SIZING RESIDENTIAL H.W. BOILER

bob young

any of our experts know a quick formula to size small one family residence with out doing a formal heatloss. i had one but cannot recall the details.

JStar

Nope. Do the proper heat loss.

Steamhead

Do the heat loss. That's the only way you'll get it right. Anything else is just a guess.

Robert O'Brien

Steamhead said:

Do the heat loss. That's the only way you'll get it right. Anything else is just a guess.

Using S/F software as an example,aren't you guessing when you select factors? I'm not saying don't do it, but don't be fooled that the number you get is correct, IMO it is at least 25% over. It's usually moot because most customers won't accept the fact that the shockingly low number the calc yields is in fact even lower in reality. Ever see a job that runs 24/7 on a design day?

SWEI

Robert O'Brien said:

Ever see a job that runs 24/7 on a design day?

Only when we have multiple (cascaded) boilers -- and it's always at least one less than we installed.

Robert O'Brien

SWEI said:

Robert O'Brien said:

Ever see a job that runs 24/7 on a design day?

Only when we have multiple (cascaded) boilers -- and it's always at least one less than we installed.

bob young

is existing radiation a factor ??

Steamhead

Robert O'Brien said:

Steamhead said:

Do the heat loss. That's the only way you'll get it right. Anything else is just a guess.

Using S/F software as an example,aren't you guessing when you select factors? I'm not saying don't do it, but don't be fooled that the number you get is correct, IMO it is at least 25% over. It's usually moot because most customers won't accept the fact that the shockingly low number the calc yields is in fact even lower in reality. Ever see a job that runs 24/7 on a design day?

Sometimes if you can't see what's in the walls, etc., you just have to do the best you can. But it's better than the "Label Method".

Robert O'Brien

Steamhead said:

Robert O'Brien said:

Steamhead said:

Do the heat loss. That's the only way you'll get it right. Anything else is just a guess.

Using S/F software as an example,aren't you guessing when you select factors? I'm not saying don't do it, but don't be fooled that the number you get is correct, IMO it is at least 25% over. It's usually moot because most customers won't accept the fact that the shockingly low number the calc yields is in fact even lower in reality. Ever see a job that runs 24/7 on a design day?

Sometimes if you can't see what's in the walls, etc., you just have to do the best you can. But it's better than the "Label Method".

The label "method" is worse than using the steam method on HW, ie. measuring the radiation!

Chester

I'm a consumer with a "small one family residence" in New England. My 1400 sq ft cape had a heat loss of approx. 30,000 Btu/hr (dropped that somewhat with insulation and air-sealing).

I started with a formula based on comparing historic energy use with heating degree days -- Implied Heat Loss (BTU/hr) = (Heating Degrees) X (BTU/degree-hour) -- using 4 months of actual winter fuel use. Basically you're using the existing boiler as a measuring device based on real-world conditions. (I subsequently had an energy audit with a Manual J analysis and it came in at 29,500.)

For my purposes I didn't really need that level of accuracy; I was simply deciding whether I could be comfortable with a boiler at the smaller end of what's commercially available (e.g. 50,000 to 60,000 vs 75,000 to 100,000). For me the most important metric was the boiler's minimum output.

BTW: Per Mr. O'Brien's comment above, I also found the Slant Fin software came in about 25% above the Manual J.

Canucker

It makes my head spin a little everytime I read that the S/F app comes in 25% high. I did a heat loss with it to see where my house would fall once my planned reno are done, and I came in at 79000 btu/hr on design day. And that is with the detached garage added to the calcs, that isn't heated right now. I have an 80% efficient, 107000 btu copper tube boiler heating my house now that I was told wouldn't be big enough to heat the place after the expansion, let alone if I added the garage.

Canucker

Good point. Makes you a little self concious though, when an installer almost laughs because you suggested a smaller boiler might be ok after adding conditioned space. If I wasn't on this site, I would have thought my numbers were WAY off, in the wrong direction.

Steamhead

Robert O'Brien said:

....... the shockingly low number the calc yields.............

