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Any downsides to oversizing radiators?

alheim
alheim Member Posts: 68
edited November 2014 in THE MAIN WALL
Hi all,

I am ready to install an all-new new heating system in my ~1910 home in Queens, NY. Living on electric space heaters was interesting, but I'm over it. Been planning this for several months now.

The home originally had nice cast iron radiators, but they were stolen while the house sat vacant after Hurricane Sandy.

I will be replacing them with panel radiators from Hydronic Alternatives (similar/identical to Buderus) with TRV's.

The new boiler is a Burnham ES2-3, a conventional boiler that can handle return water temperatures as low as 110°F! (At 85.0% AFUE, this is about as efficient as conventional boilers can get. I will add the outdoor reset in the future.)

Therefore, I'd like to oversize the rads a bit, maybe 25%, so that I can play around with lowering the supply temperatures to improve efficiency.

So, is there any reason not to oversize radiators? Besides cost. Thanks.
«13

Comments

  • Ironman
    Ironman Member Posts: 6,581
    edited November 2014
    No reason not to as long as you don't get the return water temp too low. You will probably need your chimney lined with a stainless steel liner. And it may need insulating too.

    With temps that low and considering the cost of lining a chimney, I'd be looking at installing a mod/con.

    Be advised that you cannot run sustained return water temps that low even with that boiler.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Eastman
    Eastman Member Posts: 927
    Not a pro, but I'd be more inclined to undersize a conventional boiler than oversize the radiation.
  • alheim
    alheim Member Posts: 68
    edited November 2014
    Thanks, @Ironman. But why can I not run sustained return water temps that low with this boiler (the Burnham ES2)? I've never heard that mentioned in any of Burnham's literature, including the installation manual. A comment from Nate Warren, a Product Manager of Burnham, right here on HeatingHelp.com, states the following (<a href="http://forum.heatinghelp.com/discussion/comment/1192203/#Comment_1192203">http://forum.heatinghelp.com/discussion/comment/1192203/#Comment_1192203</a>):

    "The ES2 has the ability to operate at low return water temps because of the casting design. There are no extra controls, software, valves, piping, or pumps required for the boiler operate with constant 110F return water temps as long as the supply water temp is 130F or greater. ES2 castings incorporate a sophisticated baffle design that evenly distributes return water throughout the each casting. This prevents the return water from collecting in one area of the casting, and creating a cool spot that could condense. The baffling acts like a sparge tube – by evenly distributing water throughout the casting rather than dumping it all in the same spot."

    I decided against a Mod/Con for several reasons: a) I got this nice Burham for a steal ($700). b) Conventional boilers require less maintenance. c) Conventional boilers are often cheaper to install. d) Some manufacturers do not recommend installing Mod/Cons in homes close to the sea (I am 3 blocks from the ocean) as the airborne chlorides can damage the units over time (thanks @icesailor). e) And lastly, the Burnham ES2 is as efficient as conventional boilers get, and it supports using an outdoor reset.

    I'm hoping to line the chimney for $500 or less.


    @Eastman: I've sized the boiler as close to the home's actual heat loss requirements as I could. The heat loss for the home is 50,500 BTU/hr; the boiler is a Burnham ES2-3 (their smallest); 70,000 Input; 59,000 DOE Heating Capacity, 51,000 I=B=R Net Rating (Water).
  • Ironman
    Ironman Member Posts: 6,581
    The thing that Nate did mention, but you did not, is the reason that a flue liner is not optional with that boiler: namely, flue gas condensation. He also mentioned that 110* sustained return water temp is OK as long as the boiler maintains 130* supply temp. That's a 20* delta T. That's typically what medium to high temp radiation is designed at in America, but that's very seldom what our systems achieve. The only time that most of them get anywhere close to that is at design temp and many don't reach it then. Most of the time they see less than a 10* delta T because they are over pumped and over zoned.

    I'd recommend that you install a delta P circ like the Grundfos Alpha set to "Auto Adapt" with the type of system you're planning - I'd do it that way when I have all TRVs to eliminate the need for a bypass relief valve.

    Still, I'd be concerned about short cycling which will definitely cause flue gas condensation.

    Are you using the old gravity piping or are you gonna install new piping? That would be a major factor in the design of the system.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    alheim
  • Eastman
    Eastman Member Posts: 927
    Are cast iron rads out? --they would work a bit better with that btu output.
  • alheim
    alheim Member Posts: 68
    @Eastman Yes, unfortunately all of the cast iron rads were stolen.

