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# Is it possible I just cant get enough radiant floor output and will require supplemental heating?

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Member Posts: 62
I am planning to retrofit my first floor with radiant heat. 1/2" pex with extruded aluminum panels, R-19 in the joists underneath.

So I input everything into loopcad, used a dT of 10F and targeted a max surface temp of 82F (original oak wood floors over a board subfloor). This has the water temp at 140F

LoopCad is telling me that I will need supplemental heat in all rooms. I do have cast iron rads currently providing heat. My original plan was to remove them once the radiant was operational and confirmed to be working properly.

Pictures show the loads and surface temps. Is it possible this is correct and I will need to keep the rads or is it more likely that I am missing or incorrectly entered a setting in loopcad? The heat load matches the calculation I did prior using excel and a 3d model of the house (almost perfectly) so Im fairly sure thats accurate.

«1

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It's quite possible. Whether you need supplemental heat beyond what a radiant floor can provide depends very much on what the actual heat losses of the building are, as you would expect. There is a very definite upper limit to the heat output of a radiant floor is, and at 82 for the floor you are right at it.

Another approach, however, is to see if there are ways you can reduce the heat loss rate of the structure. Draugh sealing, storm windows, more insulation, that sort of thing.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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edited February 2023
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In an old house that has standing cast iron rads, it’s very doubtful that a radiant floor will produce enough heat when the structure nears design temperature outside.

As Jamie said, how much can you tighten the envelope to lower the heat loss to match the output of the floor?

What’s the heat loss of the house per square foot? Typically, it’s around 26-30 btus in one of that era. Your floor may provide up to 20 btus per square foot at 120* SWT, depending upon the floor coverings. But these are average numbers and specific rooms may have a higher heat loss per square foot and require more heat.

You need to have a room x room heat loss calc and you’re probably gonna need supplemental heat.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
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Appreciate the insight guys. My original intent was to leave the cast iron and add radiant to warm the floors. I started thinking maybe the radiant could handle the first floor load. Looks like ill probably leave it. I will need to figure out controls to balance them.

Anyone have thoughts on how I can use an outdoor reset to control the rads to kick on below a certain outdoor temp?
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2 stage T-Stat. 1st stage in floor

What make and model boiler?

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You’ll need to create two SWT zones. The floor should see 120* max and the radiators about 165* max.

A smart mixing valve or variable speed injection mixing for the floor and the boiler’s ODR curve for the higher temperature needed for the rads.

As Paul said, a two staged stat or an ETC sensing outdoor temp to hold the pump to the radiators off until a certain outdoor temperature.

We’d really need to know what boiler you’re using and the current piping for more specific answers.

Tekmar has a couple of essays that deal with injection mixing and smart valves.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 4,955
edited February 2023
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@Ironman

The reason I'm asking is, with the radiant floors those radiators may have enough output at 140°F supply too make up the difference. Now a condensing boiler is feasible.
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pecmsg said:
@Ironman The reason I'm asking is, with the radiant floors those radiators may have enough output at 140°F supply too make up the difference. Now a condensing boiler is feasible.
Possibly, but if you run the floor above 120*, you run the risk of the boards cupping.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 4,955
edited February 2023
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Ironman said:

pecmsg said:

@Ironman

The reason I'm asking is, with the radiant floors those radiators may have enough output at 140°F supply too make up the difference. Now a condensing boiler is feasible.

Possibly, but if you run the floor above 120*, you run the risk of the boards cupping.

Agreed.
Less than 120° in floor
+
Less than 140° Radiators
=
Condensing boiler!

• Member Posts: 3,658
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A Viessmann Vitodens 200 allows for both a radiator zone and RFH zone with a 3 way mixing valve to be programmed independently. It's the easiest way to do it, and saves an extra pump in the near-boiler piping
• Member Posts: 62
edited February 2023
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Ironman said:

You’ll need to create two SWT zones. The floor should see 120* max and the radiators about 165* max.

A smart mixing valve or variable speed injection mixing for the floor and the boiler’s ODR curve for the higher temperature needed for the rads.

As Paul said, a two staged stat or an ETC sensing outdoor temp to hold the pump to the radiators off until a certain outdoor temperature.

We’d really need to know what boiler you’re using and the current piping for more specific answers.

Tekmar has a couple of essays that deal with injection mixing and smart valves.

