Replacing boiler and HW heater with Combo Boiler.

redwing11

I have a 2400 sqft 1960 brick ranch in Denver Co. The boiler is 125k and 50gal HWT with exhaust gases going up a brick chimney. Two people, 2 bathrooms. Newer windows, Rockwool wall insulation, and R38 in the ceiling. I am a welding instructor and carpenter and believe I can install this combi boiler with the help of a friend. My brother in law in Mi is a Licensed Plumber who recommended a Lockinvar Noble 199k for the replacement.

Q1 Would like to exhaust up the chimney with PVC pipe. Would this be best or use SS pipe. The chimney has a clay liner. The fresh air would come in from the side of the house.

Q2 After reading through many posts on this forum I think a Noble 150k would be a better fit for the house. We do use a lot DHW but think the 199k would short cycle too much for heat. What size would you recommend?

Thank you for any wisdom and help you could give me.
Tom

hot_rod

A heat load calculation would be a good starting point, here is a calculator to try.
I would guess your load would be well under a 100,000BTU/hr
a 120,00 combi may work. i have a 120 and a 110 at my buildings, plenty of DHW for the two of us.
https://www.slantfin.com/slantfin-heat-loss-calculator/

redwing11

Thank you, Hot Rod, I will do the calculation.

redwing11

Did the calculation and came up with BTU/HR 58430. Know which size Combi boiler DWH to use and again thanks.

hot_rod

So many good brands available, they are all fairly common under the hood.
A 110- 120 would cover that load if 2.5 - 3 gallons per minute is adequate. A 150 if more DHW is needed, that would still lock down to your heating load number.

Lochinvar, Triangle Tube, NTI are just a few brands with good support in that area.

Use functions like outdoor reset, ramp delay and the firing limits to match up to the heating load.

Look into the PP type flue piping for a chimney retrofit, CentroTherm is one brand.

What type of heat emitters? The lower the SWT required the better the boiler efficiency. Panel rads or radiant are ideal for retrofits.

Plenty of top notch installers in Denver, if you want to go that route.

redwing11

Fin radiators like Slant sell. I have no problem with having to pay someone to help with the install. I just want to cut costs as a teacher with the help of others and do not want to do this install twice. You have been a great help to me. I will buy the Teacher book on this site. I am a teacher who can always learn something new from others. 26 years as a teacher and I tell my student don't stop learning because when that day comes you are 6ft under the dirt.

I am going with the 150k combi boiler as my wife still thinks we need a 199k but I do not want short cycling.

Thank you for your knowledge you are sharing.
Tom

hot_rod

If you have a room by room heat load, this journal will give you ideas on how to run the lowest possible SWT. With fin tube you may either increase the amount of board or use high output style. It would be ideal to stay below 130 supply on design conditions to really maximize the boilers efficiency

https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf