I have a 2550 square foot farmhouse. The house came with an outdoor wood furnace that is rated at 225,000 BTU/hour maximum output. 180 degree water pumps from the woodburner through ¾ inch pex tubing into the basement over a 65 foot run. Once the water enters the basement, it flows through another 30 foot run of ¾” pex tubing before entering a SuperStor Ultra indirect fired hot water heater. Water from the woodburner runs through the heat exchanger in the Superstor, thereby heating the water in the Superstor which then heats the house via baseboard heat. As a side note, the water from the Superstor actually flows through a gas fired boiler first before heading upstairs, with the boiler acting as a backup for the house if the wood furnace can’t keep up with demand. However, for our purposes let’s ignore the gas boiler because my goal is for the wood furnace to meet the full demand of the house.
There are a few problems with this set-up, which I inherited from the previous homeowner. First of all, the underground pex tubes are leaching a ridiculous amount of heat into the ground, to the tune of 15 degrees over the course of the run into the house. As a result, I am in the middle of installing insulated pex lines, either Thermopex or Logstor Pex-Flex, on the underground run to the house. Based on the manufacturers rating I am expecting heat loss after install to be 1 or 2 degrees total – a dramatic improvement. However, after spending two days digging, replacing one broken septic pipe, one underground gutter pipe, and tunneling under a sidewalk, I want to make sure I do this absolutely right the first time. Here’s my dilemma:
Thermopex uses ¾” ID pex tubing. Pex-Flex uses a true 1” ID. By all accounts, Pex-Flex is a slightly better product, even though documented Thermopex failures are extremely rare. A buddy of mine is a heating/cooling professional and will be helping me make my final connections in the basement, but he won’t be free until September. Meanwhile, I have an open trench and a wife who wants her gardens back, so I need to make a decision between the two products this week and get the pex buried in the ground. The big question is, is it worth the extra 3 dollars a foot for Pex-Flex, and the extra hour drive to the dealer, to increase the size of my pex from ¾” to 1”? I’m tempted to go with the larger Pex-Flex so I can get more BTUs into the house quicker, but if I do so, then I will need to replace the two 30 foot runs in the basement with either copper pipe or a true 1” non-insulated pex, and I don’t know pricing on these materials. I also don’t know how much more BTU’s the larger ID will give me. Predictably, the Thermopex dealer says the 1/4" difference in ID isn't a big deal and the Pex-Flex dealer uses the larger ID as a selling point. To throw another wild card in the mix, I’m fairly certain the SuperStor setup isn’t ideal: currently, the heat exchanger in the SuperStor can’t keep up with demand, so we may end up going with another type of heat exchanger once my buddy takes a look at everything and tweaks the system. (He mentioned a steel plate heat exchanger and the outdoor wood burner manufacturer included info on “Flatplate” company products in the owner’s manual). Then again, once I’m running 180 degree water into the house with the insulated pex instead of 165, maybe the SuperStor setup will be sufficient.
I’d appreciate any advice on this. I just don’t have the knowledge to run the formulas to see what I really need in terms of volume/flow/btu’s. A few more pieces of information that might help:
· Although we blew in insulation, the house is not very efficient in terms of heat loss (old drafty farm house).
· The wood burner is a done deal – too much money into refabbing it last year so it stays as the primary source of heat regardless.
· Right now I’m using Taco pump model 007-F5, 1/25th HP .71 amp 3250 RPM (I don’t know what the gpm’s are with this pump)
· The woodburner also heats a radiant floor setup in my 4 car garage, so I’m close to the maximum square footage this furnace is rated for (3800 square foot total house and garage, I think my model is rated for 4k or 4500)
· As of right now I’m leaning heavily towards buying the Pex-Flex and having the dealer install fittings for 1” copper onto it (Pex-Flex takes special fittings), I figure that way in the short term we can just use an additional fitting to temporarily step back down to ¾” for the basement run or later on go with 1”. That is, unless I have 20 guys on here telling me I’m crazy because there’s no way I’ll ever need the extra ¼” and ¾” will be sufficient in all applications.
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