DHW Gas Bill cut in half? Is that possible?

[BirchwoodBill]

New WM97 boiler and WM Aqua Plus 85 DHW tank was installed at the end of July. We also added Thermostatic valve . Being August - we were not running any heat - but I am seeing the therms cut in half? Our water usage was the same. I was expecting a reduction of 10-15% not 50%. Is this typical?

 

[Jadnashua]

What did you have before?

 

[Sponsor]

 

[BirchwoodBill]

Old system was Weil McLain cast iron 85% efficient with a triangle smart40 set at 125f. The new tank is set to 145f and with the thermostatic valve mix to 125f.

 

[Dana]

Yes, that's a credible number.

The standby losses in cast iron boilers are ridiculous when the only load is domestic hot water, reducing the as-used efficiency to less than 50% in many cases. The WM97 has less than 10% of the thermal mass of the cast iron beast, higher combustion efficiency, and operates at a lower temperature. The fraction of the fuel heat abandoned in the boiler at the end of a call from the water heater is tiny by comparison.