Here's one where the consumer was thrilled with the lesser BTU input. It did take a bit of convincing but we guaranteed that it would work:

http://forum.heatinghelp.com/discussion/129307/our-first-burnham-es-2-install

The excess capacity that we talk about goes to the indirect in this case. Another point in favor of indirects.

Robert O'Brien

Hatterasguy said:

Canucker said:

It makes my head spin a little everytime I read that the S/F app comes in 25% high.

Blaming the app is a bit of a mistake. All it does is sum the various U values and provide a result. The U values might be slightly in error, but the app cannot be wrong by 25%.

What is common, however, is the fact that the app has no provisions for all the other heat sources that are provided to the building. The group includes people, the stove, the sun, televisions, dishwashers, showers, computers, and any other device powered by electricity that offers up waste heat. In theory, all of these values must be subtracted from the total calculated heatloss provided by the application to arrive at the number for the boiler. That's never done. Consider it a safety factor.

Get a building with no electronic gear, no cooking, no people, and no sun radiation and the app will be very close to the calculation.

I attributed it to very conservative factor selection and some fudging in the factors themselves never considered other sources of heat. Learn something everyday!

Robert O'Brien

Hatterasguy said:

All those sources of heat serve to reduce the total number of degree days at a location. It's not uncommon for the base temperature to be 60°F instead of 65°F. Take a look at how much that simple change affects the degree day calculation.

Makes perfect sense, just never gave it a thought. It is so consistent, I assumed it was in the software.

Robert O'Brien

Hatterasguy said:

What is interesting is that your method of determining heatloss can adjust for this variable simply by changing the base temperature.

Those that do the traditional heatloss calculation suffer with a larger value for the total heatloss.

In your method, with a careful subtraction for hot water and a careful application of the base temperature, you can actually be more accurate with existing fuel burn numbers.

Traditional heatloss calculations simply use the difference between 70°F and the design temperature.

I knew it was closer than the traditional method based on anecdotal evidence, but with the limited sizes of boilers available it is moot in the vast majority of real world applications

SWEI

Time for some 20-40k options in both oil and gas, methinks.

Rich_49

Either smaller boilers or start to teach the already confused about storage .

I am surprised that you never considered appliance loads Robert O . Things like that are exactly what I was talking about , being constrained by the programs as opposed to layering assemblies , adding people , solar heat gain and equivalent full load hours .

Robert O'Brien

Rich said:

Either smaller boilers or start to teach the already confused about storage .

I am surprised that you never considered appliance loads Robert O . Things like that are exactly what I was talking about , being constrained by the programs as opposed to layering assemblies , adding people , solar heat gain and equivalent full load hours .

And after all that,the smallest oil boiler is still 75K!

Rich_49

Yes , that is the case . And your point is ?

Jason_13

the MPO-IQ from US boiler is either 64k or 67k DOE. That is about 10K less input.

hot_rod

The largest variable as Hatt eluded is how the home or building is used. The lifestyle and habits of the HO makes for some, many, unknowns. This could be showers, lightning, laundry, trips to the refrigerator, parasitic energy gains, even the amount of times the doors open and close, and the wind and temperature when they are operated.

At the end of the day, regardless of the load calc method you use, and how much data you crunch to get the most accurate data, it really ends up a best effort "guesstimate"

With Robert's method, compiling actual usage data really nails the number as tight as possible. it's a real life number, not based on assumptions or predictions, so much.

How to translate that to new construction would be trickier.

bob young

jonny 88 , thanx much, babe. worked like a charm, same one i could not recall !!!! did a conventional one just to check & i was right on. bob nyc

jonny88

beautiful.lets keep it to ourselves or we might get in trouble...

j a_2

There are many rules of thumb, there a many programs available,to confirm heat loss...but what is often not found is common sense..I firmly believe a heating person who has been actually doing it for xx years pretty much knows the boiler he would use as he pulls up to the house...Not to say you should not do a heat loss,because you always should, it's politically correct....I never installed a boiler speced out by the owner based on his own heat loss, but if I did I would have been certain to inform him, you spec it, you own it..don't call me when it short cycles, or runs and runs and runs, or your family is uncomfortable, and your new boiler produces higher fuel bills...That is why heat men are heat men,it's what we do...or did

j a_2

Is that how its done, or are u being a funny guy..Or just raging on heating men based on your bad experiences?

