Boiler help

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Steve Lanham

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There is no need to repipe system. Just do primary secondary loop with outdoor reset.Also system must be properly cleaned and water must be conditioned. Also, you get quoted big boiler because probably nobody calculated how much heat your house loses on the coldest day of the year.
...... Thanks everyone...just had a stainless liner installed. Decided on a Columbia MCB 125. I had a big cast oil boiler that was 180k in. Kept my house comfortable for 30plus years. Had 3 bids all suggested MCB 150. Called Columbia and they said 150k based on cast radiators of 682 sq. feet. Settled on MCB 125 so I could use 6" vent. Boiler tech was happy with the match up. If I went with 34 k boiler, I was concerned it would have a hard time heating my large cast radiators. 34 k would do it but don't you think it would have taken long to come up go temp. That's a lot of water to heat. I would like to here what you honestly think ....Thanks to all !!!!
 

Tom Sawyer

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I think Dana wasted his time running all the numbers. ;) and that there still seems to be a large contingent of heating professionals that need to freshen up their knowledge. Did someone from Columbia really recommend the 150?.......really?
 
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Nukeman

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I can also tell you that 150k (or 125k) is way too big. To put things in perspective, I live in a similar climate (central VA) and my old electric furnace was under 80k BTU and I have nearly 2x the space (~3400 sq ft...some of which is part of a walk-out basement) and had no trouble heating the place. This is 1968 construction, single pane double-hungs, 3 fireplaces, etc., so not what you would call tight or well insulated.
 

Steve Lanham

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Hey Tom Sawyer...Really!!..I did'nt want to re-size my entire plumbing to my radiation system for a mod cond. as you suggested...Nukeman...With your 80k electric, your getting instant heat from the coils. No need to heat numerous gallons of water on a cold start. Dana, thanks very much for your sizing calculations. I actually came to understand some of the figures. But after talking to three different contractors and a Columbia rep. they all recommended a 150k boiler. Columbia's web sight had this info for the boiler...MCB 150..htg. cap. 124mbh...net AHRI rating water MBH 108...Net rating sq. ft. HW@ 170degrees 713... I have 682 sq. ft. of radiation so the 150 looks pretty close.. I had to go with the 125k because of a chimney issue. Anyone can go to Columbia's sight for a quick look. Thanks for all your input in the past and hope some of you respond to this post..
 

Steve Lanham

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I'm grateful for everyones input...can anyone explain why Columbia boiler is telling me a 150k is the proper fit for my radiator size. Maybe I had too many rad. in my house from the beginning. House built in 1932, maybe thats the issue. Does 628 sq ft. for a 1800 sq foot house sound like over kill. Does'nt a 50 gal. hot water heater use about 35k btu ? If thats the case, my house needs less BTU's then a DHWH. I can see where a mod con that can ramp up for a cold start and throttle back would be ideal but repair issues and cost swayed my decision....I think if I have to error on either side I would rather have the boiler too big then too small. Not as efficient but my house will be warm...
 

Nukeman

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The fact that you are heating with water does not matter. The steady-state heat loss is the same. Besides, the mass of the water is peanuts compared to the thermal mass of the house. When you are bring up the temperature in the place, you aren't just heating the air, but everything within the thermal envelope (sheetrock, carpet, flooring, structure, furnishings, subfloor, structure, etc.).

If you knew the approx. volume/mass of the water + the rads, we could tell you how long to bring up to temperature, but I can tell you it probably isn't as long as you might think (even with say a 35k burner behind it). Based on Dana's numbers, you'd only need a water temp of ~105F, so there isn't much of a difference in temperature from your cold condition.

You would be better off being a bit too small than too big. When it is too big, it will short cycle. This will not only cost money from a fuel point of view, but will shorten the life of the boiler as well. What you want is nice long burn times. On the morning of the coldest day of the year, it will run nearly continuous to match the load if sized correctly. With 125k behind it, you will still be seeing short burns even on the coldest days. If the boiler was a bit too small, it might mean that it may only reach 68F inside instead of 70F for a couple hours per year on the coldest days. However, using the K-factor method or manual J, the boiler would still be oversized slightly (Dana's numbers), so the temperature would still hold.

