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boiler sizing

kerry3578
kerry3578 Member Posts: 15
The contractors tell me the mod con boiler ranges from 35000 btu to 120000 btu and the boiler will only use the btu it calls for. They said that will be efficient for my house. I still haven't had a heat loss calc done. What if I don't need the max btu and I can get a smaller boiler which of course will be cheaper in price. I'm having trouble finding a contractor who does heat loss.
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Comments

  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I'm having trouble finding a contractor who does heat loss.

    As a homeowner with a mod-con, let me say that if a contractor will not do a heat loss, he is unqualified to design a heating system for you, and not even qualified to select which boiler you should use.



    "The contractors tell me the mod con boiler ranges from 35000 btu to

    120000 btu and the boiler will only use the btu it calls for."



    My former contractor told me the same kind of thing. He recommended a 105,000 BTU/hr mod-con. The way he did a heat loss was to walk across the front of my house and one side, counting his paces. Meanwhile, I got interested in hydronic heating and read John Siegenthaler's book



    http://www.heatinghelp.com/products/Hot-Water-Heating-Books/26/96/Modern-Hydronic-Heating-Third-Edition-br-by-John-Siegenthaler



    and figured out my heat loss three different ways. The first was to look at my old oil boiler (the new one was to be gas) and it had a 0.5 gpm nozzle, so 70,000 BTU/hour was the most I could possibly need, since I always got enough heat.

    Next, I used some worksheets by the manufacturer of the boiler I was going to get, and got 35,000 BTU/hour or something like that. Third, I used the calculator from Slant/Fin and got 30,000 BTU/hour. So I refused the 105,000 BTU/hr model and got the 80,000 BTU/hr model (the smallest in the product line). The contractor said that the larger one was for safety, that it would modulate down to 30,000 BTU/hour. While that is true, what he did not say (and I think he did not understand) was that that meant it would work correctly only on design day or colder, and the rest of the mime (97.5% of the time) it would be oversized. As it is, my boiler is about double the size I need, so it drops off the bottom of the modulation curve when only a small zone is calling for heat on warm days. This results on excessive cycling that I do not like. I figured out how to get around that, but you should not put up with that.



    Get a contractor who knows hydronic heating. If he does not do a heat loss, he does not know what he is doing.
  • rusty pipes_2
    rusty pipes_2 Member Posts: 9
    edited February 2012
    sizing made easy

    Check out the Slant Fin web site.  There is no reason you cannot do the heat loss calcs yourself using their guide.  And, google "heat loss calcs" and you will find other places also.

    Remember, that you do not have to be exact.  Whatever number you calculate should be multiplied by 1.2 anyway, and then buy a boiler next size over this number.  You will ALWAYS be conservative this way.  

    Allot of comments on wasting energy have been made, and allot about inefficiencies have been made.  I never want a customer to be cold.  And while efficiencies are all valid, the inefficiency of construction just cannot be underestimated.  If I put in a boiler that only runs 50%of the time on a design degree day, then I know the energy uses are right for comfort of my customer.  If he is cold for 3 weeks of the year because of losses that I did not account for, then I have lost a customer.  You guys that talk about minimum sizing for boilers .... think again.
  • kcopp
    kcopp Member Posts: 3,820
    You are kidding......

    right?  "1.2 over the heatloss and then go the next size up...." That sounds more like guessing. There are many who think the the IBR numbers have fluff in them as they are.
  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
    I certainly believe

    the IBR numbers are overinflated . I have my boiler burning very close to my design day number ( Slant Fin heatloss software )  and ran only 7 hours on a true design day . Including showers and dish washing .



    Actually design day is supposed to be 15 degrees around here . I factored mine at 0 so the numbers are even more out of whack !



    Go with the boiler that matches up with your heatloss . Smaller is better !  If you're using an indirect for hot water make sure you upsize the tank to cover all the hot water demand .

     
  • CMadatMe
    CMadatMe Member Posts: 3,085
    Might As Well

    Walk out to the front yard, face the house and use the finger trick with those numbers. Heat loss, heat loss, heat loss and trust the math it never lies. My home has 2200 sqft of heating space and my heat loss is 36,000 in a 5 degree climate. Home has updated windows, R30 in the attic but only R11 in the walls. 700 sqft is also a finished basement 4' below grade.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    edited February 2012
    They are ALL oversized...