I do not have access to gas. I have an oversized 40yr old oil burning NYer at the moment, but planning to replace it with a 75k net WM cast iron boiler (WGO-2). I have the system design set up with a 180F manifold for the upstairs rads (and downstairs sunroom rad) so its not a big deal to supply 180 to the other existing downstairs rads. I have the system designed with fixed mixing valves (caleffi anglemix) for the radiant zones.

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Ive run radiators at 120 supply, possibly a single temperature system may work

determine how much you are short in the various rooms, run a derate on the radiators and see if they make up the difference
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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hot_rod said:
Ive run radiators at 120 supply, possibly a single temperature system may work

determine how much you are short in the various rooms, run a derate on the radiators and see if they make up the difference
This is a good approach. At 140*, radiators have about 1/2 the output of 180*. That, plus the RF probably would provide enough heat.

You need to keep the boiler temperature at 140* or above to prevent flue gas condensation. Some form of boiler protection would also be prudent.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 62
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hot_rod said:

Ive run radiators at 120 supply, possibly a single temperature system may work

determine how much you are short in the various rooms, run a derate on the radiators and see if they make up the difference

• Member Posts: 22,472
edited February 2023
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Ive run radiators at 120 supply, possibly a single temperature system may work

determine how much you are short in the various rooms, run a derate on the radiators and see if they make up the difference
Cast iron, steel, copper, stainless, and a few concrete radiators 😗

good thing about cast radiators us you can calculate very accurately what the output is under different SWT

https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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If you've done any basic thermal upgrades, such as insulating and air sealing your attic, its very likely you will need only 140F max for the second floor radiators. You need to do heat losses for all rooms and then compare that to the radiator EDR. Also, you can run any number of reset supply temps off a single outdoor reset control with fixed mixing piping for each temperature. I've got picture somewhere of the piping setups from about 20 years ago.
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If you've done any basic thermal upgrades, such as insulating and air sealing your attic, its very likely you will need only 140F max for the second floor radiators. You need to do heat losses for all rooms and then compare that to the radiator EDR. Also, you can run any number of reset supply temps off a single outdoor reset control with fixed mixing piping for each temperature. I've got picture somewhere of the piping setups from about 20 years ago.

The house had UFFI blown in to the walls at some point and cellulose blown into the attic and 1st floor bump out ceilings. Original wood sash windows, but aluminum storms. Its actually pretty well insulated, though not so well sealed.

I have done the room by room calc and the rad output (though I was using 180F). The heat loss calc (65k) exceeds the actual fuel usage, though at the moment there are a few rooms with no heat. I plan to rectify this as part of this project which should bring the actual up near the calculated.

I like the idea of running 140 to the rads. I have the system designed with a caleffi thermoprotec boiler protection (140F cartridge). I just have to confirm that the control will max out the boiler for indirect SWT. I am skeptical of eliminating the mixing valve for the radiant manifolds. With 180F going to the indirect, I would need to be able to mix down when it comes off priority. I also want to keep the ability to tune the system when its in place.

My plan was to run the boiler as a warm start (140F) lo-limit all year. Ive done this with my current boiler and the fuel usage is minimal (maybe 3/4 of a tank of oil between April and October). I feel like I would need some bit of differential between high and lo-limit.

Question (maybe obvious): If I run the system at 150F (mix down for radiant, 150 to the rads), am I getting the full output of the boiler? The boiler is rated at 75k net and heat loss is 65k. Would this result in shorter or longer cycles?
• Member Posts: 1,219
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Look at your radiator output at various temps to see where it matches the heat loads of the rooms. Also, heat loss calcs need a good balance point temperature to start with ( the outdoor temperature at which typical indoor gains match the heat loss) On well insulated buildings this can be in the upper 50's... even lower with good passive solar gains.
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You could use a mixing valve with an operator that responds to outdoor temperature ODR, that way you get close to constant circulation thru the radiators, the best way to run any heat emitter is constant circulation, and vary supply temperature.
Numerous valves available to do this, tekmar, Taco, Belimo, others.

Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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If your looking to replace the boiler anyways then I would suggest going with a Energy Kinetics Frontier EK1. The boiler already has a built in bypass for thermal shock and thermo protection.

E-Travis Mechanical LLC
Etravismechanical@gmail.com
201-887-8856
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Here a three reset temperature supply manifold set up with a single full outdoor reset control running off a cast iron boiler. DHW is also thrown in with an indirect tank. Since it is full outdoor reset the zone almost run continuously.
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That answers the 140* supply water. Going to have to be higher!
• Member Posts: 62
edited February 2023
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hot_rod said:

You could use a mixing valve with an operator that responds to outdoor temperature ODR, that way you get close to constant circulation thru the radiators, the best way to run any heat emitter is constant circulation, and vary supply temperature.
Numerous valves available to do this, tekmar, Taco, Belimo, others.

