Load Calculation

When I needed a new roof, it took me over a year to find a rep who knew roofing. One rep told me the job would be a roof over and would need 24 squares. I knew the roof already had two layer and would be a tear-off - plus the roof was only 24 squares. Needless to say I am leery of home improvement reps.
But now every one with whom I have spoken about a new AC unit has a Master License (I checked). But not one of them has done a load calculation. And the lowest bid for a 2.5 ton, Seer-15 is $5,400.
Where can I find the math for a load calculation?
Dick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dick Adams wrote:

I don't show my load calculations on estimates.. You buy the job you get to see about $300 worth of load calculations. This isn't a hobby. A good computerized Load calc costs upwards to a $thousand and up to $5 thousand with all of the duct, material, etc addons. Plus it takes a few hours to input and get it right. Inspection department has to OK it along with the work plan. I don't do the paper hob for my competitors. When they worked for me I taught them right and let them do their own work. If you want to pay for the load calc..That is business.. Free.. no way!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Since you won't show me your load calculation, why should I believe you did one?
For all I know you're just looking at my existing unit and making a bid to see how much I'm willing to pay.
Dick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

The correct answer is this.....
You will get a printed copy of the load calc report and an ARI certificate of performance when we install the system. Here is the installed price from my price book, there is no guesswork, and no surprises. Would you like me to pull a certificate of insurance for this job??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Noon-Air wrote:

Nope.. First it is filed with the building officials along with an outline of the work. When the Inspectors approve the job, You pay the tab..Then and only then do you get everything that goes with it including the warrantee paperwork. There is no insurance to pull. You own that policy or you don't have a license. And a Bond. If you do Government work, it is even more complex. By the way the Feds pay for all necessary calculations before reviewing your bid. Most states require all of this in advance or you don't get your license. and you have to update your education each year. The client can of course go to Community development and peruse the Marshall-Swift for typical costs of such a job in his/her exact area and date. I have no problem with the customer getting several competitive bids either. As for price books, I have no intention of allowing my competition to get a look at that. It is a bid with all services and equipment listed with a bottom line price. This bid is good for 30 days and gives the period of time for the job. If we are financing the Job, then there is a whole other paperwork to be included. We like it that way, the customer likes it that way and both yours and our bankers like it like that. Even the Lawyers understand that. My job is to do your job with as least pain to you as possible.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Ummm... Don, here we don't have to get approval from the inspectors *before* doing the job, and I don't have a problem with the customer seeing it, as my book only shows *INSTALLED* prices.....Its all flat rate. I offer a certificate of insurance for every install that I do, and thats as a courtesy only. The only place here where licensing et all is an issue, is inside of the city limits. Outside the city limits is where the scarey stuff happens and I get called to fix it. FWIW, I don't do "estimates" I only do written quotes, and yes they are only good for 30 days.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dick Adams wrote:

I don't care what your willing to pay. The cost is what it is. If your an astute purchaser. You will list all oranges and apples and get realistic competitive bids. I would expect nothing less.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dick Adams wrote:

Sorry Dick;
Load calc's [Manual J & Manual D] come when the contract's signed.
--
Zyp



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Load calc is part of the paid job.... and FWIW, $5400 for a 2 1/2 ton heat pump and air handler is a steal. I just did a change-out for the going rate of $7,000...had it been with a gas furnace, it would have been $8,000.
BTW, did anybody give you a copy of the ARI certificate for the specific equipment??
--

Steve @ Noon-Air Heating & A/C

"Stop calling me for freebies Satan,
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Jun 15, 3:04pm, snipped-for-privacy@panix.com (Dick Adams) wrote:

Here is the organization some application are modeled after http://www.acca.org /
You can get the books from them on how to do a Manual J (load calc), D (duct sizing), T (Air distribution basics), S (system sizing).
I have done most of the design through the manuals and my advice is to hire a contractor that has the software to do the calcs. Be sure they do a complete assessment of the thermal envelope, a blower door test pressure balancing and a duct test and possible an infrared camera. Doing a heat loss/gain calc is worthless without knowing what you really have. I do not know anyone that can guess at the natural Air Changes per House of a house or the CFM duct leakage.
If your contractor only installs the AC unit without testing out it is a second rate job. 1)    Superheat or Subcooling depending on a TXV or not 2)    Duct test for leakage 3)    Static pressure in the ducts 4)    Flows from each grill to balance the system 5)    Pressure balance room to room a.    To be sure there is no back drafting of natural draft chimneys if you have any b.    To reduce forced infiltration/ exfiltration by the fan blower 6)    Measure the system flow to be sure your getting what is rated (this normally requires new ducts and a larger return) 7)    Install dampers in each duct to do balancing 8)    High efficiency filter in the return grill a.    Grill must be large enough to reduce static b.    Filter is at the return to keep the whole duct system clean
A properly sized system will be nearly silent, draft free comfortable and low utility bills.
Does the contractor subscribe to Building Science, if not find another that does. May things in a house are connected and fixing one can upset another.
By the way it is unlikely the bid for $5,400 will get you any of this, buyer beware...
Hope this helps
Andy Whole House Performance is the right thing to do
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dick Adams wrote:

using google you can find the formula but you can buy a good home version from links at http://hvac-talk.com /
their residential forum at http://hvac-talk.com/vbb/forumdisplay.php?f=1
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ashrea Fundamentals 1989 has a very comprehensive heating & Cooling load calculation section. It's often used for teaching the craft. Quite often a 2 story concrete building with a built up roof, tar & stone over foam & reasonable windows, will take a first year student 2 or 3 weeks of hand calculation to come up with something in the ballpark. Then, of course we have a storm that tears off the canopies & knocks down the big shade tree, ( I especially like that one!) & we have to re-calculate.
Rules of thumb work, but only in the regions I'm familiar with, & only because I've done numerous hand calcs... There are load programs out there that will give you the answer as well... but as Don said, they can cost a bit. Even if you ask for the load calcs prior to signing on for a new system, will you understand them?
goodluck geothermaljones st.paul,mn.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.