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# How to calculate the size and determine the correct location of radiators/BB ?

#1
11-15-13, 09:01 AM
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Join Date: Oct 2013
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How to calculate the size and determine the correct location of radiators/BB ?

I was wondering how to calculate the size and determine the correct location of radiators/baseboard for the given room.

I can understand that using Slant fin heat loss calculator I can calculate heat loss. The reason I ask this because my back family room extension has Slant Fin baseboard along two wall (3 walls of that room is completely exposed to outside) and 4th side of the room leads to open kitchen) and that room is not heating as great as I want. Mind that those 3 walls are full of windows and 1 door. Rest of the house had recessed radiators.

#2
11-15-13, 09:53 AM
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Location: USA
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The Slant-Fin program will tell you how many feet of baseboard you need in each room.

You can calculate just that one room if you want.

Location is generally on outside walls and under the windows.

How many square feet is the room?

#3
11-15-13, 10:10 AM
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Join Date: Oct 2013
Posts: 91
Total square feet is approximately 400. It has baseboard on two walls - so length is roughly 40 feet (16 + 24) feet. It has cathedral ceiling with 2 sky lights(probably 4.5 square feet each). The 3 exposed walls has roughly 45 linear feet of windows and doors.

#4
11-15-13, 10:26 AM
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Is that 40 feet of baseboard nearly all finned element? Let's use some conservative numbers.

500 BTU per foot is conservative if the baseboard is Slant Fin Fine Line 30 series.

That's 20K BTUH of heat emitters. (with 180° water, your water is probably not getting that hot at this time of year...)

Let's take a REALLY lossy number of 40 BTU/SQ FT ... that's 16K BTUH of heat loss.

IF you did have 180 water entering, you should have enough baseboard out there.

Here's what's probably happening:

Home is all one heating zone. Thermostat is located in part of home that is warmer and less heat loss.

This time of year heat calls are probably satisfied before water gets to 180.

Baseboard to this room is probably piped into the rest of the system in the middle of the loop and thus is not getting full temperature water anyway. (cooled some in other radiators before it gets there)

If baseboard is piped as monoflo, there may not be enough flow to the baseboard. There are limits to how long a run can be done with monoflo tees. (If the pressure drop of the baseboard run approaches the pressure differential of the monoflo tee there will be little flow in the run)

It may be that no amount of baseboard you put out there will improve the situation if a) the water is not hot enough, b) the thermostat doesn't call for heat in the home often enough, c) the flow through the loop is weak.

Can you take a look and see how that loop is tied into the rest of the piping? Pictures too if you think they will help...

#5
11-15-13, 06:37 PM
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Join Date: Oct 2013
Posts: 91

Is that 40 feet of baseboard nearly all finned element? Let's use some conservative numbers.
Yes, it is!

500 BTU per foot is conservative if the baseboard is Slant Fin Fine Line 30 series.
Not sure the model but it has Slant Fin written on it. It was added to house sometime in 1990-1993.

This time of year heat calls are probably satisfied before water gets to 180.
Though I have surface mount aquastat set at 180(remember other post, that you helped solve the relief valve mystery), and when I set the thermostat to 69, the boiler keep tripping every 4 minutes even though thermostat is calling for heat... it shuts off for 4 minutes and comes back on for 1.5 minutes, so I would think that Johnson Aquastat set at 180 F with preset 10F differential, water is loosing 10F within 4 minutes and boiler is bringing that back in 1.5 minutes.

If baseboard is piped as monoflo, there may not be enough flow to the baseboard. There are limits to how long a run can be done with monoflo tees. (If the pressure drop of the baseboard run approaches the pressure differential of the monoflo tee there will be little flow in the run)
Then this maybe the cause. It is monoflow system. I don't have basement and limited crawl space. This family room is an extension that was built in 1992. So, how it is connected to rest of the system is mystery because it is under ground or in a wall. Also the radiator in kitchen(that should be right before this baseboard) connection has 3/4" pipe as a SUPPLY and RETURN pipe. All other radiators in the houses are 1/2" pipes.

#6
11-15-13, 06:57 PM
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Join Date: Oct 2013
Location: United States
Posts: 2,698
You have so many heat loss factors in that room. To put that on with a t-stat that's in a regular room I can't help thinking the t-stat will get satisfied long before this room will get comfortable.
Did you ever just putting it on it's own zone with the t-stat in that room.

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