free75degrees - what type of wood boiler do you use?  What is the max output?  Is 350 feet of copper enough?

nhjohn - 14 June 2008 11:10 PM

free75degrees - what type of wood boiler do you use?  What is the max output?  Is 350 feet of copper enough?

I have Tarm 40, not yet installed.  If 350 is not enough I’ll have to add another coil or two, but I am hoping it won’t come to that.

Hello, Overall I am more then happy with the pex coils. I do not remember for sure but it seems to me, the first coil took a long time but the remaining 3 went much quicker. They do PERFORM. My boiler is rated 90K output. On the coldest days it keeps up with all usage with hot water to spare. When my tank is down to 120* with not other usage but charging the tank-the boiler CAN NOT keep up with the pex Hx. I have my aquastats set up so they stop the pump when the return water hits 140*. I have 700-750 gallons of storage. I have 4 coils in parallel at 200’ each for a total of 800’. Perhaps too much coil charging but I think this is a good thing when I am drawing from the tank. I have plenty of pump. A Grundfoss UP 26-99. I am installing a Danfoss tempering valve so this will take care of the 4-6 hours of cycling. When I said I would do it differently I was referring to a few things. One I would not want to make them again but now I have the hang of it-not so bad. Since I only have 750 gallons, I would go with the Plate because the coils take up alot of space. Although probably not a s much as I think when it comes to liquid volume. Obviously this is not an issue with a bigger tank. The more I study Hydronics - I am not convinced a Plate Hx can perform as well because of the stratification issue. I understand you can go with 2 pumps or CV’s for directional flow. However, I still think the mixing of the water I.E. turbulance in the tank must affect stratification. The jury is still out on that…

I did use a flat plate, open storage, plate hx mounted above the top of the tank, pump was mounted just off the bottom of the tank, so water always was in the pump. The pump flow was vertical, so any air in the line would move straight through the pump. Do not plumb horizontal through the pump, as air locks can develop. Keep in mind that with an open system, it will drain down to the lowest water level. When the pump kicks in and pushes water through the system, there will be air, and venting is needed at all high points. I had a vent on the top side of the plate hx to release any air that got trapped at this point. If you get air locks, the system will not work.

Sparke - thanks so much for your input.  I’m am leaning more and more toward the pex.  I think it will be the easiest to install, offer the best stratification, and be the least expensive.  The other thing is that if I don’t have enough pex I can just put in more.  I very much appreciate your input. 

Jebatty, you almost had me with your lobbying efforts for the plate HX, but there are too many variables to worry about, the cost is more than just another pump (most notably the power consumption of the pump), and they seem (never actually done it) difficult to install given that you either need to go through the tank below the high water mark or make concessions for air bubbles. 

Now the question I am trying to answer is this:  If Sparke is having success with 4 coils of 200’ each with a 90K boiler, should I go with 8 coils of 200’ for my 198K boiler?  Or 9 coils?  Is it better to go with more shorter runs?  I would think not as the hot water might not have time to exchange before its on its way back to the boiler.  Should I go with longer runs?  3/4” runs?  Or 1/2” runs? 

Sparke - do you only charge your tank up to 140?  Why not higher?