Sizing HVAC system

[webdog]

My new post frame building is a 40x64 so 2560 sqft, 12 ft ceilings. The walls are R25 and ceiling R50-60. The building is split with 600 sqft as office space and the rest is the shop space.

I had a local HVAC company come out and quote and they recommended a 3.5 ton AC and 80k but 96% furnace.

When you look online the charts are closer to 4-5 tons for AC in that sqft range,
and heating closer to 120k btu.

What do you all recommend? Go with what the HVAC guy says? I plan to order a unit and do the rough install and then have him come out for final install and turn on to validate the warranty of the unit.

 

[MattT]

Most square footage charts are based on poor to average insulation so I'm not surprised that the HVAC guys recommendation is smaller.

Not sure how well trying to condition the office and shop with one system will work though.

Edit: Forum software appears to have turned "office" into a link. I advise not clicking it.

 

[webdog]

Most square footage charts are based on poor to average insulation so I'm not surprised that the HVAC guys recommendation is smaller.

Not sure how well trying to condition the office and shop with one system will work though.

Edit: Forum software appears to have turned "office" into a link. I advise not clicking it.

That may be the case, we did try to seal this building uptight, house wrap, extra foam between girts, etc...

We want to keep the office and shop at the same temperature. The shop will be mostly wrenching on vehicles and warehouse area, all the nasty welding and fume-generating fun happen on the old building with its own HVAC system.

or is there another reason you say that?

 

[Ohmthis]

Proper sizing takes way more into consideration than SqFt. Other things to consider are insulation, type of, how many windows, size of windows and doors, where are they located, how many appliances, how many people, what area you live in. So being 1/2 a ton smaller than a chart is ok.

 

[danski0224]

My new post frame building is a 40x64 so 2560 sqft, 12 ft ceilings. The walls are R25 and ceiling R50-60. The building is split with 600 sqft as office space and the rest is the shop space.

I had a local HVAC company come out and quote and they recommended a 3.5 ton AC and 80k but 96% furnace.

When you look online the charts are closer to 4-5 tons for AC in that sqft range,
and heating closer to 120k btu.

What do you all recommend? Go with what the HVAC guy says? I plan to order a unit and do the rough install and then have him come out for final install and turn on to validate the warranty of the unit.

This is one reason why I never disclose the size of the unit until the deal is done- to prevent being cut out of the equipment sale, unless that arrangement is agreed upon.

You need to pay your money and get a load calculation performed on the proposed space.

There are people that just perform load calculations for code requirements and do not install equipment.

HVAC-Calc has a limited use homeowner license for $50 last I checked, but that does not apply to their commercial version (your building is classified as commercial).

There are other possible issues, but consultation costs money

 

[webdog]

This is one reason why I never disclose the size of the unit until the deal is done- to prevent being cut out of the equipment sale, unless that arrangement is agreed upon.

You need to pay your money and get a load calculation performed on the proposed space.

There are people that just perform load calculations for code requirements and do not install equipment.

HVAC-Calc has a limited use homeowner license for $50 last I checked, but that does not apply to their commercial version (your building is classified as commercial).

There are other possible issues, but consultation costs money

I flat out told the company that I intended to purchase and install the unit and then have them come out for final install and turn on, they had no issue with going that route. He was also here on a service call for our old unit that went out so he made some money while out giving us the quote anyway.

I did a calculation and came up with closer to 100k heat and 32k cooling not counting all the heat producers (computers, people, doors open/close, etc...). I am leaning towards the recommended 3.5ton AC and 100k btu two-stage heater, the extra heating as the shop space may have vehicles coming in and out during the winter.

 

[MattT]

That may be the case, we did try to seal this building uptight, house wrap, extra foam between girts, etc...

We want to keep the office and shop at the same temperature. The shop will be mostly wrenching on vehicles and warehouse area, all the nasty welding and fume-generating fun happen on the old building with its own HVAC system.

or is there another reason you say that?

You've covered most of the reasons I mentioned it. You might still get some unacceptable temperature variation in whichever space doesn't have the thermostat but that can be fixed by forcing the duct fan if it becomes an issue.