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Thoughts on two mod/cons. One w/ DHW, one with out. Solo TT or Embassy Onex
So i have been reading here for a while and decided to make a post with some of my thoughts on boiler replacment. Getting rid of a oil boiler with a junk tankless coil (big suprise). I have really been thinking about the Embassy Onex Combi but im afraid it will not modulate down low enough (goes down to 30K) (http://www.houseneeds.com/shop/meste...x-160c-buy.asp) But it does have a hot water coil. So i would use my 2 year old 80 gallon electric water heater as a buffer tank and pump 140 water into it and use a temp valve to lower the output to 130. giving me lots of hot water. Cost is also high for this unit and it uses it's own special venting. The other choice is to use a solo 110 76000 btu or a viessmann wb1b 87000 btu and build a fresh water loop into my electric hot water tank with a plate heat exchanger and loop the boiler to the other side of the exchanger. I think the TT Solo lends it self better to DIY installs along with the Onex. But most people speak highly of the viesmann. So there are my thoughts.. Some detail about the house. 6 year old garrison @ 1200 Sq ft. 2 heating loops and adding a third for a total of 63000 or radiation at 180 water temp. still trying to figure out my heat loss calc. I think it is 35000 at -2 but still learning. House is in central NH with 8000 heating degree days. I have my Head loss numbers for my loops and have sized what pumps i should use. Just still stuck on this hot water issue and the best way to go about it.
Thanks for viewing and sorry for the long winded post..
I would do one boiler and an indirect. The indirect is far better insulated. This is probably the least expensive way to go also. Do your heat loss twice, one regular at design temp and one at 60f, and match the boiler as best you can looking at high fire and low fire DOE output. The amount of radiation has nothing to do with your choice of boiler size.
Thanks for the feed back. That makes a lot of since sizing for low and high firing ranges. I had thought it would be best to use an indirect, but thinking if there is a way to turn my electric 80 gallon into an indirect water hear. Seems a waste to toss it as it was a fair amount of money two years ago....
If looking at the Viessman, you may also want to look at Buderus. Mine has been quite efficient in my home and has a good modulation range with more stuff built-in than Viessman (which is quite good, but can be pricey).
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
When deciding on a new boiler you first have an experienced professional perform a computer generated heat load analysis. Next the load of zones may determine the control stategies and specific boiler for its minimum output.
Condensing boilers with indirect fired water heaters are the most efficient packages available.
Your existing electric water heater can be piped in ahead of the indirect to preheat (electric off) potable water.
Guessing on boiler size will only lead to misery.
I will second that. Based on my experience I wish I had shopped around more and found someone better to do the whole thing. Now it's on my shoulders and a constant burden.Originally Posted by BadgerBoilerMN
If you have to interview 20 HVAC guys before you find one that you really like... It's worth it. This (Modcons) is a whole different world from installing a run of the mill gas boiler. Getting someone who is well qualified that can take you to previous work they've done and can be depended on to come back and do repairs when the thing breaks in 10 years is key.
I know what you saying about interviewing techs/installers. I have had 9 guys over the house and everyone one has come up with something different. Im sure i will get yelled at this for this but i have decided to do this as a DIY project. To many people with WAY to big of price differences. Some guys never to call back, most came over and said " oh a house like this has a heat loss of about 95,000 btu, but no one make a boiler under 100,000". I couldn't agree more with them untill i started learning and reading and talking with people (seems many people make boiler well below 100K). I have com to learn much about P/S piping, circulater sizing, ect. The GB142 seems the logical one as they are built in the town i have my shop in.
Back to the heat loss. Father in law is an HVAC guy but employed over seas with Brown & Root. He gave me use of a fairly easy program to use to come up with a heat loss. So at the design temp of -15 i come up with 75444 and a design temp i come up with 9888. so that put me in range of a few choices. Been reading a lot about the Viessmann WB1B and the Solo 110 (downloaded install manuals) Prices seems fair. I have ruled out the Embassy Onex as it will only mod down to 30,000 btu.
