energy use: forced-air vs hydronic

duerstad

We're planning a 3600 sf, slab-on-grade, aging-in-place house in Minnesota, about as cold as St. Paul. It's very well insulated, tight, and includes exceptional windows. Energy modeling software (BEopt, so also Energyplus, on which it is based) consistently shows that energy use (Btu's; not cost, which would involve prices of fuels) is much higher for hydronic systems than for forced-air. I'm not asking about installation cost , or COST of running the system, but how much ENERGY is used to run hydronic vs forced air in the same structure. Pump and fan energy is also separated out by the software, so this is not what I'm writing about.

What I have consistently heard is that energy use in hydronic systems is always less than with forced air for the same building, but this software is saying the opposite. It reports this result regardless of efficiency of gas or electric boiler. Using a modulating 150-degree gas boiler is much better than others supplying 180 degree water, but even that still uses much more energy than just about any forced-air system. BEopt doesn't allow for true low temperature supply with hydronic, so that's also not part of this comparison. It's modeling baseboard hydronic.

Eventually I'm hoping to also compare ground source, low temperature radiant with other possibilities. Before that, however, it seems to me that I need to consider whether something is wrong in what I'm seeing in this result: hydronic consistently taking more energy to run than forced air.

Energyplus, and therefore BEopt, have been validated with quite a number of real world buildings, so it's unlikely that the software is completely off-base in what it is reporting. In the other choices that BEopt offers, it generally seems to be quite accurate when I add energy-saving features to the models I have constructed. Sadly, it also very accurately estimates the foolish, high energy use of the home which we unfortunately occupy now!

So what I'm asking is: can it be true, disregarding COST of fuel, that energy use by a hydronic system exceeds that of forced-air (after pump and fan energy use is factored out) in the same building?!

Thanks for any observations on the subject!

nicholas bonham-carter

I don’t see the purpose in the software separating out the energy needed to run either pumps or fans in the systems.
Can you run the numbers for pure electric radiant heat, (no fans in that system)? Then compare that energy use with the other two systems.—NBC

EBEBRATT-Ed

Something is amiss with your software. A Forced air system has a burner and controls to operate + the big load is the fan motor which is at least 7 amps or more.

A hydronic system has the same burner and controls so that's a wash. So now you add in a few hot water circulating pumps which will not equal the fan motor amps from forced air.

There is probably not a huge difference but I can't see the hydronic drawing more power.

Not to mention a hydronic system will be more comfortable

clammy

On the other side of the world where both oil gas and electric is much more expensive I think u would find it hard to find a hot air system in any home .if it where cheaper to run hot air I think most of Europe would not have so much hydronic heating .i personally can’t see a hot air system using less engerny on the distrubition in comparison to small wet rotor circulator , just can’t see it . As for comfort aside from ac hydronic heating offers the best in comfort and ease of zoning another plus pipes are always smaller then duct work peace and good luck clammy

Brewbeer

If the software is modeling the temp of the boiler heat exchanger and the furnace heat exchanger at different temps, then I could see how the program comes out with different efficiencies for hot water and forced air.

Baseboard systems don't need to run at 180F. My baseboards run at about 105F when it is 32F outside, and 130F when it is 0F outside. A well-designed radiant panel system will run at even lower temps.

KC_Jones

with 150° water you aren't condensing, forced air is commonly condensing, so what are they comparing to?

If they are comparing non condensing hydronic to condensing forced air that will skew the numbers, and I might add that presents as an agenda to me. What reason do they have to purposely lock out the low temp hydronic, if they have the equations and they work this should not be a limited, unless someone wants it that way.

Also you say real world, are they modeling setbacks? If so that could skew towards the forced air.

One matrix that always seems to be ignored on these energy consumption discussions is comfort. If energy consumption is truly the primary goal, but a couple space heaters in the basement to keep the pipes from freezing and be done with it. If comfort is the primary goal, go hydronic and never look back.

