Go to www.burnham.com and ask for their DesignPro disk. It is a complete program that will automatically do the calculations for you. The good part is the disk is free. There is a similar offer on www.slantfin.com. I do building mechanical designing and I use the Burnham program all the time.
There are many variables. For the pump size, you need to know the flow, and the friction head. The flow is usually easy to calculate, and the friction head depends on the pipe size, type of pipe, and length. Usually the fittings are 50% of the total equivalent length of pipe friction loss.
To find the flow, GPM, you need to know how many BTU you need for each radiant fin-tube, or radiant panel. Manufacturers rate the btu output of each of the fin tubes based on the fins per inch, the fin size, and water temperature, they will usually have a chart published. Also, they will have a pressure drop chart for radiant panels, or radiant device.
In short, there are so many variables, that each system needs to be engineered and calculated separately.
Generally, fin tube is 4.25" square and ranges up to 950 BTU/ft heat output. The water temperature is usually designed up to 200F, and is often reset according to the outside air temperature down to maybe 140F. The Pressure is usually close to 3 foot of head per 100ft of pipe, measure the length of pipe to the furthest radiant device and multiply by 1.5 = the total head pressure. add a small safety factor, maybe 10%.
The delta T for the system might be designed to be 20F, so take the btu output at each radiator and divide by (500*20) and this will give you the GPM flow for each device. Add the devices that are circuited in parallel (not series) then you will have the total flow through the pump.
I hope this guides you enough, but there are so many different types of systems, that large systems can quickly get complicated.
Heating System
Re: heating system
