Harmon HydroFlex 60 Pellet Boiler?

[velvetfoot]

Does anybody out there have any experience with this model?
I'm thinking, it wouldn't cost that much to install and might do the job for me since I'll still have a wood insert, and oil for backup in my 2000 ft2 colonial house.
Thanks.

 

[huffdawg]

read this thread


https://www.hearth.com/talk/threads/84645/

 

[velvetfoot]

Thanks. Seems like the latest model burn pot and pressure ignition (whatever that is) solves the problem.
Not clear if it applies to the Hydroflex60 though.

Post 29 on this thread has a Harmon dealer's opinion:
https://www.hearth.com/talk/threads/68030/
"my local harman dealer told me he would rather not sell me a hydroflex. Told me they had to be cleaned daily due to heat exchange design. Told me he wouldnt promote it untill they change the design and that I would be much happier with the pb105.(which is too big and dont want) "

Daily cleaning? I know pellet stoves require maintenance, but that's seems a lot to me. Maybe I'm spoiled with my low-tech wood insert.
It doesn't seem the gassifiers require that much maintenance.

 

[EcoHeat]

Daily cleaning is obviously not going to work for many people. Makes me curious about the design of it.

If a pellet boiler is allowed to smoulder, it's going to run dirty. With any solid fuel boiler, even with automatic ignition, there's a short time at the beginning and end of combustion cycles where the fire's not hot, and so there's always going to be a little soot that needs to be brushed out (or in the case of automatic cleaning boilers, scraped off). If a pellet boiler has automatic ignition and modulating power, it will have longer run times and fewer on-off cycles. Therefore it will run cleaner.

In Europe, and here in North America, those boilers without automatic cleaning are manually brushed clean once a week, which is a much more reasonable frequency, and which can be timed with loading pellets for those who don't get bulk deliveries (as long as the pellet storage bin has the capacity to hold a week's worth of pellets).

 

[velvetfoot]

I checked one out at the dealer today. It seems a sweet little unit. The burnpot doesn't appear to be stainless.

 

[VT_Bubba]

Hello All,

I'm a newbie to this forum and looking to get some discussion going on the Harman Hydroflex 60 boiler. I purchased my Hydroflex 60 last April (2011) and installed it myself over the summer. We''ve been burning it all this winter and we love it ! So far, no problems. I have several friends with PB105's, and some folks are having problems (bad control boards, probes, burn pots, etc...). However, my Hydroflex 60 is making me proud.

My local dealer tried to discourage the Hydroflex 60, because of our severe VT winters and heating loads. However, I had space restrictions and really could not accomodate the physical size of the PB105. In the end, the Hydroflex 60 seems to be meeting our needs, although I do have smart controls and still augment my heat with a woodstove in the basement (still have wood to be burned from clearing the land).

My home heating system (self designed and installed):
- Biasi B10-4 Oil fired, with 0.5gal/hr nozzel (Direct Vented with outside air in)
- Circulator per zone, with 40gal Indirect Hot Water Tank and Priority Control on the Hot Water.
- 80gal Solar Hot Water System, with 2 Stibel-Eltron Flat Plate Collectors on my roof
- 1st floor 60ft baseboard
- 2nd floor 40ft baseboard
- Basement Man Cave (Hearthstone Mansfield Wood Stove)

I declare several Boiler Design Biases :
1) Always Pump Away (Air Seperation should always be on the low preasure side of the pump)
2) I like Outside Air In and have it installed on my Oil Boiler, Pellet Boier and Woodstove ! (It's always Good and never bad)
3) I like Indirect Hot Water Tanks

I hope folks will share their Hydroflex 60 issues/experiences, and I will try to share my knowledge with those who are interested.

