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Heat load calc( to pay, or not to pay)

BenWoj Member Posts: 33
I've been beating myself up over this, so I figured I'd ask for opinions here. Planning on having a radiant geothermal system installed in the house this summer. I purchased the "modern hydronic heating" book on this site so I'm able to do as much reading as possible. My geothermal contractor wanted me to get a heat load cal so we can determine the heat pump size, but I'm dragging my feet.

Being an engineer, I've been doing all my calculations from the book ( heat loss, water temp, flow rate ect) and I've been wondering if I should go with my calculations, or pay someone ($400) to come in and do it for me. Only thing pushing me to paying someone is so they can double check my numbers.

House is half gutted as I'm still in the process of having everything sprayed in. So whoever does come to do my load calc will be basing it off assumptions.

What do you think?


  • BobC
    BobC Member Posts: 5,401
    Pay the money

    As an engineer myself I understand wanting to trust your own calculations but unless you you have specific training in this field I'd pay someone to make sure I had not overlooked anything. $400 is literally a drop in the bucket, if your numbers are wrong, the fix could be orders of magnitude higher than that.

    I would make sure whoever you hire has the expertise you need.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • BenWoj
    BenWoj Member Posts: 33

    Thx bob, that's what I kept concluding, but wanted to make sure.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,573
    How to choose the engineer?

    I would not assume that just any engineer could do these calculations, so how can you find the right one?

    Do it yourself to start with and run it by here.--NBC
  • Zman
    Zman Member Posts: 7,446
    Heat Load

    I have to agree with NBC on this one.

    My experience with Engineers on heat loss calcs is, they round up, Big.

    Unless you have a high level of confidence in the guy you are hiring, do it yourself.

    Siegenthaler has great software on his site that make the process pretty foolproof. The biggest unknown is the air change rate. Without a blower door test, everyone is guessing on that one.


    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Rich_49
    Rich_49 Member Posts: 2,721
    Listen to ZMan

    The blower door numbers will tell the story . You will really have to be on top of insulators , and all the trades to insure the modeled tightness .  Can give references for the ONLY guy that knows about Reynolds numbers and designing proper loop fields in Central New Jersey , and trust me there is only ONE .  We have fixed many peoples short fields , bad calcs .  Remember also when choosing the equipment that the pump(s) which move the source  side fluid are not included in the COP number any longer and have not been for a couple years . Have seen many a disappointed consumer when they get the electric bill due to this . Watch out also for the point where a system may drop below COP of 4 . I have seen this all too often also .  I have seen it so poorly designed that we had to shut the HP down at 36* and allow the boiler to take over or else have excessive electric bills . If you are in Jersey you can contact me for the name of the driller , this guy only does it right .    In the end though that ACH number becomes HUGE
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • icesailor
    icesailor Member Posts: 7,265
    Looking at:

    I look at it this way.

    You or I can be 100% right in our calculations. It isn't all that hard. The hardest part is covering ALL the bases in the overall calculations. The critical number is the outside design temperature. But you are 100% right. Someone else comes along and "Rounds UP Big Time". Adds 50% more to the calculations. You might think that you have been wrong. They are more experienced than you. You wouldn't be cold or hot with either calculation. You'd just never know that you were correct but went with the oversized system.

    That's what caused me to start doing all my own. It isn't that someone wants to sell you more than you need, they just don't want to get a call that the house is cold or hot and there's nothing that can be done now to solve the problem. .

    "Round up" with common sense. "Common Sense" is not a monetary value.
  • SWEI
    SWEI Member Posts: 7,356
    Your geothermal contractor

    should be fully capable of doing the heat loss calcs.  If he is not, I'd be wary...
  • Rich_49
    Rich_49 Member Posts: 2,721
    Should be

    are scary words SWEI .  Everyone that performs any job should be capable . But if that actually was the case we all would not have made thousand of comments and offered so much help to those that weren't even aware that they should be wary .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • remodel
    remodel Member Posts: 68

    Do the calcs, state your assumptions..post on here. Rich makes a good point, I hired someone who said they were capable but I got a completely over-sized device. The wallies will scrutinize like none other. If you are comfortable with the final answer it is your baby that is the one thing I like about doing it yourself but the $400 you pay to someone with a wealth of experience is priceless.
  • Henry
    Henry Member Posts: 996
    edited May 2014
    Heat loss

    If you are doing radiant, Uponor will do the design and heat loss for free if you buy Uponor. We outsource the design to Uponor every radiant job.
  • BenWoj
    BenWoj Member Posts: 33
    Completely Agree

    The reason I was told to have someone come in to do a heat loss was because we weren't sure on what type of insulation was in the walls (old farm house), but since i've basically opened every wall and sprayed most of it, I feel a bit more confident with what Im dealing with.
  • RobG
    RobG Member Posts: 1,850
    To Henry / BenWog

    Uponor can only do the heat-loss based on the information you give them. You must already know the infiltration, air exchanges, yada, yada, yada. Then they will give a list of THEIR materials to buy.

    If you already have the information required to do a proper heat-loss you may as well use the the Slantfin program and do it yourself. Just make sure to use the correct installer / material / equipment for the job and you will be just fine. Post your info here and one (or many) of us will double check it. Believe me, there is no shortage of knowledge or people willing to help on this site.


  • D107
    D107 Member Posts: 1,832
    Pay Contractor

    HO here, fwiw: When we needed a new boiler, I paid a top-notch heating contractor to do the heat calc, then did one myself. Hiring an engineer never occurred to me; alot of them do very large commercial buildings only. Any good heating contractor should know how to a good calc; if they turn out to be your installer so much the better. 
  • icesailor
    icesailor Member Posts: 7,265
    Pay or not to pay:

    Where I worked, there were a lot of people that did plumbing & Heating.Some, heating only. As far as I ever knew, I was the only person that did my own. Everyone else had the salesman from the supply house they used, do the whole thing. They gave them a quote with a boiler and whatever materials you might need. Or they thought you might need. There was no charge. They did it for contractors. Not homeowners,

    Not everyone figures their own heat loss and some would rather not take the responsibility
  • bill_105
    bill_105 Member Posts: 429
    To pay or not to pay, that is the question.

    I'm here wondering just what Shakespeare would have to say about this dilemma:) 
  • SWEI
    SWEI Member Posts: 7,356
    Whether 'tis nobler

    To suffer the slings and arrows of outrageous oversizing...
  • Paul Pollets
    Paul Pollets Member Posts: 3,617
    Doing the Calcs

    I agree. If the Geo contractor can't do the math, you've got to ask why not? The software is neither very expensive nor difficult to use.  Sizing the system is critical and should not be guessed. 
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,573
    Shakespeare and engineers

    He wasn't partial to lawyers, but he probably would have been sympathetic to engineers--NBC