Small Boiler + Indirect Water Heater = Bad News?

[NTL1991]

Can a small gas boiler (Weil McLain CGA-25, 52MBH Input, 38MBH Net) supply a 30-40 gallon indirect water heater with priority while maintaining space heating in a 1,000 sq foot apartment (2 bed, 1 bath)?

I'm trying to reduce the number of vented appliances I have, so indirect heaters seem like an obvious choice to eliminate 3 atmospheric draft NG water heaters.

-Nick

 

[Dana]

Can a small gas boiler (Weil McLain CGA-25, 52MBH Input, 38MBH Net) supply a 30-40 gallon indirect water heater with priority while maintaining space heating in a 1,000 sq foot apartment (2 bed, 1 bath)?

I'm trying to reduce the number of vented appliances I have, so indirect heaters seem like an obvious choice to eliminate 3 atmospheric draft NG water heaters.

-Nick

The CGA-25 has more output than the burner of on a typical standalone water heater, but not three of them. Why three water heaters for a 1 bathroom apartment?

Set up properly with sufficient flow to take the full output of the boiler it will recover quickly- before you're dried off and dressed after a shower or bath, and before the temperature in the apartment has lost even 1 degree F.

A 1000' apartment with fluff in the walls & attic and glass in the windows will have a heat load less than 20,000 BTU/hr at RI design temps, so there's plenty of burner to spare with the CGA-25.

 

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[NTL1991]

The CGA-25 has more output than the burner of on a typical standalone water heater, but not three of them. Why three water heaters for a 1 bathroom apartment?

Thanks Dana. I didn’t get into all the details, but each apartment has an individual 40gal gas water heater. I’m looking at replacing all three with indirects, fired from each apartment’s CGA-25 boiler to eliminate 3 vented appliances from a taxed chimney.

I wanted to make sure that the CGA-25 (two installed currently, third boiler which is a Laars Newport NP-85 oil fired, will be replaced with a third CGA-25) would be sufficient. I’ve seen some 30-40 gallon indirects with a coil rating of 90MBH+.

-Nick

 

[Dana]

The 90MBH+ coil ratings are only relative to the first hour gallons ratings and other specs for the water heater. The coils still have (more than) sufficient surface area to deliver the full 44 MBH DOE output of a CGa-25 to the water.

At 44 MBH it would have about half the capacity ratings of an indirect rated at 90MBH, but that is still 25-50% higher than a typical 40-50 gallon atmospheric drafted standalone, which is ~28-35 MBH of burner output. The recovery time of the indirect will be proportionally shorter than the standalone.