    @Ironman‌ All new piping, from the boiler in the basement, to supply/return manifolds, up through the walls to each radiator (home run). All 1 zone. Thanks for the input re: delta T in design versus reality.

    The radiator rep from Hydronic Alternatives actually advised installing a Grundfos Alpha circulator. Here, unfortunately, is where I start to get a bit confused. Why would I need a bypass relief valve in any scenario, as long as I keep the return water temperature up? And, how does a delta P circulator eliminate the need for one?

    I know these are tricky questions. Thank you for your help.
  • alheim
    alheim Member Posts: 68
    edited November 2014
    Okay, I'm getting it, maybe.

    Without a Delta P circulator, if all of the TRV's start closing flow, but the boiler remains on due to the thermostat, the heated water will have no flow, and will cause problems - I'm not sure what exactly, maybe short-cycling, or high-pressure issues.

    With a Delta P circulator such as the Grundfos Alpha, the circ will sense high head pressure due to closed TRV's, and will slow itself as valves close, allowing it to maintain a constant pressure. (Thanks @SWEI)

    If I'm in the right ballpark - then, if you didn't use a Delta P circ, what triggers a bypass valve to divert flow? And where does that flow divert to?

    Trying to keep this simple. The home is only ~1,400 SF. Here's where I'm at:
    - 1 boiler (Burnham ES2-3, comes with Taco 007-2 circ)
    - 1 zone
    - 9 rads (4 on second floor ~14' above the boiler; 5 on first floor)
    - Supply/return manifolds, home runs to each rad
    - Expansion tank (I suppose this is a given)
    - New panel radiators w/ TRV's
    - (?) Delta P circ instead of the Taco?
    - (?) Bypass valve

    Thanks.
  • SWEI
    SWEI Member Posts: 7,356
    A bypass relief valve prevents a conventional (non-modulating) circulator from backing up its curve when a bunch of zone valves close.

    A pressure-dependent ECM circulator slows itself down as valves close, allowing it to maintain a constant pressure.
  • alheim
    alheim Member Posts: 68
    Thanks, I edited my last post. Sounds like using a Grundfos Alpha would be an easier setup.
  • Zman
    Zman Member Posts: 6,995
    I believe these are the same rads under a different brand.
    The spread sheet allows you to check the output under different water temps.
    http://www.heatlines.com/downloads.html
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Eastman
    Eastman Member Posts: 927
    I don't think you can avoid some type of low flow and low temp protection given the TRVs. So the question is: what is the best way to pipe the boiler into the system?
  • Gordy
    Gordy Member Posts: 9,514
    P/S
  • alheim
    alheim Member Posts: 68
    P/S?
  • Gordy
    Gordy Member Posts: 9,514
    All though there is no minimum flow requirements for that boiler there is the 110* minimum return water temp.

    If you take full advantage of ODR, and trvs. Being the thermostat is strictly a high limit, and the trvs wide open with ODR controling the house temp, and you are oversizing radiation.. That boiler will see less than the minimum 110 return temp a lot of the season. Especially fall, and spring.

    Maybe I'm over thinking it though.
  • Ironman
    Ironman Member Posts: 6,581
    edited November 2014
    Gordy said:

    All though there is no minimum flow requirements for that boiler there is the 110* minimum return water temp.

    If you take full advantage of ODR, and trvs. Being the thermostat is strictly a high limit, and the trvs wide open with ODR controling the house temp, and you are oversizing radiation.. That boiler will see less than the minimum 110 return temp a lot of the season. Especially fall, and spring.

    Maybe I'm over thinking it though.

    I think you're right on track Gordy and that's one my concerns. The other being on the opposite end: that during those seasons on mild days, all the TRVs shut, the circ stops and the boiler short cycles. I suppose that widening the differential in the aquastat would be an option to counter-act that.

    I do jobs like this regularly ( panel rads with TRVs), but I always use a mod/con which eliminates most of these scenarios.

    @Alheim, when you understand all the variables and their ramifications, as well as the extra costs involved doing this with a CI boiler, you'll begin to see why a mod/con makes sense.

