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Boiler sizing?

Boilerpro_5 Member Posts: 407
Analyze the homes fuel bills and calculate the BTU /hr input at the average monthly temp. Then correct for changes in efficiency and multiple out to design day. Just tell the homeowner, if you weren't using those btu's why install a bigger unit than necessary. I find this to be the most accurate way of calculating heatloss, if done carefully.


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  • Tom Hopkins
    Tom Hopkins Member Posts: 554

    I've seen two undersized hot water boilers in my life and one of those was so close it didn't matter.On the other hand I've seen 1000's of oversized boilers,2X or 3X is common.
    I constantly struggle with convincing HO's to go with a properly sized unit. They refuse to believe that a 60K BTU unit will do the job when they have a 140K presently and every other Contractor has a proposed a 140K new boiler.Even when presented with a printed heat loss it's hard to convince them.
    How do you overcome this hurdle?

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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    I can think of many reasons--most of them poor...

    1) It seems to be human nature in general and American nature in particular to believe that "bigger is better".

    2) Many people are nearly clueless regarding the nature of the mechanical components of their home yet at the same time are highly distrustful of "professionals". They'll trust the existing boiler because it gives all the heat they need but can't understand that a much smaller unit will do the same.

    3) Some may believe they'll "want it hotter" in the future.

    4) Some may think they may add on to the house in the future and oversizing will give them the needed "extra".

    5) Some utterly refuse ANY degree of inconvenience or discomfort in the event of an exceptionally rare occurrence where a properly sized boiler might not meet their expectations--particularly if they're fond of cranking the thermostat.

    6) Thermostat manufacturers (and the government) have drilled setback on a daily if not two or three times daily basis into their heads as a method to reduce energy consumption.

    7) Americans are generally clueless with regards to thermostatic radiator valves (TRVs) and floor heat valves (FHVs) and proportional control. They LOVE on-off zone control--as long as recovery from setback is FAST.

    8) Some could care less about "the numbers"--this leads directly back to problem 1)

  • Big Ed
    Big Ed Member Posts: 1,117
    Sell the Concept First

    Sell the concept first .Then give a est and if you sell the job 'then do the calulations a fine tune the price. Sell yourself and your work before you do any work..When you come back with the proper size and he wants bigger,then put it in. Why argue ?

    Its hard selling yourself measuring windows.And why do all that work if you may not get the job.Why let they run with your work to shop...

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    You're VERY correct Big Ed!!!!

  • ALH_4
    ALH_4 Member Posts: 1,790

    And people fear the unknown. They know the current boiler works and they have accepted the fuel use, so why mess with it? And they wonder what if the new boiler isn't big enough? Could everyone else be wrong and this one guy be right?

    In general, people are very poorly educated about energy. These days, everyone should have some understanding of where our energy comes from and how to use it appropriately and efficiently.
  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
    A little help

    The Department of Energy has recommendations on fiding a heating/ cooling contractor and a BIG, big thing they emphasize is that the homeowner see a copy of the heating load or cooling calculations done according to manual J.

    Take a look for this, it may give you more firepower.


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  • Mitch_4
    Mitch_4 Member Posts: 955
    big time wrestling has

    nothing on convincing a homeowner that bigger is NOT better.

    Just did one, and got it because I showed him numbers, and defined that it already had a fudge factor, in addition I measured his existing baseboard, and showed him flyers that all show 560 - 620 btu's per foot, and that that is ALL his system can deliver, his radiation was a total of 135' of baseboard. So I showed that the MOST he can emit at 180° H2O was 83700, and that the 100k unit would meet that.

    I then explained that installing a 200k unit like others proposed to replace the existing is bad practice, assuming that the existing unit is 55%, then only 110,000 was being delivered, a modern unit would deliver an additional 50,000 of useless energy consumption (@80%) that his system could NOT use!

    Then I explained that while counter intuitive, longer run times are better and CHEAPER than lots of short cycles, because it takes energy to heat that cast iron EVERY time it lites off, BEFORE it can deliver heat, so running once for 30 minutes is better than 5 cycles at 6 minutes each, because I heat all that iron ONCE not 5 x.

    I concluded with something like, so I can cut consumption 50% by using a smaller boiler (that has a higher AFUE than larger models), save additional $$ with longer runtimes, save on the cost of the boiler itself as the 100k is cheaper than a 200k, and well put it towards an ODR, saving even more MONEY in the shoulder seasons, all while still meeting the MAX their distribution system can deliver whether they have 100k, 200k or 400k..the most the system can deliver is ONLY 83,700 (which exceeeded the heat loss by about 20k anyway.

