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Homeowner Review of HVAC-Calc

Originally written March 30, 2004, updated April 18 and June 28, 2004

Why perform a heat-gain or heat-loss calculation at all?

Several months ago, I bought a license for HVAC-Calc to help guide me in a current house renovation. It's probably the best heat gain/heat loss program a homeowner can buy, as a two-month license is only $50. Homeowners who want to buy an non-time-limited license will have to put down about $200, while pros will enjoy the program at nearly $400. In my opinion, it's money well spent.

Having a Manual-J compliant calculation is the best way to ensure that your AC and/or heating systems are sized properly and work at peak efficiency. There are many problems associated with oversized systems such as short cycling (affects appliance life), excessive humidity in the summertime (because the AC can't stay on long enough to remove latent heat), etc. In other words, even if you don't personally want to complete a Manual-J heat gain/loss calculation yourself, insist on using a contractor that does. For example, you may discover that a proposed addition to your home may not require any additional heating/cooling infrastructure since the previously installed HVAC systems were too large to start with (a common problem, apparently).

What does HVAC-Calc Do Well?

HVAC-Calc runs quickly on Windows-based machines and is well-organized. Rooms are assigned to various zones within a "tree". Walls, floors, ceilings, etc. are assigned in turn to rooms. Data entry is tedious but unavoidable in all programs of this genre. What makes HVAC-Calc stand out is that many common variables get carried over from entry to entry. For example, if you have a consistent wall cavity insulation, you only have to enter it once. Ditto on ceiling heights, etc. Subsequent walls will feature common previous attributes by default, which speeds data entry.

Furthermore, the program allows the addition of a myriad of options to walls and rooms, including fireplaces, stoves, people, skylights, etc. Most houses would be well-covered by the many options that HVAC-Calc offers and the thermal effects of every component, wall, room, zone, and home can be compared later on. The program can also generate several types of reports, from comprehensive PDF files with every component called out individually to condensed room-based summaries.

The built-in list of local climate data is comprehensive and will allow you to personalize your results to the local climate. If you haven't built the house yet, the "rotate house" function will even allow you to see how the energy needs of the house change as a function of orientation.

At the end of all that data entry, you'll have a very good idea how much energy your house will use, where, and why. You can then use this information to make informed decisions about insulation, windows, features inside the home, and the heating and cooling systems. This alone is worth the $50 admission price for the homeowner license that is valid for two months from time of registration. In other words, don't dilly-dally, or you'll have to buy a new license. The unlimited-duration licenses cost a lot more...

However, you can also use HVAC-Calc to go step further than just calculating heat gains and losses. For instance, HVAC-Calc will also calculate base-board length requirements for folks who want to use hydronic heating. On the air-side of the business, HVAC-Calc also offers duct-sizing calculations that allow you to figure out the size of supplies and returns to individual rooms, combine multiple rooms into one supply or return trunk, etc.

As with all software that isn't idiot-proof, documentation and technical support is very important. Don Sleeth, the author, is usually easy to reach via telephone and typically replies to e-mail within a day if he has the answer handy. He also maintains a web-site that answers a number of frequently asked questions related to the program. However, you should read and study the manual first, as I found it to be pretty comprehensive, well-written, and understandable. Then again, I'm an engineer by training.

Another resource associated with HVAC-Calc is HVAC-Talk.com, a bulletin board run by Don. While homeowners are invited to post questions there, its primary audience is professionals. Be sure to understand the site rules before posting. Posts that run counter to Dons site policies are usually deleted and then your posting privileges rescinded. I found that out the hard way when I innocently asked how folks dealt with multiple-floor stairwell heat loads after Don didn't reply to my query by e-mail... and I never did get my answer. However, there is a ton of great hands-on content at HVAC-Talk, just nothing on HVAC-Calc except praise and ads - everything else is deleted.

Where could HVAC-Calc be improved?

There are a number of minor issues I found with the program that I'll lay out next. Some relate to a set of new features that Don may still be developing, others may be minor or not applicable to your situation. By the time you read this, he may have already addressed them (I am using version 4.045).

So, while there are many positive aspects to HVAC-Calc, there still is some improvement potential.

So, should you buy HVAC-Calc?

For professionals, HVAC-Calc makes sense if they primarily concentrate on the air-based side of the business (air conditioning, heat pumps, and furnaces). Professionals who install a wider range of solutions (radiant, for example) may want to investigate the more comprehensive (and much more expensive) HVAC suites from Wrightsoft and Elitesoft or supplement HVAC-Calc with Siegenthalers Hydronics Design Studio,LoopCAD, RadiantWorks, Wirsbo ADS, etc. I would try as many programs as you can lay your hands on, then buy the one that is the easiest to use for you. Despite the high investment costs, a professional will probably make up the cost by the third of fourth job.

While imperfect, the two-month $50 homeowner special of HVAC-Calc is probably the best solution for home-owners currently on the market that can do heat gains and heat losses reasonably quickly and accurately. For a nominal expense, some time, and interest you have the opportunity to better understand the heating and cooling needs of your home and what your options are to influence them.

So despite the shortcomings of the program and what I consider to be unfounded belligerence by Mr. Sleeth towards me, I liked HVAC-Calc sufficiently that I bought the permanent home-owner license. Home renovations have a way of evolving, and usually take longer than 2 months to get done.

However, if you're not planning on calculating cooling loads, there are a number of manufacturers offering free heat-loss calculators, such as the Slant Fin Hydronics Explorer or the Burnham DesignPro software. More importantly, these alternatives do not have a built-in time limit necessitating periodic license renewals or a high-cost permanent license. However, I have yet to use either and thus have no basis for comparison.

Regardless of whether you are a homeowner or a professional, HVAC-Calc can probably help you. Most importantly, maximize the comfort and the energy-efficiency of your home while maximizing appliance longevity by selecting heating and cooling equipment that actually matches the projected heat gain and heat loss of the house. Even if you elect not to do a heat-loss/gain calculation yourself, be sure to hire a professional that does.

Cheers! Constantin


For those interested in home-brew Internet marketing attempts, have a look at how many sites Mr. Sleeth has registered that contain the letters HVAC (HVAC.cc, HVACcalc.com, hvac-calc.com, HVACComputer.com, hvacfaq.com HVAChelp.com, HVACloads.com, hvac-loads.com, hvac-and-hvac-software.com, hvac-software.com, HVAC-Talk.com, etc.). Then there are additional feeder sites like acdirect.com, heat-loss.com, heat-loss-calculations.com, sleeth.com, etc. that also point to his main site.

From what I can tell, Google and many other search engines recognize this "mini-web" of cross-linked sites for the marketing ploy it is. For example, this review shot up to the #6 position at Google for the search query "HVAC-Calc", even though only 1 page points to it (i.e. it should have a very low PageRank). However, Mr. Sleeth's domain-name registrar must be laughing all the way to the bank. See WebmasterWorld for tips on how successful search engine placement actually works.