I have an underfloor hydronic heat system about 16 years old - 6 zones on two floors - about 7500 sq ft running 1/2 CPVC under the subfloor. It has been heated with an 80-gal hot water heater, which has been inadequate. I live in Seattle, WA, area, so temperatures do not usually drop below the 30's or so. I want to replace the hot water heater with a Noritz N-0751-DV tankless unit (199,000 btu), but someone recommended a Weil McLain Ultra UG-310 with an indirect 60 or 80 gal tank. Since that is a much more complicated system (and expensive), I wondered if anyone out there could provide some advice. Thank you.....
Why would you want such a large unit? That's a lot of heat. I'm not familiar with their Ultra series boilers but I wouldn't give you ten cents for a Weil-McLain cast iron boiler.
Thank you for your response. I picked a 199,000 btu tankless unit because the person who recommended the Weil-McLain boiler said I needed the UG-310, which is a 310,000 btu unit, to run the underfloor radiant heat and the DHW. If I don't need something that large, so much the better. What I am trying to determine is this: Is a large tankless modulating condensing boiler with an indirect tank more efficient than two separate tankless units like the Noritz, one running the radiant and one running the DHW? I would rather use the two tankless wall-hung units because the initial cost is much cheaper, but I can't find anything that talks about using a tankless for hydronic heat use. Can you advise me which option is more efficent over time? The Weil-McLain is cast aluminum, not cast iron, but it sounds like you are saying that there are much better boilers out there than that one. I appreciate any assistance you can provide. I have to do something soon because my DHW tank is leaking.
You need to determine the heat loss from the home the load on the boiler from the domestic. Slantfin.com has a good, free program for calculating the heat loss. After doing that, look at the requirement for the domestic choose a boiler which will meet your needs.
I did the heat loss calcs you suggested and came up with 146,000 - 156,000 btuh. For DHW, I need something with a first hour rating of about 216. I am thinking that probably means I need to add an indirect tank to the system for DHW, but now my question is this: Am I better off with a modulating condensing boiler to run both systems together, or will a Noritz tankless unit (the hydronic heat unit NH-2001 DV) do it? Boilers are heavier and double the cost of the Noritz unit, but they claim 93% efficiency (because of condensing, I'm assuming), compared to the non-condensing Noritz's 83%. Does this make a difference in monthly gas use in the real world? Thank you for any help you can give me.
A condensing boiler with an indirect would be far more efficient and you'd have one unit to maintain.
How many BTUs was the original 80 gallon water heater? Heatloss calculations are typically overstated - for instance mine was 57K net and yet it is only 37K gross at design based based on clocking.
I think that you'll have to isolate the CPVC loops with a heat exchanger because I don't think that CPVC has an form of oxygen barrier. You'll need a SS pump on the CPVC side.
Tags: noritz, tankless, weil, mclain, boiler, condensing boiler, heat loss, hydronic heat, indirect tank, tankless unit, water heater