SuperJ

What were your assumptions about slab insulation (both edge and below?). If you don't insulate the slab, it will just be a big infinite heat sink even if your space is comfortable. I could see forced air outperforming an insufficiently insulated slab all things being equal.

I would post on Greenbuildingadvisor.com in the QA, they have some energy modelling geeks over there that can probably help out with assumptions when modelling.

Great modelling software is only as good as the data it's fed.

hot_rod

I agree with SuperJ, poorly insulated slab radiant are real energy hogs. I think 3" should be a minimum for under slab, and an appropriate edge detail is as critical. What insulation R does their program use?

When thinking " ideal comfort" some air movement and control needs to be included in radiant design.

Jamie Hall

Somewhere in that software -- well hidden from the user, I'm sure -- there is a definite agenda skew. The worst case difference will be a non-condensing hot water system vs. a fully condensing forced air system; in that case, it is possible that the all up energy use of the hot water system might be as much as 7% greater. Never more than that. If the hot water system is fully condensing, then the two systems should be within 3%. If they are reporting results greater than that difference...

Sorry, the software is just plain wrong.

Voyager

The problem with programs like this is that they don’t tell you their algorithms and assumptions and that is where the differences likely lie. I ended up using Excel and the fundamental formulas as I got great disparity (30%+) between various heat load programs.

I would expect baseboard and FA to be very close in energy consumption. You can gain a little with nightly setbacks on FA that should offset the additional energy required to move heat via air rather than more efficient water transport.

Comfort is in the eye of the beholder. I find FA more comfortable than baseboard. I am still undecided on in-slab radiant. The radiant comfort is high during steady-state operation, but the overshoots on unusually warm days is annoying and not preventable with the high mass radiator. So, I don’t think you can make blanket statements that one system is more comfortable than the other.

The design and implementation of a given system is likely a much larger determinant of both energy efficiency and comfort than is system type.

SuperJ

Voyager said:

Comfort is in the eye of the beholder. I find FA more comfortable than baseboard. I am still undecided on in-slab radiant. The radiant comfort is high during steady-state operation, but the overshoots on unusually warm days is annoying and not preventable with the high mass radiator. So, I don’t think you can make blanket statements that one system is more comfortable than the other.

That's why I'm such a fan of low mass radiant, you can heat in the morning to take the chill off without setting yourself up to sweating all afternoon due to solar gains. Warmboard, heat spreaders, and panel rads are great for this.

Gordy

I don’t think much of any software can truly compare a forced air system to hydronic systems. To many variables on both sides in which a particular system could be inefficient, and still heat the envelope, and yet one be very efficient, and still heat the envelope.

Both types of heating systems can be very forgiving to hackery So the question becomes what are the inputs they use to compare systems.

Many types of hydronic system emitters, high temp, and low temp. The low temp being more efficient at the boiler, with the right boiler.

Also agree with slab insulation detail.

Brewbeer

The former FHA system in my home was so uncomfortable, when it died, I removed it in favor of a HWBB system, even thought doing so was twice the cost of replacing the furnace.

Gas usage hasn't really changed between the condensing FHA furnace and the condensing HWBB. The FHA used 788 units of gas in 2014 with average heating season temp of 36F. The HWBB used 705 units of gas in 2016 with average heating season temp of 40F.

Gordy

i don’t think I have ever read where hydronics is more efficient than FA other than being able to deliver the btus in a much smaller infrastructure than FA (piping verses ducts), and providing a higher level of comfort with radiant.

I don’t buy a higher, or same level of comfort at a lower air temp. At least not with me. 72 is my slot for set point no matter what system.

Jamie Hall

Gordy said:

i don’t think I have ever read where hydronics is more efficient than FA other than being able to deliver the btus in a much smaller infrastructure than FA (piping verses ducts), and providing a higher level of comfort with radiant.