Edit: BTW, those numbers that you list on the site are at 170F for radiation. You only need to run water temps of ~100F or so to meet your load and put you in the condensing range (for a condensing boiler).
 
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Jadnashua

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You really do not want that big boiler for your small load! As already said, for both comfort, economy, and longevity, you want a boiler close to your typical needs. Also, remember, most heating days are NOT the coldest of the year, so the load is even less. The smallest boiler available will generally still be bigger than necessary for many smaller houses in the US mainland, and even in Alaska, if it is built to standards with enough insulation. A boiler works best when it is running nearly constantly...on/off cycles waste energy. The only time 150KBTU might be useful is in reheating your indirect, but it's much cheaper to just size it properly...most people do not need huge amounts of hot water constantly throughout the day, so there's time to reheat it (and an indirect is faster than nearly any standard self-contained WH, either gas or electric). The upper limit on how much heating energy you need is derived from the fuel you've been using up to this time...that shows you have no need of 150KBTU.
 

Steve Lanham

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Wow..my mind is easily swayed...I,m going to get the installer to read this thread and question him about sizing...I think I mentioned ...he has a great work history and was recommended by Columbia boiler...I called Columbia to ask some questions and they suggested to listen to my installer...they said he is one of the most knowlegable installers in my area..I have'nt finalized the deal so i still have time to fine tune my heat...Thanks again !!
 

Dana

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I'm grateful for everyones input...can anyone explain why Columbia boiler is telling me a 150k is the proper fit for my radiator size. Maybe I had too many rad. in my house from the beginning. House built in 1932, maybe thats the issue. Does 628 sq ft. for a 1800 sq foot house sound like over kill. Does'nt a 50 gal. hot water heater use about 35k btu ? If thats the case, my house needs less BTU's then a DHWH. I can see where a mod con that can ramp up for a cold start and throttle back would be ideal but repair issues and cost swayed my decision....I think if I have to error on either side I would rather have the boiler too big then too small. Not as efficient but my house will be warm...

If you have "too many rad" to run a non-condensing boiler any smaller than 150K direct-pumped without some jear-boiler plumbing modifications, it means you have an IDEAL amount of radiation for running a mod-con- you can't have it both ways.

My house was built in 1923, is ~2400' (not counting the 1500' of semi-conditioned basement), and my heat load at +5F (the local 99% design temp number) is under 35KBTU/hr. This house may be tighter than the average of it's age, but it is by no means even close to code-minimums on R-value, and has the original single-pane double-hungs plus 1980s vintage clear-glass storm windows. Before insulating the foundation walls and air-sealing the attic spaces the heat load was a bit over 45K. Doing a simple-math heat load on the pre-storm window condition it comes in around 60K.

A utilitly company survey of MA housing stock a handful of years ago put the "average" heat load of 14kilowatts (= 48kbtu/hr), in a region where the average home is over 40 years old. Your observation is true that MOST houses in the mid-atlantic states have heat loads comparable to or less than the output of 50 gallon hot water heater. You could quite literally heat your place with a cheap atmospheric-drafte hot water heater, but it would be a bit marginal, and would require some plumbing-protection from condensing damage on HW heater itself.

Sure, it's OK to err to the high side- it's standard, but not 5x, which would make you "good" for outdoor temps of about -180F, a temperature not seen in MD since before the last ice age. A barely legal 82% AFUE 50K boiler has an output of ~41,000BTU/hr, which is about 35% oversized for the ~30K heat load I'd estimated, which would make you good down to the single digits below zero, which happen at most once in the lifespan of the boiler in your neighborhood (and at the measured rate of climate change probably won't happen for quite awhile.) A 50K mod-con gives you at least 45K of output and you'd be good to negative double-digits. During the all time record setting cold snap of 1912 Baltimore got down to -2F.

