Sixteen tons of number nine coal...And the straw boss said "Well, a-bless my soul...

Only a 14 SEER is the first red flag for all of them. A lot of north facing glass and no one doing the math is the other.

Thanks all for your insight.

Old system is a York system. No heat pump. New system would have a heat pump (which should help with propane use). Old system is 11 SEER.

North facing glass in the mountains seems like a good thing to me(surrounded by evergreen types). In the south you want less glass on the south from the sun heating up the house.

Let me say, this new place is in a fairly restricted area as far as access to motivated pros. We have been warned by other transplants from the big city that certain things take getting used to. I am considering offering my guy from my old town a nice bonus to come up and consult. But that may be a long shot.

" In the south you want less glass on the south from the sun heating up the house. "

Except in the winter, which is the thing here. And that it is glass, which will affect the heating load.

How well did the 4 ton unit work in the summer?

Heating in the winter is pretty easy. We get some super low temps but only for a few weeks in January. We can keep it pretty comfy with the fireplace and the heater only kicks in when needed.

The 4 ton unit did very well until it didn’t. But the house wasn’t very maintained the final years of the previous owners as they were elderly and dealing with health issues and such.

What matters for summer is generally west facing glass. South facing windows can be an issue too but you don't really have much. South windows are easy to cover.

Infiltration matters. Insulation matters.

But solar gain from windows is the most important. What is the SHGC of your windows?

The 4 ton unit did well but did it short cycle? Meaning did it run for 10 minutes and then be off for 20? Are you ducts in the attic? That is a pretty big hit and could easily be the difference between 3 tons and 4 tons.

What elevation in the mountains? Here in NC, a lot of mountain cottages don't even have a/c.

There are way too many variables that you haven't provided to give a reasonably accurate guess.

For sure a load calculation should be done. Every conscientious HVAC contractor not only knows how to do it but does so as a matter of good practice, even if done with broad estimates.

Insulation and infiltration do matter a lot. Putting in oversized units was the practice for too long, everyone in the business knows that. "No one calls to complain because they're too cool".

A smaller size, if adequate for the load, will run longer and more efficiently and will do a better job removing humidity.

If the current system is a 4 ton, the duct system maybe sized to handle the 4 ton air movement.

Putting in a 3 ton system may require you to replace the duct system and make sure it's sized properly. If you don't do that, the air volume coming out the vent will most likely feel to low.

But you know, no one comments on the existing duct work and what would be involved in properly sizing that.... (2500 square foot envelope is not small.)

Ironic huh?

If you're really that concerned about sizing put in a 4 ton 2 speed unit. 90% of the time it will run in first stage which is 70% capacity of the 4 ton unit.

Then in the event it gets really hot, you still have the extra capacity available in second stage.

SEER is energy efficiency, nothing to do with performance. The higher the SEER, the less you will pay in operation costs. (Will vary due to a host of various factors)

You are assuming the current duct work was adequately sized to handle a 4 ton system. There is a good chance it is undersized. This is why a good HVAC contractor measures the duct work and does the load calculation to determine if both duct work and system size will work together.

ManJ even the generic block load takes time to do, and you need to examine and measure details of the construction.

The ductwork is not sized by a ton(?) method.. It is sized (a) thumb rule, (b) velocity method (c) equal friction (d) static regain....

The velocity is controlled by a furnace blower. The velocity method can still be made to work with a smaller tonnage. Without knowing the details... no one can tell you if 3T or 4T is right for you. The price difference between equipment is minor.

Austin, your comments seem contradictory to me.

My recent experience, in two different homes, has been that knowledgeable contractors doing load calcs will often recommend replacing existing (oversized) equipment with smaller sizes and and that life goes on with better comfort and lower costs mostly using the existing (but better sealed) ducts. I've had a few ducts enlarged when it was thought the wrong size had been used, both for supplies and returns.

And, of course, the "blower" is in the furnace or air handler and not in the various compressor/condensers of whatever the tonnage size so that the air flow is always adjustable up and down as required. The tonnage of the ourdoor AC unit may influence the required airflow but it doesn't itself produce the airflow or regulate it.

Is your experience as an expert working in the field different?