VT_Bubba
- Harman Hydroflex 60
- Hearthstone Mansfield Soapstone Woodstove
- 16 Acres with 1/4 mile drive to my bunker on top of the hill
- B2710 Kubota Tractor for the Bubba Work
- 2003 Toyota Tundra with 7,000lb trailer (Pellet Hauler)
- Lot's of guns to keep the Crazy's out .. ;-)

 

[velvetfoot]

This is great!
How do you control the two boilers? It seems to me that if you still want to keep the outdoor reset on both boilers (I already have it on my existing oil boiler), and not mess with the aquastat settings and/or place it in manual mode, you have to have separate thermostats for each zone. That still leaves the question of domestic hot water. What did you mean when you said you had "smart controls"? I've seen a Tekmar 261 that can control two boilers but have to read more on it, plus it's 400 bucks.
Thanks for any help.

PS: Sorry for the bad manners; welcome to the Forums!

edit: Upon further reading, the 261 doesn't do dhw. I'd need something like the 374, only 900 bucks, lol.

 

[VT_Bubba]

Good Morning Velvetfoot,

This could be a long discussion... Every Installation is different, depending on system types, design preferences, and house use model. There are several ways to hook-up multiple boilers. I am a self declared efficiency and automation freak, and tend to over think, over engineer, over optimize, and over design everything I do, because I'm an Engineer and can't help myself...

It sounds like we have similar primary heating systems. I am not familiar with the Tekmar 261 dual controller , but can say with confidence you probably don't need it !

Let me try to describe my two systems. Basically, the two boilers work as two independent systems. The Oil Boiler Controls remains almost untouched (can use outside reset, or not). The Harman Pellet boilers have there own controls and when turned-on, will work to maintain pellet-boiler temperature (like 160-180 degrees). I have two simple add-on controls to integrate the two boilers :
1) Added 1 Circulator Aquastat on the Pellet Boiler (If Pellet Boiler < 140F and the House control wants heat, then turn-on the pellet circulator to provide the hot water to the manifold).
2) Added 1 Boiler Aquastat on the Pellet Boiler to Hold-Off the Oil Boiler start, if the pellet boiler is hot (If Pellet Boiler < 135F then do not allow the house control to get to the Oil Boiler).

This provides for 100% Automatic control and Oil Back-up, without ever throwing a switch or a valve ! Basically, the oil boiler will never fire if the pellet boiler stays hot and the Pellet Boiler is NOT wasting any heat or electricity running the pump, if the house or hot water does not need heat. This is simple, cheap, efficient automation, and keeps the two boiler systems almost completely independent and unmolested.

My oil boiler system uses a standard Taco SR504-EXP controller, with priority control on the Hot-Water, so if the Indirect Hot Water Tank wants heat, all heating zones are shut-off and 100% of the boiler goes to the hot water tank. This gives me almost endless hot water on demand.

BTW: This may be hard to beleive, but my 40 gal Hot Water Tank plumbed with 1" pipe requires more BTU's than the 100ft of 3/4" baseboard heat ! I don't think a Hydroflex 60 can service both Hot Water and Baseboard heat at the same time. Just not enough BTU's in the hydroflex... I think priority control on the hot-water is a requirement if you want to make hot-water and heat the house too.

I hope that helps you and others !

VT_Bubba

 

[VT_Bubba]

Velvetfoot,

BTW: I'm also using the Hydroflex Autostart feature and NOT Manual Mode. My Hydroflex 60 fires multiple times a day, whenever the Pellet Boiler falls below the Min Temp setting. Autostart seems to work great. I did hook-up my 60ft Baseboard loop as a "Safety Zone", so if the boiler gets to hot or I decide to run in "Manual Mode" my largest heating loop will turn-on as needed to bleed off any excess heat in the pellet boiler.

VT_Bubba
(Love fool proof automation that works !)

 

[velvetfoot]

Thanks VT_Bubba! I too am a engineer, but by training only at this point. But of course I have more questions!

