sizing hot water baseboards to room size

[machinemaker]

We recently bought an older home with a wood fired boiler that is tied into a radiator type heat exchanger in a forced air heating duct system. I think that installing hydronic baseboard heaters in each room with zone controls would be an improvement. I also want to build a larger heat storage tank and add solar panels in a couple of years. I have some questions: How do I size the baseboards to the room sizes? I have seen some figures suggesting 10 - 12.5 watts per square foot of room, but the base boards I am seeing have a rating of Btu / foot at a flow rate. I would love to do in floor heat, but not in this house, so baseboards look to be the best solution. Secondly, any recommendations on suppliers? I am also wanting to get some advice on design and installation, anyone have some advice or reading suggestions? 
Thanks, Kent

[artv]

Hi Machinemaker,....I can't really be of much help ,but am curious as to why in floor heating is out of the question??...I got rid of my electric base board heaters and put in-floor in my kitchen and dinning area ~300sq/ft....There is no comparaison.........in- floor is the way to go..........All I did was use old 3/4" strapping on it's flat on 16" centres ,...ran two tubes in each space with that shiny bubble wrap behind the tubes and re-sheeted with plywood.........at the max you lose a coulpe inches of head room......but the heat is beautiful.........thinking of doing the living rm next but will have to rip up new hardwood floor ,to expensive to cover up.........good luck with your project...artv

[ghurd]

Kent,

1 Watt-Hour = 3.41214 BTU  (per hour)

10 Watts for 1 hour = 10 Watt-Hour = 34.1214 BTU

12.5 Watts for 1 hour = 12.5 Watt-Hour = 42.6518 BTU

Edit-  The US and Canada interpretation and use of the term "BTU" is a bit different than many other places.

G-

[machinemaker]

ghurd, thanks! that gets me started in the process.

My reason for not doing radiant floors is in the construction of the house. It is probably 100 years old and the current floors are tongue and grove oak and or local lumber on oak floor joists. The tongue and groove is in good shape once we tore off the ratty carpet and it is fairly thick. I hate the idea of covering it up and I would only have access under it on the first floor from the basement.
kent

[ghurd]

"some advice on design and installation"

Install "more than 1" T&P valve.
Install their output so it will not do water damage.

There are times when the entire home is warm enough.
And the fire keeps burning, because that is what fires do.

Some of the local systems have an extra gravity fed loop that operates all the time (no valve at all).
The idea being that if the wood fired storage system is becoming overheated, the water flows faster though the loop faster.  The hotter the water, the faster the flow.
The heat 'lost' in the loop is not really lost because it is still in the house.
But the heat expelled in the loop keeps the pop-off from popping.

Most of the loops I see are just CU pipe 20~40' zig-zaging back and forth a few times under the 'living room' area.
Some have sections of the guts of a commercially available radiator (looks like CU pipe with many square washers along it), usually under the livingroom or bathroom.
They all run steeply 'up' from the wood stove, then go down hill the rest of the run to get back.

I guess all of the loops have a magic 'burper' thing which prevents air locks.

Might find something semi-usefull here,
http://s701.photobucket.com/albums/ww20/ghurd1/Pumpless%20Water%20Heater/

[Photon]

Kent,

I dont know what your climate is but generally 100w/sqm is close.

More important is how to deliver heat to maintain a mean radiant temperture (the measure of comfort)

Slab heating has a lower air temperture but higher surface temp. its good in old houses with infitration (outside air) its more tolerant given its 'thermal mass'.

I would look again at base boards. A correctly sized radiator/s located under the rooms window (extending 200mm either side of window width and 150mm below sill). Its tried and tested and give a near perfect comfort. The no. of panels and fins can get the right size radiator.

Intall basebords and youll feel the cold windows (lower mean radiant temperture).Im sorry if this screws your plans but part of my job is to research this stuff, baseboards in a room with windows is not a good idea. Radiators under your window is worth having a second look at.

[DamonHD]

With my eco hat on I suggest moving radiators *away* from windows and exterior walls.  Putting them under windows os for minimising temperature gradients but also maximises energy losses.  Better to improve the curtains / windows / weatherization instead IMHO to reduce gradients and draughts directly without hiding them.

We just did that while boosting the insulation in our living room, and even though we just had the coldest December in 100 years we weren't cold and our heating energy consumption dropped to the lowest ever for that month.



Rgds

Damon

[Photon]

Damon,

I agree adding insulation and reducing infiltration reduced your bills. But it will still take 'x' amount of energy to heat a room, fabric load and infiltration. Walk into any commercial building and you will see a perimeter system or sometimes called skin system. High level linear slots diffusers or low level rads its Building Services Engineering 101.
not trying to be smart but what you said is incorrect.
Put a radiator on opposite side to a window and you got a hot and cold room. Its in ASHRAE fundamentals, CIBSE guide B or A or Faber thermodynamics.
 

[DamonHD]

Our room has a low thermal mass inside the (aerogel and other) insulation, and I simply report higher comfort and lower heat demand in the face of record HDD12.

Rgds

Damon

[zap]

Put a radiator on opposite side to a window and you got a hot and cold room. Its in ASHRAE fundamentals, CIBSE guide B or A or Faber thermodynamics

Agreed... under the window makes for a comfortable room and it's been done that way for decades... for a reason.

[DamonHD]

And I am heretically suggesting that that item of conventional wisdom --- which I entirely understand the reasoning for --- may be a bad idea because it masks and encourages energy wastage.  The West (and the US and UK in particular) have been fabulously bad at domestic heat energy efficiency, but BAU may not have long to live given rising energy prices.

But let's NOT hijack this thread any further.

Rgds

Damon

[beyonder]

http://www.hearth.com/calc/btucalc.html

 There is a btu calculator you can use.  Then size accordingly, HOWEVER... you should take note though that the number of btu required for every home is different, it is all dependent on your insulation values, floor coverings, age of the house ( house wrap or no house wrap,  that cheap garbage back vapor  barrier or proper plastic vapor bare, ect ).   Also you must take into consideration the efficiency of the heaters and so on...

 Things like if you have 2 outside walls, you add 15%, 3 add 40%, northern walls you add 10%, no insulation in a loft/atic add another 15%, tall ceilings ( 10 - 12ft ish ) you add another 20% and so on.... if you google it you will find lists.   The easiest way though, The one my dad used when sizing ( he was a tin basher..( plumbing and heating guy )  for 40ish years ) in a newer house he would use the shortcut method of 10 watts per square foot,  and for an older house ( 80 - 100 yrs old are common in this area ) he would use 20.  And work an average in between...

  Hope that helps....

   Clarence