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Proper boiler sizing and equipment

I have been reading through many of the threads here to try to form an opinion on a new system as a homeowner, and I need some help. In short, I have a 30+ year old oil boiler with indirect hot water that I want to replace. The house, located in Rhode Island, has about 3,500 sq/ft on the first two floors with about 500 sq/ft finished in the basement. It currently has an Axeman-Anderson that's labeled at 200k BTU, with 6 zones plus one for HW. I have talked to three contractors about a new system, and here's what I am getting:

1) An independent contractor - replace with a Pensotti DK2-8 (222k BTU DOE) - this contractor visited the house and measured the baseboards on one floor
2) Service company my oil delivery company recommends - replace with a Biasi B10-7 (193k BTU) and a HeatFlo HF-40 indirect
3) Largest company came and is doing a heat loss calc, but I think will cost 30% more than option 2 - Recommending Viessmann V-100 series

I did a quick heat loss calculation and I am coming up with just under 100k BTU. This seems low to me, but I understand that it is normal for it to be much lower than what was originally placed in houses decades ago.

I like the idea of a triple pass boiler, and potentially a ODR. My goal is greater efficiency, a reliable system, and a good servicing company.

My questions:
1) Based on my general sizing stats, am I right that a 200k BTU boiler is way oversized? Is it possible that it actually would be better sized with something in the 100k range?
2) Any equipment recommendations? From this site, I see a lot about Viessmann controls being expensive, but they're good. I don't see much about Pensotti or Biasi. Is there an indirect tank that will last longer than others?

Any help or guidance you can provide is appreciated. Thanks!


  • JellisJellis Posts: 121Member
    You need a proper heat loss calculation for sure. Measuring baseboard in one room is a joke.
    to do an accurate heat loss you need to know things like
    window area, door area, wall area,
    have a rough idea of the type of insulation in the home
    include information about which direction your windows, doors and walls face.
    Sounds like the first guy did the "replace it with whats there and add a little to be safe" method

    200K certainly seems overkill based on what you are describing.
    I would seek more quotes.
  • heatingnewbieheatingnewbie Posts: 9Member
    Thanks for the input, @Jellis

    I just spoke with contractor #2. He said they did a quick heat loss when they came here for the first service visit and came up with about 100k BTU. That matches what I calculated. The reason they want to do the Biasi B10-7 (I was wrong, Net IBR is 168k) is that adding the hot water requirement increases the BTU demand significantly. I asked about making the hot water zone a priority zone, but he said they don't like to do that because of issues they've seen in the field ("have hot water but no heat" complaints).

    My question is: if the house has a 100k BTU heat loss and the system is also delivering HW through an indirect tank, what should the BTU of the boiler be (and do we use heating capacity or Net IBR for the boiler rating to match to heat loss calc.)?
  • JellisJellis Posts: 121Member
    adding 68K btu for a indirect sounds pretty ridiculous to me.
    I like using the priority feature for indirect tanks, unless you have excessive hot water demand the tank should only call for heat a few times a day with basic usage and satisfy itself in minutes.
    think of it this way.
    Your boiler is designed to heat your home on coldest day of the year. i think the design temp in RI is 10' F. So any day the temp is above 10' your boiler will be technically "over sized"
    So ask yourself
    Would you rather have your house get a little chilly (your room may fall a few degrees below set point) a couple times a year, because it has to satisfy your hot water demand before your heat?
    Or would you rather have your system over sized on every day of the year that is above 10'F?

    Its a matter of trading efficiency for comfort.
    If it were me. I would go with a unit more appropriate for the heat loss and enjoy its payback in efficiency and long life. I would add a secondary heat source in common rooms to take the edge off on a cold day.
    Not much better than sitting next to a fire on a colder than average winter day :)
  • heatingnewbieheatingnewbie Posts: 9Member
    Maybe I am asking for the best of both worlds. I don't want to add secondary heat sources in common areas (minus the fireplace that's already there), but I do want a system that is sized appropriately and can handle the demands of a cold New England night. The 100k figure was sized at a 0 degree outside temp, a 70 degree difference from inside to out. So two remaining questions.