This should help when searching for a qualified contractor to install a high efficiency condensing boiler. If you can't find a factory certified contractor, find a certified designer and have them specify the boiler and send a drawing that many lesser mechanics can easily install. Setup can be a problem (combustion analysis and programming) but if the piping and pumps are correct setup can always be fixed for less cost.
http://www.badgerboilerservice.com/contractor.html
Last edited by BadgerBoilerMN; 06-14-2011 at 05:32 AM.
Using the fuel use correlated against weather data for the period between wintertime fillups, so long as you haven't been running woodstoves or space heaters you can use the efficiency ratings of the existing boiler to put a hard upper bound on what your true whole house design-condition heat load is.
Most heat loss calcs overshoot, and unless they spend a lot of time measuring & inspecting the tendency is to err toward the conservative side, and you can end up with something 2x or more oversized even from some well intentioned (but not necessarily meticulous) practitioners. Using a fuel-use/heating-degree-day calc as the backstop is useful.
Some oil vendors have done part of the calc for you, if they have a "K-value" marked on the billing. In oil-dealer parlance the K-value is a HDD/gallon ratio, which can be converted in to a source-fuel BTU per degree-hour number with some simple math. From that you can de-rate by the steady-state efficiency of the boiler to come up with a BTU per degree-hour of boiler output. Then count the number of degrees between your outside design temp and 65F, and multiply by the BTU per degree-hour, and you have an upper bound on BTU per hour @ design condition number.
That will already have some built in margin- a good fraction of the fuel use is the hot water and associated standby loss, and the as-operated standby & cycling losses. Up-sizing from that would not be necessary unless you can point to specific other heat sources that skewed the result, or a much lower conditioned space temp during the billing period (say, you went on a 3 week vacation and turned the thermostat down to 50F for that period or something.)
No matter how careful the heat loss calculation methods are, it doesn't trump a measurement. Estimates of infiltration rates & U values don't have to be off by much to render errors in the 10s of percent, but a measurement using the heating plant doesn't care how the heat losses were incurred. It's common to have calculated methods indicate heat loads well in excess of what the SOURCE fuel BTU (not boiler-output BTUs) would imply, but it's simply impossible for those calculations to be correct (yeah, my ancient broken down high mass beastie-boiler runs with an average efficiency of 162%, right... ;-) )
FWIW: I live about 60 crow miles south of you in a 1923 bungalow with ~2x more conditioned space and known insulation gaps to be rectified. At the 99% design temp of 0F, my measured heat load is just a bit over 30K. At the temp I'm running my radiation it wouldn't be keeping up when it hit's -10F, according to the lowest Manual-J type calculated number I've run, but it clearly has margin even below that based on this winter's experience.
Unless your 6 year old 1200' garrison is very air-leaky your actual -2F heat load is probably less than the 35K estimates, so don't be surprised if the fuel use calc gives you a number 35K. Even crusty old-schoolers will eyeball a place and do a "less, pretty new place, decent windows, call it 25 BTU/foot time 1200 gives ya 30K", whereas they'd look at my place and say "OK, an antique with some remodeling left to do, mostly six-over-six double-hungs with 25 year old storms, call it 35BTU/foot times a couple thou feet or so, 70K", which is more than 2x measured reality. Even using the 25BTU/foot WAG-estimation it still overshoots by a LOT, which is why they get away with it- the client is never left cold.
Good info thank you! So i have two years of oil usage before we got a pellet stove....my oil co. only lists total fuel used for the year. I under stand what your saying about how to come to a actual usage but im unsure how to do the math? I get to use the eff. of my boiler and the heating degree days then.......is there a web site with a formula? If oil has about 140,000 btu per gallon and the boiler burns 1 gph and is 81% then its making 101,000 btu. But how does that play into my heat load ect? Im sure the old boiler must be sized high as to keep up with the tankless coil too.
Found a nice big crack in the back wall of the old peerless this weekend while taking the sections apart to throw out..
