Planning an oil to gas conversion, what boiler should I get to avoid short cycling

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msimm15

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Hi

I have a 4 story 18x34 house attached on both sides in Queens NY the back is in direct sunlight and doesnt need much heat at all, on a 30 degree winter day/night the radiators in the back rooms were closed and sometimes I had to open the windows a bit while the radiators in the front were open. I currently have a 3yr old 100k btu steam crown boiler running on oil. I am getting rid of the oil and steam and switching to gas and hot water. My biggest concern is what type of boiler to get to deal with 5 zones and avoid short cycling when only 2 or 3 of the zones will be running most of the time. I need to be able to zone the system with 5 zones to control things from the front of the house to the back and shut the 4th floor and basement that dont get used much and I plan on running indirect DHW of the boiler as well.

I imagine based on the current state of things that only 2 or 3 zones will be running most of the time, but if a I get a boiler large enough for all 5 zones + the indirect DHW the result would be frequent short cycling for the 2/3 zones normally in use.

From my research the obvious answer would be a mod/con boiler - however most of the ppl I spoke to said to stick with a regular cast iron (large mass i guess) boiler b/c of the extra headache and downtime involved in parts for the mod con boilers.

So my question is - Is there anyway to setup a regular cast iron boiler (right now I am looking at a Williamson 140k) to be able to handle all 5 zones + DHW when it needs to but also work well for just the 2/3 zones without short cycling. I saw a comment in another post about the intellicon economizer which sounds like it would help. Any other suggestions ?

Thanks
 

Tom Sawyer

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Jeezus man, 140,000 you heating the neighbors house too? Got to do a heat loss to do the job right. Could get fairly close using K factor but a manual J is a whole lot more accurate. Get that done first and then design the system around the load.
 

Dana

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Unless there's no glass in some of the windows or a missing door there's no way a ~2500' 4-story with heated houses butted up on both size would have any use for a 140K boiler. Your actual heat load @ +15F (NYC's 99% outside design temp) is probably going to come in under 30K, and if the abutting houses are the 34' sides, with only 18' of exterior wall frontage, it's probably under 20K.

The bigger the boiler relative to the radiation on the smaller zones, the more likely it is you'll be running into short-cycling problems, so nail down the heat load first. You may be able to heat the place with a hot water heater.
 

BadgerBoilerMN

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I just designed a Brownstone heating and cooling retrofit in Boston last fall. A condensing water heater did everything with special attention to controls.

First, as always, we start with an room-by-room ACCA Manual 'J' heat load, measure the available radiation and size the indirect or combi-water heater accordingly.

What you are asking for is not difficult if you have experience with old homes and new technology.

"From my research the obvious answer would be a mod/con boiler - however most of the ppl I spoke to said to stick with a regular cast iron (large mass i guess) boiler b/c of the extra headache and downtime involved in parts for the mod con boilers."

God knows I am trying to be nice, but this is pure stupidity.
 

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If there's nobody in Queens willing to support a mod-con, it's not AS stupid. At the likely miniscule heating load the amount of cost savings you'd have would be pretty marginal at recent years' gas pricing, and just about every boiler (mod con or cast iron) may be oversized.

A condensing hot water heater is probably always going to be a better solution for a 5 zone house with a design heat load of 15-25K than any mod-con.
 

BadgerBoilerMN

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The stupidity is in the "sticking" with cast iron to avoid down time in parts for the mod con boilers". Which ModCon? What parts? Nonsense born of stupidity and sustained by ignorance. We just serviced a Lochinvar Knight we installed in 2006 for the first time, no parts needed. And later in the morning the dreaded Weil McLain Ultra Series 3 we installed in 2007 needed a HX gasket and ignitor, couriered to the job site in one hour, all done in two, happy customers with 20% fuel savings on fin-tube with an indirect water heater. Combustion efficiency; 96%.

As for short-cycling; the mass of the radiation, as you know, has much more to do with cycling than the mass of the boiler. The first may enhance comfort and efficiency while the latter only assures wasted heated.

