How To Determine House Square Footage HVAC

[Gebo]

First of all, I know how to measure and multiply and add.

I’m considering a new HVAC system and am trying to do a little research on my own.

My main floor living area is 2000 ft 2. Downstairs is 90% underground and a finished 1500 ft2. When my system was installed 30 years ago, my basement was unfinished.

Do I just add them together or do I discount my underground living area?

My old Lennox Pulse from 1993 still running strong.

 

[brianl703]

The correct way is a Manual J calculation.

 

[Gebo]

The correct way is a Manual J calculation.

I’m not sure if you are trying to help me or make fun of me??

I’m gonna google Manual J.

 

[drtyler]

If the 1993 system is running strong, why are you considering a new system?

 

[Hillbilly Deluxe]

DO NOT use one system for multiple floors with or without zone dampers. Use a separate system for each floor. At least a separate indoor system (you can put multiple indoor units on a single condensing unit with mini-split type condensing units).

So to answer your question, use the square footage for the first floor for a system and the square footage for the basement for a system.

 

[Gebo]

If the 1993 system is running strong, why are you considering a new system?

I’m just getting a feeling…

 

[Gebo]

I’m not sure if you are trying to help me or make fun of me??

I’m gonna google Manual J.

Thank you! That is awesome info.

 

[Hillbilly Deluxe]

These people that talk about a "Manual J Calculation" are trying to sound like they have some intricate knowledge of HVAC design.


Real HVAC designers/engineers never say that. We talk about heat gain/loss calculations.... Hardly anyone does this manually anymore. Most use Carrier's HAP (Hourly Analysis Program) or Trane TRACE software for load calcs...

 

[Gebo]

DO NOT use one system for multiple floors with or without zone dampers. Use a separate system for each floor. At least a separate indoor system (you can put multiple indoor units on a single condensing unit with mini-split type condensing units).

So to answer your question, use the square footage for the first floor for a system and the square footage for the basement for a system.

You make a good point. I’ve had a single system since 1994 and it’s been fine. I’ll consider your advice.

 

[Hillbilly Deluxe]

Also.... Be prepared for sticker shock. A residential system change out today with decent equipment (not Daikin, Mitsubishi) is running $3500-5000/ton for equipment, new refrigerant piping and MINOR ductwork modification. There's some new efficiency regulations in effect for 2023, with new refrigerant regulations coming in 2024 or 2025. The manufacturers are in a tizzy....they have some major expenses renovating lines for all this and they pass that expense on to who buys the equipment.

 

[Hillbilly Deluxe]

You make a good point. I’ve had a single system since 1994 and it’s been fine. I’ll consider your advice.

I would highly suggest a modern, premium system like a multi-port system from Daikin or Mitsubishi. This is one condensing unit and you can have 2-3 indoor air handlers.

 

[KrisZ]

These people that talk about a "Manual J Calculation" are trying to sound like they have some intricate knowledge of HVAC design.


Real HVAC designers/engineers never say that. We talk about heat gain/loss calculations.... Hardly anyone does this manually anymore. Most use Carrier's HAP (Hourly Analysis Program) or Trane TRACE software for load calcs...

Us mere mortals only have access to manual J though. So that’s what we can recommend.

Having said that, if you already have a system in your house and you are satisfied with its performance, there should be no need for doing any calculations. They will most likely come up pretty close anyways.

I did the calcs in my first house since I elected to install the AC on my own instead of paying the builder to do it. They came up to around two tones. All contractors recommended 2 to 2.5 tones based on square footage. I went with 2 tones and the system performed very well.

 

[brianl703]

These people that talk about a "Manual J Calculation" are trying to sound like they have some intricate knowledge of HVAC design.


Real HVAC designers/engineers never say that. We talk about heat gain/loss calculations.... Hardly anyone does this manually anymore. Most use Carrier's HAP (Hourly Analysis Program) or Trane TRACE software for load calcs...

Manual J calculations are required in 29 states, including the one I live in.

 

[Gebo]

I would highly suggest a modern, premium system like a multi-port system from Daikin or Mitsubishi. This is one condensing unit and you can have 2-3 indoor air handlers.

I have HP with propane for heat. I have thermostat set to use propane at 40 degrees or less. 16 cents/kWh vs $2.33/gal propane.

 

[Gebo]

I get 47,800. 4 tons.

How do I calculate heat? Using propane.

 

[Gebo]

I would highly suggest a modern, premium system like a multi-port system from Daikin or Mitsubishi. This is one condensing unit and you can have 2-3 indoor air handlers.

I don’t even know what an air handler is???

Are you saying I have one outside unit with 2 or 3 furnaces inside?

 

[brianl703]

I don’t even know what an air handler is???

Are you saying I have one outside unit with 2 or 3 additional pieces inside?

Assuming you don't want to spend a lot of money and have wall units in your house, just ignore that recommendation. You already have duct work, it would make sense to use it for the new system.

 

[Gebo]

Hey, I’ve had the same propane furnace since 1993 and am on my second HP. Yes, I am ignorant at this point. I’m trying to gain enough knowledge to be somewhat aware of recognizing truth when I speak with a couple of HVAC companies. We only have 2 “reputable” ones here. Over 30 years in business.

 

[BMWTurboDzl]

First of all, I know how to measure and multiply and add.

I’m considering a new HVAC system and am trying to do a little research on my own.

My main floor living area is 2000 ft 2. Downstairs is 90% underground and a finished 1500 ft2. When my system was installed 30 years ago, my basement was unfinished.

Do I just add them together or do I discount my underground living area?

My old Lennox Pulse from 1993 still running strong.

Best to pay a professional.

Example

HVAC Design - Energy Vanguard

www.energyvanguard.com

 

[brianl703]

Hey, I’ve had the same propane furnace since 1993 and am on my second HP. Yes, I am ignorant at this point. I’m trying to gain enough knowledge to be somewhat aware of recognizing truth when I speak with a couple of HVAC companies. We only have 2 “reputable” ones here. Over 30 years in business.

Assuming that your system was sized correctly from the start, and the only change you've made is to finish the basement, the basement does not increase your cooling load. So you need to figure out how much the basement will increase your heating load, or have someone do that for you.

In my experience furnaces tend to be oversized to begin with, so you may not need a bigger furnace. (Theoretically, a furnace sized just right will run continuously at the coldest outdoor temp it was sized for. I've NEVER seen that happen anywhere I've lived..)

I saw elsewhere that you are running the propane furnace below 40F outside. That seems a little high, have you tried adjusting it down some? My heat pump (a single-stage Trane from 2017) will easily keep up even at 20F outside...but my house is very well insulated and air sealed.