    In fact, I have yet to see a system of my own design, based on my own tight heat loss calculations that has run for more than 50% of the time at design conditions. That tells me that they physical plant is 2 times BIGGER than what is necessary.



    With that said, no contractor in their right mind would take the numbers generated by a loss calc and cut them by half and run with that,,, But they should ;-)



    I did that in my own home, and it works just fine.



    I wouldn't increase it by 1.2 or 1. anything, and THEN go with the next bigger size appliance. That would be a MAJOR waste of money and energy.



    Unfortunately, there is not a loss calc in existence (that I am aware of) that takes all of the real world things into consideration, like internal gains, solar gains, body gains, flywheel mass effect etc, and these are the real things that influence heat loss/gain. Fortunately, a properly sized modulating appliance, if not grossly oversized, can "right size" itself to the actual load.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • icesailor
    icesailor Member Posts: 7,265
    Boiler Sizing:

    M,

    Everything you say is absolutely true when sizing a hydronic boiler for a heat loss load.

    However, all that is junk when you add domestic potable water to the mix. Potable water heater load can be double or triple the heating load.

    Take that 30,000 BTU design load, and try putting that to someone in the shower, washing their hair.

    My hot water experience comes from oil and tankless heaters. Gas never used tankless heaters. All the boilers were well over 100,000 BTU's. The bigger the boiler, the better the tankless worked. With the downsizing of boilers and inputs, the hot water performance dropped. Hence, storage tanks. A good band-aid.

    Many heaters have no idea of the concept that the domestic water heating load is there 24/7/24/60. And the potential to be needed at any time.

    Maximum heating load may not even be achieved in a given year and then, only for a day or so. You can always put on a coat, and with multiple zones, turn down the heat in zones and you increase the size of the boiler. Get in a shower with the hot water coming at 116 degrees and the water in the head at 108 degrees. Have the incoming hot water drop to 90 degrees, and you have a cold shower. No amount of fiddling is going to get it back up until you turn off the water get out of the shower. Any and every hour of any day, week, month and year.

    Too many have it burned in their hard drives to instinctively step over a ten dollar bill to get to the dime. Leave domestic hot water out of the calculation at your own peril.
  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
    Size a boiler to hot water demand ?

    A few things you didn't consider ................



    There is no oil fired boiler that'll burn at 30k . Mine is running around 60 k and we have a TON of hot water demand . Haven't run out of hot water yet with my little 20 gallon Superstor indirect . No priority and the temp is set at 120 . We install alot of oil boilers that run in the 75K range . 50 gal indirect is the norm when we use them . Haven't heard of any issues with this setup in homes with 2 or more baths and lots of family members . Just replaced a Weil Plus 30 connected to a Weil 3 section . Customer had 3 teenage daughters and said they never ran out of hot water either . 



    And also don't forget gas boilers that can burn at 30K also modulate up .



    I just don't see any reason to upsize an oil boiler for hot water demand . How big can a house with a 30 k heatloss be ( unless it's a supertight home ) ? How many baths can it have ?
  • KCA_2
    KCA_2 Member Posts: 305
    If you size it to big...

    The boiler will cycle.....  On for a few minutes...  Off for a minute or two...  The 90% boiler turns into a 50% boiler at sea level.....  I like to undersize....  Let the thing work for a living...  I do...  Lol... 

    My home is 5200sqft and I have a JVS160 Laars Boiler that also runs a 40gal indirect...  Never cold and never run out of hot water....  I'm a 4.5 on the BTU/sqft/deg day equation with regard to what I use.... I'd have been better but 15 years ago I didn't put in as much radiant tubing in the floor...  Darnit!



    :-)  KCA
    :-) Ken
  • icesailor
    icesailor Member Posts: 7,265
    Understanding:

    I wasn't comparing oil to gas. It was a "given" that the boiler in question was a gas boiler. And that the possible installers were using faulty ideas to size the boilers.

    I didn't say intentionally that your temperature and control strategy wouldn't work. But if it didn't, this is why.

