If he designed it with 140F AWT in mind at 99% design temp, that's "close 'nuff" to 100% at the level of "design" we're doing here, for comparison to something guaranteed to overshoot the condensing threshold every burn by setting a min-burn time with the internal controls.

But point taken- I was being less than precise. (But probably not less precise than the heat load calculations on which the system radiation was specified. ;-) )

The zone-by-zone heat loads specified add up to only ~13K, which would be hard to hit in a 1300' antique house in Belfast ME without a serious insulation & air sealing retrofit. (Design temp there is in low to mid negative single digit's F). With some down-east Maine fudge factorin' and a big WAG I figure reality is probably more like 20K, maybe even 25K. His existing radiation delivers 23KBTU/hr @ 140F AWT, so if reality is between his calc and my WAG it might actually get to 100% condensing with fine-tweaking on the reset curve, but 90% of the time seems more likely. If the real heat load is the calculated 13K even the smallest mod-cons would be running in bang-bang mode, but if it's really 20-25K there would be some modulating room for a smallest in class unit from any number of vendors.

I've yet to see a 1300' home with a 13K heat load at -5F. I'm sure they're out there, but they're not 1890 vintage timber-frames with retrofitted cavity-insulation. With 4-5" of exterior foam and U0.20 windows & doors with a similar upgrade in attic-R to match etc. it might be that low though.

The short cycle delay function delays the re lite, It does not extend the burn.
The manual on these boilers must be read like a trashy novel, some parts twice or more!
And yes the propane Laars/Baxi pops some times,
but it may be possible to tune it out,
oh well,
I need a bufferin
Dan

Condensing water heater for sure.

All propane condensing boilers must be set up by an experienced technician, using a flue gas combustion analyser.

My point early on, that's why it pops!!! This boiler requires a seamans control as well to fine to the unit
wheres that bufferin

Posted By Blueridgecompany.com on 30 Aug 2012 04:25 PM
The short cycle delay function delays the re lite, It does not extend the burn.
The manual on these boilers must be read like a trashy novel, some parts twice or more!
And yes the propane Laars/Baxi pops some times,
but it may be possible to tune it out,
oh well,
I need a bufferin
Dan

If it only delays the re-light, not the flame-out  it's worthless for regaining efficiency or saving the boiler when serving low-radiation output zones.  With bursty burns and a long re-light delay it may even interfere with output capacity to the point that the load can't be met!

Is it more entertaining to re-read in French? (The English isn't compelling enough- a real snooze! )

I'm with Morgan- a condensing tank water heater would be a better starting point, but a buffer tank solution can still work.  Unless something close to the full value paid of the combi-heater can be recouped on resale, the buffer tank will be cheaper than starting over.  Paraphrasing Rob, when you start out with a boiler 4x the size of what's called for your options tend to be limited.

Often this boiler pops and has lighting issues because there is liquid backing up in the combustion chamber. Make sure this is not the case and an additional trap does NOT help. It is also the smallest of the condensing boilers that Baxi makes and IIRC the only smaller one is the smallest Viessmann Vitodens 100 (my favorite) regardless. If your heat loss really that low, look for the smallest you can get or put in a Polaris or equiv.

Now I get your accent Dana!

Poor Dan. I have been on more than one boiler that was too "big" to heat the house...well done Dana.

The delayed ignition can be useful, but again for professionals only. In most applications it is just another trip wire for the layman and professional alike.

I have to say, it isn't that hard if you have an experienced professional produce a computer generated heat load before you buy a new boiler. Buying an over-sized boiler is just shooting a hole in your own boat.

Actually, HTP, Lochinvar and Triangle all make lower output boilers and their minimum fire (most important when designing micro-zone hydronic heating systems) is in the low teens. The Viessmann Vitodens is one of my favorites as well but has one of the highest low-fire outputs in the business at 31mbtuh.

Thus the need for experienced hydronic designers.

