ODR with radiant and hw bb

Mosherd1

Working on finishing off the basement for a spare bedroom/family room. The house has two separate heating systems and either is completely capable of heating the house. The first one is a 40,000 96% 2 stage gfha furnace but doesn’t have ductwork to the basement. This system was mainly put in to have central a/c but also provide heat while I worked on the house and got the hot water system installed and to provide redundancy. Last winter just before we got brutally cold (-20’s F) I got the radiant system functional but not completed. With the original heat loss calculations, my design called for 105 or so water for the rooms with radiant floors in the house and 115*-120* for the rooms with radiant ceilings. And I have a hwbb in the master closet that was going to run off the 120* for the ceilings. I have a 50 gallon electric water heater that I pulled the elements out of for a 4 pipe buffer tank. Originally I came off the tank and fed a taco I-series 3 way outdoor reset valve to feed my floors, and an I-series 3 way set point valve that I was going to feed 120 degree water to my radiant ceilings, and then a third line straight off buffer tank water to feed the baseboard, but after running the system, everything works great with less than 110* water except for the master closet.  Now I’m getting ready to finish the basement (which is only under a portion of the house) I sized the baseboard using 110* water (35 linear feet for a 14x24 basement) my question is if I redo so piping and I only use the I-series outdoor reset valve to feed everything, will the basement baseboards still heat enough using the same rest curve as the radiant floors and ceilings…I can see only needing 90-100* water much of the time. And I’m still trying to figure out how to heat the master closet.  Currently the buffer tank is temporarily being fed with an independent tankless water heater, we are planning on adding on a new garage, heating the existing garage and adding a heated breezeway hopefully next summer, then a proper boiler will be used. At this point I have yet to decide if I want a minimal maintenance, long lived CI boiler and loose efficiency, or maintain high efficiency with a condescending boiler and spend more on maintenance and repair with a shorter life expectancy.  

Zman

Baseboard heaters heat mostly with convection and with radiant to a lesser degree, they just don't have much surface area. I don't think they will run well on the same outdoor reset curve and true radiant.

I think you understand the different boiler options and associated pros and cons. I like mod/cons for your application.

Mosherd1

@Zman, each room has its own tstat on its own zone, so are you saying that at design temp of -1 F both the basement and the radiant will heat fine with 110* water but at say 35* the radiant may need 85* water (just pulling numbers out of the air for explanation) where as the baseboard may need 95* or warmer water to keep temp. And if that is what your your saying, then I should just feed the baseboards right from the buffer tank so their water temp never drops below 110, basically don’t run the baseboards on ODR.

Zman

I have not been able to find very much published data on this, the baseboard manufacturers usually estimate the output at lower temps.
My experience has been that baseboards don't put out much heat at lower supply water temps. I think this is because the delta T between the air and fin is not high enough to convect much air.

hot_rod

This graph may help with fin tube derate, from Idronics 25

Rich_49

https://smithsep.com/wp-content/uploads/Silent-Fin-Heating-Edge-Literature.pdf