Installing Mod-con boilers before weatherizing


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Old 09-02-08, 01:09 PM
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Installing Mod-con boilers before weatherizing

I have a brick 3 unit I need to get heat into for the tenants before they need it. I'm considering natural gas modulating condensing boilers to give the tenants the best efficiency. I can separate the bills this way too and hopefully using mod-cons will be an easier install for me since I need three. My concern is sizing. Since I don't have time to weatherize before install; how do I calculate correctly? Do I run 2 calculations; one before and one after? The updates will be mostly attic insulation and storm/replacement windows. I downloaded the Slant-Fin softwear and will work on that today. I'm a plumber/electrician but not a boiler expert. Any help would be appreciated. Thanks; Billy
 
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Old 09-02-08, 02:56 PM
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Yes, you do the heat loss calculation using the existing conditions and then change those variables that you will upgrade to what they will be after the upgrade. You then size the boiler so that the highest output is close, but does not exceed the current heat loss calculation while the lowest output of the boiler is still less than the heat loss after the improvements are made.

Be sure not to oversize the boilers because there is already a "fudge factor" built in to the heat loss calculation. Try to get the closest numbers you can for air infiltration and actual outside temperatures at the building rather than using approximate temperatures for the general area.
 
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Old 09-02-08, 06:13 PM
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Not sure of my calculations?

Furd; My first try at the Slant-Fin Calculator is with the inside temp at 70 and the outdoor at 32. I Live in E.PA so I just guessed but if you have any directions for finding outdoor temp please advise. OK my uninsulated apartment came to 19,486 heat loss and after insulating and storms it is 12,170. Kinda throws me into a tail spin since I remember all the boilers were well above 19,486 as a high setting. The ones I checked were NTI TI-100; Munchkin Contender MC-50; Triangle Tube Solo60; QHT Biasi;and Slant-Fin Bobcat B-120 and I think a Noritz. If you know any that will fit my needs please advise. One positive is that this is the smallest of the 3 apartments I will be working on. Maybe if I leave the pipes leading to this 2nd floor apartment uninsulated in the basement it will use up some of the heat and help boost the load. Billy
 
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Old 09-02-08, 08:05 PM
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Billy, I believe 5 should be good for your outdoor temp. You want that to be the coldest temp expected over the entire winter. (not exactly the coldest ... I think it's something like 98% of the days will be warmer) If you use 32, yer gonna be mighty cold when the mercury DOES dip down, cuz that heating system ain't gonna be able to keep up ...

What happens you ask if you design for 5 and you get ZERO ?

Grab a sweater...
It's only gonna be a few days during the winter.
 
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Old 09-02-08, 11:01 PM
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Trooper is correct about using the coldest temperature that is commonly experienced in your area. The closer you can get this temperature reading to the exact location of the house the better. Try doing a Google search for historic weather data and your zip code. You will get lots of hits and you will spend quite a bit of time finding out all kinds of fascinating and useless trivia about your local weather conditions.

I stress that you do this because the "official" temperatures are usually at the nearby big airport or big city and there could be quite a bit of difference between the official temperatures and the temperatures outside your front door. Where I am (about ten mile from Seattle or twenty miles from the airport) the temperature is commonly ten degrees colder than the official temperature. In other nearby areas the temperature may be ten degrees higher than the official temperature.

If your house is exposed, i.e. is on a hill with few wind buffers (trees or other houses) shielding it you may want to somewhat lower the temperature you use to account for wind, assuming wind is an issue in your area. I live in what is known as the "Puget Sound Convergence Zone" and the wind can get pretty high during winter storms and that will have quite an effect on a home's heat loss at any given temperature.

Now what you do NOT want to do is to use the lowest recorded temperature because that will surely oversize your system. Again, as Trooper related you want a temperature that will be expected 90 to 95 percent of the time. During that 100 year cold snap your system will be chugging away continuously and you might not make it to the "design" temperature inside (probably only a few degrees low) and that is when the sweater or supplementary electric space heater comes out of the closet. It will not last but a few days at the most and the rest of the time (98% of the time) you will have a system that is only slightly oversize and you will reap the benefits over having a grossly oversized system.