    1) What size would you should for if the heat loss is 100k BTU and you will have indirect hot water.
    2) What is the BTU factor used for sizing? Heating output/gross or net IBR?

    A bit more background, we have two showers in the house, a normal bathtub that is 1/3 filled nightly for little kids that will be teenagers in the age of this system, a dishwasher and a washer machine.

    Thanks for the help!
  • SuperTechSuperTech Posts: 938Member
    edited February 11
    I would definitely consider Energy Kinetics boilers if you are burning oil. High efficiency, very easy to service, clean and quiet. DHW production is very efficient, utilises a plate heat exchanger and storage tank. I've seen a cold tank satisfied to a 140 degree setting very quickly, and I've never got a complaint about running out of hot water. Not everyone offers Energy Kinetics and when you do get an estimate it's unlikely to be the least expensive, but you will have a quality boiler made in the states by a company that stands by their products, I have seen them come to the aid of just about every homeowner who post a question on here regarding their EK boiler.

    Whatever you do make sure the equipment is properly sized. You can't tell anything by measuring a couple baseboards! Try the find a contractor tool available on the homepage or keep getting estimates, just make sure they do the heat loss calculation before they start talking about boiler options.
  • Jamie HallJamie Hall Posts: 10,548Member
    To answer the question on system sizing. Consider how rarely and for how long you will be asking for hot water (that 68K load) vs. how long and how often you will be asking your system for close to maximum heat output. Think of it this way: that design heating load of 100K BTUh refers to the maybe half a dozen times in a year that the temperature does drop to zero -- late at night. Are you really going to be asking for hot water for more than a few minutes at that moment? And if there is hot water in the storage tank -- the indirect -- mightn't that suffice?

    In my view, while you can't totally ignore the domestic hot water load which you use an indirect, neither do you have to add more than a small fraction of it to the output of the boiler.

    On which number to use for output -- net IBR. That number reflects what you'll get out of the thing, which is what you're interested in.

    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
  • heatingnewbieheatingnewbie Posts: 9Member
    edited February 12
    @SuperTech - Thanks for the advice on EK. My main concerns with that that type of system are it being installed properly, parts availability for repair (I understand not all are as commonly carried with service tech, which could mean 24-48+ hours without heat if a part needs to be overnighted), and the cost appears to be 2-3x for the materials (I assume that it will be $k more). Not in EK's favor, I filled out the form for more info on their website and was contacted by a local company that gets an amazing 1.8/5 stars on yelp, so I gave up.

    @Jamie Hall - Thank you for the direct answers - I like your logic on the demand. Let's say it's 10 times a year that the temp drops before 0. The hot water demand would be nothing overnight, and with everything I am talking about the system would still have excess BTUs (the step down from 168 is 139, the next is 110 which may be too tight for my comfort).
  • SuperTechSuperTech Posts: 938Member
    If not EK than definitely explore options for three pass boilers. I'd use primary secondary piping or a hydro separator. Consider a three way valve like the Taco I series, it's operated by outdoor reset. Or perhaps an injection pumping setup. Both do the job for providing boiler protection against flue gas condensation and thermal shock. Check out your options on circulator pumps. Depending on your application a delta P pump like the viridian 1816 or the Alpha 2 works well with zone valves. The viridian 2218 is a great pump for many applications and works well for injection pumping if you don't want to spend the money on a Tekmar control.

    Anyhow right now your best option sounds like the guy offering the Viessmann. The extra money is well worth it if the company does a high quality installation and provides good service afterwards.
  • heatingnewbieheatingnewbie Posts: 9Member
    @SuperTech - Thanks for the information. I will have to research what you mention. All of the boilers that I mentioned above are 3 pass, so I am gaining that efficiency. You mention that Viessmann is worth the extra money - why? Does it last longer? Is it more efficient? I understand there's a bit of a premium to go to Viessmann over Biasi, and I am trying to figure out if it's worth paying for that when the contractor is used to Biasi (and gets it at a better price). I am fine to spend more money, but only if there's value added.
  • SuperTechSuperTech Posts: 938Member
    What made that quote the best option wasn't the fact that he chose to use Viessmann, it was the fact that he was the only one who did it right and made sure to do a proper heat loss. This makes me believe that they are also likely to do the best install. And Viessmann makes a fine boiler. I'd look into this company and find out if they have a good reputation for service. If you can get a top shelf boiler installed and maintained expertly it's worth the extra money up front, the payoff will come in years of trouble free and efficient use.
  • EmisivityEmisivity Posts: 5Member
    You can do a heat load calc by using It is free, will give you the base BTU requirements by room if you take the time (then you can measure rads to see if they are sized to meet the demand for the room) and it will give you a good idea of how to size your boiler for real. Rule of thumb is 1.5 times the demand.

