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figuring radiator size

k9mom
k9mom Member Posts: 12
in Radiant Heating
Hi,

New here. Doing a ceramic floor job in my kitchen. Moved the radiator out of the room. Want to replace it with a shorter one, and put it on a different wall.

I know there's a formula to figure out what size radiator I need for the square footage but it seemed overwhelming to figure (math is not my forte'). I've got approx. 208 sq. ft. My sister has a smaller radiator she's not using but it's much smaller. It's a 3 column, approx 25" long, by 25 inches high. Can I get by with that? The radiator that was in the room is a giant, and I never really did open the valve very far..as it would just get too warm in the room (I tend to be a person that's warm all the time). I'd like to make this smaller radiator work. It would be enuf heat for me. When I'm 95 and dead, I can let the next owner worry about putting in  a bigger one  :)  Thoughts and opinions more than welcome.

Comments

  • Brad White
    Brad White Member Posts: 2,399
    Heat Loss and Square Footage

    Square footage is a loose term regarding heat loss if you are just using floor area. There are some rules of thumb but I would not use them except for very preliminary block numbers.



    If you know the area in SF of your gross wall (separating inside from outside), insulation levels if known, floor area in SF and the temperature of the space below, glass type, roof or ceiling if below the sky or an unheated space, then your space volume, we can maybe start talking heat loss.



    I take it that your system is hot water?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    hot water

    Yes, 2 pipe, hot water system. All that stuff you just spewed out is exactly what has me so overwhelmed!
  • k9mom
    k9mom Member Posts: 12
    more info

    no exact specs on insulation. It was blown in before I bought it. Updated with new Pella windows in 2004. Best I could buy. 3 outside walls, 1 interior wall. Space above kitchen is attic space, non heated. Space below is basement, which isn't heated but stays at a comfortable 'basement' temp. The boiler is in the basement.

    West wall: exterior wall, 1 window, 1 door, 162 sq ft.

    South Wall: exterior wall, 2 windows, 81 sq ft

    East Wall: interior wall, 162 sq ft

    North Wall: exterior wall, 1 window, entire wall covered by cabinets and cupboards, 1 window 108 sq ft
  • k9mom
    k9mom Member Posts: 12
    edited March 2011
    and more info

    I might say that the original radiator, 3 column, 34" long, 38" tall and 8.5" deep more than enough heated the room. I never had the valve all the way open. And I should note that the reason I want to replace the original is because it was mounted on the west wall, right up against the cupboards and I couldn't open the cupboard doors all the way. I want to move it to the south wall, below the two windows and it's too tall. I have a max height to work with of about 27" high....I've located a longer and shorter radiator, 5 column, but it's a beast. It's about 45 inches long.
  • Brad White
    Brad White Member Posts: 2,399
    How large are

    the windows and doors in each of the walls? I take it that the overall areas you gave are the gross wall areas. And the floor area is, I am gathering, about 20 feet by 10 feet? How does that match up?



    If you can get that to me I can calculate a reasonable heat loss.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    more measurements

    Floor square footage is 204 or so. Floor measurements are 18' long by 12' wide (one area) and then an offset is 9' wide by 6' long....

    West window measures 60" high x 31" wide

    North window :  60" high x 31" wide

    Both south windows, side by side, with just a 4" trim strip separating them are each 51" high x 27" wide
  • Brad White
    Brad White Member Posts: 2,399
    And of course....

    Where is the house, city and state? And what temperature do you normally maintain in the house? I forgot to ask that basic question but will start crunching the numbers.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Brad White
    Brad White Member Posts: 2,399
    edited March 2011
    Some rough numbers

    I took what you gave me and assumed 0 degrees F. outside and 70 F. inside on the coldest day. (We call this the Delta-T, the difference in temperature inside to outside on the coldest day.)



    With assumptions of 3.5" of fiberglass batts in the walls, 6" in the ceiling (could be more), and the basement 10 degrees cooler than the occupied space (ie 60F in the basement), I came up with a heat loss of about 7,450 BTUH.  This also includes 0.8 air changes per hour of infiltration (air leakage).



    Normally, I would add a 10% safety factor to cover unknown variables and you can do that, but for discussion, let's stick to net numbers.