    Lastly I have financing package from the manufacturer I use,and just said it was x$/month..never mind the total cost, they can multiply x 60.

    Psycologically the monthly cost gives me a huge boost. When the competition say 5000.00 they go "Whoa!! big bucks" and I say 100/month for 60 months, they think "I can afford that"

    I never give total cost unless they ask because they have the $$ up front.

    This is the general approach I have been taking because I do charge more, I also write in extended warranty 5/5 parts and labour by manufacturer program included in all quotes and present it a s fait accompli.

    My bid meetings take me about an hour (lots of time for a 1 man op) but I am closing about 90% because I take the time to educate, and explain why the others are not the way to go. To present a heat loss is (I find ) generally meaning less to the average joe. Give em logical data they understand and you win 90% (at least according to my clkosings) of the time.

    I am busy enough to pick and choose, and anyone wanting an over the phone quote is told cannot do, not wont do, CAN"T do, if they insist its a flat 20,000.. they usually freak, but I say.."hey, sight unseen? I am covering ANY possibility, likely less (thanks Dan for the story I borrowed this idea from)(It pays to wander off the wall http://www.heatinghelp.com/newsletter.cfm?Id=182)

    want more exact..then spend the time and 100.00 (credited if I get the job) and well come by..hows next tuesday?

    Took me a long time to learn to sell, but it works..maybe not for you, but find a style, and method that works. I looked at what closed some and not others, what I said that made the light go off, where their eyes glazed over, and used or avoided as I narrowed the pitch.

    Good luck

  • Ken_40
    Ken_40 Member Posts: 1,320
    The OBVIOUS answer!

    The dead men DID know about heat-loads. They also "mis-lead" the dumber dead men. Here's how:

    Most boilers were installed with side arm or tankless coils during the hey-day of wet heat (1930's to 1960). The dead men knew the rule of thumb was to have 100,000 BTU's net output, to make 3-5 GPM's of shower/bath water.

    Boilers were PROPERLY sized based on domestic hot water minimums - NOT heat loads. This, because the greater demand was for domestic, not home heating!

    Over time, domestic hot water was more effectively moved to the realm of the "standard" 40-gallon free standing gas heater, a 40-gallon indirect, or some variation therefrom.

    The fact that those in the know intentionally installed boilers of the 140,000 gross input - which according to I=B=R would minimally provide 100,000 of domestic/tankless output of 3-5 GPM hot bathing water became a "standard" for any home, until the mansion-size reversed the calc.-basis to heat load, not domestic H/W production.

    The "cretins" in the trade today, missed THAT fact and now, 30-years later, incorrectly assume the dead-man's legacy of "intentionally oversizing" must be good - and perpetuate the sizing basis, failing to realize we no longer favor tankless coils!

    Talk about gross oversight...

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  • Uni R_2
    Uni R_2 Member Posts: 589
    Don't forget Mike...

    9. Some people believe that bigger boilers don't have to work as hard so they'll last longer.
  • Doc Radiant
    Doc Radiant Member Posts: 57

    I can think of a couple of ways to present this to the HO;

    1. Gaurantee your work in writing and that the boiler will be properly sized, or you will replace it with a larger one at no charge if it is too small (if you do a heat loss calc, you already know you won't have to do this).

    2. Ask them which car would get better gas mileage on a 100 mile trip; a Honda Civic with the cruise control set at 50 MPH or a Dodge Viper, acclerating from 0 to 100 MPH full throttle, coming to a full stop, and then doing the same 0 to 100 for the whole trip.

    3. Explain that an over sized boiler is like the Viper above - short run cycles mean lower combustion efficiency and more heat lost up the chimney on the burner-off cycles.

    BTW - and as you know, if you connect 200 feet of baseboard (rated at 550 BTUs/ft) to a 50,000 BTU hot water boiler, the boiler will still only "see" the actual heat loss as the load. If the HO brings this up, remind them that the output of BB is based primarily on the temperature of water flowing through the tube and the temperature of the air entering the bottom of the enclosure. If you have 120 degree water flowing through the baseboard, and the air temp entering the cabinet is also 120 degrees, there will be zero load (ignoring pick-up losses) on the boiler - regardless of how much baseboard is connected to it.
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