    Buderus has done it successfully with their CI boilers ( which can take 104* return water) for years, but they have a control that's specifically designed for it: the 2107 Logimatic.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Gordy
    Gordy Member Posts: 9,514
    edited November 2014
    I was going to add Bob the OP is designing the emitter side as most would to take advantage of the full efficiency of a mod/con boiler, only the OP is using an 85% efficiency boiler which does have lower return water temp capability. With that comes as been discussed the unintentional consequences of the flue condensing, and the need to line it. You can't make this stuff up there is real science involved here.

    Burnham I/0 manual gets you to the flue from there it's installer knowledge as to what happens, and what needs to be done to rectify the situation. It's sublimativly stated in the manual.
    alheim
  • alheim
    alheim Member Posts: 68
    edited November 2014
    Let me share a little more background. @Ironman @Gordy & anyone else, sorry if I came off as a wise-**** or as a know-it-all in my first posts. The more I learn the more I realize how elementary some of my questions are. Sometimes, it is the most basic things that are hardest to grasp, as many on the board take those things for granted. I appreciate you helping me sort through my situation, and I'd be screwed (or broke) without this board. I may not have made all of the best choices, but I still have options and am optimistic that it can work out.

    - I bought the home late this summer. She was beat up by the Hurricane Sandy, neglected since. I was looking for a project, and a project I got.
    - I am on a shoestring budget but I am trying to not cut corners where it matters. To make this work, I moved from my apartment into the home.
    - This is my first time trying my hand at a heating system. I am a civil engineer in the heavy construction industry, but I spend my spare time playing mechanic, working on my cars, boat, computers, and so on - and now, rebuilding my new home. I recently finished swapping the 4.0l I6 into my '95 Jeep Wrangler (up from the 2.5l I4) that I've owned since I was 16 y/o - took me nearly 2 years, but once done, a mechanic at the dealership couldn't tell my engine bay from that of a stock '95 that had the I6 from the factory. It wasn't easy to do it the right way- no loose ends. That include retrofitting the wiring harnesses! Anyway, clearly, I have a lifetime of knowledge to learn about heating, but I'm enjoying it, mostly. A bit stressful as we're dropping into the 30's here in NY, and I've got not heat yet - the whole home has pretty much become unusable besides the couple rooms I heat with space heaters when I'm home. I can not wait to have heat.
    - @Gordy - I've been through Burnham's manual several times - one of my best resources. I do trust my installer. That said, I want to understand the system that I'm paying him to install - and I want to know enough to ask the right questions, to make sure we're on the same page, and that he doesn't leave me with a system teetering on the edge of failure.
    - I fully intended to line the chimney, and always did. Agreed, real science - I understand the consequences of the flue condensing. I might not get it done for a week or two after the boiler is installed but acknowledge the risk. It's cold out and I'll avoid low temp return water until then.
    - @Ironman, you're right, more & more I am understanding how a mod/con would be perfect for my application, but I'm stuck with this Burnham: 6 days until install. Perhaps I rushed into making the decision, but I got it for a steal, and thought it would be a good starting point for my heating education & experience. (A couple months back I started a thread here soliciting opinions on my boiler choice. The reason that this was nearly free to me was that my company's plumbing dept had leftovers from emergency repairs done right after the hurricane. Several suggested that the ES2 would make sense for me, especially given the price, and other aforementioned reasons.)


    Enough about the past ...


    My plumber is starting the installation this Friday, December 5th, for better or for worse. I have to make my final emitter decisions by Monday morning for them to ship out & arrive on time.
    Gordy said:

    All though there is no minimum flow requirements for that boiler there is the 110* minimum return water temp.

    If you take full advantage of ODR, and TRVs. Being the thermostat is strictly a high limit, and the TRVs wide open with ODR controling the house temp, and you are oversizing radiation.. That boiler will see less than the minimum 110 return temp a lot of the season. Especially fall, and spring.

    Maybe I'm over thinking it though.

    Ironman said:

    I think you're right on track Gordy and that's one my concerns. The other being on the opposite end: that during those seasons on mild days, all the TRVs shut, the circ stops and the boiler short cycles. I suppose that widening the differential in the aquastat would be an option to counter-act that.

    You fellas have described two scenarios that I must try to avoid: too-low return water temps due to over-radiation + ODR, or short-cycling due to TRV's closing quickly (essentially the opposite, now the boiler is oversized). Interesting, to say the least.