    At 204 square feet, that works out to 36.5 BTUs per hour per SF, which is what I would expect for a room exposed on three sides with a door. The best construction might get that down into the 20's by comparison.



    A shorthand way we work on this is to give you a Q factor, which is a rough way of saying how many BTUs per Hour your space loses per degree difference indoors to outdoors. (With me here? Hang on!)



    So your Q factor is about 106. Keep that in mind. We started by saying the indoor to outdoor temperature difference was 70F.



    106 x 70F is 7,420, your heat loss number more or less.



    Now, your design temperatures may vary, so let's say it is minus 20

    outside on your design day and you maintain 70 F. as we stated. (90

    degree delta T).



    So 106 x 90 =9,540 BTUs per hour.



    A hot water radiator (your original question!) will emit 150 BTUs per Hour per SF of EDR when your average water temperature is 170 degrees F. (By this I mean you supply 180F water on the coldest day and return it out of the radiator at 160F.)



    So if your heat loss is 7,420, your radiator should be at least 49.5 call it 50 SF.

    If your heat loss is 9,540,  your radiator should be at least 64 SF.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Brad White
    Brad White Member Posts: 2,399
    I would be remiss if

    I did not suggest that you at least try radiant floors. With ceramic tile, you will not regret it. You will not likely heat the entire room but you can make a dent in it, at least in the clear floor areas. And your radiator would be smaller. You have hot water. It is within reach.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    thanks..and another question

    Thank you so much. I'm truly impressed! Now, can I bug you to help me figure the sq footage of the radiator I'm thinking of using? I will get specific measurements later today. It's sitting at my sister's house, unhooked, and she wants to get rid of it. The floor heating sounds good, even though I really LIKE the cool/cold feeling of the tile floors. I have a pretty big house and I have NO CARPET. Doesn't work with dogs and cats!

    Let me know if you'll do that one last math equation for me.

    Thanks so much....this is a great forum

    Janice
  • Brad White
    Brad White Member Posts: 2,399
    Fire away!

    We can help steer you, or at least give you some direction.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    radiator size

    Ok, size of the small radiator I'd like to use is:

    26" high

    24 1/2" long (that does not count pipe nipples)

    8" deep

    3 column

    I attached a pic.

    I will repeat myself. I don't need alot of heat, at least for myself. When I'm old and grey and want to sell this  house, perhaps I'll let the next owners worry about a bigger radiator.

    As for radiant floor heat...great idea but way out of my budget.
  • Brad White
    Brad White Member Posts: 2,399
    End section

    The tubes seem to be the nominal 1-3/8" diameter round ones, versus oval shapes. Does that seem correct?

    I am trying to find such a radiator with a width of 8 inches, most are about half that.



    What I come up with as common ranges for 3-tube radiators 26 inches high are 2.0 to 2.33 SF per section and if 8" wide oval tube types, 3.75 SF per section.



    So the overall range you might have is 20-23.3 SF (3,000 to 3,500 BTUH) up to 37.5 SF (5,625 BTUH). Quite the range! What does the end look like?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    pardon me for being 'thick'

    so are you saying that this radiator would suffice in the room I'm wanting to put it in? And, are you wanting to know what the ends of the radiator look like?

    Sorry if I seem dense! If you need to see the ends of the radiator, I'll have to go back to my sister's and snap a couple more pics.
  • Brad White
    Brad White Member Posts: 2,399
    edited April 2011
    Viscous? :)

    Sorry, I do not think you are being thick at all!  I was just trying to figure out what the end profile of the radiator looked like that would get the width to be 8 inches.



    From the side it looks like a "Fero" style which has fairly thick rounded tubes, but the 3-tube width is only 5.25" (The 5-tube width gets you to 8.5" and you said three).



    Edit: In blowing up the photo it LOOKS like a 5-Tube. If a Fero style, the EDR of your radiator will be about 35 SF (5,250 BTUH).



    The only other types that get to that 8 to 9 inch width with three tubes are column style radiators which have oval shaped tubes.



    So just need to confirm what the end looks like or how many tubes it actually has so I can reconcile the right EDR capacity.