    I just installed a Vitodens 100 26. The load in the house was no more than 40,000 at best. But everything was an outside wall and ceilings and one big room with cathedral ceilings with lights. It had one bedroom. I wanted to use a 30 gallon SuperStor. The owner told me her two sons took long showers. Enough to regularly start a fight over running an 80 gallon electric heater running 135 degree water, out. She insisted I use a 60 gallon SuperStor. It's stored hot water plus how much the boiler can recover in the amount of time in use.

    I do the plumbing and heating in a 44 bed nursing home that does their own food services and laundry. They have two Bock 73E oil fired water heaters to provide all the hot water to the building. These Bock heaters recover 220 gallons per hour at 100 degree rise, 440 degrees per hour. They would run out in an instant unless they share the loads until I took the two whirlpool tubs off the hot water load and fed them with Noritz instantaneous water heaters. They had to run 116 degree water through the building but 160 degree water in the kitchen and laundry. They still need to share the loads and the water heater inputs are close to the inputs of the heating boilers.

    The heat is supplied by three Weil-Mclain WGO-7's. with lead-lag and outdoor reset. The boilers do not run from June until September or October. The building maintained heat below zero degrees with 35 MPH winds. But the kitchen will make the system crash if they try to fill a 3-bay pot sink at 7:00 AM rather than 6:00 AM. The laundry starts at 5:00 AM. They start bathing patients at 8:00 AM. Not spreading out the load will immediately crash the system. 365 days of the year.

    So I ask you, just how do you figure out the additional load on a boiler when you are designing a heating system that will provide potable hot water. When a client calls you about a lack of hot water, you had better be able to come up with innovative solutions or they will be calling someone else. What I say here is from my being the one called and having to come up with innovative solutions to problems left behind by others.

    Like Buffer Tanks on instantaneous gas water heaters. That is a poor solution to a simple problem but effective.

    Just because someone doesn't tell you about a problem, doesn't mean it isn't there. If it is there and you don't fix the problem as the customer expects, they will think you did a rotten job. So, how will you fix it?

    Domestic potable hot water heating should be thought of as another heating zone. How will you address it? Ignore it at your peril.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    no contractor in their right mind

    "no contractor in their right mind would take the numbers generated by a

    loss calc and cut them by half and run with that,,, But they should ;-)"



    Very interesting. I calculated my house would need 30,000 BTU/hr when it is 0F outside. But design temperature around here is 14F, so I surely need less than 30K BTU/hr. Let me take your advice and say I need 15,000 BTU/hour on design day. That is 4.4 Kilowatts. 20 amps at 220 volts. When I got my mod-con and indirect, I had a 20 amp 220 volt electric hot water heater removed. If the thing had an H stamp, I could have used it instead of my mod-con. Now if it also had outdoor reset controls, ... . ;-)
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Residential Loads

    In a house, size the high efficiency the boiler to the heat load of the structure.

    Pay for a heat load to be done if that is what it takes.



    The money spent on a heat load will pay for itself immediately when you discover, as most people do, that the unit they were about to buy, or sadly already bought is twice the size they need.



    A boiler that is 1/2 the size could easily save you 1000 dollars on initial purchase, and over time will serve you much better.



    Find a DHW storage tank that will work with that btu, and set the controls to have domestic priority.



    If the dhw needs can not be met with increased storage capacity, then there needs to be a dedicated heat source for the dhw.



    A lower efficiency boiler can be over sized a bit, as cycling will not destroy the boiler, or ruin the efficiency.



    A high efficiency boiler over sized to meet domestic capacity will cycle like mad in comfort heating mode, and not run efficiently in domestic mode, b/c supply water will be between 180 to 190.
  • SWEI
    SWEI Member Posts: 7,356
    electric

    Is looking more and more like a viable option with modern (tight envelope) buildings of small to moderate size.  We settled on a Thermolec TMB-6 for a guest house after exhausting pretty much every variant of mod/con, gas tank, and tankless we could find and concluded that by the time we added a motorized mixing valve, ORC, pumps, etc. it was just not ever going to work well.



    Highlights:



    TMB (their entry-level line) comes in four sizes ranging from 10,200 to 37,,500 BTU/hr.

    Modulating controls with built-in ORC (primitive, but good enough for our climate.)

    Direct pumped - no primary/secondary needed, simple integration with solar thermal.