In my case, since we have a wood insert on the first floor, we allow the second floor to get pretty cool during the day. Then around 6:00 PM or so, it's turned on for the rest of the evening, until it gets shuts down around 11:00 PM or so. The point being, the boiler water can get pretty cool: cool enough so that in your scheme, both aquastats would be below their respective turn on setpoints. So then, both boilers would kick on, with oil dropping out after the pellet boiler came up to temp, from an electric ignition cold start. Is that indeed what would happen with your scheme? I guess this would be true for the dhw as well? I'm concerned about short cycling the oil boiler.

I guess, in short, is your unit operating as the base heat supply for the whole house, and how much does your oil boiler run now?

I'd be interested in how your unit is plumbed. I was thinking of series and using the existing zone pumps, which are the only pumps in the system. I think I could get the unit close to the existing boiler, but might have to relocate the fuel oil tank. I initially though it'd be easy to locate, but with clearances to windows and the like, it might not be that easy.

Again, thanks for any help.

 

[Blevesque]

Velvet I am assuming here but I would assume he has his boiler wired for cold start, therefore switch relay keeps the boilers from firing until there is a call for heat be it the baseboard/radiant zone or DHW. So the boilers will drop below low temp and not start up unless the switch relay calls it/them on. Hope that helps, Brian

 

[velvetfoot]

Yes, I am interested if both boilers fire on cold start.

 

[VT_Bubba]

Velvetfoot,

Let me first say, that I also use Programmable Thermostats and have the same basic house use model (Efficiency Freak) ! No problem. Please read my last post again very carefully...

The key point that you are missing is the Harman Pellet Boilers have there own controls and will ALWAYS maintain temperature when they are powered on ! Your Oil Boiler may be a cold start boiler, but your Harmen Pellet Boiler will always be running holding temperature to at least the Min Temp setting. In Automode, if the Pellet boiler ever hits Max Temp Setting then the burner is slowly shutdown and goes off, but the boiler is still at temperature (160-180) ! If the Pellet Temperature ever goes below the Min Temp Setting (160F), then the pellet boiler will "Autostart" and run until the Max Setting is reached, before it shuts down again . Basically the Harman controls never know if you are pulling heat from the boiler (with your circulator), or it just drifted below the min setting. In either case, the pellet boiler will autostart and keep the Pellet Temp between the Min and Max settings.

The other key point is, the pellet boiler never really knows if you are pulling heat with the Circulator. The house needing heat turns on the Pellet Circulator ! The house controls do NOT connect to the Pellet Controls, just kicks on the pellet circulator.

With my current control settings, my oil boiler NEVER starts ! Except, if the pellet is turned-off, or out of pellets, which means it's temp is below 135F. It's awesome. However, in the early fall/late spring the pellet boiler will cycle on/off just to keep the pellet boiler at temperature, even when there is no call for heat.

Plumbing is a whole new lesson. Get your head around the multi-boiler on/off controls, then we can talk plumbing.

VT_Bubba

 

[velvetfoot]

VT_Bubba,

This is a revelation! I totally didn't realize this was the way it worked. I thought it went totally cold. I should have read the manual better, because I think it's in there. Have you have much of a problem in the shoulder season with excess heat? Now that I think of it, I'm not sure why you would since the circulators would turn on since there's no demand for heat, and the unit can cycle on and off to maintain 160*F or whatever the min temp is.

Have you used it for DHW in the summer?

The aquastats you added: each unit already has one, but you added a couple. It would be nice to have separate and consistent readings rather than fiddling with a dial, say, like on my oil boiler. Do these aquastats have external sensors that are attached to pipes; make/model? I'm totally unfamiliar with these.

I'm psyched about this potential project, with your positive experience.

VelvetFoot

 

[VT_Bubba]

Ya baby, I got the light turned-on for you now ! BTW - Don't feel bad, I had the same misconception when I started looking at this stuff 5yrs ago and know body could really explain it to me. I had to totally change my system design point and controls, once this became obvious to me. The Harman manuals do NOT really explain the various types of multi-boiler operation.

