Seeking professional Heat Loss Calc

mknmike

Looking for either someone I can pay to perform a calculation in Wilmington, Delaware, or someone I can pay to instruct me how to do the calculation myself.  

If you want more details and background on my setup, what I’m looking to do, and my house, I will probably document it all in this thread.

https://forum.heatinghelp.com/discussion/comment/1682468#Comment_1682468

Alan (California Radiant) Forbes

You can do your own here

Mosherd1

I’ll pm you if i can figure out how to pm.

Mosherd1

just pm'd you. 

wmgeorge

Find someone who knows how to do a ACCA Manual J, pay if needed. Its software was Wrightsoft but it can be done by hand. Do not know about the Free programs.

Jamie Hall

wmgeorge said:

Find someone who knows how to do a ACCA Manual J, pay if needed. Its software was Wrightsoft but it can be done by hand. Do not know about the Free programs.

The Slant/Fin program is Manual J

STEVEusaPA

@Harvey Ramer does them. Haven't seen him here in a while.

mknmike

Thank you everyone!  Someone has offered to do the Calc for me if I can collect the info.  So next step I will be gathering information.  

Great site!  Thank you all for all your help!  

mknmike

https://forum.heatinghelp.com/discussion/comment/1683910#Comment_1683910

Just to update, that Slant/Fin app site doesn't seem to work anymore.

PC7060

Mitek provides Manual J analysis for a fee. Key is getting them good data to work with.

Alan (California Radiant) Forbes

Are there no Manual J, easy-to-use heat loss calculators available?

Teemok

Cool Calc. Free until you want to print a full MJ8 report. It will give you loads and is ACCA approved.

https://www.coolcalc.com/

Intplm.

https://forum.heatinghelp.com/discussion/comment/1805627#Comment_1805627

I agree. We were talking about this last week on this sight. Has Slant Fin has taken it down???

GGross

https://forum.heatinghelp.com/discussion/comment/1805828#Comment_1805828

Slant fin boiler maintained the heat loss calculator and they are no longer in business. you can find the old page for it by google searching, but none of the links work and they don't directly link to that page on the site. the slant fin boiler website only exists to direct owners to warranty, most likely a legal requirement. Slant fin boiler, and slant fin baseboard were separate entities with different owners for several years.

mknmike

I’ve decided that it just seems too hard to get good data and I am looking to obtain data about how long my current boiler will run when all zones are calling for heat on a cold day. Is this a bad method? It seems more practical to me than making assumptions. Thoughts?

Thank you for all the help here!

I am finally looking to purchase a boiler or 2-3 before the end of the year and now am considering 3 smaller units (2 for house, and one or garage) instead of 2 identical units. My current boiler is 175k BTU Output and ran 19 minutes of the 5:30-6:30 am 36 F when thermostats average setting was 69 F, but many places in the house were 76 F. I’m assuming that’s a 33 temp differential, 69-36 F. I believe we only need our boiler to cover a 60 F differential bc we almost never have temps below 10 F here. So I am thinking we need about 2/3 the 175k BTU we currently have. So about 116k BTU output is what we really need. Crazy? Stupid?

jesmed1

Which house are you talking about now, the 2500 sq ft house or the 4200 sq ft house? If you're talking about the 2500 sq ft house, 116MBTU still may be oversized for Delaware, unless you are also heating the garage which you mentioned.

Your run time method is not unreasonable, but it only works if you know (1) the installed nozzle size and (2) the oil pump pressure if you're burning oil, because those 2 factors determine your oil input rate (and therefore your gross BTU input), and then multiply by the boiler efficiency. This result can be lower than the 175MBTU rating, which is only a maximum. People often "downfire" their oil boilers with smaller nozzles to reduce the output of their (typically oversized) boilers. But if you're burning gas, your actual BTU's should be per the rating plate.

mknmike

thanks @Jesmed1

The 2400 sqft house with TT PA110 is sold.