The efficiency hit for 5x oversizing on a high-mass boiler isn't a subtle thing, it's an efficiency disaster, taking at least 10% off the tested AFUE number (which is only valid for boilers installed in conditioned space, at 1.7x oversizing), only partially mitigated by heat-purging controls. Check out the regression curves for the different boilers in the appendices of this document. At 5x oversizing you're never past the 0.2 point, and most of the time the boiler is operating on the steep slope left of the knee, between 0.01 and 0.10 of steady operation output.
 

Jadnashua

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Well, one way to look at it is if you go with the 150K unit, they'll be seeing you again to replace it when you short-cycle it to an early death.
 

Dana

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With his high-mass radiation even a 150K unit probably won't short-cycle itself into an early grave- it'll probably go at least 15-25 years, whether you want it or not, (and maybe even 40) but it'll run at ~70-75% net efficiency rather than it's rated 83%/whatever AFUE.

At his load, short of a mod-con I'd rather pay for a cheap 50-60K cast-iron beast, (preferably a forced draft side vented unit, since the chimney is obviously way oversized for a smaller boiler) and have the thing operating on at least SOME substantial duty cycle, living on the knee of the regression curve rather than on the shin. It doesn't take a whole lot in the way of near-boiler plumbing to set it up for lower temp at the radiation (== lower distribution losses, steadier radiation & room temps) without compromising the boiler with condensing return water temps.

OTOH, the excess standby losses of the 5x oversized unit mean the boiler room will stay warmer- it might even be the warmest room in the house, so maybe you could make the boiler room the living room, or maybe even the sauna !? :)
 

BadgerBoilerMN

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Over-sized radiation; GOOD. Over-sized boiler; BAD.

High-mass radiation with a low-mass condensing boiler is perfection in a box.

Nobody wants a cast iron boiler, some can't afford a good boiler and some don't know any better but if you have natural gas and radiation already in place...

I would rather have a boiler that was properly sized to the load. If we get the 10 year or 20 year record freeze, I will put on a sweater for the week that it may last and be happy to have the place way down to 66°F instead of my usual 68°F. Or, I might even turn on the lights or oven or televisions to make up the difference. For the other decade or two my properly sized boiler will purr along happily making all the hot water and space heating I can stand at half the cost of your "lazy man's" over-sized boiler.

I swear, my head is going to explode!
 

BadgerBoilerMN

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A condensing boiler that does not need to condense?

I don't discourage people from installing condensing boilers. In fact, I have been encouraging them to buy them for all hydronic heating systems, but more especially low temperature systems including cast iron radiator and radiant floor systems.

But, as in all things, personal responsibility is the first rule. If you, in fact, can't find a qualified installer, ModCons are not for you.

In any case, a load as small as yours should be handled by a storage-type condensing water heater for the ultimate in combination efficiency. Installation is much easier and more forgiving while service is much simpler as well.
 
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Steve Lanham

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Hey gentleman....I was wondering why someone would want their boiler to run for longer periods of time. I'm not sure what my water volumn is but lets say its 100 gal..If a 150k boiler can heat the 100gal. say in 15 minutes but a 50k boiler would take 45 minutes how much energy would I save. If the boiler took 45 minutes that means the t-stat was calling for that long, which means my house was cold or cooler then I wanted it for that length of time. The house reaches temp. and shuts off the boiler. The boiler will remain off until the t-stat again calls and it would repeat the cycle. When this house was built in 1932 it had a 180k boiler. Its still functionable !! I'm starting to wonder if maybe you guys are super GREEN and not interested in keeping your family as comfortable as you can temperature wise. Badger talks about wearing a sweater for a week and having the house be 66 degrees instead of 68. Personally we,re a 70 to72 type family..Trust me when I say I'm not trying to offend anyone...Thanks !!!......
for Badger.......Nobody wants a cast iron boiler, some can't afford a good boiler and some don't know any better ....Does this mean they don't make good cast boilers...how much does a good boiler cost...and as many cast boilers that are sold somebody has to know alittle something...PS...My cast boiler in my house was installed in 1932 with hardly a hiccup in 80 years. At least for the 30+ years I've lived here. You might want to rethink your statement !!
 