    But you should pay attention to what is written above. Heat load calculations assume that the heating demand is equivalent to 99% of the time, at night, with no equipment on, and effectively no one home generating heat. Heat calcs are designed to supply heat under the worst possible conditions with no one home for 99% of the time then increased in size by half.

    I just looked up what outside temperature that meets in Rhode Island (ACCA Manual J Table 1A) and the result is 10 degree F for Providence and 9 for Newport. That means that 99% of the time it does not get colder than 9 or 10 degrees F. Looking at county wide data for Rhode Island there is not a county that has a 99% Heating lower than 9 degree F. That you are sizing to 0 degree F means that you will be paying a good deal of money up front for those degrees from 0 to 9. Your total BTU needs will come out much lower if you are not trying to heat down to 0 degrees. Even if you decide to size to 5 degrees you will save on total BTUs. My jurisdiction requires an explanation as to why I would install a system sized for non 99% conditions. YMMV.

  • heatingnewbieheatingnewbie Posts: 9Member
    @SuperTech - I totally missed that you tied the Viessmann recommendation with the installer that is doing the heat calc. That makes sense. I am still waiting for the quote from him. Hope to see that in the next few days. The Biasi contractor is the person I just started using for service (have only owned house for 3 months). I called them to ask for a quote and knew they had taken photos of the current boiler with sizing, but they actually did a heat calc after the first service assuming I would eventually change it out.

    @Emisivity - I will have to look at the difference in calculations. I did mine at 9 degrees, and they did theirs at 0. We were only a few thousand BTUs apart, in the 90-100k ballpark. With an indirect water heater, do you still choose the boiler with the closest output to heat calc.?

    It's really interesting that the current boiler is 200k BTU. I have been in the basement a lot recently and I never hear it on for more than a few minutes, which matches to what everyone is saying here. With the oversized boiler, one of the check valves on a zone being stuck open and a bad thermostatic mixing valve creating variable shower temps, I am excited to get the new boiler installed (and save a few hundred dollars a month).
  • Robert O'BrienRobert O'Brien Posts: 3,130Member
    I'd do the heat loss again. Even 100k seems excessive. How much oil do you use annually?
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • heatingnewbieheatingnewbie Posts: 9Member
    @Robert O'Brien - I have only been in the house since November, so I don't know the annual run rate yet. I have had oil bills of about $900-$1000 a month at $2.40 a gallon, which is excessive. I can take more time to do an exact heat loss. The frustrating part is finding a contractor that is willing to install a smaller boiler and not demand I sign a waiver. I don't care about the waiver, but for service issues I don't want the default answer to be that I undersized my boiler. I assume anyone having me sign a waiver would first go to "you have the wrong boiler," so I will have to find the right contractor.
  • RogerRoger Posts: 86Member
    Thank you for your comments, @heatingnewbie and all.