    I am now leaning towards not oversizing the emitters - thoughts? It seems that I should size the emitters for the boiler that I have, instead of trying for the best of both worlds.

    Using a Delta P circ like the Grundfos Alpha on 'Auto Adapt' seems like it could help.


    But reading Burnham's manual again, and thinking about what you both and @Eastman said: I can't avoid some type of low flow and low temp protection given the TRV's. So the question is: what is the best way to pipe the boiler into the system?

    Again, thanks for sharing your expertise. I will share before & after photos and my experiences after this is done.
  • Gordy
    Gordy Member Posts: 9,514
    Read appendix D in the I/O manual for the ES 2. To help understand piping requirements.

    What is the installers plan have you discussed the piping of the boiler, and emitters with him?

    You have choices in near boiler piping. Some protect the boiler better than others, and have differing costs, but your installer has to understand the options too.

    Boiler bypass. Simple not as effective in boiler protection.

    Primary/secondary. Requires two circulators. Allows primary loop to operate at a different flow rate than the secondary loop.

    4 way mixing valve best option for boiler protection more expensive than first, or, second. The taco I valve,has ODR capability.

    To answer your original question it was still wise to oversize radiation. Wish you would have come on board before purchasing boiler is all. By the time you add the goodies to a CI boiler you are in the mod/con price range which has everything on board. We are past that now.




    alheim
  • Ironman
    Ironman Member Posts: 6,581
    @alheim,
    You didn't come across that way to me. There are just so many scenarios that can arise AFTER a hydronic system is installed and operating that we try to consider those when designing. This is especially true in the world of modern hydronics with all the new technology and gadgetry that comes along almost daily.

    I highly suggest that you read the issue of Idronics that Paul attached. It will probably cause a lot more questions to arise, but it will also provide some options you may not have been aware of.

    I think that the simplest prevention that you could do would be to add a thermostatic bypass to the boiler to prevent sustained return water low temps. A lot of what were talking about is things that show up in the long term, not the short. That would address the major one.

    A more expensive but better option would be the Taco I series valve that operates on outdoor reset and also provides boiler protection. The idea here, as with other smart mixing systems, is to provide two temperature loops, one for the rads and one for the boiler. Both could have their own ODR with boiler at a somewhat hotter one to protect it.

    As far as over-sizing the rads, here's my take: it depends upon whether you choose a smat mixing system or not. If you do, then over-sizing would be beneficial. If not, then there may not be much benefit.

    You may want to study the Buderus 2107 control and see some of its functionality. Buderus has been using that control with their "flexible" cast iron for probably 25+ years. It's not an " on demand" cold start control, but instead maintains a minimum warm start boiler temp. The ES2 is basically a copy of that design, but I don't think their control matches the complexity of the 2107 Logimatic and it's that area that we are trying to address.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • SWEI
    SWEI Member Posts: 7,356
    If I were doing this job, I would oversize the radiators and pipe it primary/secondary with a Taco iSeries-R valve (3-way or 4-way.)

    Second best choice would be a thermic boiler protection valve. We stock the LK823 from Sweden. PM me if you are interested in one of those.
  • Gordy
    Gordy Member Posts: 9,514
    Have the room by room heatloss, water temps, and flow rates been calculated?
  • alheim
    alheim Member Posts: 68
    edited November 2014
    Studying up now, thanks. I just spoke to the plumber, who is willing to go P/S.

    Here a links to my heat loss calcs, done using the older Slant/Fin software. A engineer at Hydronic Alternatives checked the numbers and felt that they were fairly accurate:

    First floor: http://i.imgur.com/SzBJvDx.png

    1st Floor

    Second Floor: http://i.imgur.com/aEUa4VS.png

    2nd Floor

    The "LR & Closet & Stairs" is the largest room, and the 2 planned rads in that room will also heat the "Hall-Stair Space" on the second floor, for a total of 8,630 + 2,939 = 11,569 BTU between 2 rads. This is the largest cumulative space and is where the thermostat used to be. This & most rooms have nice South-facing windows/exposure. I could also easily fit 3 rads into this space, esp if I'm oversizing. The old setup was 2 large cast iron rads.