I don’t buy a higher, or same level of comfort at a lower air temp. At least not with me. 72 is my slot for set point no matter what system.

There really shouldn't be when one stops to think about it. One has an interior space at some temperature -- 72 or whatever -- and all the things in it, and an exterior condition -- light breeze and 12 right now, for example -- the heat loss will be exactly the same, regardless of how one sets about maintaining the interior temperature. Where the differences in efficiency come in is with the system which takes the incoming BTUs -- oil, gas, wood, coal, electricity, sunshine, whatever -- and moves them into the space. Then the unit efficiencies of the boiler, furnace, heater, stove, fireplace, whatever come into play, along with any losses in transferring the heated medium from the heat source to the space. Then one has to be certain that one is using comparable technology in the comparisons. Condensing furnace? Fine -- but compare it to a condensing boiler, not a 70 year old snowman!

The big jump is when one can use heat pumps, of course -- but they are a completely different technology.

SuperTech

Comparison of two can't be done properly with only factoring fin tube as emitters. Radiant flooring and panel radiators are becoming more popular and are a much better choice overall.
Regardless of emitter type 180 degree supply water should only be used for fin tube on the coldest days. Every hydronic system should be using outdoor reset. My cast iron baseboards only see 180 degrees supply water a few days a year, typically I run mine between 140-160 with no comfort issues.
Comfort wise it's no comparison. Radiant hydronics is king in my opinion.

GroundUp

But is heat loss really the same when you've got 68 degree air at the ceiling with radiant versus 90 degree air at the ceiling with forced air while both systems are maintaining 72 at chest height? I think not. Apples to apples, 90% efficient condensing boiler running 110 degree SWT baseboard versus 90% forced air furnace running 110 degree HX, both set at 72* ambient; which one is more comfortable? Especially with a slab on grade, there is no comparison. I have both radiant and FA in my house, just because. When lounging on the couch, it takes 74-75 to not need a blanket with the FA. With the radiant, the blanket stays in the closet at 67-68 degrees. Never have I been in a slab home with forced air that was comfortable, for me anyway. Cold and sweating at the same time are all too common, and I would never even consider a slab on grade without radiant

Solid_Fuel_Man

There is no way I would EVER build a heated space on a slab-on-grade which didn't employ radiant heat.

My FIL has many apartment buildings. He has been building new multi unit ones as of late. He has two identical buildings, one is radiant slab on grade, and the other has full basement with fin-tube. Both employ Viessmann 200 boilers. He says the heated slab consistently uses 1/3 less propane than the building next door. There are several factors, leakage, besement, high temp fin-tube vs. low temp radiant. But 33% ain't no little number.

SuperTech

> @Solid_Fuel_Man said:
> There is no way I would EVER build a heated space on a slab-on-grade which didn't employ radiant heat.
>
> My FIL has many apartment buildings. He has been building new multi unit ones as of late. He has two identical buildings, one is radiant slab on grade, and the other has full basement with fin-tube. Both employ Viessmann 200 boilers. He says the heated slab consistently uses 1/3 less propane than the building next door. There are several factors, leakage, besement, high temp fin-tube vs. low temp radiant. But 33% ain't no little number.



Radiant heat just can't be beat!

Gordy

The bottom line is a btu is a btu. How you gain efficiency is in the making of the btu, the delivery of the btu, the release of the btu, and the containment of the btu.

Which one has more Comfort is another matter for discussion.

GroundUp

Gordy said:

The bottom line is a btu is a btu. How you gain efficiency is in the making of the btu, the delivery of the btu, the release of the btu, and the containment of the btu.

Which one has more Comfort is another matter for discussion.

My point being, the BTU needs would typically be less with radiant as you could keep the ambient air temp lower than you would with FA to achieve the same level of comfort. All other things equal, it will take fewer BTUs to heat a space to 68 rather than 74 right?