This is for the 4200 sq ft house that has a 210k BTU input / 175k BTU output natural gas boiler with no primary loop or thermal mass, and is wired and plumbed incorrectly, with no flow or boiler cutoff when none of the 3 zones are calling for heat. The 1970 Den Addition Zone is tiny and drafty as all get out, so we generally just close it off in winter and don’t heat it. I’m working on fixing the insulation and air infiltration issues in there, but even this morning we had it set to 65 F while the rest of the house was 69 F. We still only ran 2 cycles in the coldest hour at a total of 19 minutes. I think we might get by OK with half the boiler output after sealing up the house, maybe trying by with an 89k BTU output TT PA110.

jesmed1

OK. For a fairly leaky older house in Delaware, a heat loss of 20 BTU/hr/sq ft would be a reasonable guesstimate, which would put you at 84,000 BTU/hr heat loss for 4200 sq ft. So your 89,000 BTU output boiler sounds reasonable.

Once you fix the air infiltration, which is a big heat suck in older houses, you'll probably be fine with half your current capacity.

mknmike

thanks again jesmed1

When you say “current capacity” I assume you are thinking I already have a TT PA110, but that sold with the old 2400 sw ft house, and I am looking to replace the 175k BTU output natural gas boiler that ran for 19/60 minutes this morning at 36 F.

I am calculating that i I want a boiler to keep us at 70 F inside on a 10 F day, I need 60 F of heating.

This morning:

(19/60*175kBTU)/(69-36F)=

(0.317*175kBTU)/33 F = 1.68kBTU/degree F

(70 F - 10 F) * 1.68 kBTU/degree F = 100.76kBTU

So a 95% efficient 110k BTU input boiler should cut it, but for some reason 89k BTU is the supposed output of a PA110.

So how cold should a 89k output boiler be able to keep the house 70 F inside?

89k BTU/(1.68k BTU/degree) =52.97.

70 F - 52.97 =17.03 °F

So I believe I can assume a PA110 would be fine ring 100% of the time at 17 F, but below that we’d start getting chili and need to ad heat via other means. Start a fire, burn a wood stove, drink tea/coffee, get under the blankets or do some cooking or exercise.

Does my logic sound ok? Or crazy?

jesmed1

Disclaimer: I am not a heating pro. I'm a homeowner who is a mechanical engineer and who has benefitted greatly from the knowledge freely offered by the many pros on this site. I've spent the last few years learning about and upgrading the two oil-fired boilers that heat our 4-unit condo building, with much assistance from the good folks here.

Having said that, here are my admittedly non-professional comments.

1. Yes, when I said you should be about right with half your "current capacity" I meant 1/2 of 175MBTU.

2. Your math for getting a 100MBTU heating load looks right. As you know, it all depends on what design temperature you choose to use.

3. The PA 110 is advertised to have 95% AFUE. AFUE measures only "dry gas" efficiency, which means that a 95% AFUE furnace is losing 5% of its BTUs as heat carried away by the "dry gas" combustion products up the flue. AFUE does NOT measure the BTU's also carried away by the hot water vapor. In the case of a gas furnace, about 15% of the BTU's are being carried away by the hot water vapor when the furnace is not condensing. Ergo, when the 95% AFUE furnace is not condensing, it is losing 5% of its BTU's as hot "dry" gas, and 15% of its BTUs as hot water vapor. So it's losing 20% total. Which nets you out at 80% efficiency. Which means your 110MBTU furnace is giving you 88MBTU useful output. Only when you recover that 15% vapor loss when condensing do you get your 95% "AFUE" efficiency, which for the PA 110 would be about 105MBTU.

The advertised output number is further confused by the "I-B-R" rating that subtracts 15% of the output as a nominal de-rating for piping heat losses in the basement or unheated area where the boiler is located. Since the IBR 15% derating happens to be almost identical to the 15% vapor loss when the boiler isn't condensing, by coincidence the advertised 86MBTU/hr IBR rating for this boiler (when condensing) happens to be close to its net output (without the IBR factor) of 88MBTU/hr when it is NOT condensing. Confusing.

4. Yes, your math for the 17 degree "lower limit" looks correct. Now you're playing the game of "how much cushion do I want for a 1-in-1000 low temperature day?" Only you can answer that question. But since you're asking, you might also want to consider that high winds can add 25% or more to your heat loss on a cold day. We had a polar vortex event here in the Boston area last February, with 0-10 degree persistent conditions and high winds, and I measured our boiler run times throughout the 2-3 days. The wind chill and increased air infiltration added 25% to our heat loss. Normally we would have lost 100MBTU/hr at those temps without wind. With the wind, we lost 125MBTU/hr.

