Heating project for next summer

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TimR

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The wife and I purchased an old "victorian" farmhouse about six years ago and have been slowly bringing it back to life.. lime mortar, shellac, K&T wiring,vapor barriers... what I didn't know six years ago! :) Greatly appreciate the knowledge and experience on this forum and looking for help/input on heating options for next summers upgrade.

- The House: 1860ish two story brick house with 2 and 3 brick thick exterior walls. ~ 1450 sq ft on the first floor (10 ft ceilings) is heated with hot water. 2nd floor is forced air

- Current boiler: 1978 252,000 BTU Adlrich L 25 W . At some point in the past, the oil burner in the orginal boiler was replaced with an Adams Speedflame natgas burner . Boiler has no protection/plumbing in place to prevent sub 130-140F from entering the heat exchanger. It routinely gets fed 60F water (how has it survived this long!?!)

- Plumbing: "U" shaped two zone. Supply starts with 2 1/2" black pipe for each zone, steps down at each radiator, 3/4" pipe at far end of each zone. Return water is piped the same (3/4-2 1/2"). Both return water pipes are combined, enter the 1/12 hp B&G series 100 pump, and the water is forced in the bottom of the boiler, heated and spilt into the two supply runs shortly after exiting the boiler. Typical delta T for ret/sup is ~15F

-Radiators: cast iron Weil McClain Cameo's. Typical winter day they do not exceed 120-125F...on the coldest winter days over the past 6 years, the have not needed to be above 140-145F to keep the house comfortable.

-Additional heat sources: Woodstock Progress hybrid wood stove (30-70,000 btu) and Mitsubishi 2ton mini split (MUZ/MSZ GE24NA) (~24,000 btu of heat)

- Slant fin Calc: with a -20F (worst case temp) is 191,9xx btu/hr


For all but the coldest 30-45 days of year, the woodstove and Mitsubishi heat pump will provide adequate heat for the house. However, for the very coldest 2-10 days of the year they will provide no heat, and the boiler will need to supply 100%

The current boiler/burner is not very efficient and I am not sure how long it will continue to function with the very cold return water. Moreover, as I have tighten up the air leaks in the attic, basement, crawlspace, etc. the pilot light/ burner will not ignite unless I open an exterior basement door...backdrafts. (no draft hood on the boiler, etc, etc....not very wife friendly)

I have two thoughts on how to address my upcoming boiler/heating issues:

1) Replace existing boiler with a ~85% cast iron power venting (low ceilings in the basement) or go with a more efficient mod/con boiler in the same physical location in the basement.

2) The dicey option...Leave the existing boiler in place, turned "off", and add a dedicated tankless hot water heater: 20 feet away from boiler on the west zone, I have two "abandoned" 1" ports on the 2 1/2" ret/sup pipe. What if the supply from the "cold" boiler is piped to the cold inlet of the tankless hot water heater, and 130F water is returned to the boiler to mixed and distributed through the system. I suspect the current B&G series 100 pump with 4' column of water above it and 20' away would deliver 8ish gpm to the hot water heater? Something like the Rheem RTGH-95DVLN might be a good fit? (if the water heater failed, etc. the main boiler could be put into service quickly)

Dana, I have read a few of your older posts regarding the efficiency/ benefits of low mass "boilers" combined with high mass/low temperature water returns. The second option I tried to outline above is my attempt (feeble?)to use the 26 gal of water in the existing boiler, piping, radiators, etc. to my benefit.

Would greatly appreciate any/all input.....even if it is negative! ;)

Thanks,

Tim
 

Dana

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First, it's ridiculous to design and size the boiler to a 99.997 percentile temperature bin, just because the temperature got that low once in the past 100 years, especially since you have a woodstove for auxiliary heat that would allow you to survive even if the power was out when it was that cold. A more appropriate 99% outside design temp in OH would be in positive single-digits, not negative double digits. The worst you should be designing for would be 0F, and even that's a bit of a stretch, since you also have the thermal mass of the brick working in your favor, which isn't taken into account by the Slantfin tool (which is a dumbed-down I=B=R tool), nor does account for the thermal inputs from electric plug loads or warm-blooded critters.

