First time post here! This site is really great, learned a whole lot already. I'm just about to pull the trigger on an EKO 25 kw - 85k btu (gasifier), and incorporate a thermal storage tank. This system would run in parallel to a very tired propane boiler from the '80's. My house is moderately well insulated, (very old farm house renovated in the 1980's), 1150 ft2 but will add another 400ft2 in the next few years and has 2 zones of baseboard hot water radiators. I have a father in law who is a master plumber and I'm a DIY kind of guy who likes to learn about things and save money. So I think we can get through this cheap, safely and correctly. 1) My first question is, can I use oxygen barrier PEX instead of copper tubing for heat exchange in a non pressurized storage tank? (Cost savings) 2) I mostly hear that you can't have too much thermal storage or people often say bigger is better than smaller (in this case). However, the other day I was reading something that said don't over-size your storage because your boiler won't be able to keep up.I used a calculation found online which said the max should be about 660 gal. for the EKO 25 but then I saw a guy on this site (can't remember where, that had an EKO 25 with 880 gallons, thoughts? I also used another calculator that was very general based on cubic meters of inside of a building/house and figured that with a moderate insulation rating I would need at least a 13.6 kw boiler for my house (the EKO 25 is of course 25 kw). What are the physics/considerations of storage sizing and over sizing? 3) I heard you can get algae buildup in a storage tank which may reduce heat exchange efficiency between storage water and coils. Is this true? If so, could I put bleach Bleach in the storage tank? 4) I see very conflicting numbers on what the flue size needs to be for any given size boiler. For instance the EKO site says you need 8"ID for the EKO 25 (85k btu) but it also says you need 8" for the EKO 40 (137k btu)! This lead me to believe that there was more to it and, there does seem to be. I read that you need 15-20 Pa in the chimney for the EKO line or so many cubic units of space in your chimney per number of btus and the calculations are quite complex if you try to figure these out on your own. Yes, the manufacturer says use 8" but per the example above, it seems like you might not need that much. I did run the max BTU, cross-section of chimney and Pa calculations on my own and they all showed 6"ID would work but I'm not an engineer so I'm not certain my math is correct. I already have a 6"ID metal bestose chimney running through the inside of my house for good draft and recovering heat off the chimney. It's currently hooked to a 602 Jotul, great little stove. The chimney height will be about 23' when I run it into the basement for the EKO with just 2' exposed to the outside air at the top. Anyway, has anyone run a 6"ID chimney for an 85k btu boiler or know of an online calculator that is relatively easy to use to tell if I'm getting 15-20 Pa of draft? 5) Last question: My buddy is offering what I think is a good deal, $3,000 on an EconoBurn 150,000 btu, 5 year old boiler. I certainly don't need this much boiler but can I just partially load the boiler if I don't need that many btus or does it not work that way? Or maybe have 1,000 + gallons of storage and then fill it and then just run off the thermal storage for 2 days? Thanks for any information folks may have out there and stay warm!