    Stainless HX, no oxygen concerns.

    Compact and very affordable.



    I'm looking at them for a low cost development -- if mated with solar thermal they should not have to run much at all here in the southwest.  Adding off-peak storage could make them pencil out for quite a few locations IMO.



    Now if someone made a 50k mod/con with say 8 to 1 turndown...
  • kerry3578
    kerry3578 Member Posts: 15
    Did the heat loss calc

    I downloaded the slantfin heat loss calc and came up with this.  I used 10f as my design temp and put in 160 f. water and it told me my heat loss was 30,236 BTU.   I then changed my design temp to 0 f. at 160f water and it gave me 50469 BTU.  I have a few questions though. My first is I didn't see anything for a basement.  I have a basement and yes I do have 42 ft. of fin and tube running down the middle of the basement along the ceiling.  Is this considered a heated source? Or should it be calculated as wood over an unheated source.  Do we add a basement as a heat loss?  Is there a more accurate heat loss calc or is the slant fin good enough.?  It also told me I would need 114 ft of fin and tube.  I have 110 upstairs and 42 ft in the basement. that was for the 50469 btu calc.
  • Steamhead
    Steamhead Member Posts: 14,838
    Add the basement as you would another floor

    and use the floor and wall factors for below-grade or partially below-grade, as appropriate.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • icesailor
    icesailor Member Posts: 7,265
    Slant-Fin Heat Loss:

    Understand, the heat loss for the structure has nothing to do with temperature of the water in the baseboard. You put a design temperature into the calculation so they can tell you how much Slant-Fin baseboard you need to heat the room. What changes the heat loss number is the outside temperature. The lower the outside temperature, the greater the heat loss, and the more baseboard you need at a given water temperature

    As far as basement heat loss, it is there. Basically, from grade to the floor, you use an average loss of .07, the same as an insulated frame wall. Because the ground will always be warmer than the cold outside air. Then, you tale grade to the sill as a number. I think it is .56.  So, if you have a 8' wall with 2' exposed, you do a wall 6' high and as long as needed and then a 2' wall the same length. Depending on how I feel, I usually use .027 for infiltration . Add it all together and you will think that there isn't enough radiation. I've never had a cold cellar.

    I'll have to go to the Slant-Fin Web Site. I have the Heat Loss Explorer on disk on my computer. I'll need to see if they changed anything.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Chris...

    I hear what you are saying, but I have 2 houses with 50K (sea level) boilers, one with a 40 gallon tank and one with a 60 gallon tank, and I can't exhaust either one of them taking a single shower. Oh sure, we have a standing policy that if someone is in the shower, that no one else is to use hot water, including dish/clothes washers etc.



    DHW is prioritized.



    When talking to the consumer, we as heating contractors MUST find out if there is a load diversity factor as it pertains to DHW, and if the answer is no, then throw additional BTU's at it, but in my personal experience, most families are willing to work around the availability to save money on the initial costs. Kind of like the standing rule of NEVER flushing a toilet while someone is in the shower.



    Your milage may vary...



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • bob eck
    bob eck Member Posts: 928
    Boiler sizing

    I beliebe Dan Holohan said there was a contractor he knew who would do a heat loss and for the second and third zone he would take 10% off the total BTU load for each extra zone but no more than the second and third zone. Any one doing this?
  • kerry3578
    kerry3578 Member Posts: 15
    basement

    I'm trying to understand all of this so if I seam a little slow just give me a second. I appreciate all the help. My main question is do I have to include the basement in the heat loss or just the bond which is the 2 feet above grade from the start of the block wall and floor of upstairs. I don't need to heat my basement at all. It is finished and even in the winter its pretty comfortable. I noticed the calc above. I read in another forum that the basement does not have to be added in the heat loss.
  • kcopp
    kcopp Member Posts: 3,820
    add the basement.....

    in to the area . It is part of the envelope. What is your number then? Then size the boiler off that number.  Don't over think it. People get too caught up in the if and whats and can get lost in the process. I started to do that w/ my own house.... then just went w/ the number and I am fine. I even finished off the 3rd floor and did not figure that into the original m\number.... I'm still fine.
  • kerry3578
    kerry3578 Member Posts: 15
    heat loss on basement