Going back to brands that only leaves me with the Buderus GB142 @ 77000 btu (touring Buderus factory here in Londonderry NH tomorrow)
I can't thank you guys enough for this great info by the way! If anyone on this four has a SAAB, Volvo, Mercedes Benz, BMW or Audi feel free to ask me anything
www.degreedays.net can give you the degree-days at any base temp between arbitrary dates for a weather station near you. If there are days missing (as often happens, instrumentation breaks) try to find a different weather station nearby with more complete data.
But the oil/year is good enough to ball-park it. Which years, and how much in each year?
To get from gallons/year to btu/hour at design temp, you have to first convert the gallons to BTUs out.
138,000 BTU/gal x 0.81 DOE efficiency= 111,780 (not 101K, call it 112K/gallon
Then multiply that by the number of gallons. Say it was 780 gallons for one year, that comes out to 87.36MBTU.
Then divide by the number of heating degree days (use base 65, maybe even base 60, since you're heating hot water with the beast, but start at 65 and you'll have real margin). Say degreedays.net tells you that it was a 7873 heating degree-day year:
87.36 MBTU/7873HDD =11,096 BTU per heating degree-day. Converting BTU/HDD to BTU/degree-hour is simply dividing by the 24 hours in a day:
11,096/24= 462 BTU/degree-hr
At a design temp of -2, that's 67 degrees below 65F, so multiply 67degrees x 462 BTU/deg-hr= 30,977 BTU/hr @ design temp.
That's an upper bound. If you were heating hot water with it, something like 10-25% of the annual oil use went into heating hot water (or hot-water standby) discount it by at least 10%. But even with out the hot water component, By virtue of the fact that the boiler is 3.5-4x oversized for the load the combined heating and standby losses means your AFUE was at least 10% less, maybe even 15% less than the 81% steady-state number. To be conservative, de-rate the calculated heat load by 71/81, or 0.87 x 30,977=26,950 BTU/hr, call it 27K.
But run the real numbers, see what you come up with.
Note, if your numbers are anything like the dummy example or even less, even the smallest Buderus will be 2-3oversized, and won't hit it's AFUE numbers. (It needs to be 1.7x or less oversized for those numbers to be real.)
But a TT Solo 60 would still make out OK, since it's min-mod out is still under the design-day load. If it's an all-baseboard show you may need to add some thermal mass to keep it's minimum burn long enough at condensing temps though.
Also note, if your design condition load is under 20K, that load can be met with a ~$5-6K 3-ton ductless mini-split air source heat pump, and cost less than half as much to operate as a 3x oversized Buderus, assuming $3.50 oil and 15 cent/kwh electricity. It may be operating cost-competitive with condensing gas too, but a more detailed analysis would be necessary to say for sure. But you don't already have air-conditioning, the rationale for going with a high efficency "inverter" R410A refrigerant ductless heat pump that both heats & cools goes up when the time comes. You probably won't hit the savings of this guy on Martha's Vineyard though (his design-temps and average coefficient of performance are higher than in central NH- he'll average a COP of ~3 or better, but you'd only make 2.5-ish, maybe a bit more.)
But no matter what your mechanical systems and fuels end up being, a serious round of air-sealing (even on newer homes) usually pays back in very short years It's shorter, if oil is your fuel rather than condensing natural gas, but it's very short compare to condensing propane too. See: http://blog.energysmiths.com/2011/03...effective.html Until air-tightness specs are enshrined in code and verified by blower door tests, odds are you're blowing 1/4 of the fuel use or more on excessive uncontrolled ventilation, and retrofit air sealing can reduce that by half, often more. Unless your initial blower door test comes in well-under 5 air-exchanges per hour at 50 pascals (5ACH/50), odds are you can get ROI well into double-digits (after taxes, no less!) on the first $2K invested in air-sealing. While building to sub 2ACH/50 isn't hard, if the primary air-barrier on all 6 sides of the cube wasn't in the initial design and enforced during construction, you're more likely to be in the 10ACH/50 range.
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