One of the main benefits of a low-mass condensing boiler is that all are sealed-combustion and direct vent. Eliminating the chimney, and requisite combustion air may save 3% on the fuel bill right off. No open flame, no noise, you know I could go on.

Since all ModCons have on-board outdoor reset a bevy of cast iron radiators, each with its own thermostatic radiator valve, driven by an Delta 'P' ECM pump like the Alpha, could be the perfect solution once the heat load is done. If, in fact, the micro-zones are too small, a Versa-Hydro or Polaris would be in order.
 

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I totally get that you'll get the comfort & performance out of the mod-con, but it's not going to be a huge cost savings with tiny loads. If you can't find local support it can be a pain. Yes, a competent mod-con guy can make quick work out of the care & feeding of a mod-con, but that's not who he's been dealing with.

I'm sure there must be SOME competent hydronic designers in western Long Island who is comfortable with mod-cons, but from back-channel conversations it's clear he hasn't met any yet. If he has to go with plumbing hack rather than somebody who can do math, he can get most of the benefit out of a Burnham ES2-3, a direct-vented cast iron pig wearing lipstick such as smart boiler controls (with an outdoor reset option) and low return water temp tolerance.

He hasn't really said whether he's re-using the steam radiators in the micro-zoned hydronic make-over, but yes, that makes a real difference. Getting the room by room heat load numbers and the EDR/load ratios for those would tell us where it lives relative to condensing temps. The last thing you'd want to do is let a hack install an oversized mod-con then set it up at a fixed-temp 170F output or something (and we KNOW those guys are out there!) when a cheap cast iron pig would deliver the same performance. If he can't find the right contractor (and he hasn't yet), that's probably an acceptable solution, if less than ideal.

A Versa could clearly handle the whole thing, and may indeed be the "right" solution, but even there the matter of finding a competent designer/installer doesn't go away.

At least this is the right time of year to be figuring the stuff out. I've been informed that there are 3.5 baths currently served by a 40 gallon indirect off the existing steam boiler with (not surprisingly) less than stellar performance. (Seems more than just a bit on the skimpy side for serving up three showers at time.) That may be why folks are pushing ridiculously oversized cast iron at him, but that could be giving them more credit than is due.

There are several ways to skin this cat, but a ridiculously oversized burner is the least-optimal, considering the planned micro-zoning.
 

Tom Sawyer

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The majority of my customers have boilers that are at least thirty years old and some close to eighty and, they're cast iron. I doubt anything in the condensing arena is going to last half of that. However, their AFUE's suck. Still, the cost difference between a condensing and non condensing boiler is considerable and unless fuel costs sky rocket, it makes finsncisl sense to go with non condensing.
 

BadgerBoilerMN

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No return on investment. No added comfort. No safety improvements. No quiet. No outdoor reset. No space savings. No low temperature radiant systems. No direct vent. No sealed combustion. No 5 years parts and labor. No low pollution technology. No multi-temp controls. No multi-pump relays. No co-axial flex vent using the old, obsolete, chimney as a chase. No $500 rebate. No 20 to 50% fuel saving on low temperature applications such as this OP suggests.

30 years guaranteed low efficiency dependability. I guess I stand corrected...
 

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An ES2-3:

Direct vented with sealed combustion?

Check.

Smart controls with outdoor reset option?

Check.

Space savings?

It's matter of degree- a correctly sized indirect for his hot water loads has a bigger footprint than the ES2-3 boiler, which isn't a whole lot bigger than many wall-hung units (though some.)

Low temperature?

Check. (It's 110F return-water tolerant without external plumbing.)

Quiet?

Again, a matter of degree, but it's nothing like the roar of an atmospheric drafted 100K, and comparable to many mod-cons.

Despite the 2x+ oversizing factor for the likely loads it'll hit pretty close to it's ~85% AFUE if set up correctly to not short-cycle. That's still an "if", since it's output is north of 50K, into an unknown amount of zone radiation & thermal mass. But it seems at least possible, unlike a 100K+ boiler.

