calculating exchange rate in an indirect

Dave Larsen_8

Can anyone help me with the formula(s)to calculate how much domestic water I can produce with 185 boiler water, 120 domestic, 36 ft of heating surface, with boiler water at 12 gpm.

Ken_40

How about the following:

What's the BTU output of the boiler?

And, what's the storage capacity of the indirect?

Unless you have a hot-tub or three showers all filled with teen-aged girls washing their hair at one time, a boiler with 100,000 BTU inout and a 40-gallon indirect is typically larger than needed.

If you have hard water and no softenor, other issues may abound.

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ALH_4

Manufacturer Ratings

Of what material is the heat exchanger constructed? How thick is it? What temperature do you want at the fixtures? Are you looking for a continuous or "first-hour" rating? Generally, the manufacturer will publish the ratings of their domestic water heaters, and heat exchanger manufacturers will certainly have heat transfer information available.

Unknown

return water temp?

If your return water temperature were 165 degrees F at 12 GPM,you would be delivering 120,000 BTUH, if it were 175, you would be delivering 60,000 BTUH.

If it were 185 out, 180 back at 12 GPM, you would drop off 30,000 BTUH.

Other than that, you need the ratings chart, or engineering formulae for an accurate estimate, which I don't have.

Noel