If it's insulated well, where does he think the heat is going? Heat has to go somewhere, it doesn't disappear.
Any comments on the following:
1. I'm sure Gary's boiler works fine. Yes, once the oxygen is out of the system, it is not an issue. But, if you put in another backup boiler, you will get metal contamination from the carbon steel into your other unit, and they have very small orifices, and even the fire tube designs have issues with this. Like HTP, Triangle Tube, etc. That is what kills boilers over time. Send them to any early grave. Then you get to buy another. If you do that, you should put a water to water heat exchange between the two systems so the propane boiler is isolated. Extra cost. And, you should do robust filtering on the line between them. I am just getting ready to do that on mine, just to filter the incoming water.
2. Yes, you can pump out of a 1.25" pipe, and it will work. The problem you have, whether you know it or not, is that you are reading reviews from other people who are happy with their systems, and you know ZERO about their bills, and costs. What you have Dan, is a situation where you have decided to heat with wood, and you are trying to justify it. Pure and simple. And that is your prerogative. But you are unaware of the math involved, You need to educate yourself as to what you are getting into.
Typical boilers for home use use 1.25" out of the boiler, because the actual heat load are not that big. There is a direct correlation between pipe size, and heat transfer rate, and also feet per second of pumping rate. Gary's boiler is at one end of the extreme, and a wall hung Triangle Tube at the other end. Gary is aiming at high mass, super high storage btu, and very high temperatures. If you want to heat with wood, then you are doing everything else wrong in your design. The floor system you want, concrete with tubing is a low temperature high mass system. If you put HOT water into it you will have to open every window in the house all winter long, or shut it off for long stretches. OR, you will have to use a very large mixing valve, and mix the hot water with cold water to temper it. You can put 180 degree water into concrete, but over time, it will destroy the wood floor. They are not to have over 130 degree water. So why make 200 degree water?
Also, everyone now tries to run low temperature water because it is much more even heat, the boiler is more efficient, and because it can be controlled more closely. Google the Heating Wall, and look at the post by SW18X called "Pipe ID and flow/btus." It is right on the money for your situation. Read Hotrods comments. He is the guy at Caleffi. One of the top guys anywhere.
If you put in Gary's boiler, have it built with 2" NPT fittings, and run the largest pipe size you can over to your delivery system, or likely to your SuperStore tanks I think you need. If you use the water right off the huge boiler, you have to temper it period. I happen to have such a valve sitting on my shelf, Tekmar, with automatic 3 and 4 way computer controlled actuators. They are worth thousands of dollars, but tell your plumber about me, because he will want to buy them. I have a 2" and a 1.5" The 1.5 has never been used. They last forever. I can save you about $1500 on that alone. If you don't do this, and run even 1.25" pipe, you can transfer a lot of heat at high temperatures, of course, but you don't need high temperatures! So you have the added resistance to flow compared to larger pie like 2", and you have to pump cold water too. If you read that listing I told you to look up, just look at the difference, for example, between 3/4" and 1". It is huge. You do NOT want to pump at high rates. It make s a lot of noise, cost a lot of electricity. If you run big pipe, you can run a much smaller pump. I have a whole bunch of these pumps sitting around, by the way. I've been donating them to my local Masonic Temple, so they can use them to heat 40,000 sf buildings.
Your plan, as described to me, was to put in wood, and put in a backup boiler. To make sense of this, you MUST understand that they are diametrically opposed to each other, if one of them is low temp hydronic. If you go with Gary, it might actually make more sense to just go with old fashioned cast iron radiators, or modern wall hung radiators. But, at those temps, they get hot enough to burn kids. At our giant Victorian, we pumped 150 degree water into our cast iron radiators, 110 into our underfloor aluminum panels, and 90 into our concrete slabs. In my home now, I'm going to use 123-130 into my wall hung radiators, and about 80-90 into slabs. What will you need with 180-200 degree water in the Gary boiler?
If you are dead set on that, get the smallest one he makes, and get yourself several of the Superstore insulated storage tanks instead. Like 4-6 of them. They come with 2.5 inch fittings, which should tell you something about Gary's design. You will be way ahead in the game. Put them in some place convenient to your distribution system, and run the largest diameter pipe you can from the wood one to those storage units. And then get yourself some Caleffi or Uponor manifolds like the one I showed you. Or, find a UL approved wood fired boiler that is much smaller and can be indoors.
Do you know what this makes me think of, because we both like old cars? Look at the motor in you Mopar, or the one in my AMX. Heavy cast iron. Horrible gas mileage. Powerful by the standards of those days. But, by today's standards, they are boat anchors. Any small, aluminum block today, with a turbo can run circles around ours, and get 18-30 mpg while doing it. My 63 Vettes got like 13, I just looked at 4 AMG's the solar guy owns that are all around 650-775 hp and they get like 24 mpg, and are 0-60 in 2.7 seconds. Top speed probably pushing 200. I love old cars, but even a 4 cylinder can outrun either of ours now. Gary's boiler is vintage iron. The wall hung boilers are modern.
Dan, you are trying to make a decision that is going to have repercussions for ever. First, you don't even need a wood fired system, you want one. Okay, that is fair. But, if you do so, and also plan to put in a back up, they have to work together, or the whole system combined will be a giant cluster-f--k. And it will cost a fortune to run. I don't see how heating with wood will ever pay for itself. You have to pay interest on that money to your Dad, spend a ton of money doing it. It makes sense to use your 2 wood heaters in your fireplace, because they can keep your house warm, and can be run as much as you need to. You commented that they heat you out of the house really quickly. The system you are thinking of buying is a giant unit designed to sit far away, and heat up millions of BTU of water, but distribute it though a system designed for the opposite. Invest that money instead. Or, use it to put in a PV system, and at least generate your own electricity. Those do pay for themselves.
My final line: you are asking the wrong people the wrong questions. Please read that thing on Heating Wall.
NB: The biggest mistake I ever made in heating was in putting in that 275 gallon tank in our basement, and using the 2 boilers to heat it up, and then run off that tank to heat the house. It sat there and just heated up, and cooled down It was a huge mistake. You are looking at a system that is about 6 times larger than that, and my house was almost 14,000 sf.
AT 200 degrees, that Gary boiler will store nearly 3 million BTUs, not including the thermal mass of the tank itself. If you go that route, I'd advise you to insulate the entire shell of the room it is going into to a high degree with rigid insulation. Then cover all that with some non flammable material like galvanized steel. If the boiler was inside, I'd fill the entire room with sand.
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Thanks in advance