Now if you have a "tight" house, moderate temperatures during the normal heating season and a fairly small home you will find that there will be little to choose from in the boiler department, especially in the really high efficiency models. I can't give you any recommendations because my experience is with commercial and industrial sized equipment. The other "regulars" (Trooper, Who, Grady, Rbeck, etc.) either work with this stuff every day or are what I lovingly refer to as boiler nuts. They are constantly checking to see what residential sized equipment is available and they will have good information.

There are two more things I'll toss out in regard to small boilers. You may want to look into electric boilers for the three apartments or else a one or two boiler system that will heat all three apartments and then use BTU metering to bill the tenants separately for heat. The two boiler system would size each boiler for approximately 60 to 75 percent of the average heating season load and the second boiler would be used with the first during the coldest times. This can be a very good system because the boiler is properly sized for the average temperatures and will be very efficient during most of the season rather than having a single boiler that is oversized for most of the time. It also give you a back-up in case something craps out on one boiler so that you are not left with no heat at all.
 
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Old 09-04-08, 05:23 PM
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Heat Loss Calculations...

OK; here are my calcs on all 3 apartments by using Slant-Fin calculator download. First is the unweatherized; second is after the insulation and storms.
Apt.#1(1293 SF) 62,170 and 53,321btu's
Apt.#2(700SF) 39,190 and 23,391 btu's
Apt. #3(500SF) 32,082 and 19,120 btu's
Some facts: This is an old brick(3-4layers) 2 story and had a monster yellow-Flame oil guzzler serving 1 zone to Cast iron raditors. I recently installed a Rinnai tankless for the entire buildings hot water that I will pay so I only need to add boilers. I'm keeping the cast rads for ease of install and after I did the btu calcs on them they are close to what is needed pre-weatherization.
My two choices so far are the Munchkin MC-50 for 2&3 and MC-80 for 1. And the Triangle tube prestiege solo-60---one for each as they modulate from 16-60 btu.
Price is a factor but when considering the square tube exchanger in the Munchkin it makes me want to spend more for fear of clogging. Any thoughts on any other kind or what I have listed would be appriciated. Seeing I only need boilers and not combi units I may have overlooked something, Billy
 
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Old 09-04-08, 09:08 PM
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...I lovingly refer to as boiler nuts...
Guilty as charged ! I prefer 'boiler GEEK' though.

Cast Iron Rads + ModCon = perfect match
 
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Old 09-05-08, 04:43 AM
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Furd's idea for a single (or two) larger boilers with a BTU meter would be excellent if you can do it. Those loads are really small for today's boilers. If you staged two small boilers for all three apts that would be awesome. Or just go with an 80-100k BTU modcon. Check out some manufacturer installation diagrams (Munchkin, Lochinvar Knight, for example) to see how it's done.
 
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Old 09-05-08, 09:13 AM
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BTU Meter ???

Well I forgot to mention that after checking at length for weather temps on Google I ended up with 5* as Trooper suggested. Thanks Trooper. As far as a BTU Meter...The idea is perfect but a bill coming from a landlord is not as "Official" as one from the Gas Company---if you know what I mean. At 54 I'm trying to prevent as much stress in life as possible. Any suggestions on which gas boilers available would be best suited for my conditions?

furd wrote:>>>You then size the boiler so that the highest output is close, but does not exceed the current heat loss calculation while the lowest output of the boiler is still less than the heat loss after the improvements are made.
 
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Old 09-05-08, 11:54 AM
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Billy, as someone with a Prestige Solo 110 in a home with a "true" heatload of under 40K (installed 18 months before the Solo 60 hit the market), I would have no hesitation in using a Solo 60 for each unit. With 3 of them the same you could even justify pricing a full service kit in with them. They all need to be programmed and serviced, so it would be way easier if they were all the same.

Heck, if you wanted a simple hot water solution, the Prestige Excellence 110 would do the trick in each unit (the cabinet also holds a 14 gallon indirect). I think they are about a grand more but from a space conservation standpoint they can't be beat and they won't short cycle, even at the 110 size.

The Prestige can make piping simpler in that if you're running a single zone it can be piped direct and everything run just off of one pump. Primary secondary actually allows some mixing which doesn't help in keeping return temps at their absolute minimum which helps with the condensing.

No straw grasping required!
 
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Old 09-05-08, 01:08 PM
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Who; you had me excited there for awhile until I called Triangle-Tube. Talked to a Greg and he said to prevent short cycling in apts. 2&3 with the Solo-60; I would need to add a buffer tank however they don't normally recommend them. Sounds like a little double-talk. I'm not sure what he meant either. Would that be similar to an indirect but much smaller?
 