Assuming the calculation was done based on a 70F indoor design temp, at -20F you have a 90F delta, but a 0F you'd have a 70F delta. That reduces the more realistic (but still overestimated) peak load to 190,000 BTU/hr x 70/90 = ~148KBTU/hr. The Slantin tool reliably overshoots reality by at least 15%, so call it 0.85 x 148K= 126K.

It's probably really a bit less than that, which is why you've been able to get by with a 2-ton mini-split and a really nice 70K soapstone wood stove for all but the coldest days.

A tankless hot water heater (or a mod-con for that matter) isn't really designed to take the full system flow with a monster pump. A tankless is a pretty lousy excuse for a boiler when the load is north of 100KBTU/hr, but with some type of hydraulic separator you could get away with it (in practical terms, if not letter-of-the-law terms, which vary by state.) To make it work well and survive for very long requires as much system design math as it would for a mod-con solution.

A 5-6 plate cast iron beastie could take the full flow though, but you'll have to plumb in a system-bypass and tweak the flows so that you don't abuse it too badly. A Burnham ESC5 would very likely cover your actual heat load, and an ESC6 certainly would. This series are all internally compensated to tolerate continuous return water temps as low as 110F, which isn't bad, but you'd still have to externally protect with a bypass loop to guarantee return temps of 110F or higher into the boiler. You may be able to substantially down-size the pump too, but as with a tankless or mod-con system re-design, that would require more system analysis than is appropriate on a "design by web-forum" approach.

If you're planning a mostly DIY installation, the cast iron boiler is by far the safer choice, with the fewest system design "gotchas". And, if it's only being used for the 2-10 coldest days when the mini-split craps out and you don't have any wood left for the stove, it's by far the sanest choice. You'll never recoup the higher cost of a mod-con unless you actually RUN it, and MOST of the time.

To keep the current beastie alive it's better to set & forget the thermostat so that it doesn't get long burns with 60F return water and/or cut in a bypass branch to feed boiler output water directly into the return water stream. Odds are if it was running that cold with an oil burner on it the fire side of the plates are corroded with all of turbulence inducing knobbies pretty much gone. The stack temp might give you a real clue as to just how far gone it is, but you're probably looking at 70% efficiency or less, no matter how perfectly tuned the retrofit gas burner is.

But you HAVE to do something about the make-up air situation if you intend to keep running it!

Insulating 2-3 wythe brick is possible, but there are lots of issues to look at for how & where you do it. It can make a real difference on comfort too.
 

TimR

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Dana,

Thanks for the quick response and additional input...greatly appreciated!

For a variety of reasons, I think your suggestion of Burnham's ESC 5/6 is a good fit.

If we go with the ESC 6 and take a look at the "recommended system piping" on page 52, figure D-2

http://s3.supplyhouse.com/product_files/ESC6-Install.pdf

It appears that Burnham prefers a "boiler bypass" to a "system bypass"? If I understand correctly, the boiler bypass piping will not help to keep the return water temp above 110F, but will allow a longer residence time in the boiler so that the water will be heated to higher temps , avoiding condensation. Do you think the boiler bypass would be a good fit for my application, our would you go with a system bypass?

Additionally, if you went with a system bypass, do think it would be acceptable to abandon the preferred "pump away" from the boiler and pump toward the boiler return to make the plumbing/piping easier to install?

It appears that the ESC6 is supplied with a Taco 007 pump (or Grunfos UP-15 or B&G NPF-22). Comparing the flow rates of the B&G series 100 i have currently installed and the Taco 007, it appears that the Taco 007 flow rate is ~45% lower at 0 head. The B&G series 100 delivers a deltaT of ~15F in my current system. Do you think the Taco 007 with decreased output of new boiler coupled with boiler/system bypass would by a good fit? or would you stick with the B&G series 100?