I'm not sure what the hydronic heating talent pool in sleepy Belfast ME is like- it's a pretty low key real-folks kind of town compared to the more moneyed & touristy spots on Penobscot  Bay.  (It's been awhile, but I have friends living in Belfast.)

I'd hate to think he would have to go as far as Gardiner to find competent help for a system re-design or a heat load calculation.  There must be someone closer.  SOMEBODY is designing fully functional hydronic systems for those empty-but-winterized & heated summer palaces on Penobscot Bay.

I know that you know, the location of the designer is irrelevant as long as he knows what he is doing. I even design systems in Quebec and hardly know my de jour from my Alouette!

Posted By Dana1 on 30 Aug 2012 12:10 PM
<...snip> it's probably less risky to put the buffer in series with the boiler's radiation-return & hydraulic separator rather than plumbing the tank itself as the hydraulic separator.

Dana,
if I understand this suggestion correctly, this configuration would have the two conventional loops, one primary, one secondary.  The P/S loops are connected through a 'hydraulic separator', AKA Closely Spaced Tees.  The return from the hydraulic separator to the boiler would have the buffer tank installed in series (would the Boiler side of the buffer use the 'cold' or 'hot' side of the tank?  I expect 'hot', but want to make certain).  An external expansion tank would have to be installed somewhere in the loop due to the increase in water volume (again, on the 'hot' side of the tank?). The secondary loop would be plumbed from the secondary side of the separator with its own circulator pump connected to and drawing from the 'supply' side of the separator and the 'micro zones' (as they've been referenced) would tap off the existing manifold/zone valve configuration.

Is this a correct interpretation?

If I understand this correctly, the buffer tank would buffer the primary side and the secondary loop would only draw from the buffer tank when the boiler circulator is operating. Is this correct?

Tom

When using a HW tank as a buffer you want the direction of flow to be into the cold, out of the hot. If you do it the other way the turbulence will cause mechanical fatigue the dip-tube (which is attached to the cold side). It's not a disaster to hook it up backwards, but the dip tube may fail sooner, and all of the flow would be across the top of the tank, bypassing the thermal mass of the rest of the water.

Depending on your flow you probably want to build the hydraulic separator out of something fatter than closely spaced tees on a foot long section of 3/4" pipe, but the concept is right. Using a a short section of 1-1/4" copper pipe with the full sized tee on each end, with 4 reducers to match the diameter of the plumbing to the boiler/buffer and the radiation side would be more similar to the well-engineered commercial versions. eg:

http://ecomfort.com/images/Watts_Radiant/watts_radiant_hydraulic_separator_sweat_union_medium.jpg

Posted By Dana1 on 31 Aug 2012 12:29 PM
<...snip> Using a a short section of 1-1/4" copper pipe with the full sized tee on each end, with 4 reducers to match the diameter of the plumbing to the boiler/buffer and the radiation side would be more similar to the well-engineered commercial versions. eg:

http://ecomfort.com/images/Watts_Radiant/watts_radiant_hydraulic_separator_sweat_union_medium.jpg

COOL!  I just so happen to have some left over chunks of the 1 1/4" manifold I used for the zones...   "Well Engineered"?  Probably not, but serendipitous, absolutely!

Thanks again,
Tom

Just curious,
Before you do put in the bufferin tank solution $$$,,,
try my suggestion and report back on the popping if you wouldn't mind.
We assume that the system has had the CO2 checked adjusted with seamans control and meets CO2 design parameters for a propane system.

Lower delivered heating temp to 135. Check
Pump speed in 1
Now, open manually 1 of the zones, call for heat on the other.
See what happens?
Popping on re lite,
There is also I think a setting to spread the delta T between the supply and return temperature, perhaps a setting of delivered water out at 140 with a 20 degree delta T would also solve the issue with out reconfiguring the boiler room. The boiler would not be compelled to re lite until the lower temp was The appliance has some fairly sophisticated built in functions. It would be a waste not to try them.
Dan

even if you stop the popping, you will not stop short cycling with a boiler this large on a heating system this small. settings can't fix physics. a 20 degree dt on a small amount of water is still a small number of BTUs to extract before you hit limit and cycle off... period.

heat has to go somewhere. or it won't. solving a popping sound doesn't fix a short cycling issue. It just removes the most noticeable symptom.

could add a buffer tank for a few hundred. doesn't have to be big bucks. cheaper than a premature service call or boiler replacement by a fairly wide margin.

