Help sizing pipe and heat exchanger

Heatexchanger output is as much a function of it's design as it is the outside dimensions. So to say any specific certain dimension will "work" would be further misinformation.

Have you run a free heat loss calc on your house? If not, google "slantfin heat loss" and run the free application to get an idea of where to start. There are plenty of coils/heat exchangers out there and being an informed buyer will help significantly.

Have you researched ice melt systems? They require UNGODLY amounts of BTU to work and typically they are glycol based systems. This will make your system a lot more complicated. Do you then run water to your house and use a flate plate HX to heat a glycol mix for your driveway? Or do you run the whole thing glycol? This impacts efficiency, materials, performance, cost, etc. Everything I've read on ice melt seems to suggest doing it with wood for residential applications rarely, if ever, turns out to be a feasible or even remotely attractive project to undertake.

Here's the reasoning I went with for my coil in the plenum: I went big. A 22x22 3 row coil is far larger than I need to heat my house. I can vary the flow through the coil by closing off one of the manual valves to/from it a little bit. If the coil is larger than I need it won't 1) restrict air flow in the plenum 2) be undersized at all for my house 3) restrict water flowing through it. Restricting water flow through the coil can make it work to the proper size for my house, but had I installed one that was too small, I would have to buy another one of the proper size to fix the problem. Just my two cents on that...

As far as GPM, download this PDF and go through the formulas. I'd use 200,000 btu's as your target rate of heat transfer since your boiler would be capable of 200,000 btu's. Size the pump and underground piping properly to be able to handle 200,000 btu's and use a ceiling fan speed control switch to slow your circulator down when you're not going to be using 200,000 btu's at once (most of the time I'd imagine).

In my opinion, the best way to run more than one zone is to use a two manifold system that has a supply manifold and a return manifold. You can get custom made manifolds/headers or one of their standard headers from Earth Lee (www.earthlee.com). I had a pair of custom headers made for my boiler for an excellent price (about $75 shipped if I remember correctly). You'd use one large circulator to flow the water to/from the boiler through the headers and the zones connect the supply header to the return header. For example, my coil, hot water exchanger, and cast iron radiator are the zones that connect my supply header to my return header. You'd also need to install a differential bypass between the headers to let the excess flow pass through when a zone valve closes or such. This type of two manifold system ensures that the hottest water goes through your zones and all of the cooled water returns through the return manifold. There are other ways of setting this up, but once again, just my two pennies...

If you need to melt snow with your boiler, it is a good idea to use a separate heat exchanger to separate that system from your main system in case that system freezes and fractures (even with glycol). You'd obviously need another cirulator for that separate loop. I'd also probably put a strap on aquastat on your main loop that will shut down the snow melt loop's circulator if the water temp of your main loop is below a certain temperature, so you don't excessively cool the main loop just in case the boiler can't quite keep up.

Welcome. Great place to get info and varying opinions.

I am not trying to be a smart @@s here, I am just looking for specific info. What I have seen so far is an awful lot of people (including some boiler dealers) out there are just guessing at what size pumps and line and exchangers to use, and I dont want to design my system that way

Click to expand...

.....
That's the truth and this forum is filled with guys trying to sort out problems... as well as successes.
Here's a link to some basic boiler info. On the 3rd column "Other Useful Info"
http://www.comfort-calc.net/tech_area_index.htm#HWB
I have installed a 10 acre tree nursery irrigation system, boilers are different animals. Pipe / pump size is critical to delivering BTU's.
Fan Coil. I have forced air too. You want to look at oversizing your coil so you can make use of lower temp water. Most coils are rated for an oil boiler delivering a constant supply of 180? water.
What kind of boiler do you have ? You mention 100G ? (or 1000G) What kind were you thinking there pressurized or non-pressurized ?
Did you see the "sticky notes" at the top of the Boiler Room home page ? Good info there too. One on underground pipe.