Gordy

I don't find that true personally. 72 is 72 when the feet are not on the floor. Of course I'm a minimalist when it comes to clothing indoors........

I enjoyed ceiling, and floor radiant. Some rooms having both.
I can tell you the ceiling radiant was enjoyable when feet were not on the floor, and the floor enjoyable when you were walking on them. The rooms with both. Well just enjoyable

Now forced air in a slab home. Well that's not joyful at all.

If anyone ever went through the water bed phase. Then you know when you first set it up, and try to sleep on it that night before it was 82degrees, or so. It sucked the btus out of your body.........

That's my take on unconditioned slabs in a home. Even with carpet.

Jamie Hall

Folks, do my feeble brain a favour. If you are going to discuss comfort, discuss comfort If you are going to discuss efficiency, discuss efficiency. I would make, for example, a very strong argument that for me, in Cedric's home, the most comfortable situation is sitting in front of the big Keeping Room fireplace, half a dozen four foot lengths of ash or oak blazing away. But is it the most efficient? Not by a long shot. Perhaps the fallacy comes from telescoping the two, and effectively asking "what method of heating gives me (or my client, or whoever) the most comfort for the least money?" That is not the same as asking which heating approach is the most comfortable, nor is it the same as asking which heating approach is the most efficient.

I might add, though, that the telescoped question probably is the one we should, generally, be asking -- realizing that it won't have one best answer, nor will it have numbers attached to it -- or be suitable to be put into a computer program.

Voyager

SuperTech said:

Comparison of two can't be done properly with only factoring fin tube as emitters. Radiant flooring and panel radiators are becoming more popular and are a much better choice overall.

Regardless of emitter type 180 degree supply water should only be used for fin tube on the coldest days. Every hydronic system should be using outdoor reset. My cast iron baseboards only see 180 degrees supply water a few days a year, typically I run mine between 140-160 with no comfort issues.

Comfort wise it's no comparison. Radiant hydronics is king in my opinion.

Properly designed FA is the comfort king in my opinion.

I would use in-slab radiant to maintain sufficient floor temp to keep my feet comfortable, but then use FA for the balance of heat required, for fresh air management, for air filtration and for AC in the summer. That would be my ultimate system.

Voyager

GroundUp said:

But is heat loss really the same when you've got 68 degree air at the ceiling with radiant versus 90 degree air at the ceiling with forced air while both systems are maintaining 72 at chest height? I think not. Apples to apples, 90% efficient condensing boiler running 110 degree SWT baseboard versus 90% forced air furnace running 110 degree HX, both set at 72* ambient; which one is more comfortable? Especially with a slab on grade, there is no comparison. I have both radiant and FA in my house, just because. When lounging on the couch, it takes 74-75 to not need a blanket with the FA. With the radiant, the blanket stays in the closet at 67-68 degrees. Never have I been in a slab home with forced air that was comfortable, for me anyway. Cold and sweating at the same time are all too common, and I would never even consider a slab on grade without radiant

I have not read an analysis on this and have not tried to do my own. I doubt the gradient is anywhere near as high as you suggest. I will try to remember to grab one if my electronic thermometers and put it at my ceiling and measure the temp. I really doubt you will have 72 at 5’ and 90 at an 8’ ceiling. Or are you talking about a 30’ ceiling?

Similarly, Heat loss into the ground can be very high. An FA system with a cooler floor temperature will lose much less heat into the earth than will a radiant slab which can lose a lot of energy downward and at the edges if not properly insulated. So, yes, I could easily see a poorly installed radiant slab being much less energy efficient than a well-designed FA system.

Gordy

"Properly designed" is the operative phrase. The other is properly installed......

Solid_Fuel_Man

Let's talk apples to apples, both FA and radiant are "well designed and installed".

My PERSONAL OPINION, having lived with hot water convectors, hot water cast radiators, fin-tube baseboard, one pipe steam, FA, wood stoves, and radiant slab.