    I have read a few other articles and they say not to calculate the basement in the heat loss.  I also have read to only calculate the bond which is above grade, which is approx 2 ft and has insulation inside of it. I do notice I don't get a straight answer.  I did find the slant fin calc has the basement, I also could separate the heat loss calc between the bond and top plate which is just above grade.  I do have that 42 feet of fin and tube that runs along the ceiling of the basement however it is also connecting to my main bath upstairs. 
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Heat loss in strips...

    or stripes or bands if you will. The below grade wall will still lose heat, but not at the same rate as the fully exposed portion. Do this;



    Calculate the upper exposed portion based on design OSA temperature and normal inside temperature differentials. (assumed to be 70 F inside)



    Take the difference in elevation between the exposed wall and the buried wall and divide by 2. Calculate the lower half with a soil temperature of 40 degrees F OSA temperature and the middle half of the lower third at 20 degrees F OSA temperature. This will get you close enough to be and stay comfortable.



    And don't listen to people that tell you not to do a load calc on the basement. It would not hold water in a court of law...



    And don't forget to allow for infiltration.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • kerry3578
    kerry3578 Member Posts: 15
    basement calculation

    Mark are you saying to do 3 seperate calculations on the basement? Calculate the exposed wood bond that is just below the floor and top of basement foundation. Then divide the basement foundation by 2. So that means the top of the foundation to the middle and that's the second calculation. Use 40 f for outside temp. What is the inside temp used? Basement doesn't reach 70 f. Then the last section of the wall would be calculated using 20 f. And again what inside temp is to be used? Is this what you meant? I do appreciate the help.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    In door temp depends...

    If you EVER think it will be used as an occasional occupied space then use 70 degrees F.



    If it will ALWAYS only be storage, then use 60 degrees as your indoor design temp.



    Better safe than sorry. I'd use 70,because you never know what the next owner is going to do with this space.



    Do 3 strips. One for the upper exposed portion (average R values), and two for the balance of the basement foundation wall. The lower portion would be the 40 degree OSA (ground temp constant) and the upper portion would be the 20 (more surface influence on the soil temperatures).



    Don't get too nit picky, because there are a LOT of things that your loss calcs don't take into consideration that ARE in your favor. This is just a tool to get you close, and it is not (obviously) an exacting science.





    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • kerry3578
    kerry3578 Member Posts: 15
    boiler output size

    What do we use for the boiler output the DOE. Or the IBR?
  • kcopp
    kcopp Member Posts: 3,820
    IBR...

    the smaller number. Again another reason to not oversize... and to not get too crazy getting it perfect.
  • icesailor
    icesailor Member Posts: 7,265
    Indirect Sizing:

    ME,

    I just realized that I didn't respond to this to you.

    My choice for this installation would have been a 30, and hope to stretch it to a 40. The customer demanded the 60 gallon. I consider the 60 gallon to be over-sized. But the customer is correct. Explain that they don't need that one (did that) and if they insist, give them what they want and are willing to pay for. She got what she wanted.
  • kerry3578
    kerry3578 Member Posts: 15
    heat loss completed

    Mark I did what you told me and broke it down to 3 different calculations.  the upper basement which is above grade with windows is 2 feet.  at 5f was 11439 btu, the middle basement which is 2ft 11inches at 40f was 638 btu and the bottom basement which was another 2ft 11inches at 20 f was 4141 btu heat loss.  70f inside temp was used. total 16218btu. The main floor was a total of 52655 for a grand total of 68873 btu of heat loss.  I used the slant fin program.  I'm looking at the slant fin lynx lx90  which is 90,000 btu input and doe of 80,000 btu and ibr 70,000 btu.  will this boiler work???  I am also looking at the bobcat which is 120,000 btu and has a doe of 109,000btu and ibr of 95,000 btu.  which one to choose....??? 
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Use

    The doe output capacity.



    The IBR institute rating de-rates the boiler by assuming losses for piping in the structure. This is a clever way to sell the next size larger and more expensive boiler.



    IBR = Institute of boiler and radiator manufactures.



    I never use IBR ratings to select a boiler. I only use DOE output. If I have a pickup load, I factor that in myself. But in the hot water world, it is irrelevant.