j a_2

No way I don't need to ponder, I also had no idea they made two size boilers. 125k and a 200k one...that's totally awesome.... Was wondering do oil guys size oil.lines based on btu, like gas fitters size gas piping...lol

j a_2

Wondering,this, if your in the business of selling oil, are you more prone to oversize or undersize.? And if your in the business of selling baseboard heat would you set the program to oversize or undersize....Woops back to that stupid common sense thing

JStar

That's when we come in and install an outdor reset and run below 140F. Maybe those perimeter-baseboard guys weren't so bad afterall.

j a_2

Thinking we may now be on the same page....like ur style, sometimes. Lol....It's crazy out here and no one is watching the farm...Same mistakes over and over again..
Simple crap to, circs on returns,no boiler bypass on old high mass systems, make up air,who.needs that

j a_2

Not all, sir...are bad. Because you know why, they don't know enough to know there bad...Like I said one can have all the nice state of the art yupie crap...Nice cad drawings and flow rates and velocities... Try using that on a 10 finger gravity flow swap out...Hay what are them there gas cocks doing on a the five returns...let's cut them out of there. And gee a couple of them are not even open all the way.well that's just plain stupid....lol

SWEI

JStar said:

Maybe those perimeter-baseboard guys weren't so bad afterall.

Worked quite nicely in rooms that did not have floor to ceiling windows or sliding glass doors.

Harvey Ramer

Earlier comment about why no smaller oil boilers. I'm not a manufacturer so I can't say positively, but I would say it has to do with nozzle size and oil quality. With smaller nozzles, .65 GPH and down. You should have a spin on filter. Some say you should have them on larger nozzles. Couldn't hurt.

Can you imagine a .25 GPH nozzle? You would need a really dense filter and likely a heater in the oil line-nozzle assembly. May even have to redisign the pumps.


As far as sizing the boiler. Never put in a boiler that has greater capacity than the emitters. That is the first, and often neglected rule. I don't know how many people think a bigger boiler will heat the house better when it gets really cold, and all the while the boiler is limited by the connected emitters. That's stupidity!!

Strictly on the subject of oil, and boiler swapouts. I know the smallest oil boiler I can get and I know a house that falls in that category. In that case the only time I do a heat loss Calc is for other purposes or to impress the homeowner and increase my odds of making the sale.

j a_2

I am not sure I agree on never installing a boiler bigger than the emitters,in fact some manf. Will specifically say not to do that....a quick whole house heat loss and overall evaluation will get you right there.....The bulk of my business was conversions, oil to gas, I would be quick to tell them if you have issues upstairs the is a pretty good chance you will have the same issues when I am done, I am changing the type of fuel you burn and that's it....I would always gladly offer my verbal opinion, new boilers don't fix leaks, or filthy dusty baseboards, or a improperly adjusted and located thermostat...or rad. covers made by some blanket making company...it was amazing what you saw out there...some people are savoy, but most don't have a clue, that's why they called us...and that's fine...some people listen with there head some listen with there wallet...Landlords listen to the down and dirty ell cheapo....Then call up when the tenant pisses and moans at them about the heating issues...As an installer you also have to be savoy enough to cover you butt,at all times....or you can loose your butt...Mike the mechanic next door may be able to look at a pic. Install it to perfection....Just a wee bit more to it than pretty pipes, I think....There is a cold side to the heating business, it's sad but true because people will try to get what they can out of you..Don't get me going on condo yuppies they are beyond the worse....they all seem to hate each other....That's my basement spot, that's my basement air, you can't use that common area, you can't abandon the chimney,or we will have to resize it, you can only use 1/3 of gas capacity the rest is ours because when we convert we need it to...the basement boy is making to much noise and my baby sleeps in the day....can he come back later after his nap....no one can enter my unit unless I am there, so don't shut down water or gas something might happen....I need a weeks, that steam riser heats my bathroom, you can't affect that....