Radiant slab is the most even heat and I feel more comfortable at 66-68 degree air temp with high mass radiant. But that system is in a new, super insulated building.

All the others were old leaky buildings. The FA being the worst comfort wise, hot/cold swings! Wood stoves are wonderful to sit in front of, but overheat one area.

The one pipe steam was quiet (did not bang) but vents hissed and I didnt care for adding water to the already rusty open system. Also seemed to over heat the rooms once the call was satisfied, that 212 boiling point!

I liked the water cast iron better as it was on outdoor reset and didnt seem to over/under heat the rooms as much as the steam did. Both were controlled with same thermostats and in similar construction.

Voyager

If you had hot/cold swings, then you did not have a well-designed and well-installed FA system. I have had one for 19 years and lived with poor ones for 40 years prior to that (mobile homes on up) and a good FA system is nothing like everyone describes here. Mine does not swing any more than HWBB and I believe a fair bit less. The thermostat stays dead on the setpoint and responds quickly in the morning from my nightly setback.

It holds temp much better than in-slab radiant during rapid outside temperature swings as high-mass means slow response and there is nothing you can do about that, at least nothing that is both economical and energy efficient.

Jamie Hall

Go back to my previous comment. If you want to talk efficiency, talk efficiency. if you want to talk comfort, talk comfort. Efficiency is quantifiable: how many BTUh (gallons oil/LP, cubic feet gas/kilowatt hours) do I have to put in to get X BTUh out in the space. That's a measurable number.

Comfort is not quantifiable.

Please do not mix the two up.

Voyager

GroundUp said:

But is heat loss really the same when you've got 68 degree air at the ceiling with radiant versus 90 degree air at the ceiling with forced air while both systems are maintaining 72 at chest height? I think not. Apples to apples, 90% efficient condensing boiler running 110 degree SWT baseboard versus 90% forced air furnace running 110 degree HX, both set at 72* ambient; which one is more comfortable? Especially with a slab on grade, there is no comparison. I have both radiant and FA in my house, just because. When lounging on the couch, it takes 74-75 to not need a blanket with the FA. With the radiant, the blanket stays in the closet at 67-68 degrees. Never have I been in a slab home with forced air that was comfortable, for me anyway. Cold and sweating at the same time are all too common, and I would never even consider a slab on grade without radiant

Well, just for grins and giggles, I got my electronic thermostat with remote probe and checked my dining room gradient. As background, it is 15 F outside at the moment with a fair bit of wind here in northern PA. It is 68 F at the thermostat level (61” off the hardwood floor). The average temp at a couple inches below the ceiling (94” off the floor) is 68.9 F and the average temp with the probe lying on the hardwood floor is 65.3 F. This floor is on the cool side as it is above my unheated basement garage.

So, a total gradient of about 3.6 degrees on average floor to ceiling in a house with forced air heat that is running several times an hour given the outside temps. The furnace only runs a few minutes each time. So, I really doubt that this slight gradient is going to have a significant effect on the heat loss compared to the normal heat load calculation assumption of uniform temps on the walls, ceiling and floors.

The temps at each location varied about 0.2 degrees above and below the average based on whether the furnace was at the start or end of a run cycle. This is consistent with the thermostat which never is off of its setpoint value. I believe Honeywell does fudge a little and only changes the display if the temp is more than 0.7 off the setpoint, not the 0.5 one would expect.

I agree with the others that there is something goofy in the program you are using and I would not trust its results.

Now I need to check the gradient in my radiant slab heated workshop. Trouble is, a little hard to get to it 14’ ceiling. Although, even the gradient over a similar 94” span would be interesting. I would suspect it to be linear to slightly inverted, but I will check it if I get a minute.

Gordy

But that’s the beauty of radiant floors. Why would you want it 68 14’ up, or what ever your set point is. Obviously the gradient will be large with a heated floor.