Elmer,

A heat load calculation is more or less a set of metrics to determine the load characteristics of a structure during the worst days of the year (hot or heat load--- how much cooling is needed) --- (cold --- how much heating is needed)

The worst days.

So this sizing is so accurate that unit will be sized properly for a total of 2 weeks. 1 week in the summer and 1 week in the winter.

The home in question was built 20 some odd years ago. Is different than most homes of that time period... because it's: DRUM ROLL--- a log cabin.

What information we have about insulation factors to make this educated guess so that we *can make sure* the HVAC system is sized right for those 2 weeks out of the year...

I know let's guess some more.

Velocity of air coming from the duct. In some circles they call this 'throw'. So in other words if you reduce the equipment size (the furnace that produces the blow power of the HVAC system) the velocity of air coming from the vents due to size of the duct system.

Look I talk to people and ask the tough questions like how has the current system performed -- Because the people who have lived in the structure know their system. Sizing is mostly relegated to guessing... in the old structure replacement market. Completely different for new construction.

With that said, as I have always said... Manual J heat load calculation is a tool for those who know how to use it. So if you lack the sizing information of the structure OR if I were to see something that doesn't make sense... then I would require a heat load calculation to be performed.

A manual J heat load calculation is not some magical method that will deliver 100% accuracy.

Heat of the day is from 3-6pm and in worse case scenarios is from 3-7pm. Do the math... 90% of the time your air conditioner is 'oversized'. How can this be? Follow the trajectory of the sun. Since the dawn of time there has never been a heat generation source greater than that flaming rock in the sky....

But hey we're doing this heat load to be accurately sized for one small moment in time... at best 2 weeks of the year.

Sizing is important, but it is also confounded with this so called need for accuracy that 'doesn't exist'.

Accuracy = 90% of the time -- it's wrong.

So if accuracy is so poor how can we get closer?

Answer: install multi stage equipment. 2 speed or more AC / 2 stage furnace.

I service Katy, Texas area.

Austin - you know that size matters. Your point about accuracy and correct sizing is misleading.

Sure - units are oversized for much of the year ... which is why you limit the size so they aren't ridiculously oversized most of the time.

The 1 week a year comment is just BS. I live in Raleigh. Our design temp in the summer is 95. We hit that for about 7 days a year. We hit above 90 - 38 days a year. So while yes your week is correct, it is really close for 6 weeks. And then we hit above 85 probably 80 days a year.

If we are sized for 95, then we are barely oversized at 90 and just a little more at 85. Much better than being oversized at 95.

Of course, sun matters far more than temperature. It has 1 peak day but it varies a small percentage from day to day.

HVAC contractors tend to make smaller ducts than ideal - cheaper and easier. My last house they planned a 4 ton unit without telling me. After the house was done, they swapped it for a 3 ton. The duct work was still too small. While that is not true in every situation, it is pretty easy to check.

GA mountains. Mostly north facing glass. Do you honestly believe 4 tons is likely correct? I'll take that wager. Log cabin or not. At some point the delta T is so small that the poor insulation doesn't matter much. A 1 ton mini in the master bedroom is what I would do in the NC mountains at 4,000 feet.

Austin,

It sounds like you don't do load calculations. Do you disparage them in an effort to discredit the value of doing them?

I don't know if true only in my state or nationally but here a load calculation is required to be submitted with a building permit application for installation or replacement of HVAC equipment. I suspect the contractors at the lower end of the spectrum must dummy up something to submit but they're doing a disservice to their customers. Are they required in Katy, Tx? Do your customers ask you do to them.

I'm soon to have work done for a new furnace and to add AC to a recently purchased smaller second home. All furnaces are 80%, it's a mild winter area.

Contractor #1 with no load calc bid 70K furnace (that's the existing size and it warms up the place too fast and produces uneven results), 3 ton AC.

#2, also no calc, 70K furnace and 4 ton AC.

#3 did a load calc and came up with 45K furnace and 2 ton AC and highlighted some duct modifications he wanted to do.

Prices for all were comparable. Guess who got the job?

Elmer - that is an impressive spread of tonnage.

In my jurisdiction, load calcs are required. I have seen pretty bad garbage in and garbage out. Using defaults makes a load calc pretty quick.

