I am a homeowner with a Tekmar 256. Its sensor reads the buffer tank temp and controls a geothermal heat pump. I did not install it but I have done my homework and can program the Tekmar. First, my Tekmar 256 Outdoor Sensor reads too high by 2-5 Degrees. I believe the Tekmar is off because I have another thermometer next to it that is giving a reading consistent with a third outdoor thermometer (and subjective feel). Being off by 5 degrees throws the boiler target curve off. Since there is not an offset adjustment for the sensor, is there another way to fool it into adjusting the curve correctly. I've tried raising the Indoor Temp by 5 degrees but this doesn't correctly compensate - too many variables. A second question. I would like to better understand how the auto differential mode works. My "boiler" is a geothermal system and I'd like to know what differential the Tekmar is shooting for in light, medium and heavy loads. Lastly, I have noticed that the differential setting doesn't always equate to a correct cut in/out (especially when first installed). Are there cases where let's say a 10 degree differential doesn't cut in/out at 5 degrees above / below the Boiler Target? Thank you for your help.

I am totally messing up my calculations. My new garage has 4 250' 1/2" PEX loops. The manifold supply and return is 3/4" PEX, this loop will be near 100'. I know that is quite a long main loop for 3/4", It is a somewhat temporary setup using a heat exchanger in my house. The problem: I can't calculate head loss to size a pump. I have been using Taco's [URL="http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf"]"Selecting Circulators"[/URL] guide. I believe the flow through my floor loops should be about 1.5gpm, putting my primary loop at 6gpm. The equivalent length of the Primary loop would be about 118' and the floor loops 257' (or less.) I will be using 40-50% glycol. When I calculate this I get a head loss of 30 feet for the primary, and 30 feet in a floor loop, totaling 60 feet. This is using head loss in one floor loop as it says to use head loss of the highest loop (all being the same.) I think there are multiple errors in my calculation. I know that head loss is decreased having the parallel loops, but this is not how it says to calculate. I also have a good idea I am doing something wrong because I am way off the charts for pump specs. I know there are similar setups for outdoor boilers, as far as head loss goes. Please help, if there is any for me. Your assistance is greatly appreciated...the garage is cold here in ND. Jacob