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Old 09-05-08, 04:10 PM
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You most likely spoke with Greg Manna who I believe is head of technical service. I don't wish to refute anything he says but I'll explain a bit about the boiler, controller and its operations based on my own observations.

Warning, this is long and boring...

Imagine you are driving a boat. Out on the water, the speed you want to go determines where you set the throttle. That's similar to when a boiler is modulating. Now when you come in to dock, many times, just idling in gear is more power than you want for the situation. When that happens, you take it in and out of gear. Boilers are just the same. Once the actual heat load gets below a certain threshold (which happens to be the minimum BTU modulation for the boiler), they become on/off devices.

I don't know of any modulating boiler that can modulate down to levels sufficient for when it's 40 or 50F out. Mine sure doesn't. I don't truly modulate until it's under 10F outside. With a Solo 60 that might have corresponded to about 35F. The normal modulating ratio on small residential boilers is between 3:1 and 5:1. Play with a heatloss program and you'll find that by varying outdoor temperatures from design day conditions right up to 55 and you would probably need to be in excess of 30:1 in order to modulate throughout the full season - which would essentially allow the boiler to run non-stop. That doesn't happen and we all have thresholds where instead of the system modulating a gas valve it just modulates the burn time and idle time.

What I've observed with my Prestige by using a wattmeter that can graph long intervals is that my Prestige is hardcoded to fire for 10 minutes at a time when the load is below the minimum modulation level. What it does then at lighter loads is vary the time between firing intervals. When its cold enough to be close to matching the minimum modulation it might only be a couple of minutes between 10 minute burns and when it's mild it might be an hour in between firing cycles.

To me, the 10 minute firing cycle is the important part of this equation as far as you're concerned. Take your minimum modulation and divide it by 6 and that's how many BTUs you have to deal with each firing cycle.

Some of those BTUs (or energy) will heat the house but we have to remember that you're delivering BTUs faster than the house needs needs it (you're doing the neutral idle deal as you're docking the boat). Some energy (or BTUs) in that 10 minute period will get transfered to the house, while some will just build up the temperatures of your water and piping. The MCBA senses the return water temperature and once it gets close enough to the supply temperature or if it just simply rises too fast it is programmed to stop the heating cycle prematurely (before the full 10 minutes are up). So in this aspect, any time the boiler fires for less than 10 minutes, it is short-cycling.

The big question becomes, what is the energy absorbing capacity of the distribution system? Black iron piping, cast iron rads, lots of water capacity all add some buffering for those BTUs. If you only have a few loops of PEX in a staple up application, that return water will heat up in a hurry, you want enough mass for 10 minutes at minimum modulation.

A BTU is simply the amount of energy required to raise the temperature of a pound of water 1F. Every gallon of water is 8.3 pounds. Suppose you have 10 gallons of water in these smaller apartment units and the Prestige HX holds 2 gallons.

(10 + 2.5) = 12.5 gallons
12.5 x 8.3 = 100 pounds rounded

Lets also assume that you have about 500 pounds of piping and rads in each apartment and that we'll treat them as only being able to absorb energy (BTUs) at half the rate of water.

500 / 2 = 250 so...

100 + 250 = 350 pounds

Each heating cycle, we'll assume we are raising the water temperature 10F.

350 x 10 = 3500 BTUs

On top of this, some BTUs will also be transferred to the house to make up for the heat it is losing, let's say 500 get lost from the heating system to the house over 10 minutes.

3500 + 500 = 4,000 BTUs

Triangle tube tends to claim more modulation than I've observed so let's go conservative here and use 2.5:1.

60,000 / 2.5 = 24,000 (we'll assume near 100% efficiency)

24,000 per hour / 6 = 4,000 BTUs (BTUs for each 10 minute firing cycle)

If for any reason the boiler's number was higher, then you could add a tank into the heating distribution system and warehouse some more BTUs.

I think you said you have cast iron rads. I'm not so inclined to agree with Greg about you needing a buffer tank if that's the case. He does this for a living, I sure don't. He may not be aware how much mass you have in the attached load. That certainly plays a part.

I'm all typed out...
 