Tx and GA - especially outside of cities - I would not expect strict permitting. This is somewhat of a red/blue state issue although certainly not always.

Heating is a wild card for a mild winter market. The air flow that furnace delivers for AC in a predominantly hot market (like mine) is in my opinion more important. If you want a furnace that doesn't produce such hot swings put in a 2 stage furnace.

Elmer, your AC climate in Cali is probably less severe and similar to Mike's seasonal attributes in New Jersey. At best 3 months AC season. (depending on various factors as California to the south is mostly desert)

I am a AC repair specialist. So do I run heat load calculations all the time, no. I am there to repair... because all systems break due and that market is much larger than the replace only market... so most cases for me to do a heat load calc would be pointless. I would never have lasted 11 years running my own company doing this. People are more likely to not have the money to repair the system let alone pay for a heat load calc. LOL.

Was just in a 5000+ sq. foot mansion here that had a 4 ton furnace on a 5 ton AC. The tenants, that are renting the place complaining of low air flow in one of the 3 AC systems at this house. Probably somewhere in the realm of 11 tons of air conditioning for this place. I didn't check all systems as the Land Lord was not present.

Never been to that house before.... but I know what to look for. It would be a waste of time to do a heat load calculation under those circumstances.

With that said, running a heat load calculation in a current standing home is a lot of guess work. Insulation values in walls, in some cases ceilings over head is nothing more than a educated guess in a lot of instances in performing a heat load calculation in an older home.

You walk around the home (the person doing the calculation) jot figures down as you measure them. Easy as pie to make mistakes. Somebody calls you, texts you etc. Yeah it's an excuse to not do one. You could say that... but the only real reason you do one is for 'accuracy'. If you're not doing it for accuracy... well you tell me.

Certainly my neck of the woods, the figure for time on the high end -- you know time we hit the 95 mark or design temperature is actually much longer than a couple of weeks.

It's not uncommon for my area to have 100 degree heat waves that last 30 days or more... so you have to put the climate you're talking about into perspective.

The things I stated are for the most part correct. The heat of the day is still mostly relegated from 3-6pm which is 1/8th of a day.

3 hours... 24 hours in a day. Math is simple 3rd grade variety.

Do I think 4 ton is right for the log cabin. I don't know it's not my market. My vision of a log cabin may be entirely different than what is actually there.

But 2500 square foot structure is going to require some air movement... 3 tons is only 1200 CFM. If it were me... I'd probably put in a 4 ton inverter (5 speed AC, with 2 stage variable speed furnace) and call it a day. (For the log cabin home)

I am a repair man first... so my climate is predominantly AC motivated. Meaning I can count on one hand the number of furnaces I install a year. A furnace can easily last 30 years in my climate. An AC usually in the realm of 10-12 years is a very realistic average in my location.

When the conversation of replacing the AC comes up, people here want a larger AC system... not smaller. So here's another excuse to not do a heat load calc... you take all that time to do a heat load calc the people living in that home don't believe you if it comes out any thing different than what they have in there.

If it comes out different then instead of only replacing the AC, now you also need to change the furnace too... you know that furnace that is only 10-12 years old and still probably has another 15 years left of life in it.

Where I live homes are valued from 150K to maybe 450K for a 5,000 sq ft. mansion. Homes in Cali probably start at 600K for a cracker jack box. Completely different market. If you don't know your market, you're dead before you get started.

Big city life isn't for everyone, while Katy, Texas isn't big our neighbor to the immediate east is everything extreme from heat to land mass. People come here mostly to work. So the homes they are living in are not homes they intend to keep outside of the time they live here to work. Yeah another excuse to not do a heat load calc.

The cost to do one. $300 per system. You have a house with 2 systems I can do it for $600.

BTW, I just replace a builder AC unit yesterday... the thing lasted 14 years in my hot climate. Imagine that. Furnace for this home probably has at least another 15 years to go yet.

So after much reading and such we have 2 of the companies sending guys back out on Monday to do a more in-depth quote and explanation. But one thing that may have been answered is why some went from 4 ton to 3 ton. The existing (dead) system is a 3 zone system with dampers. Newer thinking is to just do a single zone system.

