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How many BTU's do I need?

Lael
Lael Member Posts: 4
in THE MAIN WALL
How many heating BTU's do I need? 

I live in Stamford, CT 06901 and I recently expanded the bathroom (installed all new insulation and drywall and taped and sealed joints) and need to install the right size hot water baseboard heater, however, all the website calculators I've tried give me different answers.  I'm looking at the Runtal baseboards because depth spacing is critical as my vanity drawers are 2.5" from the wall and the Runtal baseboards are 2" from the wall.   Here are the specs:

Bathroom dimensions from wall to wall 5'x12'x8'(ceiling)

The bathroom has two exterior walls one is 12' the other is 5'.

The bathroom shower is a steam shower and will be completely enclosed by 1/2" glass.  The enclosure size on two exterior walls is 5'x3.5'x8'.  Insulation on exterior walls for shower enclosure is R-30.

There is 1 brand new Castle Window double hung window measuring 1.5'x3'. 

Porcelain tile on floors of bathroom and floors, walls and ceiling of shower/steam room.

The attic is above the bathroom and there is R-30 insulation in the attic.

There is a 1st floor below the bathroom which is heated, however there is no insulation in the floor joists.

The bathroom has a 30" pocket door.

I hope this is enough information.



Thanks,

Lael

Comments

  • CMadatMe
    CMadatMe Member Posts: 3,086
    2 Candles

    What water temps are we running? A 2' of hydronic baseboard would heat this space easily. Did you consider a towel warmer instead of the board?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Lael
    Lael Member Posts: 4
    I'm using 180 degree water.

    I'm using 180 degree water. A towel warmer will extend out more than 2.5" from the wall and I need no more than 2".



    I don't think 2' of standard slant fin would suffice as its approximately 600 btu per foot. Is 1200 BTU enough for this bathroom?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited August 2010
    Not Necessarily

    What's the flow rate of the zone? Can't tell me if you don't know the heat loss of the home and the zones. We must use the 1gpm flow rate which puts it at 550 ft. A 60sqft bathroom such as you described is not putting out more than 20btu's a sqft Releastically probably between 12 and 15.



    After I posted the above  I ran the loss based on the given infromation. 1006 btu's
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Lael
    Lael Member Posts: 4
    Flow rate is 4 gpm

    I've tried calculating the heat loss but remain confused as I'm not a heating pro. So assuming my heat loss is 20 btu's a sqft how many btu's would I need per sqft or total for this bathroom. Is 2,400 overkill? There is a product with 1,868 I would consider. Please give me a number.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    So that Zone's Heat Loss

    Is 40,000 btu's? Where did that number come from? I would willing to say your wrong but don't know the entire floor plan. 
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Lael
    Lael Member Posts: 4
    Let me clear the air, I have no idea what the heat loss is

    The zone is comprised of 6 rooms all on the 2nd floor and this room is half way through the entire zone. There is probably a total of 30 ft of slant fin before this room and an additional 20 ft after this room.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited August 2010
    Please

    Do't get upset or frustrated. Just trying to help you out the correct way. So 50 foot of board at a 4gpm flow rate would only give me 30,000 btu's of output so we know you do not have a flowrate of 4gpm. Use the 1 gpm flow rate and as I posted previsouly the loss is just over 1,000 btu's so a 2'piece of fin-tube board would do the job.



    Flow rate is calculated in your case as 500 divided by heat loss of the zone = gpm. If your heat loss was 40,000 btu's (4gpm flow rate) you would have more board than you stated. When the heat loss is unknown we always use the 1gpm ratings of baseboard from the mfg's baseboard chart. I calculated the heat loss based on what info you gave and used the 1gpm rating for the board which is 550 btu's a foot. At a minimum it's oversized if your flow rate is more than 1gpm. Which it probably is. Your more likey to see about 580 a ft out of that board based on the information prodvided. The smallest length of fin-tube board sold is 2'.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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