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Jadnashua

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There are hundreds of thousands of boilers installed where the IWH is a priority zone (probably millions). Their houses do not get cold when the WH needs to be reheated! Mine works this way, and I've never noticed it cooling off while needing to reheat water, and I've got a deep 6' tub that gets filled up on a regular basis, so you'd think I'd notice. The point is more, size the IWH for your anticipated load. A boiler setup to treat it as a priority zone will fire to max temp while reheating the indirect. It rarely would need to be on full fire (assuming it is a mod-con) when heating the house. If you're really worried about the IWH as a priority zone, don't treat it as one. If you size the IWH properly, it will easily be hot by the next big use you require of it. Keep in mind that an indirect is much more efficient at being reheated than a typical stand-alone WH - you'd probably have lots more BTU for it, and you'd be heating it with a MUCH more efficient boiler.

Any boiler is more efficient running constantly. It will last longer, too. It's the start/stop cycles that have it coming up to temp (just like the first few minutes of your car's operations - try running lots of short trips and see what your mileage is!), then, you're wasting the heat it has after it satisfies the call while it returns to idle state; might keep your basement warmer, though.

There are lots of hacks out there...the easiest thing for them is to specifiy a boiler that is too big...the house is always warm, no call backs, damn the efficiency. A right-size boiler does not mean you have to compromise on comfort...that comes from a qualified installer, proper install, design, and setup.

It's sort of like buying a MacLaren supercar to run errands in town...a big waste. As you've already said from your energy use, you don't need much of anything for your design day worst temp. The smallest boiler you can buy is bigger than that. You will not be uncomfortable if it is installed properly. Buy the bigger one, sleep well, pay more for the install, and forever...it's your money, but you're wrong to think you need a 150K BTU boiler for your house!
 
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Nukeman

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What you are forgetting is that the efficiency is really a steady-state number. The more that you cycle on/off, the lower that number gets. Badger was stating an example. Based on your numbers, Dana has already calculated an upper bound of what you need (based on your previous use). If you got that exact size, you would never be cold. The worst that could happen is that a record 100-year cold snap hits and maybe it will be one or two degrees colder in the house than normal (may just be a few hours out of a 100-year period), but even the smallest boiler that you will buy will probably be oversized to some degree and will even keep up under these conditions.

I'm not super green or anything, but you don't need that boiler unless you keep your windows open all winter. You can do what you want, but you will see many threads in here with people in Alaska getting boilers less than half your size. It all starts the same way. The installer wants to put in some huge beast, we educate and show them the real numbers. They end up with something 1/3 to 1/2 the size that the installer wanted to put in and they still stay nice and warm. They save money now and for all the years that they have the boiler. Why you wouldn't want that?...I'm not sure. You have to also remember that when you are heating the house, you aren't starting from "cold". Maybe you have a setback and the house cools to say 64F and night and you want it 70F in the day. It only has to gain 6F. It isn't like you are letting the house get to 20F every night and then wanting to heat it to 70F in the day. For that kind of climb, you would need something bigger. However, the temperature is really mostly constant (maybe vary a few degrees if you use a setback). As such, the boiler only is balancing the heat lost out the windows, walls, etc. and that is the number that Dana was giving you.
 
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Dana

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When the house was built in 1932 odds are it had NO insulation, single pane windows (no storms), and the 180K boiler was STILL oversized for the heating load. The net efficiency of that 180K boiler was likely 70-75% steady state, maybe less, and retrofitted with a post 1980 flame retention burner might have hit 80%.

Apparently you didn't actually read the Brookhaven effciency report I had referred to in a prior post, nor looked at the regression curves to ponder just how big the true efficiency hit is at gross oversizing levels. You might also want to download the FSA Calculator from the NORA site which uses the data from lab testing several different boilers & types, which would also estimate what your actual operating efficiency would be in comparison to a more right-sized modern oil boiler with heat purge controls. The tool also estimates your heat load, and would tell you fairly accurately how much you'd waste by going with the 150K Columbia vs. a 60K Burhham vs. a 50K mod-con, if you figure out to use the tool correctly. (It's not bug free or particularly user friendly, but it works.)

