Again I suggest that you get pros out to your home before you decide which facets to educate yourself on.
Chewing through hourly loads can be mind numbing. Most pros design by software now and will be happy to print out a bin report for you. Believe me when I tell you though, I don't spend any more time looking at a bin analyses than it takes me to staple the pages together.
J

Bin data allows one to quickly see how relatively few hours outdoor temps exceed design data - might give a clearer understanding of validity and soundness of designing for 95%.

I agree that can be discerned in about the time it takes to staple the pages together.

(we use them to entertain engineers so we can get our work done with less "assisstance"....;)

So bin data shows 5% of my days will be under 20* (using 50 yrs of data), if I run manual J at 20* winter temp, I still need 50K btuh which means the 5 ton unit.

This part of the process is generally done with an operating cost calculator. It arrives at a size with pretty much the same math.
We shoot for ~95% (some will tell you 92-98%). Would you say 48K or 60K is closest to 50? The closest to your load will be the least expensive to put in and close and some times lower in operating cost.
My advice again would be:
1) 5 tons is too much for the loads you've mentioned.
2) You need real pros to design it.
3) You need to extract yourself somewhat from the design process.

You continue to dispute my size selection and miss the end point that you and your original bidders don't know how to size a system.
I honestly mean no disrespect, but if you have pros to your home and disagree with their PROFESSIONAL opinion repeatedly, they will either decline to work with you or raise their price to compensate themselves for the extra time you will demand from them.
Where you have people offering you advice for free...........

I better clarify when I say "pretty much the same math" it is not identical. Varying EWT's etc have to be factored in as well which is why we use software to help us with that design......and yes I know a 48K unit doesn't provide 48 K in the dead of winter that's all part of the equation.
Why would you carefully calculate the load and then discard the information by
not using the same care (pro design software) in sizing?

Just in case it is not clear, the numbers should be something like 70% of design temp should cover 95% of your heating load.

Thanks Jon. I have trouble articulating the point.
Curiously nobody ever asks how ACCA arrived at a given value for a given component in a heat loss calc. But many, many people, want to know the nuts and bolts of size design. This question comes up over and over and over and......
It's usually in the form of (you don't know what you're talking about), 36,000 btus is not 95% of my 49,000 btu load....(obviously you did poorly in math in school).....
;)

Not meaning to dispute anything. If it came across that way, I didn't mean it that way. Just trying to learn, and hopefully in the process, to teach others.

You came across as curious.
That's okay.
Do not take offense to this statement (I reality check myself for application routinely);
"you don't know what you don't know" (quotes to show it's not my line).
None of us do.
Questions are the surest cure. (I'll claim that one)
j

To clarify, hopefully, some of the discussion of percentages here is some of the data I crunched for my own house and heating calcs.

Here in the Boise, ID area the design temp for heating is 9°F. Thirty years of hourly temp readings show that only about 0.5% of the hourly readings were below 9°F. 3.7% of all hourly temp readings were 20°F or colder. These percentages are of all the readings for a year. When looked at as a percentage of the number of hourly readings below 65°F, assuming any temp below 65 meant heat was wanted, below 9F is 0.7% and 20F & below is 4.9%.

This means that if I design the heating system to keep the house at 72F with an outdoor temp of 20F, the heating system would be undersized only about 5% of total heating season. Supplemental heat would be desirable for those times.

buckeye, Is your house well insulated, and particularly, is it air tight? If so, give credit to heat generated by daily living activities such as cooking, tvs, computers, light bulbs, solar gain, and bodies. I've found that in my new ICF house those heat sources are significant contributor to the heat supply, so much so that on days above about 40°F the heating system hardly ever kicks on.

Hello Buckeye,

Very surprised at some of the recommendations on this particular forum thread.  System design is critical here - in order to do this right requires a two system solution.  The manual J seems correct based on the data you provided.  But why noone suggested foaming the attic and box beam (rim joist) to lower the heat load requirement to approximately 48,000-54,000 BTU's (can likely be reached) is a key component of the overall solution..  Lowering the heating requirement will assure the cooling capacity isn't oversized.  This is just good system design.and saves money on the installation and equipment.

Then, you should look into a DX system.  There are several very good equipment manufacturers and designer/installer brands.  Do your research and you'll find a system that not only works well, but meets or exceeds everyone's expectations - for comfort AND performance..

Hope this helps...

Paul
Managing Partner
Total Green Geothermal
www.TotalGreenUS.com



  

Some times it pays to add insulation, which would likely come up in a pros presentation if it is indicated.
Routinely we find that <5% reduction of loss is achieved even with thousands of dollars in extra insulation, if the house was built in the last 20 years.
Main thing is to get real designers to the site, not us cyberdesigners or the clowns you already had.
j

Sorry Paul,
I'm very surprised at your insistance that you know that right system for this application. Have you been to the authors home?
My crystal ball is in the shop. Since I don't know what he has for insulation (or if he has fireplaces), I'm reluctant to suggest improvements and predict savings.
Of course a pro on site (I think somebody suggested that once) could easily determine if insulation is indicated. I have indeed done so where significant savings was indicated through calculation; not speculation.
j