Tools for planning duct layout and size

[75gmck25]

Not really a garage question.

My 2 story house (750 sq ft/ floor) has a gas boiler and radiators for heat, and a ducted A/C system in the attic. It works reasonably well, but after using a tool to measure air flow I confirmed that some rooms are coming out much better than others. I've also found that cooling for the kitchen in the 1st floor has difficulty keeping up if we are using the gas range for an extended time.

- The original ducting has a square metal insulated plenum coming off the A/C unit, with flexible insulated ducts running to each room. Some of these ducts are quite long. It seems that most of the rooms have 7" ducts, regardless of the length (shortest duct is about 3 feet and the longest is about 20 feet).
- My attic has now been spray foamed as conditioned space, so I no longer need to worry about duct insulation.
- I would like to replace several of the flexible ducts with metal ducts with balance plates so I can tweak the air flow. I could also change where each duct is connected to the main plenum.

Any suggestions for tools I could use to lay out the current system and then look at the effect of tweaking the duct size and connections to optimize the flow?

For example, if I upsize the longest room duct from 7" to 9" will that help out the air flow in that room, or would I also have to connect it closer to the main A/C unit (its currently the last duct connected to the square plenum)?

Thanks for any input.

 

[metaldad]

tool for planning - ductalator.
gives friction of duct, to size a duct system.
volume dampers, will help.

https://www.amazon.com/dp/B006XIQ7DM/?tag=atomicindus08-20

 

[fitter30]

Round duct has a lot less restriction that even pulled tight flex. Every takeoff should have a balance damper right off the main. Every joint should also be sealed with duct sealer.

 

[75gmck25]

Thanks. I ran across a youtube video for the air duct calculator tool and it looks like it has most of the information I need for basic calculations.

The one part I'm not sure of is when you use a square plenum as the main feed, with round ducts off of it, do you need to worry about how far each round duct connection is from the A/C unit. For example, if the square plenum is 15 feet long, one round duct might be connected only 2 feet from the A/C unit, while other round ducts might be connected up to 14 feet from the A/C unit.

 

[bonneyman]

tool for planning - ductalator.
gives friction of duct, to size a duct system.
volume dampers, will help.

https://www.amazon.com/dp/B006XIQ7DM/?tag=atomicindus08-20

X2 Ductulator is the only way to go.

Here's one for flex duct: https://www.hvacwholesaledirect.com/buy/product/Atco-Rubber-Products-Ductulator/102

Here's a website with several styles of ductulators, including the slide rule type that I'm familiar with. Plus instructional videos!

HVAC Air Duct Slide Calculators | Custom Duct Calculator Slide Charts | Datalizer

Air Duct and HVAC Slide Charts. Superheat and Subcooling Calculators. Duct Wizard Ductulators. Fan Law Wheel Charts. Refrigeration Slide Rules and more.

www.datalizer.com

 

[mrobins297aaa]

I would start with making sure you have volume dampers in all the branches.
See if you can get the air flow you want in each room by adjusting the dampers, if that doesn't work I would try adding a extra 6" run to the rooms that your having a problem with.

 

[karoc]

Know this isn’t answer to your question, couple things come to mind. Is system size properly, do you have correct size return air? And is your coil clean if you have one? Hard pipe now days is very expensive plus duct wrap and very labor intensive. Dampers can be installed at plenum to help balance the air or you can install motorized dampers that’s operate off thermostat. I guess basically it’s matter of how far want to go. If it was me and I was going spend that kind of money, I would call in professionals. My comments are from my yrs in trade in my younger days. There’s no telling what’s available now to help customize HVAC system

 

[duneslider]

You can go it alone and it isn't impossible to figure out but you might be happier if you get a Manual D report assuming a manual J was done to size your equipment. You can usually get a Manual J and a Manual D for under $500 and that will tell you what equipment you should have and what the ducting should be.