Buderus boiler sizing

Robert O'Brien

Assuming no whirlpool or full body shower,I've never had a problem with DHW ouput with a 115/21.I always use a mixing valve to operate at a higher DHW temp which boosts output among many other health and safety benefits.

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Rich_29

Buderus boiler sizing

My house is app. 1200sq.ft. My heat loss is app. 47,000 btu's. I would like to purchase a 3-pass buderus with o.a. reset and the buderus 32gallon indirect. The G115-21 seems to fit my needs, however several installers have told me I needed the G115-28 because of the DHW recovery. Indicating that the smaller buderus would not be correct even with priority. None of the installers did a heat loss, I supplied them with the footage of the house. Any help would be appreciated. Thanking you in advance.

Ron Schroeder

Hi,

I run a Buderus G115-21 with an LT-160 indirect and it is severly OVERSIZED. It all depends on your heat loss.

I also allways use a mixing valve, run the indirect at higher temperatures and make sure that the indirect's aquastat can be set to a wide differential for less burner cycling.

Supply House Rick

First Thing To Do...

Is to hire a Contractor to professionally perform Heat Loss Calculations and to size your Domestic Hot Water Tank. This is ALWAYS ALWAYS ALWAYS your best move. What did they base the 47,000 btus on? How do you know this is correct? You will never know at this rate.

You could get advice all day long here,BUT if your system doesn't work properly who can you hold accountable? Not anybody here...

Best of luck to you. (why are you hiding your email?)

My 2-cents
Rick

S Ebels

I would dare bet..........

Your heat loss is even lower than 47K. That equals roughly 40 btu's / sq ft. A LOT of heat loss for that space unless it's built like a chicken koop or your design temp is -50*. Assuming a more normal heat loss of 25-30/ sq ft, your load would be in the 30 to 36K. The 21 will do just fine if that's the case. Don't worry about the DHW output unless you have one of those human car wash showers that flow 10+gpm. You can run the tank hotter and add a mix valve as suggested above or install a larger capacity tank. I have a 30 gallon which I run at 160* and then mix down. Our family could take 6 showers in a row, with both baths going simutaneously on Sunday morning getting ready for church and not run out.

Bottom line. Nail your actual heat loss down and size the boiler as close to that as you can. Installing a heating plant without a good heat loss is like driving from New York to LA without a map. You'll probably get there either way, but it's a lot better with the map.