According to GBA's Martin Holladay,

"Energy nerds can be fetishistic about their load calculations. The everyday variety of this species is the Manual J Fetishist — usually an engineer who warns homeowners that they will be uncomfortable and will face high energy bills unless they invest in more engineering."

The article can be found here: GBA

The sum of the article is that load calculations on very air tight and highly insulated homes can be done without having to hire a high priced mechanical engineer. It still recommends running a Manual J but the old pencil and paper method can be done with good results on a tight home.

"The sum of the article is that load calculations on very air tight and highly insulated homes can be done without having to hire a high priced mechanical engineer. It still recommends running a Manual J but the old pencil and paper method can be done with good results on a tight home."

Sorry, but that is a load.

We are in many homes built by "good" contractors whom hired "good" HVAC guys, whom submitted Manual "J" loads to the city. In fact I just spent 4 hours moving a thermostat and balancing a warm air system in a million-plus house. We were called out to run supplemental heat in a cold sun room. After performing a proper heat load for the room, using Wrightsoft with an Uponor module for radiant floor, we determined that the floor would more than make up for the poorly designed warm air. The results were disappointing until we realized just how bad the system was installed.

We specialize in radiant floor designs but find that we have to correct many elementary mistakes in the forced air systems in order to integrate the radiant floors. Doing this kind of work without the benefit of software is just silly. As the vast majority of heating contractors do not know how to perform a Manual 'J' long or short hand it is really irresponsible to degrade this critical tool.

After you have done a few hundred heat loads, you are better able to guess. But most guess without pertinent experience.


Oh yes, and Marty says a lot of things.

I was just quoted a rate of $6,000 by a energy consultant to do a Manual J, D & S for a residential home. Even so, in the fine print it states that they don't guarantee their work as every home is unique and can still experience unforeseen issues.

Everyone talks about ROI, so what is the ROI for running a $6,000 calc and designing a system that I can do myself with the help of a qualified HVAC installer for $340?
$6,000 vs $340 and the $340 quote is using WrightSoft to do the calcs.

I am not downplaying running the software and seeking a pro but I agree with what the GBA article stated. People use fear to sell or market their products. There are systems that were "professionally" designed that have problems and systems that were designed by the homeowner that work great. The home I am currently in was "engineered" by a mechanical engineer and I have nothing but problems during both heating and cooling seasons.

Sounds a bit steep to me. My experience is that few loads are done at all. This is the real problem. A mechanical engineer should be capable of running the loads but they are typically in a scale that they are unfamiliar with. We are a design/build mechanical contractor with proven experience. I think this is the ideal and every home, new or old, should have a load done before equipment is ordered.

Marty's article is misleading and insulting and most noteworthy in that he echos what seems to be the common idea that modulating burners negate the need for a proper heat load. Sounds good until you go out on a no-heat and find a boiler twice too big for the house. We find that as the houses get tighter the equipment stays the same, like the contractor installing the equipment...we don't need no stinking heat loads...yah, right.

My interpretation of the article was along the lines of:

IF you are an experienced builder who understands Manual J calculations, and
you have already built a few new homes and
you have a good rule-of-thumb and
the new home you are building falls into the same general category, with similar insulation levels, glazing specifications, and air leakage rates and
code allows you to not do a Manual J

Then a Manual J may not be necessary. That's so many "ifs" that it's hardly worth discussing (ie, it almost never applies).

xxx warns homeowners that they will be uncomfortable and will face high energy bills unless they invest in yyy

This is probably true of all but the best of everyone in the field (or any other field).

Over-sizing equipment is no big deal? I guess, if it is not your house.

Most heat loads are done by distributor salesman. They are, for the most part, not exceptional. If you had a heat load done on a particular model and had success (loosely defined) then you may not need to do another heat load. The article was meant to be provocative but the contradictions would be confusing to the already ill-informed. Especially if you are in the majority that think "rules of thumb" are acceptable when designing HVAC systems with an expected life span of 20 yrs. There were a couple of valid points, but the I got; If you pay a "professional to perform a proper heat load for your new house, you are a fool.

Most of the experienced builders I know couldn't do a heat load for their lives and if they did, they would still use the low bidder for all their HVAC needs. My advice to homeowners or those who are building a new home is to contract the mechanical trades directly. Do not hire builders that won't give you this option and specifically, don't hire an HVAC company that can't produce a copy of a Manual 'J' heat load. sadly, this will eliminate 9 out of 10 contractors but it is their money.