I like this idea. Does it make sense to run the floors at a fixed SWT (to max out their output) and run the rads at variable SWT so they compensate for increased heat loss at lower outdoor temp? If thats true, I wonder if it even makes sense to run the an ODR on the boiler itself. The included hydrostat control has thermal targeting that adjusts the boiler temp based on thermostat activity.

Only problem I see is that I was planning to run the upstairs rads (no floor heat) at max temp. If I went this way, I might need a separate pump for actual high temp. Though I was planning to zone the upstairs rads so maybe it would work pushing them all through the variable. This all gets really complicated
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I would run the floors on the reset temperature. The radiators on a fixed supply possibly with TRVs for individual control and near constant circulation, as the TRVs are modulating valves by design.
Proportional, non electric valves, with an ECM delta P circulator, 15-58E or the new Alpha 15-58
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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hot_rod said:

I would run the floors on the reset temperature. The radiators on a fixed supply possibly with TRVs for individual control and near constant circulation, as the TRVs are modulating valves by design.
Proportional, non electric valves, with an ECM delta P circulator, 15-58E or the new Alpha 15-58

Im looking into this now, question

With this tekmar valve and actuator

https://www.supplyhouse.com/Tekmar-743-Actuating-Motor-for-34-Way-Mixing-Valves
https://www.supplyhouse.com/Tekmar-710-3-4-Brass-3-Way-Mixing-Valve-4864000-p

It seems like the actuator only has open and close functions (the documentation isnt great). Is there something I am missing? Will the control allow this valve to modulate for different temps?
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With tekmar components you need 3 parts. The valve body, the motor, and a control to run it.

Another common product for that is the Taco I valve, everything is included, it has ODR built in. I've not used one, they seem to be a good option.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 62
edited February 2023
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Here a three reset temperature supply manifold set up with a single full outdoor reset control running off a cast iron boiler. DHW is also thrown in with an indirect tank. Since it is full outdoor reset the zone almost run continuously.

I would be interested to know more about this. You have one outdoor reset with variable mixing on the boiler supply temp and then mix down with fixed valves for each of the other temps? Or do you have independent variable control on each temp?
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The mixing valve down at the bottom of the panel is a simple Esbe thermix valve to maintain the boiler return temp at minimum of 140F. The pump at the right top moves water through the boiler and also the primary loop, which branches into the 3 rungs. The flow through each rung is balanced by the globe valves on the far right ( round blue handles). These valves allow you to set the relative temperature of the supply to each zone. The boiler is fired to follow an outdoor reset supply temperature curve at the supply to the rungs on the ladder on the right side of the board. The zones are piped primary/ secondary so that no matter what the flow is across the rungs, the flow rates are correct for the zones. IIRC the top rung supplies the highest temperature zones which are the water temperature calculated by the outdoor reset control. The lower rungs mix supply water coming from the left with the return water coming back from each zone to provide lower temperature mixed water to the zone. For these two lower rungs, there is water flowing backwards across the P/S tees on the rungs... hence the lower supply temperatures for these zones.

This setup allows the highest water temperature to be reset and through fixed mixing occurring at the primary/ secondary tees, will also reset the other lower water temperature supplies proportionally to the highest water temperature.

As you can see, I have come to greatly prefer the KISS principal for systems,.... just use the fundamentals to best advantage.
• Member Posts: 62
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The mixing valve down at the bottom of the panel is a simple Esbe thermix valve to maintain the boiler return temp at minimum of 140F. The pump at the right top moves water through the boiler and also the primary loop, which branches into the 3 rungs. The flow through each rung is balanced by the globe valves on the far right ( round blue handles). These valves allow you to set the relative temperature of the supply to each zone. The boiler is fired to follow an outdoor reset supply temperature curve at the supply to the rungs on the ladder on the right side of the board. The zones are piped primary/ secondary so that no matter what the flow is across the rungs, the flow rates are correct for the zones. IIRC the top rung supplies the highest temperature zones which are the water temperature calculated by the outdoor reset control. The lower rungs mix supply water coming from the left with the return water coming back from each zone to provide lower temperature mixed water to the zone. For these two lower rungs, there is water flowing backwards across the P/S tees on the rungs... hence the lower supply temperatures for these zones.

