Combi Boiler: Bosch vs Dunkirk

[TCBUCKS2020]

So it has come time to replace my 30 year old Burnham gas boiler (XG2000A). I was hoping someone could reassure me that the options I am weighing are appropriate and if one might be better than the other. I am running three zones in my home outside of Philadelphia:

Zone 1: Main floor = 31ft (5 total baseboards)
Zone 2: Upstairs = 34ft (4 total baseboards)
Zone 3: Master Bdrm = 12ft (1 baseboard)

I received two quotes for the following:
Option 1 = $10.2k Installed: Bosch Greenstar Combi 151 (ZWB42-3)
Option 2 = $9.2k Installed: Dunkirk DKVLT 100,000 w/ 40 gallon indirect

Option 2 adds a 4th zone for the separate water tank. Both options replace my electric water heater which I definitely want to do (need to free up space on the breaker). I would greatly appreciate any insight you could provide!

 

[Fitter30]

77' of 3/4" fin tube @ 160* water 34650 btu's. Burnham was it 200k and did it cycle on the coldest days? With any combi or indirect have to know what is the lowest incoming water temp you will see and max flow rate. If two showers are running and a clothes washer it has to be calculated in. Even though the specs are 4 gpm it might be only be 40* rise, 50* incoming = 90*

 

[Sponsor]

 

[TCBUCKS2020]

77' of 3/4" fin tube @ 160* water 34650 btu's. Burnham was it 200k and did it cycle on the coldest days? With any combi or indirect have to know what is the lowest incoming water temp you will see and max flow rate. If two showers are running and a clothes washer it has to be calculated in. Even though the specs are 4 gpm it might be only be 40* rise, 50* incoming = 90*

These points you have made are exactly why I was trying to find additional information. I thought it was odd that I received two estimates to move to a combination boiler and neither installer looked at the length of baseboard piping - nor did they take any measurements. They took a picture of my current boiler, asked how many zones were setup, then left.

I uploaded this picture of the current boiler specification plate. The boiler has never had a problem keeping the house warm. I couldn't tell you the incoming water temperature or flow rate as I have no way to measure that.

If it is not possible to provide a recommendation based on what I have provided, then I completely understand. I appreciate your time and expertise!

 

[Fitter30]

What are you using to heat domestic hot water sincej your bids include dhw?

 

[TCBUCKS2020]

We have a 20-year old 50 gallon electric water heater which we want to remove to free up space on the circuit breaker.

 

[Fitter30]

Couldn't find water temp to gpm to water temp rise for the bosch but the 5-1 turn down ratio enough. A condensing boiler has to have under 130* return water or less to get 90+% efficiency. Above 130* 84%.What is your boiler running now? Didn't look at dunkirk. Have to measure your cold water temp, have to come up with a gpm flow that you would be happy with. Then can pick a water heater with the right temp rise and flow.