    We never did settle on where you live, so I can plug in your design temperatures and that will define your heat loss. Then I can get a handle on how warm we could keep that room.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    edited April 2011
    I was mistaken

    Sorry...I screwed up. It IS a 5 tube, made by American Radiator. I measure the circumference of the tubes and I got just shy of 4".

    I'm including a pic that shows both ends of the radiator. I really want to use this in my room, even if it isn't as big as I need. The size will just work out better!

    Also, where would be the best place to find the valves and/or fittings for this radiator? I've found many places online but not quite sure what to order. My plumbing shop has a few parts laying around from yesteryear.

    Let me know what you think...oh...I live in Northeast Indiana, just south of Fort Wayne.

    Janice
  • Brad White
    Brad White Member Posts: 2,399
    edited April 2011
    Well, OK, we are getting results!

    For Fort Wayne/Baer (USAF weather data), I get a 99% temperature of 1 degree F. (meaning that 99% of the time "it is warmer than") and a 99.6% temperature of -4 degrees F. I will use that.. How does that square with your experience?



    So if you desire to keep your kitchen at 70 degrees and it is -4 outside, your heat loss would be about 7,800 BTUH on that coldest day.



    Your five tube radiator (do I know my radiators or what?, he asked rhetorically.. :), will emit about 5,250 BTUH. Against that heat loss and assuming no "contribution" from the rest of the house, the temperature could be maintained at about 46 degrees. That is "on paper" for what it is worth.



    The reality is, the rest of your house will "chip in" and heat will flow to the colder room to a point. Conservatively, I would say your room here would be about 60F when the rest of the house is held at 70 F.



    As for radiant, you may be surprised, especially if the underside of your floor is open. At least keep the option open.



    As for fittings, your radiator could well be served by as small as 1/2" pipe but if your radiators all have 1" or larger iron pipe, I would definitely use those larger sizes. Brass radiator valves are commonly available at nearly all plumbing supply houses or on-line retailers. Many choices. I like Tunstall (Chicopee MA), Hammond is another and there are some salvaged valves you may find that can work just fine. You do have a good installer I trust who can re-pack and set up the valves correctly?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    Wow!

    Ok..you've impressed me all along....and yes, you DO know your radiators! Thank you so much for all your time and hard work. It's really been a big help. I will look into radiant floor heat. I may report back on what they tell me.

    This forum is an awesome place and I will be bookmarking it!

    Thanks again,

    Janice

    ps: as for the weather in Indiana...well...it's Indiana. 80 one day and spitting snow flurries the next. It's unpredictable as heck!
  • Brad White
    Brad White Member Posts: 2,399
    Janice

    You are entirely welcome and may I add- Welcome!

    Nice group of folks here, led by Dan H. (H. for "Himself" or Holohan but we love him regardless). A loose rabble of people passionate about comfort. And some of the finest people I have ever met. Truly.



    Stick around!



    Brad



    p.s. No wonder New England weather is so unpredictable! We get your "used" weather.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    repack and set?

    I just saw this in your post and thought I'd better ask. What does this mean:  "You do have a good installer I trust who can re-pack and set up the valves correctly"

    My plumbers are a 3rd generation company here in my small town, but the guys doing the work are the young guys and I don't know if they know this stuff.  Can you explain what that means?

    Janice
  • Brad White
    Brad White Member Posts: 2,399
    Packing

    is actually and old-time skill, I am sure they can handle it. There is a nut that goes over the stem and under the knob you turn, which seals in the water. There is a material called graphite packing which is wound around this and the nut tightens it together.



    This is what enables the valve to turn open to closed without leaking. I am sure they are up to it!
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • k9mom
    k9mom Member Posts: 12
    ok thanks

    Good morning! Sipping coffee...ahhhh. Thanks for that info. As for "you're sure they know this"...I wouldn't be so sure. The 1st and 2nd generation of this outfit were fantastic but these new 'kids'...they don't know and don't wanna know the "old stuff". They actually were scoffing at me for having this marvelous old system.

    Hopefully, they can figure it out...I may have a talk with one of the kid's Dad, that still is with the business...

    Hope you enjoy your Saturday.
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