I want to caution you, the controls I described for my Hydroflex 60 are somewhat unique to my multi-boiler design point. Several of my PB105 system designs always circulate the pellet water to the oil boiler to keep the internal DHW coil hot and keep the Oil-Boiler boiler from starting because it is always hot (this is a totally different multi-boiler design point). Given that you have a cold start boiler with a Indirect DHW Tank, I'm trying to coach you towards a very efficient system design that will use significantly less pellets. BTW: I have yet to see any multi-boiler system installed that is as simple, efficient, and as fully automatic as my Hydroflex 60 hook-up in my house. Eventually, we will talk multi-boiler plumbing, once we fully resolve your control questions.

Comments on DHW :
- I have Solar Hot Water and use almost no energy over the spring, summer, fall months. Only a little energy on cloudy days, and 1-2 times a day the oil boiler will fire to keep the water hot in my primary 40gal tank, when we are not using hot water (My tank loss is about 1F/hr). If we use Hot Water during the day, the Solar Tank keeps my primary tank loaded with hot water and the oil never fires, but will fire if needed. BTW- Pellet Boilers work great in conjunction with Solar Hot Water, because when I'm not generating much Solar (winter), I'm at least using pellet. Solar DHW design is a whole new topic that I like too...
- As you figured out, I have NO problems with excess heat in the shoulder months because of the Harman Autostart Operation (Manual Mode would be a problem). Isn't that awesome ! However, I hate to keep the Pellet Boiler HOT when we are gone all day and do not need heat or hot water. I'm cheap like that. So, in the shoulder months, I wake-up and fire the Pellet Boiler, make coffee, turn-on the heat, and take my shower. When I'm done, my wife showers. When we are done showering and the DHW has fully recovered for the day and the house is at temp, I shut the Pellet Boiler off for the day. Small hassle factor, but very efficient for those few transition weeks.

Comments on Aquastats :
- The Hydroflex Controls and Aquastats (which are really thermocouples or thermisters) are all self-contained in the boiler (No hook-up required).
- The two additional Control Auquastats that I describe above are standard Boiler system components and can be placed in a well, or strapped on the pipe :
1) Pellet Circulator Aquastat (Honeywell L4006B - set to 140F) can be put in the Hydroflex using one of the available 3/4" holes using an aquastat well.
2) Oil Boiler Hold-Off Aquastat (Honeywell L4006A - set to 135F) can be "Strapped-On" the Output pipe of the Pellet Boiler (Only 1 Avail Well on the Hydroflex)

I hope that helps !

VT_Bubba

 

[katman]

VT-Bubba-
Your post is just in time for me. I'm installing a PB-105 in my barn, about 100 feet from the house. Have everything plumbed, wires to the PB 105 but I'm stumped on the controls. I was going to put the pellet boiler in series with my oil boiler, which has three zones with taco vales and one circulator. My plumber installed a slightly different arrangement which he says will not flow heated water from the pellet boiler to the oil boiler. We did install a circulator at the pellet boiler, but powering that circulator and sending the thermostate demand to the pellet boiler is were I am searching for a solution. I'll read over your stuff again but it sounds like you have what I need. Thanks for the insight! Regarding the well on your Harman, I have only one on my PB-105. Doesn't the Harman sensor probe need to be there? Also, curious to know what kind of programable thermostats you are using.

 

[velvetfoot]

And I think I might be ready for the plumbing schooling, lol.

katman, I'd be interested in how your pellet boiler ties in to your oil boiler, while bw're waiting for VT_Bubba to return...

 

[VT_Bubba]

Hello Katman,

I'm using cheap Honeywell Programmable Thermostats. Sorry, I don't know the model# off the top of my head. They are 5day-2day scheduled. I can't say I have strong bias on any Prog T-Sat's, or love the Honeywells that I have, they are what they are and seem to do the job of matching our life-style schedule.

Yes, the PB105 only has 1 Available aquastat well, located on top of the boiler, and that well MUST be used for the Harman Temperature probe. This means that any additional control aquatats you might add to your system are best "Strapped-On" to the boiler output pipe. This is typical for a PB105 Boiler install.

