Adding Indirect to Buderus GB142/45 Need help Sizing

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Old 06-15-09, 06:49 PM
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Adding Indirect to Buderus GB142/45 Need help Sizing

hello... I currently have a Buderus GB142/45 Mod/Con Boiler my friend a plumber installed last year. He set it up for me to add an indirect heater but we did not do it because we were doing it in stages because of the money. Well now we have the money and we want to make sure we size the tank right. My boiler has a BTU output of 142,000. I would like to go with a Buderus Indirect hot water heater. I don't know if I should go with the ST-200 or the ST-300. The ST-200 is a 53 gallon indirect that needs 149,000 BTU from the boiler
and the ST-300 is a 79 gallon tank and needs 161,000 BTU from the boiler. I am little confused on the sizing of my Hot Water Demand. We have a 2800 Sf house with an in law. We have 3 adults, and 3 children living here, with 3 baths, 2 dishwashers, and 2 kitchens. We don't really use hot water for clothes that often. The dishwashers are new and energy star, and all my shower heads are 2.5 gpm. Sometimes two people will take a shower at once. We do have one whirlpool tub that is approx 45 gallons. So that is my concern. I did a calculation using the following website below and came out with a First hour rating of 144.50 Gallons. The ST-200 is rated for 199 gallons for 2nd hour (no 1st hour rating) and the ST-300 is rated for 267 gallons for 2nd hour) I know that the ST-300 is too big for the boiler output, but wouldn't it be better to have more hot water stored? Anything will be better than my current hot water setup, We are currently using a 80 gallon Electric and keep it at the lowest setting so it preheats the water before it goes into an old oil burner hot water boiler that has a tankless in it. Believe it or not, it works not to bad, but will not fill the whirlpool tub with real hot water.

Any help is appreciated.



Storage-tank water heater peak demand and first-hour rating calculator
 
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Old 06-15-09, 08:05 PM
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ST-300. Run the tank at 140F. Use an anti-scald tempering valve (e.g., Sparco/Honeywell; Taco) on the domestic output to provide the proper, safe temperature to the taps.

Set up the GB to have domestic priority. The tank will charge back up in the time it takes to listen to Supper's Ready. Maybe less.
 
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Old 06-16-09, 04:52 AM
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Ok thats what I thought. I was planning on running an mixing valve anyhow. When I asked Buderus in there forum, they didn't recommend it because the tank was two large for the boiler.
 
 

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