New Boiler Sizing

Brad White_26

If you can wait for the Slant Fin CD, do so. Your heating system is a 25+ year investment and a little time (very little in the scheme of things) will pay BIG dividends.

If you want to skip the learning curve, I can calculate a heat loss for you, but you have to provide me the square footage of all exterior surfaces: Gross wall, glass, doors, roof/ceiling, floor area, ceiling and wall height and what each surface is made of. General age and condition will help too. The age issue goes to air leakage, a real wild card factor in heat loss.

I can contact you off-line if you like. The better your information the less I would need to charge. If it takes less than an hour, no charge.

("But you must call now and I will thrown in a Ronco Somethingorother.")

Gut Check:

Your house is not unlike mine in size. Mine was built in 1873, Boston climate, (+6 design) has 4 inches of blown-in wall insulation, lots in the attic too. Single pane storm windows, occasionally heated basement. Heat loss is 55,000 (it is a tad leaky and I still seal the place).

Second Gut Check:

Your boiler should not be much larger than your radiation's potential output. Some factor for piping is fine, but no point in having 50,000 BTU's worth of radiation hooked up to a 100,000 BTU output boiler, you can see.

sidney r. bray

New boiler sizing

I've had five different contractors come to my home to price me a new hot water cast iron boiler..they all seem to think my existing HE 5 Weil Mclain is undersized (133k btu in/109 out). Only one of the five asked me about my sq.ft. of living space, sq.ft. of radiation, lineal feet of piping, R value of wall/attic insulation, etc and even he thought I was undersized. Talking to two different contractors from outside the area seemed to indicate to me that I may in fact be oversized already, but because of the distance could not be competitive in bidding. I did order the Slant Fin free cd rom, but haven't received it yet but would still like an analysis on the right size boiler from someone outside the area. Is there anyone out there who does it for a homeowner at a reasonable charge?
I'm a single level 1434 sq.ft. home with 78% basement area, well insulated walls/ceiling, all new double paned low E glass windows and steel insulated entry doors. Any ideas on who I could contact?? My boiler has a hairline crack which we couldn't fix with a sealer and leaks about a drop a second when cool, and less than that when cycling.
It's 18.5 years old, but is a hi-eff (82.2%) cast iron boiler.

Mark Hunt

Your boiler is


grossly over-sized and replacing it with a larger one would increase your fuel bills.

Worst case....1437 x 50 btus/hr of heat loss = 71,850 btus/hr.

That 50 btu/hr would equate to a home built like a horse barn.

Do you live in Point Barrow, Alaska?

I'd bet your actual heat demand is no more than 50k on design day.

Find another contractor.

Mark H

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

sidney r. bray

Another contractor

Mark-
Unfortunately, there's not much else to choose from locally, I have one other contractor coming later this week to look at it, don't know what school of thought he subscribes to as far as sizing goes...everyone seems to think the size of radiators, piping is what matters, not the sq.ft. of heating space and btu's per radiator, insulation, etc. I hope the cd from Slant Fin arrives soon and if it says a substantially smaller boiler will work then I can only hope a local contractor would install it properly and service it when needed.

Constantin

Give us some more info...

... where are you located? From what I can tell, you're heating with hot water? If so, size the load to the heat loss, not the attached emitters. The only reason I could see to upsize is domestic hot water production and a large indirect water heater is usually a better solution than a larger boiler.

As a fellow homeowner, let me ask you an elementary question: Does the present heating plant keep you you toasty warm throughout the year? If it does, there is no need to upsize. Under those circumstances, the contractors that advocate going with bigger heating plants perhaps need to be shown the door or explain their logic.

Besides the Slant-Fin software, another way to determine your heat loss is via your gas bills. If you can look up the number of heating degree days for several months in your area (see historical section for your zip code at wunderground.com, for example) and give us your gas consumption figures, we may be able to come up with yet another approximation of your heat loss.

Yet another way to do it is to sit next to your boiler for an hour at night in very cold conditions (as close to a design-day as possible) and to see how much of the time it is running while trying to maintain 68°F or whatever upstairs. Ideally, the wind will be piping up at 15MPH or more. Account for the boiler efficiency and the run-time, and you'll have another good idea of what the actual heat loss is.

Ultimately though, your challenge will be to find a heating professional who cares enough about the project to do a heat loss calculation on his/her own, followed by detailed system recommendations. Such contractors do not come cheap, but they're worth every penny. If hot water heat is in your life, consider a condensing, modulating boiler and an indirect water heater. Hard to beat, efficiency-wise.

If no one in your area can be bothered to do things right, you might avail yourself to the services of Northeast Radiant or Hydronic Pros. They'll do a heat loss and a system diagram for a fee that hopefully a local installer can follow. All the best, and I hope your boiler change-out has a happy ending.

jp_2

heat load

sid, I live in houghton, north of you. my house is about 1,200sq ft. poorly insulated, single pane drafty windows, 1/2 basement walls exposed and I have a 80,000 btu hot air furnace. just to give you an example.

call superior drywall

http://superiordrywall-paint.com/

Superior Drywall & Paint, Inc. - N10205 Crestview Road - Ironwood, MI 49938
PH: (906) 932-0152 - FX: (906) 932-1053 - E-mail: superdry@up.net

they do gypcrete, they 'might' know of someone good in that area.

Weezbo

You may be suprised at

the size and configuration of a boiler that would meet your needs. previously, i'd be willing to wager (and i am not a betting man), you had some pretty bad advise on the piping arrangement and the boiler sizing . and i do happen to live in one of the interior land masses where 50 below is just about a sure bet Every Winter.

sidney r. bray

Boiler sizing

I live in the south central portion of the Upper Peninsula of Michigan and yes, no matter what the temperature outside the boiler always satisfied the room temperature inside, the only issue ever has been that the boiler never heated warmer than 120 deg's, which improved to about 135 deg a couple of years ago when I did a by-pass, however that was 15 years too late and the colder water running thru the boiler may have led to the hairline crack I have leaking water now.
I tried contacting our natural gas supplier but they don't do a boiler sizing analysis, I will try getting my gas bills together and let you know about my gas consumption figures. Thanks.