The problem with discussing controls details and plumbing is, the right controls depend on many issues :
- Multi-Boiler Plumbing design
- Existing Boiler system Design and Controls
- Expected level of automation, circulators -switches-valves, etc (Manual vs Auto).

You may have limited options, based on your existing boiler design (Zone Valves with 1 Circulator). Hooking the two boilers together in series is usually the easiest solution. Basically, NO controls or extra circulators required. Plug in the PB105 and let it maintain it's 160-180 temp with the factory on-board controls, and let the house circulate the water through both boilers using your existing circulator. The 100ft may be an issue and require an extra helper circulator ?

But, you don't talk about your DHW situation, so it's hard to know what all of the implications are for this design.. What's your DHW system like ?

I personally Do NOT like Series installs, because they are very inefficient ! When you run your Oil-Boiler, you must also heat the pellet boiler, and when you run your pellet boiler your also heating your Oil-Boiler. Yes, you can add manual valves to bypass the off boiler, but that gets to be a hack too ! I just dislike wasting energy and I hate manual intervention if I can avoid it by design.

I personally like Parallel System designs. However, most people hook them up with manual gate valves so that only 1 Boiler is driving the Boiler Zone Header at a time. This usually requires manual boiler switch over using gate valves. I struggled with these trade-offs myself and ended up with my current Parallel Design point, but I have a Circulator per zone, Indirect Hot-Water Tank (Not a Tankless-Coil), and wanted a system with no manual switch over and had NO LOSS when using 1 boiler, or the other. To accomplish this, I use Primary and Secondary Loops with 2 Swing Check Valves and 1 Weighted Check-Valve (IE: 2-Way Flow Control Valve). This puts the Hot Water right on the Header at the consuming zones, no matter which boiler is supplying the hot water, and there is always ZERO flow through the unused boiler, This results in a Fully Automatic switch-over (I do have gate valves for maintenance, but NO Manual Valves are needed for boiler switch over - just Turn-OFF the Pellet and the Oil is in the loop !) and has No Heat Loss in the unused boiler !

VT_Bubba

 

[velvetfoot]

Of course, at this point, I can't say I understand your piping scheme. My current scheme, which I've tried to link to a picture below, is a Burnham V83 oil boiler, .75 gph nozzle, 3 zones including one indirect dhw tank, one circulator per zone pumping toward the boiler return. It's looking like without moving the oil tank, I'd have to locate the pellet boiler to the right of the oil tank.

The oil supply and return pipes off the boiler are 1.5" whereas the Hydroflex60 is .75". Wouldn't a series connection also cause some potential flow restriction?

Reading the Burnham boiler manual, it seems there are a couple of supply and return connections that might be used in some (parallel?) arrangement.

 

[katman]

VT-Bubba-
I deliberated series vs. paralel for some time and was tending toward series for ease of operation and simple install. My plumber's arrangement has me a bit puzzled. He says the oil boiler will be bypassed; I can't see how he is doing it without another gate but he's the expert. It will require manual switching, which I can deal with for now but ultimately I'll have to make some changes. I have options now for DHW. The oil boiler has a coil so during the cold months when I was burning oil I would let the oil boiler heat the hot water and send it to an electric water heater, which basically served as a storage tank. With only two users, storing the hot water worked. During the warm months the oil system was shut down and the power to the electric water heater was turned on. I'll probably use electric for the water heater all year once the pellet boiler is hooked up. I also have heat pumps for the house, which are used for summer cooling and heating until the cold weather sets in. Normally, the switch to oil isn't until December and I go back to heat pumps in March. This year I'm switching back and forth. I'm looking at adding some solar capabilities but I am not far along. As I understand, under current law 20 percent of the power used in Maryland must be from renewable sources by 2015. State grants are available for installing residential systems. I have some nice rooftop space so I'm looking at my options for using it. I was considering your boiler but my local Harman dealer didn't know a thing about any of the boiler or furnace products. I picked up the pb 105 from a dealer in Pa. who had it inventory. I think it will be fine for my needs but I'm looking forward to hearing how your units works out for you.

