Replacing Boiler in a high mass system

goodguy

My son has a 100 year old house with a converted gravity fed hot water system. The boiler has developed a leak. He is happy with the company that has been doing his service and they are recommending a Bosch KRB283 100k boiler. The quote says nothing about system controls or system pump. 2 story, 12 CI radiators, single zone, with all the large piping still there. I want him to set up with ODR and continuous run. Looking at the Bosch literature they have FW 200 which can be used either attached to the unit or as a room controller. Then they also have The BCC100 that talks about IDR and it will as I understand connect to the boiler without needing the FW 200. So my question is which of the Bosch controls should he get to run the system as a continuous run system? Secondly, since the quote did not talk about the system pump, what should he be looking for a system pump.

EBEBRATT-Ed

First thing would be a heat loss calculation to determine the right boiler size. In this day and age guessing is bad.

Once the boiler size and heat loss are known and the radiation size checked the the flow of water and temperature of the water can be decided. Then the pump is selected based on the pipe size #of fittings and the flow required.

It all starts with the heat loss.

EdTheHeaterMan

I recall making contracts for new boiler installations and that I liked to put in writing as many things as possible to make it look like m job had a better value than my competition. That way if there was a chance to salvage the job from my competitor, I could say something like " OK, I can meet the price of the competitor by removing this item from the job," and lowering the price.

However, I do recall that I did not list every pump, component and valve by name. That would make every contract into a 30 page short story. No one wants to purchase something with that much detail for simple residential replacement, so I might say "in accordance with manufacturers instructions and industry standards" as a catch all line to include in my job what a customer might ask about like in your situation.

I would answer your concern with. That is already included in this line here "in accordance with manufacturers instructions and industry standards". But if you want me to write it in specifically, then I have no problem with that, since it is already included.

So with your concern, Ask the contractor if they are going to use a primary secondary design or some other bypass design to insure the boiler works well with your large water capacity system. The manufacturers instructions are pretty specific on the large water capacity systems.

But the first thing I would ask is why they selected the boiler size. Ask them for the Load Calculation that was done, what insulation they think your home has? If they are going by some thing like the old boiler size, then you need to find a different contractor. Bosch makes a ZBR21 that may be perfect for your home.

goodguy

I understand your and appreciate your comments about heat loss and radiation, but my question was about controls. I understand ODR and the one control gives him that. IDR is a new concept to me and in reading all the posts on this wall regarding Bosch controls, some of them use IDR. Which is better? Are the IDR controls more friendly for someone who is not going to mess with adjusting the ODR curve for best efficiency.

hot_rod

In some, maybe many cases indoor reset is a better option compared to ODR. Early tekmar with PID logic was another attempt at optimizing system control.

Some good explanation here

http://www.exqheat.com/