# BTUs you need for a given area.

#### biferi

Joined Apr 14, 2017
394
I had notes on the Math you use to find how many BTUs you need for a given area.

Square Footage in Feet X

I do not have the other part of the Formula.

What do you Times the Square Footage by to find the BTUs you need for an area?

I live in the USA.

#### BobTPH

Joined Jun 5, 2013
9,299
There are so many other factors, one more cannot possibly give a very accurate result.

First of all, are we talking about heat or cooling?

In what climate?

Ceiling height?

Insulation?

And certainly others I am mot thinking of.

#### MrChips

Joined Oct 2, 2009
31,106
Units of area is length x length, hence square footage is feet x feet = feet squared or feet^2.

#### MrSoftware

Joined Oct 29, 2013
2,212
There's quite a bit more to it. What you really need to be accurate is total square footage of the ceiling, walls and floor, insulation factor for each surface and desired temperature differential for each surface. Then you can calculate heat loss through each surface and determine how many BTUs are required to maintain some temperature. It's a bit involved, so when you're reading the suggestions on the box for an A/C or heater unit, they just assume some averages for most of it. Tell us more about your ultimate goal and maybe we can help more. i.e. are you trying to pick out an A/C unit for a room, or are you trying to build a calorimeter?

#### MrSoftware

Joined Oct 29, 2013
2,212
Units of area is length x length, hence square footage is feet x feet = feet squared or feet^2.

View attachment 322238
These recommendations are so general they're almost misleading. For example, a small 6k BTU unit will keep our master bedroom cool at night, but the same unit can barely keep my similarly sized garage below 90 degrees on a summer afternoon. There are just so many variables.

#### BobTPH

Joined Jun 5, 2013
9,299
This site shows how to calculate based on square footage and climate zone.

#### MrChips

Joined Oct 2, 2009
31,106
It is well understood that the TS has omitted a lot of important parameters.
For example, heating/cooling, and “I live in the USA”, Texas vs Colorado?

#### ronsimpson

Joined Oct 7, 2019
3,229
In Colorado you must build houses with 6-inch-thick walls for insulation. I have seen many houses in the south without insulation at all.

#### MrChips

Joined Oct 2, 2009
31,106
Let's be more specific.
For 2400 sq. ft in Zone 5, my Trane furnace is 80,000 BTUs.
That works out to 33 BTUs per sq. ft.

#### BobTPH

Joined Jun 5, 2013
9,299
Let's be more specific.
For 2400 sq. ft in Zone 5, my Trane furnace is 80,000 BTUs.
That works out to 33 BTUs per sq. ft.
Which is only good enough for Zone 1 according to the site I posted a link to!

#### MrSoftware

Joined Oct 29, 2013
2,212
In Colorado you must build houses with 6-inch-thick walls for insulation. I have seen many houses in the south without insulation at all.
I'm a S. FL native, the house I lived in as a kid had only concrete walls with no insulation. But it also did not have whole house air conditioning or heat at all. Now that houses have air conditioning, insulation is a lot more important for your power bill. Though the temperature differential isn't as bad as up north so they tend to skimp on the insulation, much to the disappointment of my wallet. If it's 100 outside and you cool the inside to 75, that's only 25 differential, compared to up north where I guess it could be 0 outside and maybe 65 inside?