I prefer to use MRT. “ Mean radiant temperature” which is the temp of all the objects, and surfaces in the dwelling. Cool objects, and surfaces create discomfort. A 3.6 degree difference from set point is a cool floor pulling heat off of anything warmer.

GroundUp

Was the FA blowing when you took those readings? Were you anywhere near a register? I know my FA in my house is not well designed, but in near proximity to any register while the heat is blowing, the gradient from floor to 10ft ceiling is all of 20 degrees. When I start walking on the ceiling, I'll likely agree that forced air is more comfortable but while I'm still upright I'll stick with the warm floor and let that ceiling do whatever it wants. To each their own, but being in the commercial heating profession I spend 8+ hours a day in different buildings with different heating systems and I cannot think of a single radiant system that made me say "hmmm, I sure with this were forced air". On the other hand however, it's almost a daily occurrence where the opposite is dreamt of

Voyager

Gordy said:

But that’s the beauty of radiant floors. Why would you want it 68 14’ up, or what ever your set point is. Obviously the gradient will be large with a heated floor.

I prefer to use MRT. “ Mean radiant temperature” which is the temp of all the objects, and surfaces in the dwelling. Cool objects, and surfaces create discomfort. A 3.6 degree difference from set point is a cool floor pulling heat off of anything warmer.

I agree and that is exactly why I chose hydronic in the slab for this building. It is the right choice for that building and its purpose.

However, I will stick with FA in my house. Too many advantages with only a couple of disadvantages that aren’t that important to me.

Voyager

GroundUp said:

Was the FA blowing when you took those readings? Were you anywhere near a register? I know my FA in my house is not well designed, but in near proximity to any register while the heat is blowing, the gradient from floor to 10ft ceiling is all of 20 degrees. When I start walking on the ceiling, I'll likely agree that forced air is more comfortable but while I'm still upright I'll stick with the warm floor and let that ceiling do whatever it wants. To each their own, but being in the commercial heating profession I spend 8+ hours a day in different buildings with different heating systems and I cannot think of a single radiant system that made me say "hmmm, I sure with this were forced air". On the other hand however, it's almost a daily occurrence where the opposite is dreamt of

No, I was probably 6’ from the nearest register. Sure, if you put a thermometer above a register, the gradient will be high, but it will also be in reverse with the 100 degree air coming out of the register being much warmer than the ceiling.

Different strokes for different folks. That is why we have different system types.

I don’t sleep well when it is warm. I like it 65 or cooler. When I stay in a building heated by steam or high mass hydronic, I am either too warm to sleep, or I freeze during my shower and the first hour after getting up while waiting for the heat to catch up. My FA at home comes on 10 min before my alarm. Usually, by the time the alarm goes off, the temp is up to 68 from my 64 setback and by the time I get out of the shower, the temp is pretty close to my 71 setpoint. I find that supremely comfortable. And most of my house is carpeted so the only floors that are cool at all are the hardwood and tile above the unheated garage. The rest of the basement is heated so the floors are actually pretty comfortable.

And I don’t have to worry about pipes freezing and bursting and the maintenance of FA is pretty minimal compared to hydronic. A 6 year-old can change a filter.

I agree that heated floors are nice, but so are setbacks at night, fast recovery, and integration with my HRVs and AC. Comfort is isn in the eye of the beholder and I find FA to be the most comfortable for me.

ChrisJ

@Voyager

You don't have indoor plumbing? Is that even legal?

By the way, thanks to TRVs my bedrooms stay 65 and my bathrooms stay 72-74. Even with "high mass steam"


Because I have 5 TRVs my system to an extent behaves like 6 zones. Also, I have Central air conditioning with diffusers in the ceilings where they do best for cooling.

I don't do set backs because I don't have to. My rooms stay the temperature I like them at. Oven going all day? The kitchen doesn't get steam. But other rooms do.

