. The way that your recirculation loop interacts with the new tank could be a lot different. It may allow for more heat loss. If you want to save fuel, get rid of that loop. The other advantage of the indirect over the Bock is that you don't have an open flue going up the center of the tank. That results in more heat loss.
 
  #47  
Old 05-10-11, 03:08 PM
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drooplug,

I hear what you are saying and agree that I'm not comparing apples to apples exactly. My instincts simply tell me something is wrong.

One other thing that I'm suspicious of is the aquastat on the indirect. When I had the temperature set point at 125 the water coming out of a hot water faucet 20 feet away was 142 degrees when I measured it with an accurate digital thermometer?

I thought the aquastat turns the boiler burner and/or circulator off for that zone when the temperature of the indirect reaches the set point? Then when the temperature in the indirect drops to the differential set point ( I have adjusted it from 5 to 15) the aquastat turns the burner/circulator on to heat the water back up to 125? Isn't that how it is suppose to work?

My next step will be to shut off the recirculation loop for a couple of days to see if that has any effect. I will be very surprised if it does because once you get more than 10 feet away from where it comes out of the back of the indirect, the pipe is hardly warm to touch. Unlike the actual hot water pipes which are all hot for a long distance. It may be that insulating those pipes will make a very noticeable difference once I can get it done. I'm trying to do one thing at a time so I know what helps and what doesn't.

Thank you for your comments.
 
  #48  
Old 05-10-11, 03:19 PM
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You're right about how the aquastat is supposed to work. Your water should be around 125. The fact that you are measuring 142 says there is a problem. I would expect the water to be less than 125 at the tap from heat loss during it's travels. I think you should call your installer back at this point to troubleshoot the aquastat.
 
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