 

[katman]

Velvetfoot-

I haven't had a chance to give the pipes a really good look since my plumber hooked everything up Monday afternoon. That's when I saw the new circulator and asked his assistant how it was going to be controlled. I don't think I'll be home long enough to check it out until this weekend or next week if I have to work the weekend. However, I'll post as soon as I can look things over and see it in operation.

 

[VT_Bubba]

Velvetfoot,

Now that your more comfortable with some of the control issues, it's time to discuss multi-boiler plumbing. As a starting point, please read my previous post to Katman, as I try to discuss some of the pros/cons of the various multi-boiler designs and the benefits of my proposed design point for your Hydroflex solution (Which will be just like my installation). Basically, we want Hot Water right at the consuming zone without ever losing any of the heat in the unused boiler.

Yes, In your case the 3/4" Hydroflex connections make a series design very undesirable for flow reasons !

I have some important comments on the Hydroflex 3/4" connections :
1) As I learned the hardway, part of the Multi-Boiler problem is meeting and matching flow rates for all of the various flow situations (Oil vs Pellet operation, with 1 zone running, 2 zones running, DHW going etc...).
- Can you confirm that you can setup "Priority" for your DHW zone ? (I think this is a requirement for Hydroflex because of the limited BTU capability)
- Can you tell me what circulators you are using (Taco 007 ?) ?
- What Diameter pipe for the Heating Zones (3/4") ?
- What Diameter pipe for the DHW Zone (1") ?
2) For the Hydroflex, I highly recommend you use 1" piping to maximize flow on your Pellet Primary Loop ! Use 3/4" to 1" fittings right at the Hydroflex Boiler connections and then plumb your new pellet loop (with Air-Scoop, Expansion Tank, etc...) using 1" pipe to your 1-1/2" manifolds. This will allow maximum flow and BTU extraction from the Hydroflex Boiler and the 1" pipe can handle Qty=2Zones of 3/4" pipes worth of water volume ! Use 1-1/2" piping for any changes on your existing 1-1/2" Header pipes ! Flow rates are important !

In general, the Tarm Wood boiler plumbing schematics are the best that I have found anywhere. These Tarm guy's really know how to plumb multi-boilers and have my respect ! Based on the installs I have seen, most master plumbers could use a lesson from these Tarm guy's. I hope I don't get in trouble for posting this link, but please reference this Tarm document :
==> (broken link removed to http://www.woodboilers.com/admin/uploads/public/WoodBoilerPlumbingSchematic0111Web.pdf)

You will be using the basic design of section 2.4 Plumbing Example - Solo2 (Two Boiler Direct Design - No Thermal Storage), except the Wood Boiler is your pellet boiler, and you don't need some of the mixing connections shown for the wood boiler. Please look at this drawing and read my post to Katman. Basically, your going to :
1) Add 1 (1-1/2") swing check valve to your Oil Boiler Supply pipe, before your new Pellet Connection-T, then feed the pipe to your Zone Loads.
2) Add 1 (1-1/2") swing check valve at the capped End of your Supply manifold and connect the other side of the swing check to the capped-end of the Return Header. This creates the "Primary Loop" and allows any non-used flow to continue back to the boilers.
3) Add the 2nd Pellet Connection-T on the other end of the return header pipe, after all returns have come into the header and right before the Oil-Boiler.
4) Hookup the pellet loop to the two connection-T's using 1" pipe :
Top of Pellet Boiler ==> Air-ScoopExpantion Tank ==> Pellet circulatorlanges ==> to Header Supply Connection-T
Bottom of Pellet Boiler ==> 1" Weighted Swing-Check (2-Way Flo Check) ==> Shut-Off Bleeder valve ==> to Header RETURN Connection-T

Look at the Tarm drawing, think about the flows (Pellet vs Oil), and let me know if you have any questions. Hopefully, you can see the benefits of this design point.