The first house me and mrs purchased was 1600 sq ft and 3.5T Junkatrol AC [ASHP] @Indiana. In predominantly heating climate it was sized for heat. Never lived in something more uncomfortable in my entire life. System would run for 5 min off for 20. It would not removed moisture correctly. And in the winter it struggle to warm up the house... It was oversized for cooling and undersized for heating.

=

If it is Your house and you know the insulation and can measure windows do at least the block load to see the ballpark. Not hard. I do ManJ for mine, I run duct calc to at least do the correct Equal Friction Method [if you have the software - TEL/Static Regain Method ]. Never had a good contractor that would do these properly and and correctly engineered the system. Now if I provide it - most companies will use it. Some warn that it could be "undersized" in their opinion. [ So far it was ok]. IMHO .5T or 10K BTU rarely make a difference for larger homes >2500 sq ft.

Annette, I think you're doing the right thing. Remember that proper load calcs are location specific and so whether a home in the desert or in a swamp, the relevant factors are considered.

Austin, you seem to have yourself convinced that doing load calculations are a waste of time. Here, as I said before, it's a requirement of a building permit, Building codes exist to minimize short cuts or mistakes. I'm not naive enough to think that something built to a code standard is ideal in all respects. It's to keep honest people honest and measures that exceed code requirements are often desirable.

In my opinion, to suggest that doing load calcs is a waste of time or not needed in what you do, is at best an unsupported rationalization. At worst, it's something more.

Oh, and in discussing my 3 quotes above, I forgot to say that #1 and #2 were both willing to do the work without a permit. # 3 wasn't but the cost was included. Permits also require 3rd party HERS tests be done. So the equality of the quotes meant that #1 and #2 were pocketing the avoided extra costs.

In my state, when a house is being sold and the homeowner is aware of unpermitted work that was done, it needs to be disclosed to prospective buyers. Does it matter? Probably yes in some cases, no in others. Why take a chance, the risk/reward relationship doesn't justify it.

We have the same permit disclosure question on RE transactaions. I presume that is national?

Funny you mention the builder's series A/C. My experience with tract builders is that they properly size A/C's because it saves them money. They build the house over and over again so a proper load calc is super easy - just change the orientation. I remember signing something that stated I needed window coverings and shouldn't expect my house to get below 75 in the summer. Back in 1999. I am not sure why but I remember very long run times on that house. Build by a local company that Lennar purchased just after we closed.

This is one area that custom tends to mess up.

An Indiana ASHP that isn't staged is absurd. In NC, we are pretty close with window orientation and insulation levels making some houses cooling dominated and some heating dominated. But mostly they are close enough. Go North and you are heating dominated.

In my opinion, to suggest that doing load calcs is a waste of time or not needed in what you do, is at best an unsupported rationalization. At worst, it's something more.

Ok, so I go into a home I've never been in before and my job is to repair the AC. So I repair the AC without doing a load calculation. The AC works again for a time. The home owner is relieved.

Year or two later the AC breaks again it's either repaired another time maybe more in some cases... the only reason for the call is the AC is broken.

At some point, the owner gets tired of the constant repair cycle wants a better alternative. The furnace typically still has life left in this scenario could be as long as a decade.

I know that the AC sizing is right because after fixing it there are no complaints.

But I know all to well that common sense is lost these days.

Here's an elaborate example why you can't necessarily trust a heat load calculation:

Manual J heat load calculation screw ups

Your mileage will indeed vary... Because your blind approach is to go with those who create a heat load calculation and trust that calculation is correct. Is it really correct?

" I know that the AC sizing is right because after fixing it there are no complaints. "

I was going to say "You can't be serious" but I think you are.

As for the silly article you cite, of course the result of any calculation can be rigged to come to a desired result, if you want to call it that. Conscientious HVAC contractors I've come upon use a load calc (like as done by the Wrightsoft product) as an important tool. And know that equipment being replaced is never undersized, rarely right-sized, and usually oversized. Sometimes by a lot. Without a calculation, what's left is only to guess. True experts in any field do better than that, especially with HVAC where the parameters are easily measurable and easy to analyze.

Old ductwork often needs attention too, not just for leakage but certainly for that too.

It's not a place for guesswork.