At the likely loads of this house at recent years' gas prices they'd probably save on the order of $100/year by going to condensing equipment:

Even if the heat load is as high as 25,000BTU/hr load @ +15F it'll takes about 12,000 BTU/HDD to keep the place fully up to temp. In a 4800 HDD climate that's 57.6MMBTU/year. To deliver that with ~85% efficiency equipment takes 678 therms/year. To deliver it with 95% efficiency equipment takes 606 therms/year. The 72 therms difference at $1.50/therm is $108, and actual wintertime gas rates have been cheaper than that recently. The real space heating load is probably smaller than that.

The annual hot water use might be almost as much as the space heating, so call it $200/year savings, even if the delivered price rises to $1.50/therm. While natural gas has been trading near historical lows, with nowhere to go but up, I don't expect residential retail prices to double any time soon.

If they install a 100-140K+ cast iron pig (with or without heat purge controls) there's literally no way it will hit it's AFUE numbers, due to the severe oversizing factor and low zone loads, unless they also install a ridiculously sized well insulated buffer tank to match. Even with high-volume column radiators, in a 5 zone system it would almost surely short-cycle on 100k of input.

An ES2-3 paired with a 40 gallon buffer tank could be micro-zoned to the Nth degree with impunity, and somewhat cheaper than an HTP Versa. But is sure is a kludgey Rube Goldberg solution compared to a Versa. (A Versa would take about as much space as a correctly sized indirect HW heater.)

Assuming he can't find a better contractor, the li'l pig with the direct vent and smart control lipstick still isn't insane.
 

BadgerBoilerMN

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We have several Burnham ES-2 boilers installed here in Minneapolis. They are a very "dressed up" cast iron boiler. In fact they look like a high efficiency boiler and have nearly all the "optional" attributes of a condensing boiler save one. They don't condense. You will have to have a viable chimney such as a Class B or equivalent since the ES-2 is a Category 1, non-positive pressure gas-fired appliance.

They are in fact not direct vent, as they have no blower. Nor are they sealed combustion, rather they use conditioned air from the room in which they are installed and often require combustion air from outside piped into the room they occupy. Though they have many rather expensive options, direct venting and sealed combustion are not amongst them.

We typically install the Burnham ES-2 series boiler where outdoor reset is of little value e.g. fin-tube systems and those with fan coils and in retrofit situations where funds are short or conversion too expensive. Burnham is a great company to work with and their products are exceptional. They even "make" a condensing boiler, the Alpine using the all-to-common Giannoni heat exchanger.

In the end the ES-2 must maintain a 350F stack temperature and the condensing boiler less than half of that under most conditions. The relatively low return water temperature is still well above the real-world return water temperature of most of my radiant systems and all of my cast iron systems most of which operate from 85F to 150F the majority of the time well below 140F with returns often in the 60's .

If you add the considerable cost of the ES-2 outdoor reset module you can buy the fully condensing HTP Contender in 50mbuth for the same money.

If you really need ODR, LWCO and an auxiliary aquastat you can have the NTI tft 60 for a bit more.

You and I will never argue about over-sizing equipment, whether we depend on your natural intelligence or my artificial Manual J, but I would like to do a proper heat load and then decide on condensing water heater vs. condensing boiler :- ).

I would also like to operate an ECM pump full time an control the rads with TRV's. No short cycles, just perform, practical comfort.
 

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Mea culpa- I keep getting the direct-vented ESC-3 and atomspheric drafted ES2-3 mixed up. They're the same boiler underneath it all and most of the cabinetry is the same too- they're nearly twins. The ESC sheet metal is slightly different to seal the combustion and accomodate the intake vent. It's not co-axial venting, but neither are many mod-cons. AFUE is still in the 85s though. Installing the atmospheric drafted ES2-3 would be more expensive than the ESC-3 , since it would almost certainly require a new narrowing flue liner.

I'm not saying these are a great choice or a slam-dunk , just a heluva lot better than most of the cast-iron options previoiusly discussed. With enough thermal mass on the zone radiation it'll do OK. There is smaller, lower efficiency dumber cast iron out there, but the ESC-3 would beat them, and he could seal up that 24/365 infiltration driver (aka the 4 story chimney.)