    If you find the load of your house is on the boiler between a boiler that's just shy of the load vs one that's overshooting the needs by more than a couple thousand btu, go with the slight undersize.
  • icesailor
    icesailor Member Posts: 7,265
    IBR vs DOE

    Maybe I misunderstand what IBR and U of Illinois said about the boiler sizing's in their courses. You were supposed to calculate ALL the piping, fittings, and any place that caused heat loss in the system. As I remember, it is called "piping and Pich-up". Once you calculated this mind numbing figure, you subtracted it from the gross output of the boiler. That gave you the NET output. As I remember, IBR and Uof Illinois did these calculations and decided that you could use a rule of thumb of subtracting 15% from the Gross output as a rule of thumb unless you had "unusual situations" in which case, use a higher percentage and de-rate the boiler more.

    So, according to IBR, if you do a heat loss calculation and do a pipping layout, if you use the IBR , normal allowances for piping and pick up are allowed. Gross boiler and DOE outlet is for just what the boiler, standing in a field, connected to nothing is that rating. The IBR rating is to a connected load.

    Someone can tell me that my premise is wrong. I'm still sticking with using the IBR rating.
  • bob eck
    bob eck Member Posts: 928
    Boiler sizing

    Take a look at the Triangle Tube Prestige Solo PS110 boiler only or PE110 boiler with built in stainless steel indirect water heater that delivers 180 GPH of domestic hot water. www.triangletube.com they use a stainless steel heat exchanger and have this design out about 10 years. They have a great new control that will run the primary pump plus two heating zone pumps plus a pump for the indirect water heater. Real easy to set up the outdoor reset control curve. Please check it out and ask your professional heating contractor for a price on it.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    edited February 2012
    Response...

    Go with the lesser of the two load calculations (IBR vs DOE). You have a LOT of things going for you, in your favor.



    As for boiler choices, I am not a big fan of any aluminum block boilers. It is a known fact that their block will dissolve over time due to the pH of the condensate. I've seen too many failures in the field compared to stainless steel. I am a big fan of Lochinvar Knight's new fire tube wall hung (WHN) series boilers.



    If this boiler is also going to be doing DHW, you need to make sure you and your family members are aware of the limitations. YOu could upsize it for doing DHW, but that may create problems during marginal calls for heat.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • CMadatMe
    CMadatMe Member Posts: 3,085
    IBR vs DOE

    Boiler in an unconditioned space use IBR, boiler in a conditioned space use DOE. Also should be insulating your boiler piping. I also agree with Mark, stay away from alum block condensing boilers and stick to stainless steel heat exchangers. Seems like this is a very basic system so in my opinion a very basic condensing boiler with simple control package like a Viessmann Vitodens 100 would fit nicely. Lifetime warranty HX.



    http://www.viessmann-us.com/etc/medialib/internet-ca/pdfs/wall-mount.Par.6530.File.File.tmp/Heating_with_Gas.pdf
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • kerry3578
    kerry3578 Member Posts: 15
    stainless steal

    Thanks Chris,  I looked at the viessman vitodens 100 and I believe with my btu loss calculation, I would use the 26 which is 91,000 input and 83,000 output.  I will research some more for stainless steel.  I will do some research on the aluminum heat exchangers. 
  • Jason_13
    Jason_13 Member Posts: 299
    What a cluster F............

    How can we ever expect our customers to ever trust anyone in our industry when so called professionals can't agree on something like heat loss! This makes us look like jerks.

    I have been doing heat losses for 20+ years always sized off DOE especially if there were multiple zones. Never tore a boiler out for being undersized but i did save people tons of money through the years. If an emergency came up and I did not do the heat loss I never size a boiler larger than the connected load. If the connected load was between two boiler sizes I usually dropped to the smaller boiler.