True experts in any field do better than that, especially with HVAC where the parameters are easily measurable and easy to analyze.

Old ductwork often needs attention too, not just for leakage but certainly for that too.

It's not a place for guesswork.

Ok so you're in a 30 year old house... the attic has flooring, the walls are all sealed. The windows are who knows how old or what R-value should be used to determine the heat gain / heat loss in the things listed below to determine the heat load of the structure?

The home owner recently bought the house a few years ago, so you're not getting much information from him.

So because Elmer is so smart in choosing to 'accurately' predict what R-values are to be used in a heat load calculation. You know because this is not a place for guesswork.

What R values should be used for wall insulation?

What R values should be used for ceiling insulation?

What R values should be used for entry ways into structure?

What R values should be used for windows?

Don't forget this is not a place for guesswork.

Tell me how long it will take you until you start guessing...

But hey the heat load calc says it's correct! LOL.

Experts know what they know through training and experience. R values for insulation - at a minimum, they know the what building code requirements were when the structure was built. Or standard values for particular materials (as log walls) can be found. Attic insulation - go up and look. The rest you mention is BS and you know it. If uncertain about a particular input, run the calc a few times changing the variable or two to see how much the result changes.

There's nothing controversial or uncertain about Man J load calcs. I'm not sure why you're so dismissive about tools and steps that have long been accepted by the engineers and contractors of YOUR industry, to the point of being incorporated into building codes. If you work outside of what's considered minimum acceptable standards, that's your choice and a consequence for you and your customers.

Don't forget - rural Texas doesn't have inspections. So perhaps it is not really known what is in a 30 year old wall. The door comment is ridiculous of course - doors don't matter than much and if you can't tell if a door is wood or fiberglass - then perhaps you shouldn't do Manual J's.

But in his defense - infiltration is pretty hard to guess at. And it can be a big number.

What really matters for a/c is window size, orientation and SHGC. I am sure there must me a way of field measuring (or estimating) SHGC.

Elmer, you are fighting the loosing battle. Should manj be done. Yes, and some states mandate . Is manj an approximation.... yes. You expect hvac contract to measure every single one of your windows, determine the insulation , check the depth of your insulation everywhere @ the attic and determine wall assemblies figure leak factors .... to bid on a job... Never seen this happened . You also seem to imply they should reverse-engineer your ductwork -good luck with that. I can't even find a contractor who is using nitrogen when brazes the system and properly purging... Trust me ... I decided to take 608 universal next week .. it is so crazy.

I agree and understand what both of you are saying. I just think someone who follows something short of well accepted best practices shouldn't be expounding his views of how things should be done and dismissing common industry standards. If he can get by with doing less, fine for him. Less so for his customers.

I learned some time before contracting for my first major equipment replacement job that brazing with nitrogen in the system similarly wasn't a fluffy nicety but rather is pretty important to do. That's how the first job was done and also too the second one in a different location next week. Again, that's what conscientious installers do.

Doors can also be made of glass or part glass part other material --- that's ok it's a small number we'll GUESS at it... (but every single one of you was lost on this one)

Blown in insulation in Attic what R-value? yeah go look. That's going to help a lot thanks!

Part of the Attic is inaccessible.... so what do you do for that? Guess? We'll just assume the whole attic is the same. Guess!

Remember your words exactly 'This is not guesswork'.

If you guesstimate on one thing... how long until you start guessing on other things?

Remember Mr. Fudd, again your words: 'This is not guesswork'.

It's not guesswork so much that we've begun guessing... but the number is so small it won't matter. (so much for accuracy huh?)

Yeah we know how all of this I've brought to light in this post is BS. Learning about heat load guesswork is so much fun! --- don't pay much attention here because I am merely guessing that you are having fun!

Does this mean I never do a heat load calculation? No. But I understand the pitfalls of trusting a calculation that is based on estimated guesses.

Now everything I've laid out in this post as to the inadequacies of blindly trusting a heat load calculation... how did I get so knowledgeable about such things?

From actually doing heat load calculations. I know where, what, if & how they can fail. It is a tool in the hands of someone that knows how to use it. That's it.

So my 10 y.o. N coil [copper] completely failed last year, even tho I am 608 -2 certified and have the accounts to purchase... I always used this HVAC dealer... however quickly realized this dealer moved away. And this is the house we would like to sell .. not wanted to invest.

