# How much heat is lost through finished basement concrete floor



## Drewbabich (Jul 29, 2016)

Hi. I'm going through my first winter and I am trying to gauge how much it'd be worth insulating my basement floor.

I live in Maine an hour north of Boston. I have a 1200 SQ foot basement that I had 2.5 inches of spray foam put on the walls.

We are running 4 water fed baseboard heaters totalling about 20 feet in length. 

They are all on the interior walls of the basement

I have 3 bedrooms with carpet and foam under the carpet which should provide an r value of about 2. 

In the other half of the basement I want to put in vinyl tile right on top of the concrete.

My HVAC guy says once you heat up the concrete floor it 'holds the heat real good'....

I have trouble believing that. But I'd love to not insulate the floor if its not a huge heat loss. Cold floors don't bother me so as long as the space is warm.

Advice or any statistics to support pros cons of insulating the floor would be great.

If I ever build a house I'll insulate below the concrete. That wasnt done here.


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## user_12345a (Nov 23, 2014)

it's pretty low. you can make the floor more comfortable with insulation, but shouldn't make a big difference when it comes to energy use.

floor is well below the frost line, probably no more than 2000 btu/hr.


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## Nealtw (Jun 22, 2017)

Heat goes up so little is trying to heat the floor I doubt you would measure a difference in floor temp if the house cold.
We put foam under the concrete just around the perimeter when the slab is at surface level outside.
And under the whole floor when hot water is going in the floor. And I question that. As the heat still goes up and if you do warm the sand below it will only take heat at start up and will maintain heat when power is out.
If I had water heat in the basement I would look at a skim coat of concrete with heat in it.


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## Bud9051 (Nov 11, 2015)

I've seen the temperature gradient illustrations for basement floors and below grade foundations and the deeper the source of heat the longer it takes to migrate to the surface. And insulation is exactly that, slowing the time it takes the heat to escape. Thus, all of that soil below and up to the surface amounts to a very large r-value. A quick example. If you had 10 rooms adjacent to each other with heat in the first one and one exposed cold wall at the last one the temperatures would decrease uniformly from room to room with the same temperature difference across each wall. Same temp difference would mean the same heat flow. Thus the net heat flow would approximately 1/10 that of a single wall with the total delta temp.

With a basement floor only a limited area actually leads to the surface. The rest just soaks into the ground extending that 10 room example to 100 rooms and a very slow rate of heat loss.

The exception to all of the above would be water intrusion. Some homes set very close to the water table and that water will greatly increase the heat loss.

The basement floor will not feel warm but its contribution to heat loss will be minimal. 

Bud

Sorry I type slow


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## user_12345a (Nov 23, 2014)

> Heat goes up so little is trying to heat the floor I doubt you would measure a difference in floor temp if the house cold.


Heat moves in all directions, warm air rises in presence of cooler air.


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