There are a few more small details to discuss, but this should get you 95% home.

VT_Bubba

 

[VT_Bubba]

Velvetfoot,

Looking at your recent boiler room porno... lol... It looks like your zone circulators are located on the boiler return side and not on the Boiler Supply side as the Tarm schematics show, and I had speculated in my last post to you. If I'm seeing your oil boiler correctly (circulators on the return side), we should make a few small changes to my plumbing suggestions, as follows :

4) Hook-up the pelllet loop to the connection-T's using 1" pipe :
- Top of Pellet Boiler ==> Air-ScoopExpansion Tank ==> 1" Weighted Check Valve ==> Shut-off/bleeder valves ==> to Supply Header Connection-T.
- Bottom of Pellet Boiler ==> Pellet Circulatorlanges ==> to Return Header Connection-T

Basically, I'm recommending that you keep the Pellet Boiler Circ and Oil Boiler zone circ(s) plumbed the same way (Air-Separation on the Pellet Hot side, but Circulator(s) on the return side.

Based on your answer to my DHW zone pipe size question (3/4" or 1" ?) :
- If 3/4" pipe on DWH Zone, then NO other modifications need. (Pellet flow should exceed DHW zone flow).
- If 1" pipe on DWH Zone, the you should probably add one 1" Weighted Check Valve" on the DHW zone loop, just to keep the 1" pipe flows of the DHW Loop equal in Resistance to the 1" Pellet loop. Without this extra "2-Way Flow Check" on the DHW loop, you will probably get some parasitic flow through your oil-boiler when you run the DHW zone using your pellet boiler (Pellet Circ also running). Basically, we want to match the resistance to flow on both of the 1" pipe loops. If you have a Taco-007 circulator on the 1" DHW zone, then you should use a Taco-007 Circulator as your Pellet Circulator, or consider using a Taco-00R which has the same flanges, usually about $3 more, has a little more horsepower (1/20hp vs 1/25hp), and has 3-speeds which may help you balance flows. The Taco-007 flow is very close to speed2 on the Taco-00R, but the Taco-00R does use a little more electricity on speed2 than a 007).

I know this may sound funny to you, but think about the pipe sizes and the resistance to flow.

VT_Bubba

 

[velvetfoot]

VG_Bubba,

1)
-Yes the control unit does priority. I had to rig up a relay to make the reset unit work (it has no built in dhw), so that now the Argo unit goes into priority mode on a dhw call, drops the heat zones, but the boiler temp goes to the max of the boiler aquastat as oppiosed to the relay curve.
-The circ pumps are Tacos, but I don't know the make; will supply later.
-Diameter for all zones is 3/4"

2-4)
I don't understand all this...yet. Will continue study and undoubtedly ask more questions.

On the goal of keeping the non-running boiler "out of the loop", so to speak: would there be advantaqes to keeping a boiler that's not running warm, at least once in a while? I'm thinking, maybe condensation/rust? Have you had any problem? I can see that you'd be heating an additional 13 gallons of water in either boiler (my Burnham has the same water capacity), and it'd be a matter of how much heat escapes the boilers, which are insulated, and the one in use already is incurring this heat flow, which is in the envelope of the house (useful in winter). I can see there being stack losses, but I plan on putting an automatic oil vent damper in the oil boiler ( (broken link removed to http://www.fieldcontrols.com/ovd.php) ).

edit: Now that I read that Field Controls brochure again, I better make sure it works well in any combo arrangement.

 

[ewdudley]

On the goal of keeping the non-running boiler "out of the loop", so to speak: would there be advantages to keeping a boiler that's not running warm, at least once in a while? I'm thinking, maybe condensation/rust?

I figure it sure can't hurt and costs next to nothing.

It's a bit of a kludge, but I put an old salvage bimetalic type room thermostat next to my oil boiler supply line, wrapped with insulation, and set it for 80 degF. It's wired in parallel to energize the oil boiler secondary loop pump and keep the oil boiler well above damp cellar dew point.

--ewd