Lastly, if you have any thoughts on the use of thermostatic mixing valves from Caleffi, etc to control the return water temps in the either boiler or system bypass loops. Expensive overkill compared to ball/globe valves or worth the cash? more interested in a simple/robust boiler system than saving cash.

Dana thanks again for all the help...as my old boss use to say "no good deed goes unpunished" ;)
 

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Either a system bypass or boiler bypass should work, but boiler bypass is probably more appropriate here- the burner may be undersized for the radiation with both zones running.

The system is probably over-pumped as-is, and probably just fine with the Taco-007 class pump, but it remains to be seen if it's worth changing pumps. What's the delta-T on the radiation with both zones calling for heat after the system is up to temp (not when it's still in cold-start mode returning 60-65F water)?

When tweaking in the new boiler, use the ball valve on the return side of the boiler (the one marked "shut off valve", next to the check valve) to back off the total boiler flow to increase the delta-T across the boiler. A boiler delta-T between 20-30F is good, more is OK, don't go over 50F for extended periods or run it chronically under 15F. Use the ball valve on the bypass branch to adjust the return water temp and delta-T across the radiation (10F-20F is fine once it's up to temp.) You'll have to play around with it a bit to balance it all so that the temps and delta-T measured work out in the "reasonable" range, and delivering 110F+ water into the boiler after it's been firing for a few minutes.

Check and re-check the heat load numbers. Even for an uninsulated 1450' zone with 10' ceilings, the 126,000 BTU/hr @ 0F guesstimate seems high- that's 87 BTU/hr per square foot of conditioned space. Even uninsulated I would expect no more than 50 BTU/ft. (A typical new code min house would be under 15 BTU/ft.) If it really IS that high because you have a gazillion square feet of antique single-pane windows without storm windows, it's well worth retrofitting l0w-E storms, which will cut the window losses by about 2/3 from what a wood-sashed single-pane double hung delivers on it's own. Clear storms would only cut it in half- and even though they're more expensive, a hard-coat low-E glazing will pay back quicker on energy, and is more comfortable to boot.
 

TimR

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Dana, thanks for the very helpful response.

- deltaT for the radiation on the current system is ~15F ( no zone valves, single circulator...two B&G balancing valves in the branched supply exit of the boiler "control" the flow for east/west radiator circuits)

The house is a traditional german cross hall. The staircase is located in the center of the house, the rooms are arranged radially around the staircase and are connected by 64" x 96" doorways. Doors are always open, makes for great heat flow from the wood stove/mini-split, and Bert, the bird dog, loves to work off energy by running around the interior of the house ;) There are thirteen 32" x 74" inch single pane, double hung windows with storms on the main level. These will stay, and are slowly being rebuilt with new weather stripping/tracks. The original windows on the second floor were replaced years ago with crappy inserts...upgraded them to Anderson Woodwright inserts.

I suspect in the near future I will add radiators to the two baths upstairs. So, while the ESC6 might be not be ideally sized, it might a good choice. Additionally, the other family members are not as "frugal" as I, and sometimes conveniently "forget" to close the door at the top the stairs...makes for cozy warm bedrooms


- If I understand correctly, Burnham's ESC6 exhausts through 3" AL29-4C (category IV) venting. It appears that a similar boiler, Weil McLain's CGI-6 does not have as stringent a requirement? When we first moved into the house, surprise!, it became apparent that the existing 25' boiler chimney was venting through deteriorated brick and mortar into a "hidden" attic. I lined the 25 ' chimney with a 6" insulated 316Ti liner (chimney has since been rebuilt. .liner still in use...yes, I know this is not ideal for my current boiler)

Couple of questions:

- Do you think there is a meaningful difference in the reliability/build quality of the ESC6 or CGI-6?

