eyecal said:
How far from the house can these boilers be installed. My thought wtih an owb was to set in undercover at my outbuilding and pipe it about 120 feet to the house. Am I able to heat both these buildings and be this far away from the house?
With decent quality pipe, the heat loss is relatively small. Pumping distance will end up being limited by your willingness to pay for pipe or pumps. The smaller the pipe, the more friction loss the water will suffer (remember, 120 feet will be 240 feet, since it's a loop). The friction can be overcome with a larger pump, or by using larger-diameter pipe that has less friction.
How much heat do you need to pump through the underground pipe (ie, how much heat does the building at the other end need)?
For example, if the heat load is 100kbtu, 10 gallons per minute would be a decent flow rate. Figuring for a 50/50 water/glycol solution, and an average temperature between the supply and return of 165 degrees... 1-1/4" pex will give you a head loss of 15.6 feet, while 1-1/2" pex will give you a head loss of only 5.5 feet. You'll need to add heat exchanger head loss to that for the far end, as well as that of the boiler and piping at the near end - call it 15 feet total head for that.
So, you're looking at 20 versus 30 feet of head, depending on the pipe size. 20 feet of head at 10GPM can be handled by a Grundfos UPS26-99FRC on it's high speed setting, or a Taco 0011IFC. 30 feet of head at 10GPM is going to require a significantly larger pump, or two pumps. In parallel, so each only sees half the GPM, the two pump option would be a pair of Taco 0013IFC pumps. In series, so each pump flows the full rate, but the heads add, two Grundfos UPS26-99FRC's could be installed and run on medium speed.
Doubling pumps gets expensive in terms of initial cost (have to compare that cost to the cost difference between the two pipe sizes), and the electricity required to run the two pumps. Larger single pumps like a Taco 1615 (at 1750RPM) would work, but the cost is pretty high, and replacement if/when it fails isn't going to be simply a matter of grabbing one off the truck, whereas most decent service trucks have a Grundfos UPS15-58FRC and UPS26-99FRC on them, as those two pumps replace so many others, just by using the right pump and the right speed...
Personally, I'd err on the side of larger piping, using a single pump. It might be slightly more expensive to install, but the long-term cost difference in electricity and maintenance is significant.
If the price difference between the 1-1/4" and 1-1/2" stuff is large enough, you could always run four 1-1/4" pipes, and use two in parallel for the supply, and the same for the return. That also means that if one somehow developed a leak, you could drop down to three or even two pipes, and only at
that time add that second pump to overcome the added head loss.
Joe