This setup allows the highest water temperature to be reset and through fixed mixing occurring at the primary/ secondary tees, will also reset the other lower water temperature supplies proportionally to the highest water temperature.

As you can see, I have come to greatly prefer the KISS principal for systems,.... just use the fundamentals to best advantage.

Thats a neat system. I actually love the idea of using a single ODR at the boiler level and scaling down each temp proportionally using a fixed valve.
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I’m a huge fan of proportional mixing. Just be careful if you have zones off the mix
as flow rates vary, the “dumb” valve cannot adjust so SWT will vary

From Idronics 7
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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hot_rod said:

I’m a huge fan of proportional mixing. Just be careful if you have zones off the mix
as flow rates vary, the “dumb” valve cannot adjust so SWT will vary

From Idronics 7

Yes, if you really want to keep a tight reign on each zone supply temp, you would need a single rung on the ladder for each zone, except the highest temperature supply can have multiple zones, like the panel pictured. The nice thing is that each rung is probably only 3/8 inch or 1/2 inch in residential systems so it is quick and cheap to make up the ladder.
Even on commercial radiant floor systems I've use only 3/4 inch copper to supply heat to big 40,000 radiant floors with 15 foot ceilings. Big delta tees can move big amounts of heat with very low flow rates.....oh course not nearly as much as steam's 150F delta tee and the 7 times more heat from the heat of vaporization ( you just know I had to add that...)
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I install 10,000-20,000 feet of radiant heat in Manhattan and Brooklyn every year and every installation includes a secondary source of heat whether it's radiators or some forced air that the HVAC companies install.
Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
Consulting & Troubleshooting
Heating in NYC or NJ.
Classes
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I also should add that if you are running full outdoor reset and maintaining steady indoor temperatures, Most of the zones will be running all the time, so even if there is some cycling of mulitple zones on a single lower temperature loop, it probably would not be for very long.
• Member Posts: 62
edited February 2023
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hot_rod said:

I’m a huge fan of proportional mixing. Just be careful if you have zones off the mix
as flow rates vary, the “dumb” valve cannot adjust so SWT will vary

From Idronics 7

I love this idea. I was planning to zone the upstairs rads but I may just skip that and go with TRVs. I still need to figure out if I can get away with one SWT for all rads (upstairs as primary and downstairs as supplemental).
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The required SWT will need to be whatever the upper radiators need to cover design load, call it 180f at design.
The lower supplemental radiators would use the same SWT. If you use TRVs on all the radiators they will do the temperature control. Quite nicely if you run those radiator zones via a delta p circulator. That way the circ is also a proportional device, flowing only what the TRVs call for

If the boiler runs on ODR then the entire system is running via “cruise control” The boiler, the circulator and the TRVs are all constantly modulating to the ever changing load. You will need to play around with ODR settings, get the shift dialed in accurately so you never fall behind the load.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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JohnNY said:
I install 10,000-20,000 feet of radiant heat in Manhattan and Brooklyn every year and every installation includes a secondary source of heat whether it's radiators or some forced air that the HVAC companies install.
I did that amount in the Chicago area for a single family home and many times over in any given year. Rarely, did I need supplemental heat like baseboard or toe-kick heaters unless it was a kitchen or a sunroom. For homes that size, there was always multiple boilers that were staged and rotated.

It’s probably been said already but you have to start with a room by room heat loss. From there you determine the btu/h/sf needed to meet that loss and the supply water temperatures needed to achieve that. Types of floors and floor coverings are going to play a large part in that so that needs to be considered during the design process. The goal is to have the lowest SWTs possible so that the modcon will be in condensing mode most of, if not all of, the heating season. Another goal is to have as few different SWTs as possible. For me, if it was within 10* of each other, I’d use a single temp in the middle. It’s almost always better to spend a little more on the front end by keeping the tube spacing tighter than it is on the back end by being forced to use higher water temps or supplementary heat.
And I really like the simplicity of the Taco iSeries valves for mixing. Sure, you can add more bells and whistles and spend a lot more money, but for me the simpler the better.

