# Thread: Electric Baseboard Heat Calculation

1. Senior Member
Join Date
Jun 2005
Location
Massachusetts
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1,508
Originally Posted by K8MHZ
I have a LUX line volt tstat that goes as low as 45.
I'd be concerned that the additional 5 degrees would add a lot of cost for the power. We pay about 20 cents per kWh. Of course I don't know if it would be be an additional \$100 or \$1,000 per year

2. Like K8 said, the lows and highs don't matter much. Concrete has a lot of thermal mass. The temperature tends to reflect the daily average as long as draft is kept out. Radiant heater is effective for human comfort when its not practical to heat the air.

Air that dryer vents out has to come in from somewhere so you have to be careful to avoid drawing air with dew point higher than the wall surface behind the insulation. This is especially in the shoulder season when the average temperature is quite low but it gets warm and humid in the day.

3. Originally Posted by Electric-Light
Like K8 said, the lows and highs don't matter much. Concrete has a lot of thermal mass. The temperature tends to reflect the daily average as long as draft is kept out. Radiant heater is effective for human comfort when its not practical to heat the air.

Air that dryer vents out has to come in from somewhere so you have to be careful to avoid drawing air with dew point higher than the wall surface behind the insulation. This is especially in the shoulder season when the average temperature is quite low but it gets warm and humid in the day.
If you are discharging dryer heat into the space, it is not drawing any fresh air from outside

4. Originally Posted by kwired
If you are discharging dryer heat into the space, it is not drawing any fresh air from outside
If you discharge it into the space, you dump humidity into the air. If you discharge it outside, the air is drawn in from somewhere. If the outdoor air at the time has a higher dew point than the basement wall surface it will condense.

5. Originally Posted by Electric-Light
If you discharge it into the space, you dump humidity into the air. If you discharge it outside, the air is drawn in from somewhere. If the outdoor air at the time has a higher dew point than the basement wall surface it will condense.
Correct, but also consider that zero degree air won't hold as much moisture as 40 degree air. Bring that same air inside without adding any moisture to it, as it heats up it's dew point goes lower not higher.

Open a door on a cold day, any "fog" you see is existing primarily existing indoor moisture condensing in the cold air that entered.

Add: you can't have dew point higher then actual temperature - you will be under water if you did.
Last edited by kwired; 09-10-17 at 12:50 PM.

6. Senior Member
Join Date
Apr 2007
Location
Berkeley, CA
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Originally Posted by kwired
Bring that same air inside without adding any moisture to it, as it heats up it's dew point goes lower not higher.
If you heat the air without adding or removing moisture from it, the dew point will stay the same.

Cheers, Wayne

7. Originally Posted by kwired
Correct, but also consider that zero degree air won't hold as much moisture as 40 degree air. Bring that same air inside without adding any moisture to it, as it heats up it's dew point goes lower not higher.

Open a door on a cold day, any "fog" you see is existing primarily existing indoor moisture condensing in the cold air that entered.

Add: you can't have dew point higher then actual temperature - you will be under water if you did.
You're forgetting that heavy thermal mass lags behind significantly such as heavy concrete walls below the frost line.
Low average temperature will keep basement walls chilled but the local dew point can swing rapidly along ground level as sunshine hits the ground. When you use your dryer, the negative pressure draws in the make up air.

The airflow stops when dryer stops but the remaining moisture gives plenty of chance for things to grow.

8. From Wikipedia - "Dew point is the temperature to which air must be cooled to become saturated with water vapor. When further cooled, the airborne water vapor will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface"

Warm air is capable of holding more water vapor then cold air. You take cold air into a warm space and it will absorb what moisture was in there easily, it will not condense. If any condensation occurs it is moisture that was already in the warm air condensing when it hits the cold air.

Condensation on a foundation wall would be from the wall temperature being below dew point of whatever mixture of air is near the wall.

9. Originally Posted by kwired
From Wikipedia

Condensation on a foundation wall would be from the wall temperature being below dew point of whatever mixture of air is near the wall.
Where do you you bathroom fans and dryers get the air they exhaust?

Warm, moist shoulder season air from outside or upper living area that flows around behind insulation when the dryer is running will condense out onto the interior facing foundation wall and the insulation will get wet. Insulation is for the cold season but since it stays year around, it has an influence all year long.

Leave something like a big gallon jug of water on a plate of starch in the shed. in a box. The jug will chill nice and cold when the average temperature is low but but when moist outside air wafts around the ground, it will condense and drip down the side and wets the flour and high humidity will slow down drying. Eventually the starch can get moldy. The worst happens when slow warm moist air is drawn around it when the container is still cold but without free airflow during the time it's above dew point to dry it out. Like the area in between vapor barrier and cement.

https://www.extension.umn.edu/enviro...and-solutions/

Exterior humid air that enters the basement and condenses on cooler surfaces.
Last edited by Electric-Light; 09-10-17 at 11:55 PM.

10. Originally Posted by Electric-Light
Where do you you bathroom fans and dryers get the air they exhaust?

Warm, moist shoulder season air from outside or upper living area that flows around behind insulation when the dryer is running will condense out onto the interior facing foundation wall and the insulation will get wet. Insulation is for the cold season but since it stays year around, it has an influence all year long.

Leave something like a big gallon jug of water on a plate of starch in the shed. in a box. The jug will chill nice and cold when the average temperature is low but but when moist outside air wafts around the ground, it will condense and drip down the side and wets the flour and high humidity will slow down drying. Eventually the starch can get moldy. The worst happens when slow warm moist air is drawn around it when the container is still cold but without free airflow during the time it's above dew point to dry it out. Like the area in between vapor barrier and cement.

https://www.extension.umn.edu/enviro...and-solutions/

Exterior humid air that enters the basement and condenses on cooler surfaces.
I do not see any examples in the link of cold outside air coming in and condensing, just warm moist outside air coming in and condensing on cooler surfaces.

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