Granted a combustion is necessary, and a tank the "easy" fix, but I would lean to one zone for all and/or added radiation (the real thing, not fin-tube).

Dan,
I'll try your suggestion (probably won't be able to for a day or two) to see the effects.  I'll report back when I've run the tests.  The popping is significantly lower since the service man tuned the CO2 and gas pressure settings.  Now it only pops occasionally and it seems that the pops occur mostly when the boiler has run recently and is somewhat warm (not hot since there is no immediate burn, but warm).  Obviously the boiler is only being used for DHW at this time of year so I have no idea what it will do on heat demand.  Also, the outdoor reset is still disconnected and this needs to be reinstalled to run the test.

I do understand the principle that NRT.rob and Dana have been discussing and it makes sense to look into adding the buffer.

One thing, in all this 'redesign' discussion taking place no one asked me WHY I chose this particular boiler.  I knew it was oversized for the heat load, but, as someone observed, I need the high heat output for the on-demand HW.  And while there may be other combinations that are more optimum from an HVAC/efficiency perspective, this one combi boiler had the smallest footprint of all the solutions I saw available to me.   

When I bought this old house, the services (Oil fired forced Air furnace, electric service panel, and electric HW heater) were in the crawlspace.  A dirt floor maze of old tree trunk piers that made it a nightmare to change a simple fuse.   I've since removed EVERYTHING from the crawlspace and have all the services easily accessible in the kitchen.  I couldn't have done this without this boiler. 

Now, it seems I may have to go back into the crawlspace with the buffer tank, but, at least, this is a passive device and I should be able to fit it in without too much trouble.

Again, Thanks to all.  I enjoy this forum and appreciate the 'education' (and tolerance for my ignorance) 
Tom

Excess BTU, This is the beauty and curse of a combination boiler.
I was the one early on that mentioned the DHW side and the BTU load.
These have a 3 way valve and flat plate heat exchanger, diverts H20 from heat loop to flat plate with heat demand.
You have the benefit of on demand tank-less DHW, and if I now understand it pops on the demand for DHW as well as heat,
Buffer tank will do nothing for the pop on DHW. It is the gas build up and ignition sequence, Might check the quality of the ignitors, check condition and gap
Perhaps pre gas calibration if you ran this for a year or so and the fuel was out of set if has carbon in the ignighter. also cleaning the combustion chamber helps, They call for service every year in the manual If I recall.
I am skeptical if bufferin will help on the heat side though I understand the idea of fuel savings.  ... . ..  maybe... ;)
The Baxi/LAARS Mascot on propane from what I have seen on some units is just plane hard to iron out the pop. Not sure why, we have a similar situation with a unit installed locally by one of our regular contractors could never settle out the occasional pop.
I wholly agree with Morgan, merge to one zone, a 1,300 sq ft place is not that big to need micro zones. But it is not my choice.
I am curious how your test will go. Doesn't have to be heating season to try, just a cool night.
Dan

Dan,
I think the "pop" issue is independent of the Heating efficiency question, although it may have been the short cycling/poor CO2 calibration that exacerbated the "pop" problem.  The "pop" occurs less often, maybe 30-40% of the start up firing,  and occurs regardless of if the cycle is a heating cycle or DHW cycle.

The upstairs zones are separated so that we could actually turn off one room (Guest Bedroom) which will be rarely used.

The downstairs zones exist, uh, because I could..

These would be simple to join into one.   I think I'd still like to have the upstairs and downstairs as separate zones, however and I'd be willing to add a buffer tank to the system in order to have the multiple zones work effectively.

Tom
PS: Does this forum have a private message mechanism?  I'd like to ask you another question about the HT 330 that perplexes me...