HeatingHelp Anonymous?

Mr Takagi

First of all, is there some sort of support group for Wallies? My wife is ready to throw my @%# out of the house for spending so much time doing "boiler stuff". She just told me to "just pick a damn boiler and get off the computer!", so I need to make this quick :) I've had several posts on here asking about what to use in an old gravity system. I was leaning towards a dunkirk quantum, then my plumber friend told me he can only get Weil Mclain, so I am going with the Ultra. The only question I have left is which one. I had two different contractors come out (one was from Sears, so that may not count), and they both measured radiators and said I needed approx. 90MBU. I used the slant fin IBR calc. forms, and came up with 78MBU. So technically, the Ultra 105 should be enough boiler, but just barely. I am having a hard time going with this instead of the ULtra 155 since the current boiler is 210MBU input with 165MBU out. I would love to compare my house to some other home with a 105 installed to see if I am in the right ballpark, and my figures are right. This is a 100 yr. old, 2 story, 1800sq. ft. home with the original windows, aluminum storms added, and almost no insulation in the walls as far as I can tell. The attic is insulated, and the boiler is in the basement. Anyone have an install close to this for comparison?
One more thing, I am in central Illinois so it does get cold and windy all winter. Design temp will be for -10.

Thanks for the help.

Mike

ScottMP

Mike

Measuring the radiators is not the way to size a boiler. You should do a heat loss for your home using the design temp of -10 for your area. You have now idea whether the rooms have the correct radiation installed. Tradesman have a habit of oversizing and it tends to steam roll. Then see where you stand. Also think about any additions you may want to do to the house and how realistic those plans are. You may want to go up in size to cover any future work.

Oh and by the way .... " Just pick a damn boiler and get off the computer " lolololo.

Welcome to the club.

Scott

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Boilerpro_3

Mr. Milne hit the nail right on the head

Also, I would look for another contractor. If they don't know how to properly size a boiler, who says they will know how to properly install it? B sure to get a newer model with the corrected outdoor reset control...I understand the original was misprogrammed.
If you need some reassurance on sizing, my 100 year old 2800 sq ft home that is well insulated with 700 sq ft of windows heated very nicely with a 90,000 btu/hr INPUT boiler. The boiler had been 270,000 btu/hr input and load calculations said I needed about 50,000 output at design.

I have used boilers in the size range of your current boiler to heat poorly insulated 10,000 sq ft structures at that design temperature.

Nearly all heat load calculation methods tend to be conservative when compared to real life because they assume no internal gains...like people that live ther beathing, cooking, taking showers, sunlight coming in windows etc. So be rest assured, if anything the boiler may be too big.

Boilerpro

Mitch_4

If your installer

Cannot get you what you want... I would look around. I carry my preferred product, and I get a better price for it, but I can get ANYTHING the customer specs.. It's your money (not that the WM is a bad product)

Mike

Floyd_5

A couple of things.....

#1 The reset control can easily be reprogrammed for whatever reset you want......
#2 Are you planning to ever hookup your boiler for DHW????
If so you amy want the larger boiler for faster recovery....
if not the 105 will probably be plenty....
#3 With the Ultra boiler you have the extra comfort of the boiler being of the modulating variety, so if it is oversized a bit it will not hurt your eff. but actually can help it a bit....with the boiler running at a lower fire, my observations are that the exhaust temps. will run closer to the return water temps. meaning that the eff. of the boiler is higher than when it is running at a higher fire.
#4 Make SURE!!!!! That your contractor knows what he is doing.....these boilers have to be hooked up correctly to run properly.


Floyd

Mark Hunt

Scott and Boilerpro are right on


Measuring cast radiators is how you size a steam system, not a water system. I would be willing to bet that you have more radiatior than you really need.

I would trust the Slant/Fin calcs more than I would the EDR, otherwise you will end up with a boiler that is too big.

I would not increase the size of the boiler for an indirect tank, I would prioritize that zone.

Size it right and squeeze every penny you can out of your new system.

Best of luck!

P.S. Sears is a good place to buy clothes and refrigerators. Nuff said.

Mark H

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Carl PE

Minus Ten?

Are you sure you want to design this system around conditions that only happen a couple hours a year?

I'm the engineer for a p/h contractor in Springfield, btw.

ASHRAE says -4 for our area, and that's still 2% of the time. Would you prefer a system that's going to work great 2% of the time, or 98%?

Constantin

That depends, no?

I mean, many guys have no problem with "enjoying" a house at 60°F for the two days a year that a "close" heating calc like yours suggests. Just put on some more clothes and/or take a hot shower.

Then you get married. 'Nuff said.

Besides, if your heating plant can modulate and condense the way most modern gas systems can these days, your heating plant will operate efficiently on just about any day, more so than any older fixed-output systems operating on the bang-bang on/off principle. So you might as well set your design day at the extreme end (0.5%) and enjoy a faster IDWH recovery rate at the same time.

I see the benefits of modulation actually as a bit of a challenge to the more dedicated folks in this industry... modulation allows hacks to better get away with way oversizing a system.

Mark Hunt

Depends yes


but we must also keep in mind that regardless of the heat loss, he can't get more btu's from the boiler than his radiators will put out.

Won't matter if it's -10 or -6, if the EDR doesn't cover the load, a 1,000,000,000 btu boiler won't help.



Mark H

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R. Kalia

> different contractors come out (one was from

> Sears, so that may not count), and they both

> measured radiators and said I needed approx.

> 90MBU. I used the slant fin IBR calc. forms, and

> came up with 78MBU. So technically, the Ultra 105

> should be enough boiler, but just barely. I am

> having a hard time going with this instead of the

> ULtra 155 since the current boiler is 210MBU

> input with 165MBU out.


Your problem is not that you have spent too much time here...you have not spent enough time here!

IF indeed you need 78-90 (output), then 105 (input) is just fine. You should not oversize the boiler, this leads to decreased efficiency---even if you have a modulating boiler, it does not modulate all the way down to zero, so a right-sized boiler is still best. (As Mark Hunt points out below, if your radiators can't put out more than 90MBTU, there is nothing to be gained by getting a boiler with more than 90 output, and money and efficiency to be lost.)

Even with DHW you do not need a bigger boiler. What you have now is totally irrelevant, because people didn't care about these things in the good old days and put in huge boilers because they could.

The best way to size a boiler is through experience, assuming you have the data. What is your gas consumption in winter PER degree day? (You can get gas consumption from your monthly bill, and degree-day data from wunderground.com or your gas company). Multiply by the 75 (the number of degree-days in a -10F design day). This gives you the peak INPUT needed. OK, add 5% to that for safety, but no more than that.

Our house (in Illinois) is about the same size as yours and about the same age. It needs about 65MBTU output (it had a 160MBTU cast-iron boiler when we moved in, and radiators consistent with that size boiler, but this is more than is actually ever needed). However, it does have double-pane windows and insulation in some walls in addition to the attic, and we are near Lake Michigan so the design temp is 0F. So 105MBTU input sounds quite safe for you.

PS Many, many contractors use radiators to size boilers. It's not that they think they're installing a steam system; rather, they are trying to figure out what BTU the system was designed for, and assuming that that is what it still needs. This is nonsense; it was most probably overdesigned to begin with, plus you now have attic insulation and storm windows.

R. Kalia

80MBTU model might do it.

The Ultra comes in a 80MBTU size. That will probably be fine.