At your heat load a 50K barely-legal 82% AFUE cast iron boiler would literally never leave you cold enough to be reaching for a sweater any time before the next ice age, and would yield higher comfort and higher average efficiency than a 150K 86% AFUE cast iron boiler. Set it to 72F and forget it, it'll keep up just fine and use less fuel than the 150K boiler would using a deep setback strategy, and it would pretty much hit it's AFUE numbers, whereas the 5x oversized boiler wouldn't come anywhere close unless retrofitted with heat purge controls.

A 76KBTU/hr condensing Vertex hot water heater would still have 40-50K of burner to spare for the hot water load when it's -2F outside (like it did briefly 101.5 years ago), and would use 15-25% less fuel than the 50K cast-iron boiler, and 30-40% less fuel than the 150K Columbia, in rough terms.

Green? I definitely have a green side, but recommending a 50-60K 82% AFUEcast iron beast wouldn't exactly put me in anybody's Super Green club. You actually have enough radiation and a low enough heat load & operating temp to run with a Daikin Altherma high efficiency modulating air-water heat pump, which would cost slightly less to operate than a condensing gas-burner and alsoe with a somewhat lower carbon footprint at MD's grid source average. But spending 20 grand or so just for some marginal green-cred isn't exactly cash-green, eh? ;-) Even for the carb counter Super Greenies there would be much cheaper carbon reduction to be had out there than the upcharge between a cheap right-sized 82% gas boiler and a high-efficiency heat pump. (Don't even get me started on how ridiculous and expensive ground source heat pumps are, and how heavily they are subsidized!)

At a low enough load (and you're getting close) the absolute efficiency matters a lot less. My recommendation here are far more about comfort & upfront cash than it is about any environmental stuff. Seriously- I'm heating my own house with an ~82% efficient burner. But it's a modulating burner operated at or below the design condition heat load during heating-only calls, ramps up to about 2x the heat load on very long showers if there is a simultaneous call for heat, but that's it. It replaced a still functional 4x oversized cast iron boiler, and the comfort levels have improved, not diminished.

With high mass radiation the rads don't change temperature very quickly even with a monster burner behind it, and with a right-sized burner you can narrow the hysteresis on the T-stat to something very small without short-cycling the sucker (not so with the monster-boiler). With an outdoor reset control and a PID algorithm T-stat and continuous flow you can keep the indoor temps at an amazingly tight temperature range (like 0.2 F) if you really wanted to, but that would cost more money. Right-sizing the boiler and long burn times on high mass systems means it never overshoots the setpoint, and the radiators never actually get cool- they stay within a range, and the heat emission is very very steady, even as the boiler fires on & off.

In the spirit of Jim's McLaren analogy, if you only need to get home from the store in 10 minutes to keep the missus happy and you know to a dead certainty you can get there in a cheap & reliable Ford Focus in 6 minutes without snapping your neck, there's simply no point to buying the 5 liter Mustang that could get you there in 2 minutes burning more fuel to no good end. (That is unless you get some thrill out of the roar of the bigger burner, and the extra operating & upfront costs get filed under "entertainment value." :) ) I personally don't find the roar of a 150K burner all that appealing. YMMV.

I'm dead serious about just how grotesquely oversized a 150KBTU/hr boiler is- it's tough to convince people just how low their heat loads really are, especially when swapping out an oversized behemoth like yours. But to replace it with another oversized behemoth does literally NOTHING for you other than drain your wallet faster. It costs a few hundered more now, and a hundred or so every year thereafter. If you want more comfort, right-size it, (or get at least as close as you can- your heat loads are on the very small end of what's rightly served by a boiler), and spend the few hundred on nicer controls like a PID algorithm thermostat or a outdoor reset controlled mixer or something.
 
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