Dealer 1: w/o looking declared total replacement provided est 14k - "best" (4k wholesale equipment), 12k better (2 speed), 11k 80%AFU 13SEER cr@p I can purchase for a little over 2k.

Dealer 2: total replacement

Dealer 3 fluent in Spanish but not english, said sure I can replace the coil, as soon as he found out where we live declared total replacement .. because he provides long warranty and he is "certified". ( I can find my name, but not his .. was seriously considered EPA bounty )

Dealer 4: declared he can swap the coil, but will not use Nitro

Dealer 5: I can replace coil for $1100 (steep for $300 coil)

Because of 90F week agreed to the dealer 5.

(1) He replaced the coil (2) asked him to remove the outside dryer because system was opened - he refused. (3) observe him brazing .. Nitro is hooked but tank is empty because you need that extra regulator .. that he does not have. (4) Pulling vac - fought him for 15 min ... He wants to check if vac holds for like 30 seconds. I am telling him 10 minutes. In the end he underchanges system by 1#. But he did came in next day to fix it.

=== Now planning new build...

Did ManJay, ManS, ManD - could not trust the dealers - they don't do it; visually size, ductwork engineering - unheard here. Thinking of investing in StayBright8 and mix acetylene M tank and $150, Testo, $83 - vac. Still less than the cost of the install.

'Contractor #1 with no load calc bid 70K furnace (that's the existing size and it warms up the place too fast and produces uneven results), 3 ton AC.

#2, also no calc, 70K furnace and 4 ton AC.

#3 did a load calc and came up with 45K furnace and 2 ton AC and highlighted some duct modifications he wanted to do.'

Elmer.....those quotes are a 'complete' ripoff!!!!!! I've read numerous articles over the years that HVAC companies on average 'double' the HAVC seer to cover their A&$#^#%#%*.

Annette....I would recommend hiring an independent professional to run log calculations on your house. It shouldn't cost much and could save thousands.

Have you thought about geothermal? No....I'm not in that business.

I"'ve read numerous articles over the years that HVAC companies on average 'double' the HAVC seer to cover their A&$#^#%#%*."

Can you please explain this and give an example? How does an HVAC company "double" a HVAC SEER?

I am thinking they double the sizing....

I went back and took another look and my recollection of pricing was wrong- #1 was the most expensive using house brand equipment, #2 was $800 less than #1, and #3 (with a much better brand of equipment than either of the others) was $1000 less than #2, which is $1800 less than #1.

The equipment costs don't account for the difference since the lowest bidder, also the most competent guy with the best recommendations and who did the load calc, will use a better brand and mid-range models, so the best equipment of the 3. My experience highlights the importance of getting multiple bids and asking probing questions to understand how the project is seen and how fair the pricing is.

So here we are 2+ weeks with no working a/c. We had 2 companies come out and requote. I finally had to check out of the process as I was losing my mind with all the back and forth. We have a Lennox system on order to be installed on May 28th. It is a dual fuel 2 stage system with a heat pump(we are on propane up here so this should help with having to refill the tank mid season). It is 16 seer.

We had discussions about 3 ton versus 4 ton sizing. What size will be installed? Since this is a dual fuel system will they be installing back up heat strips?

3 ton. The back up heat is the propane system I believe.

My husband has started reading reviews of the system we settled on and is not impressed with what he’s finding. So basically this means he will probably call the guy and put the brakes on and start all over again. I’m moving out until further notice lol.

There are a lot of opinions about Lennox equipment. Some love it, others hate it. You will read bad reviews on every brand, so I would take what you read on line with a grain of salt.

What is more important is you hire a competent HVAC contractor who will do a proper installation and stand behind his work. It appears your contractor wants to install the proper size and not copy the size of the old equipment. That is a positive sign in my opinion. Let's see if he can install in correctly and not cut corners.

To me, nearly all equipment is the same. Don't care what vendor. Some make it difficult for other dealers to obtain the parts. Bryant, Carrier AmStand, Lennox, Rudd, Amana, Trane, Ducane etc

This is why we went with this quote. The company behind it has great reviews.