Will Multiplying Linear Feet Of Baseboard x 560 BTU's Give Accurate Boiler Size


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Old 12-23-09, 12:29 PM
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Will Multiplying Linear Feet Of Baseboard x 560 BTU's Give Accurate Boiler Size

I have a 30 year old Slant Fin boiler with baseboard units along with a stand alone 32E Bock oil fired hot water heater. They run fine but I'm thinking I should seriously consider replacing them due to their age. I have a 1900 sq ft ranch house that's built pretty well and presently use about 1000 gallons of fuel oil a year for heat and domestic hot water which I don't think is too bad.

To start the search and info gathering phase for possible replacement, I had a heating equipment sales guy, who I know, stop by to look at my current equipment and to give me some ideas on replacement and replacement cost. He was quick to look at the specs on my boiler and say it was way too big although it was downfired. (142,000 btu output)

He said to determine boiler sizing I should simply measure out the linear feet of baseboard units and multiply by 560 btu's and that would give me a pretty good idea what size boiler I need. Is this accurate or close to accurate?

He also said that after 40 years in the heating business in his opinion after you boil everything down and consider reliability, serviceability and design its hard to beat a Buderus boiler.

Is this guy giving me good and accurate advice and information?

Thanks
 
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Old 12-23-09, 01:10 PM
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Huh? The amount of radiation in a building has absolutely nothing to do with sizing the boiler. Heating equipment is sized with a Manual J heat loss unless it is a steam boiler. The new water boiler does not have to match nor should it match the amount of radiation in the building. Most homes have excess radiation so if you match the radiation with a boiler size you are wasting money now on a larger boiler than you need and fuel and maintenance down the road.
Here is a link for FAQ about heat loss.
http://www.comfort-calc.net/faq.html
 
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Old 12-23-09, 03:29 PM
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The new water boiler does not have to match nor should it match the amount of radiation in the building.
Just a teeny clarification... this sentence should probably read something like this:

"The new water boiler does not have to match nor should it [be sized to] match the amount of radiation in the building."

The amount of radiation in the building COULD match the boiler, IF and only IF the radiation is matched to the HEAT LOSS of the building.
 
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Old 12-23-09, 04:12 PM
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Originally Posted by targa View Post

He also said that after 40 years in the heating business in his opinion after you boil everything down and consider reliability, serviceability and design its hard to beat a Buderus boiler.

Is this guy giving me good and accurate advice and information?
the 2 guys that already responded are experts....run from that guy that told you that's the right way to do it by measuring baseboards. I had to 2 oil companies come out for an estimate and they both measured the baseboard and came away with 150K or higher boilers. Even after i told them about the data i found on this board, the one guy said you MUST get a 150K boiler or your house will never be warm and he did it the right way.

My own calculation of heat loss was about 110 and the guys on this board thought i could get away with a 90ish boiler. I wound up with a 122K because i thought a 91K may have been too small. (the only 2 sizes the installer i choose had in my range). I got lucky and my barber recommended this contractor and i'm very happy. I saved 349 gallons over last year so thats a nice bonus too

also if you get a new setup do yourself a favor get outdoor reset as well. It's a wonderful thing. I have the tekmar 260.

next contractor you call ask on the phone how they figure the size boiler. If they say anything like measure baseboards, dont waste your time.
 
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Old 12-23-09, 05:26 PM
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I realize your boiler is oil fired, but that notion is akin to this: based on the size of the gas line, calculate the maximum flow of fuel to the boiler. Size the boiler accordingly.

Or, go by the size of the original boiler, maybe add 10% for good measure.

Or, based on the size of the flue, estimate the boiler size that will result in proper draft.
 
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Old 12-23-09, 05:46 PM
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Just another voice saying "size the boiler to the heat loss."

Buderus makes nice oil-fired 3-pass boilers. So does Burnham (the MPO), and Biasi (B-10), among others.

The most important part of the installation is the installer. Even the best equipment in the hands of a hack will be inefficient junk. Be more concerned with the installer than the particular brand of equipment.
 
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Old 12-24-09, 12:30 PM
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Based on everyone's comments I searched for and found a pretty nice online Heat Loss calculator and have spent the last three hours or so measuring and plugging in numbers.

The results are pretty interesting and seem to confirm my current boiler is way too big.

Though, one calculation that has me wondering if the calculations are right involves the breakdown of individual losses specifically the heat loss through the floor.

In the calculation input I indicated I have carpet on the floor over an unheated basement and the heat loss through the floor in most rooms is 2 or 3 times as much as the heat loss through the ceiling (I have R30 in attic) in those rooms?

Does this make sense?
 
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Old 12-24-09, 12:54 PM
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I would not consider the basement an unconditioned space even though it is unheated. The heat loss program is figuring the temperature on the other side of that floor to be the design temperature which would not be the real world scenario.

Having no insulation makes a difference. Just for arguments sake, what would happen to the heat loss of the ceiling if you remove the insulation from it?
 
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Old 12-24-09, 01:21 PM
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Wow!

If I plug in zero insulation for the ceiling in my family room which is 250 sf, the ceiling heat loss goes from 531 btu's to 9842 btu's.

Now if I select carpet + R-11 over an unheated basement the
heat loss for the floor goes from 1796 btu's to 581 btu's.

Since carpet + R-11 is the lowest level of insulation value I can select for a unheated basement in the formula,
is the 581 a more realistic heat loss number?
 
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Old 12-24-09, 02:36 PM
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targa,

you mind linking that program to us?

thanks a Bunch
 
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Old 12-24-09, 03:35 PM
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Here's the link to the program I used:

WarmlyYours | Heat Loss Calculator
 
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Old 12-24-09, 03:43 PM
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Thanks for the quick reply. Have a Very Merry.
 
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Old 12-24-09, 07:38 PM
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I wouldn't consider the basement into the heat loss. If anything, you should calculate the basement walls above grade. You should only be putting in walls and ceilings that have unconditioned spaces on the other side. If there is living space above your family room, you should not enter it.
 
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Old 12-25-09, 06:15 AM
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If the room over the basement has no floor insulation they have achoice for over unheated basement, no insulation. That is the choice. You do not want to fudge the output as they have plenty in their program. I ran a room from my house and it was higher than it should have been. The biggest thing I saw a problem with was the OD design temperature. The ASHRAE number is 11 and they used 2. That makes a difference.
My room was off bu 3418 btu's.
 
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Old 12-25-09, 07:03 AM
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rbeck,

When I originally calculated the heat loss, using the program I linked earlier, I selected the choice for floors of "carpeted floors with no insulation over unheated basement" for the entire house.

It sounds like you are saying to stick with that so I will.

By the way, my entire house (1900 sf) has a dry unheated basement under it which is almost totally below grade and never gets below 55 degrees. So in reality, the heat loss program is likely to overstate the heat loss?

Thanks.
 
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Old 12-26-09, 07:32 AM
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It assumes the basement is sub-grade. A good and accurate program will ask for the amount of wall above grade and the height of the wall.
That program is better than some I have seen but a Good Manual J program is about 20% over, what is a quick extra fluff program put you over?
That program is still way better than measuring the radiation.
 
 

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