Time to replace my 50 year old Triad boiler

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Old 06-05-07, 09:23 AM
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Time to replace my 50 year old Triad boiler

After 50 years of service from my old gas fired Triad Boiler Iím ready to upgrade to a new higher efficient boiler. I have a chance to buy a new in the crate Slant Fin boiler at a drastically reduced price but Iím afraid it is larger than I need and am wondering what the problems I would encounter using this boiler. My current boiler has an 112,000 BTU input, this new boiler has a 140,000 BTU input. I have approximately 75 feet of finned registers in a 1950 square foot 1957 brick ranch house. A few rough estimates that Iíve heard about are 75 feet of register x 600 = 45,000 BTU or 1950 S.F. of house x 25 BTU = 48,750 BTU. If this is the case than I really need about the smallest boiler in most manufactures lines. Can this be correct?
 
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Old 06-05-07, 10:10 AM
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You should do a heatloss calculation / Manual J calculation.

The 75' x 600 BTU/ft is probably overstated. It's tough to know how much the boiler and branch piping itself adds but if it doesn't add much it is doubtful you're getting 600btus/linear foot out of your radiation when it is at design conditions outside (your coldest typical winter day). The boiler probably heats the area it is in directly and you'll have to give that some thought when you replace it with an efficient boiler.

A modulating condensing boiler will probably cost you more coin up front but cut your fuel bills dramatically even compared to a properly sized conventional gas fired boiler. Either boiler is going to have venting considerations that you'll have to account for. Are you more concerned about long term operational costs or upcoming installation costs? Do you have a budget? If so, is it very flexible?
 
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Old 06-05-07, 10:34 AM
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What Who said.

Free heat loss software can be had at www.slantfin.com. It's worth doing. Takes a couple hours.

For my fin-tube baseboard, which is ~30 yr old generic stuff, output of 550 BTU/hr per foot of element seems to work out about right. 550*75 = 41250.

If your existing boiler supplies ~180F water to your baseboard, and you are happy with how the house heats on the coldest days of the year, then the output rule of thumb is probably pretty close.

If you are not using the boiler to heat your domestic water (DHW), then yes, the 140k slantfin unit would be way way oversized and you will pay for that oversizing every time it fires for the next 20 years. Given the perpetual increase in energy costs, you'd probably spend more money over the years than you'd save on the bargain boiler.
 
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Old 06-05-07, 04:03 PM
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Thanks for the info, I do have a few questions and comments about your replies. Dose anyone know what the longevity is on these super efficient boilers? I would hate to spend twice as much just to have the thing only last 10-15 years. I would like to get 25-30 years out of my new boiler, is that asking to much?
Who wrote
ďA modulating condensing boiler will probably cost you more coin up front but cut your fuel bills dramatically even compared to a properly sized conventional gas fired boiler. Either boiler is going to have venting considerations that you'll have to account forĒ I understand that the modulating boiler needs fresh air from outside but why would a new conventional boiler need anything different than the one I have? It is out in the garage.
Xiphia wrote
ďIf your existing boiler supplies ~180F water to your baseboard, and you are happy with how the house heats on the coldest days of the year, then the output rule of thumb is probably pretty close.Ē
Actually my old boiler circulates the water at 112 degrees and Iím not happy with it at all, it has always been cold in the back end of the house furthest from the boiler. Should the old boiler have circulated 180 degree water? Is that the standard on these new boilers?
I do understand that the Slant Fin I was looking at is out do to it being to large for my house and I do appreciate the info on that.
 
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Old 06-05-07, 07:13 PM
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What's your annual fuel bill? Think of a third of that with rising fuel prices... and 10-15 years is the number I'd use for a mc-boiler. They may last longer but it's too early to tell. When it comes time to replace it will be cheaper... there are far less materials in these. Right now, they are overpriced IMHO, but I still bought one...
 
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Old 06-05-07, 08:47 PM
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Originally Posted by 50 yr old Triad View Post
Actually my old boiler circulates the water at 112 degrees and Iím not happy with it at all, it has always been cold in the back end of the house furthest from the boiler. Should the old boiler have circulated 180 degree water? Is that the standard on these new boilers?
A gas-fired boiler supplying 112F water is rather low. Generally a minimum would be 130-140F. 112F in a present-day, standard cast iron boiler would probably kill it in a few years due to flue gas condensation. A 50-yr old boiler, however, likely has a huge amount of cast iron "beef" to it so it has survived.

A "standard" supply temp is 180F for copper/aluminum baseboard, but could be reasonably lower (120-160F, guestimating) for cast iron baseboard because it has better radiative capacity.

In the modern era, there really isn't a "standard" supply temp anymore. Outdoor reset is the new thing. Basically, a sensor outside the house talks to a boiler control and tells it what the outdoor temp is. Based on some simple initial programming, the boiler control says "oh it's 40 degrees out, so I only need to supply 140F water," or "oh it's 5 degrees out so I need to supply 180F water." A decent explanation of this, though somewhat dated, is at http://www.taco-hvac.com/uploads/FileLibrary/RisingFuel_100-40.pdf

If you go with a standard atmospheric boiler, make sure that how you vent the new boiler is completely in line with the manufacturers specs for flue size, total equivalent length, etc. etc. Poor or incorrect venting can kill you, even if it's in a garage. The old boiler probably had different specs.

If the back room is always cold, the first thing to do if possible is add insulation and seal any air infiltration points. The second thing is to add more radiation.
 
 

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