    Mostly ignore the 'Sunroom' for now. I might tie a loop into the existing baseboards in there. I think the boiler will have enough input left to heat that room down the road, especially as I tighten up the home's envelope over the next few years. (Or, I could just add more of the same panel rads right now. Hm.)
  • alheim
    alheim Member Posts: 68
    Water temps and flow rates haven't been calculated beyond knowing what the ES2 can handle.
  • Eastman
    Eastman Member Posts: 927
    thoughts...

    So your getting an oversized fixed fire boiler with no ODR, and hooking it up to medium mass emitters. We're really talking about a system that is never in equilibrium, with two processes that need to be optimized: a short thermal loading cycle and a long thermal unloading cycle.

    Given that, do we really want a fully TRV'd setup? I'm thinking we want the majority of the system to load btus unfettered into the rads --with TRV's applied only to hot spots that are difficult to balance out. Would not a directly piped fixed max delta T with thermostatic low temperature protection be the best configuration for short cycle prevention and efficiency?

  • Gordy
    Gordy Member Posts: 9,514
    At a 20* delta you need 5.1 gpm to the supply manifold. You are home running the supply returns correct? You would benefit from using flow control valves on the return manifold to tweek the flow rates to the rads. Since home running may cause some very different loop lengths.


    Examples of flow requirements needed per room are as follows. To heat that space. Based on 20* delta. At ODT.


    .86 gpm
    .36 gpm
    1.2 gpm
    .47 gpm
    .30 gpm
    .63 gpm
    .42 gpm
    .20 gpm
    .20 gpm
    .29 gpm

  • Eastman
    Eastman Member Posts: 927
    Good example. Yeah, on average about a 1/2 gpm per rad for 9 rads. That means the installer should be looking at 5/16 diameter pex.
  • Paul48
    Paul48 Member Posts: 4,470
    Gordy......Is there any flow controls that can get you down that low? Caleffi's 1/2" w/ gauge only go down to 2 litres/per/min.
  • Gordy
    Gordy Member Posts: 9,514
    I would stick with 3/8 or better 1/2 we don't know home run lengths, and just for circ head. Bigger is better as far as head loss goes relative to flow rates.
  • SWEI
    SWEI Member Posts: 7,356
    We use almost exclusively Belimo CCV's for zoning. They come in Cv's ranging from 0.3 to 400. Proper sizing will result in a reasonably balanced system without adding more parts.
  • Gordy
    Gordy Member Posts: 9,514
    Uponor tru flows,get,down to .15 gpm. I like those ccv valves Kurt.

    I guess what needs to be addressed is zoning in a 1400 SF dwelling?
  • Paul48
    Paul48 Member Posts: 4,470
    With balanced radiation in a tight envelope, I don't see the need. Maybe in sleeping areas. In this case, I'd subscribe to K.I.S.S. I just don't think you'll get the r/o/i for too many bells and whistles.
    alheim
  • Eastman
    Eastman Member Posts: 927
    I think SWEI posted in the wrong discussion?
  • Eastman
    Eastman Member Posts: 927
    What about a setup like this?image
    alheim
  • Gordy
    Gordy Member Posts: 9,514
    edited November 2014
    The OP did say ODR was in the future.

    No mention of wanting an indirect. Which cost of indirect would be double an I valve. Which would give boiler protection, and ODR capability. I would much rather see the ODR capability implemented

    Why two pumps in parallel? We are only looking at 5.1 gpm for system, and boiler. At design conditions actually.

    If an indirect was in the budget how would it see high enough supply temps with return water mixed with indirect supply water? Especially with ODR?
    alheim
  • alheim
    alheim Member Posts: 68
    edited November 2014
    Gentlemen, I am astounded at the amount of thought that you've put into this.

    I am indeed in a position to add an indirect. (Similar deal - I got a nearly-free AO Smith NG 40-gal hot water heater that my plumber was also going to install on Friday, but I can easily unload it for what I paid. It's a pretty basic unit.) I like indirect for a few obvious reasons, and during our discussion here yesterday I was thinking about how an indirect might make sense, to add heat mass etc.

    The ODR module for the Burnham ES2 (which I don't have yet, but could purchase now) includes a DHW priority feature, for what that's worth - I assume it's standard. How do others with mod/cons etc. handle having an ODR with an indirect?

    Or, I could scrap the ODR (saving ~$500) and run a constant temp, with a setup similar to the schematic by @Eastman (plus an mixing valve if oversized)? Whew.