In backchannel conversations using this site I started him on the room by room heat load calcs and recommended fuel use numbers for sanity checking, as well as directing him on how to do the radiation sizing but he hasn't gotten back to me with the hard numbers yet.
 

BadgerBoilerMN

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I was picking on you a bit. The ESC is also a find "cast iron" boiler but still old school, loud, heavy, inefficient and costs the same as a "cheap" ModCon. Once you buy the mandatory stainless steel vent pipe and fittings you will have more money in the ESC than half the ModCons on the market. You know how I am...

Why do they always choose the good looking guy?
 

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Here's the thing. Take a thirty year old Burnham or Weil McLain cast iron boiler and it's a veritable poster child for inefficiency. Air leaks around old gaskets, no damper to alleviate stand by stack loss, a half an inch of crappy insulation, vented into a masonry chimney that's probably sucking as much air out of the house as an open window. No modulating or set back controls, the damn thing is probably maintaining 160 degree water year round too and yet when you run the numbers, the payback period is almost always in excess of fifteen years and statistics show that folks don't generally hang around that long anymore. I don't see anyone doing depreciation on the new equipment either. It's all well and good to think it's going to last but experience tells me that it won't and perhaps it shouldn't for that matter. I truly believe that boilers and furnaces, regardless of the fossil fuel burned, will be a thing of the past within the next twenty years. Advancements in photoVoltaics and other cheap electricity sources are going to take the market over and they should because electricity is 100% efficient. All this condensing crap is an interim solution at best.
 

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Your points are well taken but your conclusion leaves much to be desired.
First, energy remains primarily a regional consideration. The market, even with often misguided government interference, is driven by logistics. On the east coast oil was king but gas is taking over. In the northwest hydro rules. Here in the Midwest gas has been the primary fuel for decades.

The "100% efficiency" claim of electrical power advocates is of course only valid at point of use, and if we ignore heat pump technology, easier still in modest residential hydronic applications such as this. Given the 6% transmission and distribution cost, not to mention the operating rate producing less than 50% usable energy.

I know Dana loves the sun, but in Northern climates I think is safe to say the vast majority of solar energy will be had from that stored in fossil fuels, no matter how much we wish, pray or legislate. OK the balance may shift by 2060 or so.

Since the operating heat rate for natural gas is some 20% lower than coal, oil or even nuclear and NG is ever abundant, the logical conclusion is than we will be making the majority of our power in N. America with gas. Same is true of residential and commercial boilers, most especially where gas infrastructure is already in place. Here in Minneapolis, and in other older towns with boilers and furnaces in place, gas will be king for decades to come.
 

Tom Sawyer

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Mark my words, 20 years tops. The technology emerging is mind blowing. Think about this. Circulating hot water through pipes is hundred plus year old technology. Heating air and blowing it around is even older. Even the technology behind the most modern of condensing boilers is decades old. Only the electronics have changed. A high efficiency Riello, carlin or Beckett oil burner is only fractionally more efficient than the same models from forty years ago. Gas burners have changed even less. Besides the dated technology, like it or not there is a safety issue as gas explosions are still a fairly common occurance and oil tanks continue to spring leaks and cause all sorts of environmental problems. Speaking of environmental problems, both oil and gas share equal responsibility for doing their part to contribute to global warming as well as fluctuating economic problems. You do know the real reason why we are fighting and dying in the Middle East don't you? It has nothing to do with religion or politics. It has everything to do with energy.
 

BadgerBoilerMN

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I'm marking but the numbers don't add up.

Actually steam preceded gravity hot water heating, which in turn was the precursor gravity air finally "improved" with the advent of electrical blowers creating the general nuisance known as scorched air.

Only people who sell oil pretend to be afraid of gas. Since nearly all the NG in N. America is delivered by pipeline, the safest way to transport any fuel, NG wins this argument for people and the environment.

http://www.manhattan-institute.org/html/ib_23.htm#.VYXc7fmrRhE

http://www.semcoenergygas.com/media/pdf/Connectivity 2013 july august.pdf

http://www.propublica.org/article/p...e-are-americas-2.5-million-miles-of-pipelines

The condensing boilers I am using now are light years ahead of the boilers I built in the 90's including Lamda controls, outdoor reset and ever more efficient and durable heat exchangers. Don't forget pre-purge and post-purge for blower and pump.