    I’d like to address a few of the rumors we sometimes hear about Energy Kinetics products. As a family owned company, we would not sell or support products that would be difficult to service or potentially prevent anyone from having heat while waiting 24 to 48 hours for parts. We have a very large market share of boilers in Alaska, and that is certainly a testament to efficiency and reliability in remote areas with climates that reach -60°F in the winter.
    • Service Support If a service person is having difficulty with any of our boilers or products, have them call us at (800) 323-2066. We're here to help.
    • Can't Get Parts Parts are easy. Nearly all parts are industry standard, and oilheat and most gas systems can be run without the manager or relay board for emergency heat by moving 3 wires. Or use our service board. Here is more information on parts.
      Heating professionals (not just EK dealers) can buy parts direct from a deep inventory stocked in several warehouses and our factory, and they also have direct access to the best tech support in the industry.
    • Will it be properly installed? I think that more than any other boiler manufacturer, we work with and train installation companies and have many of the best heating companies as dealers. We know them, and especially their service people, installers, and management. We have very good relationships with our dealers and they are very responsive. You can be assured that when we recommend a dealer, they will deliver on high quality; in the unlikely event that is not the case, we will help facilitate a speedy resolution.
      We've been in business for 40 years and we've worked with thousands of heating companies - if they install our heating systems, we know they have the professional credentials to do it right.
    • Pricing A rule of heatinghelp is that pricing is never discussed. I'll only say that we have a tremendous record on energy savings and payback vs other options if there is any price premium. This makes our products an easy decision.
    I'm proud of our team of technical support, customer service, and territory managers - they all do an excellent job, and I'm also glad to be part of such an exceptional industry filled with so many professionals that help people stay warm and comfortable every day.

    Thank you, and happy heating!
    Energy Kinetics, Inc.
  • RogerRoger Posts: 86Member
    Just chiming in on sizing methods as that was the basis for this thread...

    We have been using the following calculation method for 40 years; it's based scientifically on degree days. Running a heat loss calculation is certainly a good idea, although I wish more programs/stats/municipalities requiring heat loss calculations would accept this method as it is very simple, quick, and accurate.

    If you're new to the home, you may be able to call the oil company listed on service tags and ask for the prior fuel records and respective degree days to help with sizing and budgeting.

    For oilheat:
    Model EK1 (up to 1 GPH) will be correctly sized for homes that consume up to 2000 gallons of oil per year. Before we had the EK1, we used 2500 gallons per year, so this has a 25% safety factor.

    Model EK2 (up to 1.75 GPH) will be correctly sized for homes that consume up to 3500 gallons of oil per year.

    Model EK3 (up to 3 GPH) will be correctly sized for homes and buildings that consume up to 6000 gallons of oil per year.

    Here's an example in action:
    From this heating degree day site, Providence had 5519 heating degree days from 2/1/2018 through 1/31/2019, and 1084 degree days in January, 2019. So if 375 gallons were used in the same period in January, that would extrapolate to 375 gal x 5519 HDD / 1084 HDD or 1909 gallons per year (a System 2000 EK1 will easily handle this per above). This calculation also includes hot water and it is gallons consumed by a less efficient older system, not the heat loss, so it is a safe estimate to ensure the boiler is not undersized. It's good to make sure the tank is topped off to get an accurate use, of course.

    Further as our boilers with Energy Manager controls have virtually no oversizing penalty, you will get very high efficiency and tremendous hot water output.

    You can also flip the calculation over to estimate design day hourly heat loss. Here's Providence with design day of 10°F (or 55 heating degree days), and standard 140,000 BTU/gallon in heating oil, and 24 hours per day. Heat loss is then 375 gallons / 1084 HDD x 55 HDD on design day x 140,000 BTU/gallon / 24 hours per day for an estimated home energy use of 111,000 BTU/hr. A very safe figure to use for sizing.

    Energy Kinetics, Inc.
  • SuperTechSuperTech Posts: 938Member
    As a service technician I can confirm that Roger is telling the truth. They have great training for technicians and offer the best support that I've seen from any manufacturer.
  • heatingnewbieheatingnewbie Posts: 9Member
    Thanks @Roger! For what it's worth (maybe others looking at this thread in the future), I received a follow-up call (from my online info request a week ago) from EK earlier today. Assuming they do that for each info request, that's a nice personal touch this is hopefully indicative of the service and support the manufacturer provides. I am definitely taking a second look at their system.
  • RogerRoger Posts: 86Member
    You're welcome, @heatingnewbie - and thank you for taking a second look at EK! We do try to reach back out where we have responded to a request and we don't know the outcome. As a family owned company, we encourage anyone who needs help to reach out to us.
    Energy Kinetics, Inc.
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