- If I installed the CGI-6, do think it would be acceptable to vent into the existing 6" insulated 316Ti liner installed in the brick chimney?
( CGI-6 info http://s3.supplyhouse.com/product_files/381-357-866-Install.pdf)

Overall, I am looking for the simplest, most reliable, efficient boiler upgrade, cost is not a big factor. If I need to remove the existing liner and install AL29-4C venting, fine...will just give me another reason to move the liner to next chimney and buy another woodstove! :)

Tim
 

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Since I'm a bit skeptical that the actual heat load is anywhere near the output of the 5-plate versions, even if you add another zone the 5-platers would still be fine. The key to getting Manual-J calculations right is to be really aggressive on your assumptions rather than overly conservative, even though that's a bit against human nature.

The ESCx Burnhams have the advantage of being direct-vented taking ducted combustion air rather than depressurizing the house, but there is nothing "wrong" with CGI-x series. Quality and lifespan-wise they're probably comparable. Both companies have both been making decent mid-efficiency boilers for decades, and while the controls may change a bit over time, the basic boiler technology underneath the tin hasn't changed much, with only minor evolutionary change to the heat exchanger plate designs, etc. Both have trended to lower water-volume/thermal mass over the decades, but they're still very massive compared to mod-cons and finned water-tube boilers.

With either of them you can side-vent rather than using a chimney flue, which reduces the amount of the vent material. That frees up the flue with the stainless 6" liner for another wood-burner. If there is any way at all to side-vent it, that would be the preferred solution. In snow country it's important to keep the outlet of a side-vented boiler at or above the snow pack and respect the code clearances to operable windows or ventilation air inputs, but it's really pretty straightforward.

With mid-efficiency boilers vented into a chimney flue you DON'T want to over-size the liner diameter, since that increases the likelihood of running into flue condensation issues. A 5" flue has a cross section of about 19.5 square inches, compared to about 28.25 square inches for a 6' incher. That means stack velocities will be slower, and the amount of condensing surface higher than with 5". If a 5" flue meets spec for length, that's what you really want to go with especially since you'll be running the boiler near the low end of its operating temperature range.

If the delta-T on the radiation is running ~15F with the bigger pump it'll likely be ~20F with a Taco-007 class pump, and not as high as 25F, which is fine.
 

TimR

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Thanks again for the helpful response.

Unfortunately, with the boiler in the current location, it is almost impossible to side vent it. If I vent north, it terminates in the garage; go east and it terminates at the front door...south and west have their own issues.
Existing chimney is by far the easiest venting solution, but will give it some additional thought...not comfortable enough in my abilities to move the boiler to the west wall and vent horizontally.


It has been a while since I used the Slant Fin software for the heat loss calculation. If I recall correctly, the two variables that stood out for their unexpected weight in the heat loss calc for my house were the flooring and ceiling. I knew the solid brick walls had very low R values, but 70% of the house over the crawlspace is only separated from unconditioned air by ~ 1 1/4" of fir or pine flooring. More than 1/2 of the 2nd floor is unheated in the winter. In the Spring 2012 issue of Fine Homebuilding, the author outlined an "Home Energy Diet for an Old Victorian" which I have been slowly implementing to address my crawlspace heat loss/humidity issues....more digging and mummified cat removal in my version.;)

Overall, I suspect you are correct that a "5-plate" boiler will be the best fit for my heating needs. As you are aware, my knowledge of boilers is limited. In my mind, the dangers of oversizing a boiler is that it is likely to "short cycle" in the spring/fall and will not achieve desired/rated efficiencies. Is the only down side to under sizing a boiler the possibility that it may run 24hr/day and not be able to keep the house at the desired temperature on the coldest day(s) of the year? I doubt the service of life of the boiler /pumps in an undersized unit would be decreased? Any other factors to be considered? (just trying to better understand the impact of being "wrong"....have spent 20+ years in R&D, and I am wrong a lot)

Thanks for the patience and help
 
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