1st - EFE Ratings

These are similar to a rating a car's mileage per gallon rating. Gas and Propane Boilers are only rated for efficiency at full operating temperature. A typical cast iron boiler starts at 50% efficiency and slowly works its way to 85% efficiency as the massive cast iron heat exchanger heats. This can take up to 20 minutes.

On moderate heating days, the typical boiler will heat the home in a 10 minute cycle and shut down, thus never reaching its 85% efficiency.

Because of its low mass, the MZ boiler reaches peak efficiency in less than 90 seconds and maintains peak efficiency until the home is heated. Therefore the fuel used is usually 30% to 70% less with the MZ! Thus you save Propane or Gas - and this saves money. $1000 to $3000 per year on a typical house with a typical pre-1980 gas boiler.

2nd - CONDENSING

When natural gas or propane burns, they produce water vapor by products, In a conventional boiler, the temperature must be high enough to prevent this vapor from condensing on the heat exchanger. This would ruin it in a short period of time. Therefore the heat exchanger has to be maintained at a high temperature and the boiler has to be oversized to prevent the water returning to the boiler from falling below 130°: the temperature at which damaging condensation occurs.

Most Condensing Gas Boilers are made of stainless steel so condensing will not harm it. Thus, it can be sized precisely to the heating requirements of the structure and the resulting condensation drains harmlessly away after the heat energy has been transferred to the home.