Who should do Manual J calc?

[Ed D]

My question has to do with industry standard practices. The evaporator coil is leaking on my 9 year old Carrier AC. At 9 years the AC isn't real old but I have had problems with it and decided to replace the system with a 16-18 seer unit. I intend upon getting 3-4 bids for this work.

One of the contractors gave a price for running the Manual J calc.I don't want to pay for this three times. Should I have an independent run the calcs, or can I get one of the bidding contractors to run the numbers and supply the same print out to all?

[mlstark]

some contractors will charge a price to do load calcs, but if you choose them they'll deduct it from quote. Some will even do it for free, but sometimes you get what you paid for.
It is a good idea to know up front exactly what size equipment is needed so all bids will be apples to apples.

[Ed D]

Thanks. I have a related question. My house is two stories and we have some difficulty balancing the temperature on the second level. The house is well insulated but Orlando can get hot and we use AC year round. Will the Manual J calc help identify any issues with the current ductwork and design?

[mlstark]

A manual D is for duct calculations and sizing, that may be helpful for your situation.

[beachtech]

a properly done load calculation should help determine this issue.

if you continue to go forward with one system, a cone system will help and can help even the tempuratures between upstairs and down.

apples to apples also includes the type of system, warranties, and efficiencies.

[Ed D]

Thanks for the feedback.

Ed

[simplyrollin]

My question has to do with industry standard practices. The evaporator coil is leaking on my 9 year old Carrier AC. At 9 years the AC isn't real old but I have had problems with it and decided to replace the system with a 16-18 seer unit. I intend upon getting 3-4 bids for this work.

One of the contractors gave a price for running the Manual J calc.I don't want to pay for this three times. Should I have an independent run the calcs, or can I get one of the bidding contractors to run the numbers and supply the same print out to all?

In NC, we are required to do Manual J calcs. It takes about half a day to do them. Would you work for half a day for free?

[dan sw fl]

In NC, we are required to do Manual J calcs. It takes about half a day to do them. Would you work for half a day for free?

Work Process and type of calc need to be reviewed

:whistle:
After you perform 6 calcs and use appropriate templates, whole house calcs should take < 20 minutes for house < 2,000 square feet.

Whole house calcs and room-by-room calcs have distinctly different functions.

A room-by-room calc can be performed in less than an hour with a little practice.

[lynn comstock]

...if you continue to go forward with one system, a cone system will help and can help even the tempuratures between upstairs and down. ... I almost asked what a cone system was... only to realize you meant ZONE system. :) and Yes, I agree.

[Hunter844]

I almost asked what a cone system was... only to realize you meant ZONE system. :) and Yes, I agree.


I was scared to ask...thought we had warped into something new. :whistle:

[heaterman]

Work Process and type of calc need to be reviewed

:whistle:
After you perform 6 calcs and use appropriate templates, whole house calcs should take < 20 minutes for house < 2,000 square feet.

Whole house calcs and room-by-room calcs have distinctly different functions.

A room-by-room calc can be performed in less than an hour with a little practice.

Have to agree here :) As far as the OP, Manual J is part of the job but to give you the info up front makes it easy on the c ontractors to follow. I have mixed feelings about charging up front for a Manual J . We do a quick whole house to put us in the ball park for estimate purposes and do a refined Manual J (room by room) when the situation warrants it. We do not supply ANY printed Manual J information until the job is signed, sealed and delivered :)

[HVACTechNC]

A simple block load for a change out situation should not take more than 30-60 minutes, and we do those for free on any change out we quote. If there is a need to do a room-by-room or a manual D then we do charge for it as it is more labor intensive. We do deduct the cost off the job if it is awarded to us. Minor variations on block loads may occur from one contractor to another so don't be suprised if there is some minor differences. So long as the difference is not more than 5-10% of the total load then I would not worry about it too much.

If one says, say a cooling load of 34,000 and another says 35,500, dont worry about it. If one says 34,000 and another says 42,000 then someone has something wrong and needs to check their math.

[skibme]

I found using a distance meter in addition to a tape measure helps you do it faster.Tape measure for windows and doors.

[Ed D]

Gentlemen,

Thanks for the great feedback and advice. Unless someone has a different perspective I think I have enough information to proceed. My profession is road contracting so I do appreciate the personal sacrifice each of you made in pulling away from your families and business to help me. I am an avid DIY but I learned along time ago if the pro makes it look easy, IT ISN'T!. Fixing my AC problems is one place where I want to hire the best and make sure they do it right. Thanks again.

Ed

[Gunslinger]

I perfer to do my own load calculations as I will not trust anyone else since I will responsible if the sizing is incorrect. Every changeout should have a whole house calc done. The old unit may have been the wrong size to start with and with today's more efficient equip, you may get away with a smaller system. And yes you may have to pay for it.

[tipsrfine]

A manual J is not your first step in sizing your new a/c system. The first step is determing what can be done to improve your homes "thermal envelope". This can be done by a BPI or RESNET trained energy auditing company. The odds are very good that your existing system was oversized by as much as 1 or 2 tons, that your ductwork is undersized to accomodate your existing system, and that the only reason you havn't noticed a problem with these facts is because your home is too "leaky" (air infiltration) and your ducts are too leaky.
It is estimated (by someone with a brain) that only 1 in 10 existing duct systems were installed in a manner that will allow newer higher efficiency systems to operate at even 80% of their rated efficiency levels.
Forget "industry standard practices" and find a company that is re-writing those practices.

[pdlandry]

beachtech
great Neil Young link ...... thanks

[dan sw fl]

I found using a distance meter in addition to a tape measure helps you do it faster.Tape measure for windows and doors.

I just keep my stride and eyes calibrated.

...
__ GreAt MeaSUREment TOOLs.

[Furpants]

Well sh*t. Now what do I do? Ask the best contractor to do a heat loss evaluation on the site?

[rickboggs]

The odds are very good that your existing system was oversized by as much as 1 or 2 tons, that your ductwork is undersized to accomodate your existing system,My shop manager and I were just discussing this yesterday.... we were just kinda saying.... Why?? It was prompted by an estimate I was working on. Big beautiful house, big oversized equipment, way undersized duct.