boiler sizing and fan coils

kev

I am doing a boiler install where the hvac techs have installed all of the fan coils and I am to supply all piping to units from boiler with 80 gal. indirect. I asked the installers for the heating load of house and was told 240,000 btus'. the house is 5000 sq ft. and new const. with all low e glass. The number sounded very high to me, so I did my own heat loss and came up with 125,000. I also looked at the 3 zones of fan coils and the numbers are 90,000 34,000 and 51,000 btu's at 140 degrees. So if I go with my numbers I need to size to the hot water indirect load and if I use their numbers I will be oversized in my opinion. How do I interpret the numbers on the coils? I feel unsure of the correct way to approach this. Thanks for any input.

Nron_9

set up

set up boiler to run at 140 degree water temp and allow for a higher temp in the controls , and ask if they used a rule of thumb or did proper heat loss calculations

dconnors

sizing

From your figures, it looks like 175,000 btu of heat. You cant deliver more than the coils will put out. That should more than handle the tank on priority. A safe bet is to add 10% to the total or about 193,000.

Don_11

Hydroair

I run into this and occasionally and wonder what is the correct way to size the boiler. I get a call from a contractor looking for me to help spec a boiler. The HVAC contractor has all ready specified and sometimes installed his air handlers with hydroair coils. If you add the btu's of the coils it can be double what the heat loss of the building is.
Do you size the boiler to the coils so if all are calling for heat that your boiler temperature does not run to low?
Should you put circuit setters on the coils so only the GPM flow needed to supply that particular area of the building is let through the coil and you can maintain a reasonable delta T and keep the boiler temperature constant?
Do you size the boiler to the building and let the boiler temp drop drastically if all of the hydroair units are calling at the same time?
How do you guys size a boiler with the hydroair coils are on the job before you get in?