    When there is DHW involved the tanks are oversized as much as boilers are usually. Calculate the DHW needs and apply the math.
  • kerry3578
    kerry3578 Member Posts: 15
    boiler size

    My heat loss calculation came out to 68,337 btu with a 0 f outdoor temp.  I also used 5 f temp which was from the 2011 manual j for design temp in my location and my heat loss was 63799 btu.  I'm looking a boiler with 90,000 btu input, a 80,000 btu doe output and a 70,000 btu ibr output.  it looks like this boiler will work.  the next size up boiler I had in mind was 120,000 input, 109,000 doe and 95,000 ibr.  My current boiler is 150,000 btu input, 124,000 doe and I think 109,000 ibr.   what are your thoughts?
  • kerry3578
    kerry3578 Member Posts: 15
    Aluminum heat exchanger

    I did some research and the slant fin manual states the ph balance should be maintained at 7.5-8.5 ph with a water hardness lower than 7 grains/gallon. See for me I have a well and I'm a nut when it comes to my water being right.  I tested my ph and its at 8.0 ph and my water is soft.  According to slant fin their heat exchanger is non corrosive and they back it.  I also looked at a few boiler company manuals with ss heat exchanger and they recommend soft water one of them also recommended maintaining a ph balance.
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    boiler size

    Use the doe output as the basis. and size as close as possible to the 63,000 btu.



    If you find a boiler with a 60,000 btu output use that. You will not notice the difference.





    Piping insulated or not is not a heat loss, unless the piping is outside the structure being heated, or in the attic. If the piping is in the floors, walls, or basement, that heat radiated from the piping aids in limiting the heat of the structure that is lost to the outdoors. The heat radiated off piping goes into the structure. Energy does not just disappear.



    Pick up load is not really a factor for hot water boilers, just steam boilers.





    Besides that how often do we see design outdoor temperatures? Not very, and when we do, that don't last long.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    how often do we see design outdoor temperatures?

    I became interested in this when I got my new mod-con boiler. I have an indoor-outdoor thermometer that keeps track of the hottest and coldest it has been since I last reset it. I reset it each year on September 1. The sensor is always in the shade, about 6" below the eave of the roof on the east side of the house. Design temperature around here is 14F. So far, since September 1, 2011, the coldest it has been is 12.7F and the hottest was 91.6F. That coldest was at night when I was asleep and by 7AM it was warmer already. Statistically, it should be less than 14F here 2.5% of the days. If the heating season is 180 days, that means 4.5 days.



    It did heat a little in September, and the year before, it heated at least a little until about June. I am not sure how to count that. If I did not have my boiler on all the time, I would probably have turned it off May 1 and not turned it on until October or possibly November, depending on just how cold it was outside.



    If that is true, it has been warmer than that because I have noticed "really cold" (because I used to live in Buffalo, NY) only about two to three days each year and by no means was it that cold for an entire day. In the last three years, the coldest I remember was between 9F and 10F, and that night I was asleep. It was not that cold in the daytime. My recollection was that two years ago was the coldest, last year was next, and this year was the warmest. I have not even had to shovel snow this year. This does not prove global warming, but it does tend to induce belief.



    Since my downstairs is heated by an on-grade radiant concrete slab with copper tubing in it, a change in the outdoor temperature below design temperature of an hour or two would make no difference; the thermal mass of the slab would coast right over that.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I did some research

    I seem  to be doing research on an aluminum heat exchanger. I had not thought of it as a research project when I bought it.



    It seems to me that choosing my boiler with wonderful controls and an aluminum heat exchanger vs. another boiler with different controls and a stainless steel heat exchanger and what for me is a lesser control system is an interesting exercise in priorities when I do not have all the data I require to make such a decision.



    It is certainly true that my aluminum heat exchanger has lasted almost three years. That is too little to prove anything. The manufacturer of the boiler specifies that I use Sentinel X-100  in it, which I do. It specifies that my water be pH 7.0 to 8.5, and the water company says it is between 7.2 and 7.6. I have a pH meter that says it about what the water company says. The manufacturer says the hardness should be less than 7 grains and the water company says it is less than 6 grains. The manufacturer says the Chlorine must be less than 200 ppm, and the water company says it is always less than 2 ppm, and usually around 1 ppm. I check the pH in the summer each year. The new contractor checks the Sentinel X-100 concentration just before each heating season starts.



    My new contractor dumped the "water" out of the condensate trap and had it analyzed for aluminum. There was "a little" in it the first year, but not since. It does not look especially difficult to replace a heat exchanger, other than paying for one. My impression, as a non-professional, is that it should only take two or three hours labor, and my guess is that the labor is less then the cost of a new heat exchanger.
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