New and Improved Heating System


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Old 03-19-07, 12:06 PM
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New and Improved Heating System

Hey all,
Well this summer I am replacing the entire heating system in the house. I currently have scorched air on the first floor and electric baseboard on the second floor. My house is square (25ft x 25ft) totalling about 1,300 sqft not including the basement which is not finished. I am coming up with 67,000 Btus of heatloss using the Slantfin program and Elite software. I want to use staple up radiant floor heat on the first floor and baseboard heat on the second. Oil is my fuel type. I have heard a couple opinions about what kind of heat source I should use. The traditional way would be to use a Weil-McClain with reillo burner running at 180F feed with a mixing valve to the radiant system to about 130F. The other opinion would be to use a oil fired water heater with an outlet temp of around 130F and just oversize the baseboard on the second floor to overcome the 50F difference in feed temp. The system would be simpler this way and have less controls and worries about overheating the radiant system What has other people done and what works the best? Thanks all for your opinions and comments.
Brian
 

Last edited by aldy54; 03-19-07 at 12:16 PM.
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Old 03-19-07, 12:18 PM
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Initial reaction is the heat loss may be too high for radiant. 67,000/1300 = 51 btu/sf. I think radiant has a practical max output of about 35 btu/sf. What's the design outdoor temp? How is the load partitioned between the two floors? What's the building envelope like?

I would use a real boiler. Water heaters seem to do ok for low temp radiant (~100f or so), but a higher temp radiant, plus a whole floor of baseboard is probably asking too much.

If radiators are an option instead of baseboard, you might get the temp difference down a bit.
 
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Old 03-19-07, 12:35 PM
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The load distribution is about 42,000 btus on the first floor and 27,000 btus on the second floor. The first floor was built in the late 50's and is 8" block with plaster exterior and drywall interior with no insulation. The 2 doors and 8 windows on the first floor all have storms and have weather stripping. The second floor is an addition that is frame up with 3" insul batt, vinyl siding, insulated ceiling and all newer anderson windows with storms as well.
If 35 btu/sqft is right radiant won't work since my first floor is more like 67 btu/sqft. Is 35 btu/sqft a rule of thumb or some other area of concern?
Thanks
 
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Old 03-19-07, 02:20 PM
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It may be a rule of thumb. To be frank, right now it's a dim recollection where I "remember" that from. Something to do with max floor temps (I think you don't want them hotter than about 82-85f?) before you start cooking your feet to the point of discomfort, and heating up the floor coverings to where they are deforming or degassing.

I'm going to guess that 67btu/sf is out of the range of radiant. And totally out if you have any significant carpet on that floor. In which case, my personal fallbacks would be cast iron radiators, then a toss-up between cast iron baseboard and panel radiators like Buderus or Myson, to toss out a couple brands I've seen.

There's a set of calcs you can do with some of the radiant design software packages that allow you to figure up output/sf using various floor coverings, radiant installation types, etc. WIRSBO I think, among others. Might also try the forums on www.healthyheating.com as they are radiant-oriented.

All that said, if the rule of thumb is indeed around 35, if you came in at 40, I'd say go for it. But 67 seems right out.

Where's Who? He knows this stuff better than me.
 
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Old 03-19-07, 02:51 PM
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Xiphias I see your rule of thumb at http://www.radiantdesigninstitute.com/page5.html which states typical floors give off about 30 btu/sqft. 625sqft * 30 btu/sqft gives about 18,750 btus of heat which is way under my heat loss. So in my case the uninsulated block walls are killing my load and throwing me out of the radiant ballgame. Any other comments or suggestions? Thanks all,
 
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Old 03-19-07, 07:45 PM
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New heating system

To get 42000 out of "standard" baseboard you would need 70 feet, presuming 600 btu/ft. If you want to stick with baseboard & 70 ft. is more than you have room for, there are high output baseboards, such as Slant Fin's Multi Pack 80 available. Radiators, either cast iron or steel panel type, are another option.
 
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Old 03-21-07, 12:43 PM
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aldy, how long do you plan on living there and what would you figure you have for a budget to do this?
 
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Old 03-22-07, 07:05 AM
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I plan on being in the house for the next 6 to 8 years depending on the children situation and things like that especially just getting married last summer. My budget is as follows: My material costs might sound cheap since I work for a mechanical contractor:
~$1800 Crown CT-3 with reillo burner
~$500 1,000' roll of PEXA with o2 barrier
~$600 controller and manifold
~$200 various fittings
~$300 aluminum plates
~$200 misc.

I plan on doing all the work myself over this summer.
 
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Old 03-22-07, 07:40 AM
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Is there any usable wall cavity between the block and the drywall, such as 2x2 furring? An older house might have something more substantial than just 1x3s on the flat. With such a high heat loss, it could be very cost-effective to foam in the wall cavities. Even an inch would give you a bit of R (5 or so) and really tighten things up.

Insulation and sealing usually win the payback game. If you're already doing the heating system to get away from FHA and electric, fine. You gotta do it. But don't forget the envelope.
 
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Old 03-22-07, 05:39 PM
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Originally Posted by aldy54 View Post
Xiphias I see your rule of thumb at http://www.radiantdesigninstitute.com/page5.html which states typical floors give off about 30 btu/sqft. 625sqft * 30 btu/sqft gives about 18,750 btus of heat which is way under my heat loss. So in my case the uninsulated block walls are killing my load and throwing me out of the radiant ballgame. Any other comments or suggestions? Thanks all,
Sure the block is totally uninsulated? In Florida construction we poured vermiculite down the cell cavities.
 
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Old 03-23-07, 10:32 AM
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aldy, if your numbers are right, you won't be able to keep your floor temps under 86 when it's cold out - not even close. What about using panel rads and maybe a bit of floor warming done at system temp? That way as you tighten your envelope, you can keep lowering the water temp you need. Underfloor does not bode well to cheaper control strategies. A Taco RMB is about a grand and that's about as cheap as good underfloor control gets.

Make sure you know your heatloss numbers and try and get a good handle on what your infiltration is and what you can do to lower it.
 
 

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