All of these processes are repeatable for every single radiant project. Uponor has a nice way of presenting all of this in their worksheets in their CDAM manual which is available in hard copy or pdf on their website.
Steve Minnich
• Member Posts: 62
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hot_rod said:

The required SWT will need to be whatever the upper radiators need to cover design load, call it 180f at design.
The lower supplemental radiators would use the same SWT. If you use TRVs on all the radiators they will do the temperature control. Quite nicely if you run those radiator zones via a delta p circulator. That way the circ is also a proportional device, flowing only what the TRVs call for

If the boiler runs on ODR then the entire system is running via “cruise control” The boiler, the circulator and the TRVs are all constantly modulating to the ever changing load. You will need to play around with ODR settings, get the shift dialed in accurately so you never fall behind the load.

The problem I am seeing is that the upstairs rads require 150F at design temp. I dont have much room to reset my SWT at the boiler. Would it make sense to run a variable injection valve with downstream dumb valves (for radiant) or a 4-pipe buffer run at a lower SWT with ODR?
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Tinman said:

JohnNY said:

I install 10,000-20,000 feet of radiant heat in Manhattan and Brooklyn every year and every installation includes a secondary source of heat whether it's radiators or some forced air that the HVAC companies install.

I did that amount in the Chicago area for a single family home and many times over in any given year. Rarely, did I need supplemental heat like baseboard or toe-kick heaters unless it was a kitchen or a sunroom. For homes that size, there was always multiple boilers that were staged and rotated.

It’s probably been said already but you have to start with a room by room heat loss. From there you determine the btu/h/sf needed to meet that loss and the supply water temperatures needed to achieve that. Types of floors and floor coverings are going to play a large part in that so that needs to be considered during the design process. The goal is to have the lowest SWTs possible so that the modcon will be in condensing mode most of, if not all of, the heating season. Another goal is to have as few different SWTs as possible. For me, if it was within 10* of each other, I’d use a single temp in the middle. It’s almost always better to spend a little more on the front end by keeping the tube spacing tighter than it is on the back end by being forced to use higher water temps or supplementary heat.
And I really like the simplicity of the Taco iSeries valves for mixing. Sure, you can add more bells and whistles and spend a lot more money, but for me the simpler the better.

All of these processes are repeatable for every single radiant project. Uponor has a nice way of presenting all of this in their worksheets in their CDAM manual which is available in hard copy or pdf on their website.

unfortunately, im stuck with oil for now. This means non-condensing, which means ~150F is the lowest I can go on SWT at the boiler.
• Member Posts: 22,472
edited February 2023
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The required SWT will need to be whatever the upper radiators need to cover design load, call it 180f at design. The lower supplemental radiators would use the same SWT. If you use TRVs on all the radiators they will do the temperature control. Quite nicely if you run those radiator zones via a delta p circulator. That way the circ is also a proportional device, flowing only what the TRVs call for If the boiler runs on ODR then the entire system is running via “cruise control” The boiler, the circulator and the TRVs are all constantly modulating to the ever changing load. You will need to play around with ODR settings, get the shift dialed in accurately so you never fall behind the load.
The problem I am seeing is that the upstairs rads require 150F at design temp. I dont have much room to reset my SWT at the boiler. Would it make sense to run a variable injection valve with downstream dumb valves (for radiant) or a 4-pipe buffer run at a lower SWT with ODR?
How complicated and \$\$ Do you want to make this system?  And to what final goal, comfort, highest efficiency, simplicity, serviceability, etc

It is almost impossible to check all those boxes, determine your priorities, build the system to that. Or them
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Great Conversation.   Beautiful work Steam Whisperer!  Mad Dog
• Member Posts: 62
edited February 2023
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hot_rod said:

How complicated and \$\$ Do you want to make this system?  And to what final goal, comfort, highest efficiency, simplicity, serviceability, etc

It is almost impossible to check all those boxes, determine your priorities, build the system to that. Or them
I dont mind spending a little extra on the front end but I value comfort, simplicity, reliability/serviceability over efficiency. Once I get this installed and tuned, I want to be able to forget it. I want to preserve the ability to tune the system wherever possible when its first installed since im not a pro with years of experience. If I make a mistake or oversight in calculations, I want to be able to adjust it out rather than rework the hardware.

To be honest, Im skeptical of the variable injection valves reliability in the long term though I feel that may be the only way to actually have an effective ODR on the entire system with a conventional boiler (which I want more for comfort than efficiency). What I dont understand is the tangible impact to comfort over a fixed temp system. I could probably just run the boiler at 150F all year with fixed temp RF zones and TRVs and get decent efficiency for a conventional setup. But if spending an extra \$1-2k on (reliable) hardware nets me some tangible comfort benefits and as a bonus I get slightly better efficiency, I dont mind doing it.