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Seeking advice for high efficiency boiler/hot water tank replacement

pmo
pmo Member Posts: 2
Hello, we are looking into replacing our electric hot water tank and separate standard boiler (both 20+ years old) with a high-efficiency boiler that can do both home heat and hot water. For background, my house is 3 stories, 100 years old, and approx. 3300 sq. feet. Our gas bill on the budget plan has ranged from $180-$260/month since we moved in 3 years ago, depending on the severity of winter. We are a family of 6 with 5 bedrooms and 2.5 bathrooms (full baths on 2nd and 3rd floors) and plans to add an additional bathroom on the second floor in the next year or 2.
I got 2 quotes, and one of the businesses proposed two different options- so a total of 3 options. Without any understanding of how these systems work, I am seeking advice as to which system would be best for our situation (and not necessarily a technical explanation of them- I'm not sure my non-technical brain can grasp much!)
The cost is acceptable for all options, so really what I want is just information to help me make the smartest choice for fuel savings, adequate hot water (currently we have to space out our showers/laundry/etc. or we run out of hot water), reliability of the system, etc.
One more bit of info: We originally were just going to replace our electric hot water tank with a tankless water heater since our boiler is currently working fine, but when we had a different service provider come give an estimate on that, he suggested this whole two birds with one stone approach since our boiler is old/expensive and we plan to stay in this house for at least the next 10 years. His company doesn't install boilers so he referred us to couple who do, but in telling me in general terms about the options, he advised against getting a system with a hot water coil-- (I don't know what his reasoning was) which turns out to be one of the options we were given.

All that said, the options presented to us are:

1. Burnham K2 95% gas boiler with an Alliance 30LT gallon indirect hot water tank;

2. Bosch Combi KWB42-3 combo boiler, 94% efficiency with hot water supplied by a 4.0 GPM domestic hot water coil inside the boiler

3. Weil-Mccain Ultra 155 series 4 gas boiler 94% efficiency with Mega Stor II 40 gallon stainless steel indirect water heater.

Thank you for any insights you can provide!

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 15,350
    edited April 2020
    Before I even begin to comment on the best way to go...

    Did either of the folks who quoted you a boiler do a heat loss evaluation of the house? It's very easy to do -- there are several good applications on the web for it (I like Slant/Fins, but there are others).

    Point is that if you are looking to go to a high efficiency boiler, and actually expect it to be able to run at high efficiency, it must be sized to match the heat loss of the house. No options on that. Granted, a really experienced individual can get pretty close by eye -- but he or she will run the heat loss calculation every time.

    That out of the way... I'd go an indirect. Which one? Well, I don't know if either of them are correctly sized. With three bathrooms, you are going to be very close to if not over the capacity of the combi (three showers at 1.5 gpm each is 4.5 gpm...) at times. As to which brand, the installer is more important than the brand (they are both good units).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • pmo
    pmo Member Posts: 2
    Thank you! One of them measured all our hot water radiators and then came back and took additional measurements outside the house. I’m not sure what that was all about, to be honest. I’m not sure if the other did any evaluations, but I will ask them how they determined what size unit we needed.
    I will also check out the app you mentioned to do my own heat loss calculation.
  • STEVEusaPA
    STEVEusaPA Member Posts: 4,813
    Heat Loss, Energy Kinetics.
    steve
    szwedj
  • Jamie Hall
    Jamie Hall Member Posts: 15,350
    pmo said:

    Thank you! One of them measured all our hot water radiators and then came back and took additional measurements outside the house. I’m not sure what that was all about, to be honest. I’m not sure if the other did any evaluations, but I will ask them how they determined what size unit we needed.

    I will also check out the app you mentioned to do my own heat loss calculation.

    Measuring the radiators does figure in to what efficiencies can be achieved. It is not part of a heat loss calculation, however.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Brewbeer
    Brewbeer Member Posts: 612
    Definitely perform both the heatloss and radiator survey, room by room. If the radiators aren't big enough, a condensing boiler won't condense, and won't achieve 94-95% efficiency.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • hot_rod
    hot_rod Member Posts: 14,552
    this could be a helpful app for doing a radiator survey
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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