mknmike

that 25% for wind is a new one for me. I guess I hope it’s only that much. Due to space and pricing, I’m starting to get real tempted to go with a TR Instinct Combi which only comes in 115/142/123 and 199/184/159 ratings for input/DOE/Net I=B=R. The effective minimum 5.5:1 firing rate of a PA110 is about the same as the combi 155 and much lower than the combi 199 despite their 8:1 turndown ratios. The higher DHW production rate of the 199 is nice, plus it could be better if we decide to use the garage unit for swimming pool heating. So maybe it wouldn’t be totally nutso to go with the combi 199 since it doesn’t cost nothing significant more than the 155. On the other hand, the Low NOx of the Prestige might make more sense, just leave me wondering how I will make hot water in the garage. I have been looking at indirect tanks for the house and also have gotten excited about using a heat pump water heater for hot water in summer and also a potential storage tank. All that could at the very least make the more efficient 155 Combi unit, if not the Prestige Solo 110 seem reasonable.

I hope I finally make a decision on the soon, but I wonder if I should wait for another cold period for measurements.

jesmed1

If you're not in a hurry, time is your friend. Get a temperature recording data logger and use it to record actual boiler run times. Then use recorded temperature data from your nearest airport to plot boiler run time vs your temperature differential, and you'll get more confidence in your numbers.

mknmike

Well, the big ole pumps (2 of 3) are on the fritz, jammed due to water leaking at bearings) and the old piping has no isolation valves for replacement. So I am looking to get started having the new boiler, exhaust and pumps on the opposite side of the basement. Then I would try to find the fastest was to pipe in, perhaps a big primary loop through the whole basement and connect into the old piping, planning ahead for alterations.

Besides the milky oil needing to vacuumed out of the bell & Gossett bearing every week or so to be replaced with water-free oil, I am in tbe middle of installing digital / wireless thermostats to resolve some of the thermostat issues too. Once I get them all moved over to new wiring, I can then use the Taco SR503-EXP switching relay to also shut off the boiler when no zones call for heat. I can do that prior to installing a new boiler, but it will end up all temporary work, and perhaps a waste of wire.

So there’s as real decision about whether to just get on with the new install or spend time on the existing. I just found a really low price from a website called pexuniverse.com and wonder if anyone has had issues with them, out of Brooklyn, NY. At some point it’s time to stop fretting over the details and get on with it.

mknmike

So heat loss calls are about sizing the boiler right? Well, I just had out 175k BTU output boiler run for 40 minutes straight.

I finally got our programmable thermostats setup and set them up to be 67 F through the night for cool sleeping, and then at ~5 am switch to 70 F to help everyone get out of bed more easily. I know a 3 degree rise might not be smart, but…

This morning it is 38 F outside. The pump for the zone that manages the bedrooms has a 4” pipe around the whole basement with lots of thermal mass to warm plus all the second and third floor, and even a few radiators on the first floor. So that circulator is going to be calling for heat for a while. The boiler finally hit that target of about 140 F after about 40 minutes of run time.

That maybe another sign that the boiler is about 1/3 too big for our needs. If we wanted faster recovery, I could see. It’s tempting to say we wanted even faster recovery, but that’s a recipe for some serious over-sizing.

But it does make me think that have the Combi 199 with 184k BTU output might not be too bad of an idea. If turndown of 8:1 drops the 199k BTU input down to 25k BTU, that would be a lot better for the smaller zones and maybe even handle this loathed zone better with more output BTU than our current boiler at the highest burn rate (and still always lower than what we currently have on the input/consumption side, 210k BTU).

hot_rod

correct you are that those wide modulation ranges make over-sizing much less of an issue

With all the control functions and ODR you can get real close to constant circulation

To me that is the holy grail, the boiler runs continuously during the heating season, the burner modulates to the ever changing load

mknmike

https://forum.heatinghelp.com/discussion/comment/1822611#Comment_1822611

Yes. I was able to even get close to that with the oversized 5.5:1 Prestige Solo 110 at my old house. This house seems to have about twice the heat loss (or worse). And I am starting to hope that I can justify 199k BTU with 8:1 turn down. The hot water and more “recovery” due to a nighttime setback (that we didn’t do at the old house, but will not that there’s so much loss at the new house) are reasons I am oversizing a little with a combi 199 … I think. No major rush and looking to obtain more data before pulling the trigger (on only about $2500 for one boiler).