    I love the late-night diagram, we are both night owls.
  • alheim
    alheim Member Posts: 68
    edited November 2014
    From the Outdoor Reset IQ Card manual (http://s3.supplyhouse.com/manuals/1288284671664/41040_PROD_FILE.pdf):
    Ensured Domestic Hot Water Supply:
    As the supply water temperature is reduced to match home heat demand for warmer days, it is possible the operating temperature setpoint may be lower than required for an indirect water heater. To overcome this situation, a domestic hot water heat demand contact input is provided. Upon a domestic hot water heat demand (as sensed by the contact input) the operating setpoint is set equal to or greater than the Domestic Hot Water Setpoint (ds_) parameter. The supply water setpoint is now at least warm enough to satisfy the domestic hot water demand. When the domestic hot water demand is over the operating setpoint is released to follow the reset ratio as discussed above. Additionally, sometimes it is desirable to rapidly recover the domestic hot water temperature. For this reason it is possible to stop the system circulator during a domestic hot water heat demand. When there is a domestic hot water demand and the Priority Time (PT_) parameter is not set to zero the system circulator is forced off for the duration of the priority time. When the priority time is set to zero the system circulator is not forced off during the domestic hot water demand.
    The schematic by @Eastman is a nice, simple setup, it seems. But before that, I was leaning to P/S. But, can I oversize rads in P/S with a smart mixing valve? I'm back to reading on P/S now. Didn't get as much study time in yesterday as I would have liked.
  • Gordy
    Gordy Member Posts: 9,514
    edited November 2014
    May I suggest you look at some piping diagrams in the I/O for MOD/CONS. to get a grasp of it.

    In a P/S piping the indirect would be another loop of the primary with closley spaced t's and its own circulator. Most indirects would require higher flow rates than 5 gpm.

    You really need to now look at the indirects literature to see what its requirements are for SWT verses recovery, and GPM flow rate through the HX.

    Remember advice was given on a tight budget. Now parameters are changing.

    Actually a buffer tank would be the most obvious choice to prevent cycling. Could be used in Leu of primary /secondary piping as a hydraulic seperator. again budget. Installer knowledge.

    Keep in mind these different things can be added later. Just make sure installer adds stub outs with isolation valves in the primary loop. For indirect

  • SWEI
    SWEI Member Posts: 7,356
    Apologies -- yes, I somehow replied in the wrong tab. Let me see if I can find the correct one and have it moved.

    You might want to check the price on that IQ ODR card before you commit. When I looked earlier this year, a Taco SR501 cost less than half what Burnham was asking for it. A small Taco iSeries-R valve costs roughly what the IQ card does -- and will give you a lot more flexibility.
    Gordy
  • alheim
    alheim Member Posts: 68
    edited November 2014
    I'm looking at the piping diagrams for several mod/cons, right now the Slant/Fin Lynx. It seems they recommend P/S piping. (Conversely, the ES2 manual appears to show a 'conventional' loop in series with the emitters, with a bypass valve, but the Indirect on a secondary-type loop.)

    @Gordy You just blew my mind with the advice to look into the indirects "SWT verses recovery, and GPM flow rate through the HX", but I'm looking into it. Taking suggestions.


    What about:

    1. P/S, Taco I-series mixing valve (3-way) on the oversized emitter loop w/ TRV's, and an indirect on another loop. Not sure on how this all plays with an ODR.

    This might be an unnecessarily complicated version of @Eastman‌'s schematic, though, since all emitters are on one zone in a small home.

    2. Or, since we now have a P/S Primary loop plus an indirect to protect the boiler, forget the mixing valve, and use the Burnham ODR card (with DHW priority). So P/S, ODR w/ DHW priority, with emitter loop w/ TRV's, and indirect on another loop. I'd draw it, but you guys get it.

    3. Or similar. Feels like we're getting close.


    @SWEI The Burnham ODR card is just under $500. The Taco SR501 'Zone Switching Relay' that you suggested is only about $50 (link). I am not sure what this would do here. The Taco FuelMizer SR501-OR-4 Switching Relay w/ Outdoor Reset is ~$160. And a 1" Taco I-series 3-way is about $300-$400 (4-way is $400+).

    Yes, budget is a concern, but becoming less so. I've already saved a lot in several ways and not trying to cut corners. I'm very happy with my plumber's cost also. An indirect is one less venting & combustion appliance to deal with. Hot damn I wish I had a few more weeks to think this through!