Boiler with indirect water heater

Old 02-25-11, 11:31 PM
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Boiler with indirect water heater

I am getting a Weil-Mclain WGO4 oil boiler with a Superstor 45 water heater. The instalation manual on the water heater said to use 1 inch copper and a 1 inch zone valve between the boiler and the water heater. The installer said he wants to use a 3/4 zone valve like on the other heating zones for a total of 4 valves.

He claims he does this all the time with no problems. Does this seem like a good practice?
Old 02-26-11, 12:31 AM
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Whats he is going to pipe it all 3/4? You may want to find a new installer.

You may not get the full benefits of the recovery rating. Indirects are sized by boiler size, having the correct flow rate to the indirect, and pressure drop. (How long of pipe, elbows, check valves, etc. is all calculated for 1")

You need 10 GPM for the 40 and 8 for the 30

For that tank you boiler needs a min. of 141,000 BTU out to meet 1st hour ratings. I think your boiler has a IBR of 126,000 BTU. You might be better of with a 30 gal, It needs a min of 113,000 btu. If installed properly I think full recovey is like 10 minutes.

People usually way oversize a indirect. So you may want to rethink this whole thing.

I am not big on the # crunching and I might be off on my statments, and I am sure the more advanced BTU pros will be replying soon.

Mike NJ
Old 02-26-11, 05:30 AM
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Pipe the indirect with 1" like the manual says. Also use a dedicated circulator for the indirect and separate circ with zone valves for the space heating. Use a control (e.g., Taco ZVC) that allows priority on the indirect.
Old 02-26-11, 06:22 AM
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We went from a 50 gallon direct fired to a 35 gallon indirect. We never run out of hot water with the indirect.
Old 02-26-11, 06:38 AM
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As Lawrosa stated to achieve the number of gallons the correct flow and velocity must be achieved.
The 40 gal will supply 154 gallons first hour rating @ 141,000 btu boiler output.
If you are concerned with capacity think about stone lined indirect.
A 35 gallon stone lined tank will give you 200 gallon first hour rating @ 99,000 btu boiler input. This still uses 1" pipe and 6 gpm flow in the boiler piping side instead of 10 or 8 so possibly a smaller pump coulg be used.

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