A $6000.00 Manual 'J'...sounds fishy. But we have done some very elaborate HVAC packages and the time to design was in the weeks.

Still, thanks for sharing. Marty usually gets me cranked up and makes go back to the books to confirm my math.

Six grand for running a load calculation may be a new world record!

Simple I=B=R spreadsheets of the type Martin Holladay uses work reasonably well for calculating heating loads, but don't cut it at all for cooling loads. Read the whole series, not just part 4 (in Lbear's link) where he talks about maybe punting with rules of thumb. He's pretty much an I=B=R approach kind o' guy:

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-perform-heat-loss-calculation-part-1

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-perform-heat-loss-calculation-part-2

See also:

http://www.greenbuildingadvisor.com/blogs/dept/musings/saving-energy-manual-j-and-manual-d

and

http://www.greenbuildingtalk.com/buildcentral/sip/article_hvac_sizing.aspx

No, Manual-J isn't perfect, but it's way better than a WAG. But it shouldn't cost $6K for just a load calc either.

Also note, in Martin's rule-of-thumb approach blog he only refers to sizing low-mass modulating hot air furnaces, which come with far fewer cost, design and efficiency penalties to oversizing than with hydronic systems. 

Almost all hot air furnaces (and most modulating condensing boilers too) are oversized for the heat loads of high-R homes (or even IRC2009 & IRC 2012 code min-homes.) But the cost of oversizing the radiation 2x is far more than oversizing ducts by 2x.  If you KNOW the load is going to come in under the smallest available furnace size, there's little point to running a meticulous heat load calc if it's known a-priori that the heating will be a hot air furnace. It's somewhat more important in hydronic systems, to be able to get the room-by-room radiation right.

His caveats for using a rule-of-thumb approach also makes sense:

-----------begin copyright violation---------

There are a few caveats, however:

• A rule of thumb is only useful if the homes fall into the same general category, with similar insulation levels, glazing specifications, and air leakage rates.
• A rule of thumb won’t work for a house with unusual features (especially unusual glazing features).
• My advice only applies to people who have actually performed an accurate Manual J calculation or who have hired a knowledgeable professional to prepare one for them. If you're just guessing, you will almost certainly oversize your equipment.

------------end copyright violation----------

Posted By Dana1 on 04 Jan 2013 05:36 PM
Six grand for running a load calculation may be a new world record!

I almost hung up after I heard the quote but I was courteous.

I like the LG ductless mini split Art Cool models. The wall units are a lot more aesthetically pleasing than a white box on a wall. The way it looks now, I will do the LG ductless mini split for the Living Room as getting duct work in there is not feasible. Also the south glazing can create higher cooling loads during the spring and fall equinox. Having that area zoned with its own mini split will prevent overheating problems.

Is it better to install the ERV/HRV completely separate from the rest of the central air system?

Lbear; should cost about $400. , If you can't find anyone , my guy has done calcs for other people in different areas of the country

Posted By cmkavala on 05 Jan 2013 06:20 PM
Lbear; should cost about $400. , If you can't find anyone , my guy has done calcs for other people in different areas of the country

Thanks, I will keep that in mind. I got in contact with someone locally (good rep, 20 years in business) who said they will run the Manual J calcs for around $350. If they don't work out I will send you a PM.

Still can't believe that one group wanted $6,000. Completely insane.

Still can't believe that one group wanted $6,000. Completely insane.

Sounds like the "We don't want to do work for you" price.

Posted By jonr on 06 Jan 2013 10:00 AM

Still can't believe that one group wanted $6,000. Completely insane.

Sounds like the "We don't want to do work for you" price.

Not sure what you mean by that but that is their standard price for 3,000 - 3,500 square foot homes.

Lbear,

Sometimes a contractor will not want a certain job for some reason.  For example, they may think the client will be too demanding.  Instead of plainly saying they are not interested, they will quote a very high figure to assure that there is no chance they will be selected.  And if they are selected, then the high quote will help them overcome their objections to working with a demanding client.  By the way, I am not implying that is the reason you received such a high quote. 

When I have seen Manual Js done by qualified engineers it usually takes the form of a total energy analysis on the home. Once you have the specific information entered in the computer, there is hardly any more effort to do a matrix comparison on various heating and cooling strategies. Most often you do this before the home is built, allowing changes (ducting, insulation, windows, radiant slabs, etc.), to be added before construction starts. Think of being able to do a complete "What If" analysis in order to get the most efficient possible design. Sort of like having Dana1 on your project, but with software.

