How can I figure out if a Combi Boiler will be adequate for my house?

by nnamerz   Last Updated September 11, 2019 02:21 AM

We recently moved into our new home that currently has a Super Hot MG-100 Hydronic Boiler (installed in 1986, when the house was built). Clearly, it's done its job and in need of a replacement. We had a couple of boiler companies come give us a quote and one of them suggested putting in a Bosch 151 (ZWD-42) Combi Boiler as he noticed that our water heater is also near its life expectancy and because the combi unit is much more efficient.

I did some research on the internet and can't get a clear answer if this unit, or a combi boiler in general, will be suitable for our house. Some sites said it depends on how many gallons per minute of hot water are used throughout the house since this unit can only output 4.0 GPM. Others said it's based on the number of bathrooms in the house and one site even said mentioned calculating the total length of all the baseboard heaters.

I don't know how many GPM of hot water are used throughout the house or how to even figure that out easily, but I did go and measure all the baseboard heaters.

The house has 3 levels and is located in Vancouver, BC, where it can get pretty chilly during the winters. The boiler is located in the basement and supplies hydronic baseboard heating to the basement and main level only. The upper level is heated by electric baseboard heaters. The basement has a total of 38 linear feet of baseboard heaters and the main level has 61 linear feet.

As for our hot water demands, the basement is a rental suite that has a kitchen sink, washing machine and a single bathroom with a stand-up shower. It is currently occupied by 2 people. The upper and main floors are occupied by my wife and I (and hopefully a child in the near future). On the main floor, there is a kitchen sink, laundry sink, washing machine and a half-bathroom (no shower). The upper floor has 2 bathrooms, one with a tub and the other with a stand-up shower.

How would I figure out if we can suffice with a combi boiler? Would this unit work in our household? Any help or advice is greatly appreciated.



Answers 1


You estimate the hot ater requirements ie start with some of the “rules of thumb” such as each person uses between 40 to 60 litres of HW at 60 deg C per day and include all the other HW demands... once you have that then you can equate what you need.

Solar Mike
Solar Mike
September 11, 2019 02:08 AM

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