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Old 09-06-08, 03:27 PM
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Understood; kinda :o)

Thanks Who; That was not boring at all but long it was. I kinda get the picture. Since I have cast iron radiators with all that mass it will reduce the cycle time even if I don't call for the higher btu ratings. I don't remember mentioning the radiators to Greg but I can see now how that may have changed his reply. Your illustration of looped pex explained that difference very well. There is another radiator I can add for more mass if needed. It will add another 6200 btus of mass. It would take the place of that buffer tank too; yes? Why add a buffer tank and not use the heat it stores? Correct me if I wrong.
OK now I want to ask you about another boiler...the Peerless Pinnacle or Purefire. They have slightly lower output ratings of 18-50K and 16-50K respectively; and they are locally available which means parts, if needed, won't bee hard or timely to get. Have you had any experience with these? I can't find any info on the Pinnacle as to weather it is for heat only. I don't need domestic hot water and I don't want to pay for a feature if I don't need it.
 
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Old 09-06-08, 03:45 PM
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The Pinnacle is a rebadged Munchkin. I like the downfired self-cleaning open passage design of the TT for more than the Gianni HX of the Pinnacle/Munchkin.

To me the Solo 60 would be a no-brainer for all three. There isn't much difference between 16 MBH and 18 MBH. One will just go into on off mode a little sooner. Your electrical is reduced under on/off mode if you really want to look at pennies.

Take the Solo, pipe it single zone with just one 15-58 pumping direct.
 
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Old 09-06-08, 04:29 PM
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Another thought...

Any thoughts on this approach? Due to the uncertainty of a boiler working properly I have been also looking at Rinnai RHFE-1004FA Wall mount Heaters. They do put out 9-32K btu that would meet the required heat load I'm just leary about this choice. We use a corn stove for our 1800 SF house and have friends that use a Monitor kerosene fired unit for theirs. Neither of us have any problems trying to save on energy costs but I don't know how this wall mount would be for a tenants use. Could this be a solution for the 500 and 700 SF apartments and just use the mod-con downstairs for the 1300 SF unit? Pros and cons please..........Billy

PS: I really appreciate all the help here folks---this is a great forum...so please forgive me if I don't seem settled on a solution yet. It is just a very big expense and I want to get it right the first time.
 
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Old 09-06-08, 06:02 PM
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Space heaters? Nah.

Another vote for a trio of Solos....
 
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Old 09-09-08, 07:58 AM
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Not yet convinced.....

I have yet another option I'm looking at. Slant Fin Sentry S34EDP boiler for the smallest (500SF) apartment. It has a 34K in and a 25K out btu rating at 85%. What do you all think as compared to the Solo60? Billy
 
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Old 09-09-08, 09:04 PM
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Originally Posted by Who View Post
You most likely spoke with Greg Manna who I believe is head of technical service. I don't wish to refute anything he says but I'll explain a bit about the boiler, controller and its operations based on my own observations.

Warning, this is long and boring...
...

I'm all typed out...
AWESOME explanation!!

For the tiny loop maybe an instantaneous electric? For the tenant, the little extra per btu cost might actually be made up in not having that fixed monthly gas billing fee.

For you the equipment savings is huge, particularly when you consider the wear and tear from being oversized.
 

Last edited by NJT; 09-10-08 at 05:13 PM. Reason: Awesome yes, but no need to quote entire post...
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Old 09-10-08, 08:26 AM
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Sold on TT...

After talking to a distributor/owner and another tech rep from TT at length I am sold on the solo 60 working and not short cycling. Only because of the mass I have with the old cast iron radiators was I able to come to this conclusion. If I had radiant via pex or baseboard for example it would not have been my choice because of the small size of the apts.500 & 700SF. Now my search is for the best piping design. I was told by the rep at TT that a reverse return loop would be the best and most even operation for the three one zone applications I have. I will install air separators and wye strainers for each boiler but if there are any other goodies that should be added please advise. I want this to be as trouble free as possible...Billy
 
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Old 10-04-08, 09:04 AM
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Did anyone have thoughts on the electric boiler option for the smallest apartment?
 
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Old 10-05-08, 11:57 AM
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No one responded on the electric boiler. I could not use electric because the electric company is owned by the town and holds the landlord responsible for the bill if the tenant does not pay. This is unfair but cannot be changed so I went with the TT solos natural gas.
 
 

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