I had a number of Manual Js done at no cost by heating companies who wanted this business. Every single one was grossly incorrect. The two best efforts were only off by about a third, but that was only because they made gross errors in two different directions that tended to cancel each other out some. Two of the companies had dedicated individuals who did nothing but this and system design. They were a little better than the others who were either tradesmen or salespeople. Everyone talked about this "service" being worth from $400 - $800. That is a reasonable price to have someone look over plans and make the calculations off those. If you have someone out to look at an existing structure, I would think the costs would change. In order to verify that that the home really did have the features claimed, seems like you would want to have a partial inspection and that might take additional time and effort, including travel. If you are talking about decisions that involve a large amount of money like complete systems, it would be reasonable to add a blower door test, particularly with older homes. Therefore, a fair price for existing homes might be up to $1200 plus the costs of blower door testing.

I had a number of Manual Js done at no cost by heating companies who wanted this business. Every single one was grossly incorrect. The two best efforts were only off by about a third, but that was only because they made gross errors in two different directions that tended to cancel each other out some

Could it be true - some people would get more accurate results with the right previous experience and a rule of thumb?

Posted By Alton on 06 Jan 2013 09:08 PM
Lbear,

Sometimes a contractor will not want a certain job for some reason.  For example, they may think the client will be too demanding.  Instead of plainly saying they are not interested, they will quote a very high figure to assure that there is no chance they will be selected.  And if they are selected, then the high quote will help them overcome their objections to working with a demanding client.  By the way, I am not implying that is the reason you received such a high quote. 

This company was persistent, they kept calling me to see if I was going forward.  Just to check the validity of my quote, I had someone else call a week later and give them a different project proposal. The quote was in the same range like mine.

Posted By jonr on 06 Jan 2013 10:09 PM

I had a number of Manual Js done at no cost by heating companies who wanted this business. Every single one was grossly incorrect. The two best efforts were only off by about a third, but that was only because they made gross errors in two different directions that tended to cancel each other out some

Could it be true - some people would get more accurate results with the right previous experience and a rule of thumb?

Of course!

The trick is to find somebody with the relevant previous experience, when you are looking at tighter/higher-R/more-massive construction than typical code-min houses in your neighborhood.  Few residential HVAC companies in my area have any experience at all with ICF construction, let along anything that remotely resembles Net Zero Energy or PassiveHouse construction.

It is remarkably difficult to find those HVAC specialists who have seen anything but the (98%?) of "other" homes out there. Some of them seem to treat this heat thing more like "magic" than physics. One company that didn't get the job dropped by during a cold snap to see if I "needed any help". They found the 6000 sf home being heated by two 9K BTU minisplit heads. Their description: "Amazing!". I remember when their proposal came in looking more like a standard amount of heat per square foot. I reiterated to them that this was quality energy-saving construction and they said that they already backed off on their estimate some to take that into consideration. I asked them if they had ever done homes that had an extraordinary amount of insulation. Their answer was "of course", but that "it didn't seem to make much difference in the heating" talking about one in particular that had a huge amount of insulation in the ceiling.

Posted By ICFHybrid on 07 Jan 2013 02:57 PM
It is remarkably difficult to find those HVAC specialists who have seen anything but the (98%?) of "other" homes out there. Some of them seem to treat this heat thing more like "magic" than physics. One company that didn't get the job dropped by during a cold snap to see if I "needed any help". They found the 6000 sf home being heated by two 9K BTU minisplit heads. Their description: "Amazing!". I remember when their proposal came in looking more like a standard amount of heat per square foot. I reiterated to them that this was quality energy-saving construction and they said that they already backed off on their estimate some to take that into consideration. I asked them if they had ever done homes that had an extraordinary amount of insulation. Their answer was "of course", but that "it didn't seem to make much difference in the heating" talking about one in particular that had a huge amount of insulation in the ceiling.

I agree. Finding someone who is capable of doing a correct calc job on a tight and highly insulated home is not an easy task. Some still don't even know what a mini split is.

It would be interesting to see more analysis of Man J errors. Not putting in the right data? Saying "that's impossible" or "be conservative" and adding more? Inaccuracy of Man J itself?