The green house emissions for condensing boiler is less than half that of oil will lower NOx and SOx emissions than practically any gas-fired vented appliance made. You might note that you don't do a "soot" test on gas-fired appliances.

The pathetic part of the cast iron argument starts with cast iron at three times the weight and ends with 15% of the fuel sent directly up the chimney to fall later as acid rain instead of being recovered and sent harmlessly down the drain.

No one fights or dies for NG in Canada or the N.Dakota. Yet another great reason to get off the oil teat!
 

Tom Sawyer

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You're still short sighted. I agree that oil is pretty much gone now with the exception of thousands of customers in the northeast, northwest and Midwest, and Canada that don't have access to natural gas. Still, oil has no doubt run it's course and natural gas is close on its heels. The history of "central" heating is an interesting one indeed but it's a short history at best as for most of our existence we have heated by burning wood or coal which by the way, millions of folks still do today. Pre and post purge are nothing new either. They have been around for over fifty years. Again, some advances made but too little, too late. Get the money while you can because it's going away fast. We have quadrupled the number of mini-splits we install every year to the point where we sell and install more of them than boilers and furnaces.
 

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Your points are well taken but your conclusion leaves much to be desired.
First, energy remains primarily a regional consideration. The market, even with often misguided government interference, is driven by logistics. On the east coast oil was king but gas is taking over. In the northwest hydro rules. Here in the Midwest gas has been the primary fuel for decades.

The "100% efficiency" claim of electrical power advocates is of course only valid at point of use, and if we ignore heat pump technology, easier still in modest residential hydronic applications such as this. Given the 6% transmission and distribution cost, not to mention the operating rate producing less than 50% usable energy.

I know Dana loves the sun, but in Northern climates I think is safe to say the vast majority of solar energy will be had from that stored in fossil fuels, no matter how much we wish, pray or legislate. OK the balance may shift by 2060 or so.

Since the operating heat rate for natural gas is some 20% lower than coal, oil or even nuclear and NG is ever abundant, the logical conclusion is than we will be making the majority of our power in N. America with gas. Same is true of residential and commercial boilers, most especially where gas infrastructure is already in place. Here in Minneapolis, and in other older towns with boilers and furnaces in place, gas will be king for decades to come.

Within the life cycle of a gas boiler I'd hazard that's about right- fossil fuels will still be a major player for the next 20-25 years. But at the price trajectory of grid-scale wind power and photovoltaics as well as grid-storage technologies I wouldn't necessarily bet on a fossil-burner for the replacement in 20-25 years. Grid storage technologies have had similarly jaw-dropping price trajectories (a 80% decrease in price since 2010!). Heat pump technology is nowhere near the thermodynamic theoretical limits, and seeing significant incremental year-on-year improvements.

By the time this year's shiny new fossil burner is toast I firmly believe there will be hydronic air source heat pumps capable of handling loads as big as msimm15's or higher, even in climates as cold as International Falls MN.

So it's a matter of how many decades to come before gas is no longer king. I say two or three decades you say maybe five, and either is really little more than an educated guess. But in a NYC climate the best in class air-to-air mini splits are already cost-competitive with condensing gas hot air furnaces on a lifecycle basis right now, (even at NYC style electricity rates) and will only become more so in the next decade. It'll be another decade before cold climate ducted air source heat pumps are up to snuff at Minneapolis type outside design design temps, but they'll get there in another decade at about the same time that cheap wind & PV and cheaper grid storage (on both sides of the meter) starts driving slow but steady electricity price deflation (even in already cheap electricity markets like MN.)

When it's cheaper & easier to install cold climate air source heat pumps in new housing developments than it is to extend the gas grid to serve those loads, gas will be heading into decline. And that date seems closer now than I ever would have believed just a decade ago.
 
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