Jean-David Beyer

Regardless of emitter type 180 degree supply water should only be used for fin tube on the coldest days. Every hydronic system should be using outdoor reset. My cast iron baseboards only see 180 degrees supply water a few days a year, typically I run mine between 140-160 with no comfort issues.

I have copper tube with fins baseboard upstairs in my house here in New Jersey. Design temperature is 14F and I keep the upstairs at 68F. I have a mod-con with outdoor reset and for the upstairs zone, it runs at 120F supply if the outdoor temperature is 50F or higher. Supply increases to 150F if it gets to 0F outdoors (which it does almost every year, but usually for only an hour or so). The only reason the minimum supply is as high as 120F is that the boiler will not fire any less than 20% so it cycles too often with lower supply temperatures.

(Downstairs is radiant slab at grade and runs from 80F to 130F, depending on outside temperature.)

Voyager

@ChrisJ

I don’t like my bedroom 64 all the time, just when I am sleeping.

I would not try to talk anyone who likes steam out of steam or who likes radiant floors out of that either. I just overall like FA better now that I have experienced a professionally designed and installed system.

ChrisJ

> @Voyager said:
> @ChrisJ
>
> I don’t like my bedroom 64 all the time, just when I am sleeping.
>
> I would not try to talk anyone who likes steam out of steam or who likes radiant floors out of that either. I just overall like FA better now that I have experienced a professionally designed and installed system.

So, you do have pipes to freeze?

george_42

I built a 3000 sq ft home in central pa 2 years ago and installed 3 ton geothermal water to air. Our electric rate is about 11cents per kw and for two years my heating or cooling has cost about $100 per month. I have an amp meter on just the geo unit so that I can see what my usage is for just that unit.

Voyager

ChrisJ said:

> @Voyager said:

> @ChrisJ

>

> I don’t like my bedroom 64 all the time, just when I am sleeping.

>

> I would not try to talk anyone who likes steam out of steam or who likes radiant floors out of that either. I just overall like FA better now that I have experienced a professionally designed and installed system.



So, you do have pipes to freeze?

Of course. With a log home, however, most pipes for domestic water are in interior walls and thus the house would have to cool a lot to freeze, and it is very easy to drain the pipes if the home needs to be winterized or the furnace fails. Winterizing a boiler is a much bigger issue than is shutting off the well pump, opening faucets and draining the water heater which is the low point in my system. And refilling is a snap. No need to purge zones and such, just turn the pump back on and go close the faucets once the air is out.

When our boiler failed at our church building, the heating pipes froze and one split long before there was any problem with the domestic water pipes as the heating pipes were at the perimeter of the crawl space and froze first.

SuperTech

I'm not an expert but I think release and containment are what makes radiant superior by design. You are de.> @Jean-David Beyer said:
> Regardless of emitter type 180 degree supply water should only be used for fin tube on the coldest days. Every hydronic system should be using outdoor reset. My cast iron baseboards only see 180 degrees supply water a few days a year, typically I run mine between 140-160 with no comfort issues.
>
>
>
> I have copper tube with fins baseboard upstairs in my house here in New Jersey. Design temperature is 14F and I keep the upstairs at 68F. I have a mod-con with outdoor reset and for the upstairs zone, it runs at 120F supply if the outdoor temperature is 50F or higher. Supply increases to 150F if it gets to 0F outdoors (which it does almost every year, but usually for only an hour or so). The only reason the minimum supply is as high as 120F is that the boiler will not fire any less than 20% so it cycles too often with lower supply temperatures.
>
> (Downstairs is radiant slab at grade and runs from 80F to 130F, depending on outside temperature.)

I wasn't implying that fin tube should always be run at 180 degrees, just that the typical 180 degree high limit that the original poster was basing his efficiency tests on should only apply to fin tube emitters at design outdoor temperatures. Typically cast iron emitters do just fine with 160 degree supply water.

@Jean-David Beyer sounds like you have a pretty nice boiler setup