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Buderus G115: what does the word "necessary" mean in your opinion
The Buderus G115 installation manual in section 3.2.1 General Operating Requirements (p. 9) talks about getting the boiler to 150F within 10 minutes when the boiler is controlled by aquastat, as ours is.
"During burner operation one should achieve the minimum boiler temperature within 10 minutes after burner start-up by means of flow reduction and one should maintain this temperature."
We have two zones: radiators and DHW. When the radiators zone is calling for heat, and if the radiators are cold, our G115/4 (aka G115/28) boiler with 98,000 btu Riello takes 20 minutes to reach 150F. If the DHW is cold and calling for heat, it takes 15 minutes to reach 150F. I haven't tested the scenario where both radiator and DHW zones are calling for heat simultaneously. It stands to reason it would take longer than 20 minutes.
The manual has a matrix that appears to state that a mixing valve is "necessary" ( page 9, section 3.2.1.) A mixing valve is on my to-do list.
As a professional installer who is familiar with installation manuals from a variety of manufacturers, would you say the Buderus manual is clear about this mixing valve requirement? About the minimum boiler temperature within 10 minutes requirement?
Or is it reasonable to argue that the manual does not make either or both requirements clear?
Me, I happen to think the word "necessary" is unambiguous, and the requirement that the boiler reach 150F in 10 minutes is also very clear, but I'm just the customer, not the installer.
The upshot of this is not simply academic--I want to deduct the cost of having the mixing valve installed from what I owe the heating oil company for the last oil delivery at $4.50/gallon, about $800. I think they've not only been wasting my money by not installing the mixing valve, they've possibly shortened the life-span of the boiler, since inadequate temperatures can lead to condensation. I think the manufacturer put this into the installation manual for a good reason, and that it must be important.
BTW, I've calculated the volume in our Direct Return system, less than 15 gallons in the pipes plus ~11 gallons in the boiler. About 25 gallons total. 192 linear feet of 1-1/4" supply and return mains, plus about a dozen convector-style radiators with 1/2" supply pipe and 1/2" return pipe, in a 3-bedroom two-storey post-WW2 brick colonial, uninsulated with old windows. Climate: near Philadelphia PA. So we aren't a "larger water volume" system, yet with the old uninsulated house with old windows, whose radiators are located on exterior walls, our house presents some of the same challenges.