efficiency of hydronic vs forced air?

mattmia2

This made me think about how e do heat loss calculation some more. It is designed to find the worst case to make sure the equipment is big enough. If you just change the delta t for your average or mild or warmest day you will need heating the ACH will still be too high because it is designed for worst case there too.

mattmia2

GroundUp said:

mattmia2 said:

@GroundUp I disagree because different delivery methods change the heat loss of the structure. In an ideal world forced air wouldn't change the heat loss of the structure but in virtually all installations it both uses panned cavities for air returns that ultimately have leaks in to unconditioned spaces and causes pressure differentials between rooms that increase infiltration and exfiltration.

Heat loss calculations may not be able to account for it and it may be less than the effects of wind on the worst day but on a calm day it is making things worse.

Perhaps you did not read what I typed. "IF" every square inch of area is the exact same temperature, the heat loss is the exact same. Forced air vs radiant, the temps are only the same at thermostat height- if even that.

I have played with this in my outbuildings. Both about 1600 sq ft, both with radiant floors, and both with forced air coming from floor level. One has 10ft sidewalls and the other has 14ft sidewalls. The shorter one will use approximately 10% less fuel to keep at a given ambient temp with the radiant versus the forced air. The taller one, close to 20%. The reason for this is because in order to maintain 60 degrees at 5ft high, the average temp in the space is considerably higher using forced air because the hot air rises to the ceiling and stays there to leak out through the lid, ceiling fans or not. Do you often see ducted returns at the ceiling instead of the floor? Me neither. Of course the argument can also be made that the same comfort level is achieved with a 3-5 degree lower thermostat setpoint using the radiant, so again fuel usage is further reduced.

I agree with that, that radiant achieves better stagnation in a beneficial way. I also agree that heating that space with forced air vs some sort of convector would use similar energy if it is all one open space and uses duct work separate the space or sealed combustion unit heaters. Where I think there is a difference is in a house heated with forced air where there are partitions and relatively tight doors between partitions and the blower increases pressure in some rooms and decreases pressure in others increasing infiltration and exfiltration in different areas at the same time. In my house where central heat was added in the 50's the supply duct work is graduated and beautiful with rectangular ducts and bends all the way to the register boxes (although leaky at all of the cleat type joints) but the return is just panned joist bays with the returns basically panning out to the foundation and the bottom plate and subfloor cut away and all sorts of leakage at the foundation/rim joist/sill/wall junction for the blower to pull in outside air directly.

Solid_Fuel_Man

Total distribution wattage heating my personal 3200 square foot home/shop is 67 watts. Two Grundfos Alphas. One running at 43 watts, boiler pump moving 14gpm. The other Alpha running the slab at 24 watts. 

Is there a blower that could move enough air to heat 3200 feet that uses 67 or less watts? 

ChrisJ

Solid_Fuel_Man said:

Total distribution wattage heating my personal 3200 square foot home/shop is 67 watts. Two Grundfos Alphas. One running at 43 watts, boiler pump moving 14gpm. The other Alpha running the slab at 24 watts. 

Is there a blower that could move enough air to heat 3200 feet that uses 67 or less watts? 

No,

But a steam system can do it with a fraction of what you're using.

ChrisJ

To @Solid_Fuel_Man s point.

It's a shame we don't have a rating system that goes by how much energy it takes to heat or cool the space rather than just efficiency.

Efficiency is great, but what about when multiple sources are being used and one of them is much more expensive than the other.

hot_rod

The other part of efficiency that gets missed is cycle efficiency. The best efficiency is at steady state running, below that the number drops. This graph from Brookhaven plots that.

Also missed is the efficiency hit when fixed speed boilers are at partial load, cycling. When compared to a modulating boiler.

When comparing operating cost of a mod con and non modulating boiler, that should be considered.

So your assumed 85% cast boiler is running down into the 70% the more it short cycles.

ChrisJ

hot_rod said:

The other part of efficiency that gets missed is cycle efficiency. The best efficiency is at steady state running, below that the number drops. This graph from Brookhaven plots that. Also missed is the efficiency hit when fixed speed boilers are at partial load, cycling. When compared to a modulating boiler. When comparing operating cost of a mod con and non modulating boiler, that should be considered. So your assumed 85% cast boiler is running down into the 70% the more it short cycles.

Mine doesn't short cycle

mattmia2

Though it costs more, the energy used by the circulator or blower mostly gets transferred to the conditioned space.

ChrisJ

mattmia2 said:

Though it costs more, the energy used by the circulator or blower mostly gets transferred to the conditioned space.

That's true.

But that heat was created using a significantly more expressive fuel.

Jamie Hall

eh? Not sure what the choice of fuel has to do with it...

ChrisJ

Jamie Hall said:

eh? Not sure what the choice of fuel has to do with it...

 I care about the cost of operating the system not the efficiency.

Seeing as that's how efficiency keeps being sold to everyone im thinking that's their goal as well.

delcrossv

hot_rod said:

The other part of efficiency that gets missed is cycle efficiency. The best efficiency is at steady state running, below that the number drops. This graph from Brookhaven plots that.

Also missed is the efficiency hit when fixed speed boilers are at partial load, cycling. When compared to a modulating boiler.

When comparing operating cost of a mod con and non modulating boiler, that should be considered.

So your assumed 85% cast boiler is running down into the 70% the more it short cycles.

I wonder how much of the low cycle gain in a Mod Con is due to the modulation as opposed to the condensing.

Solid_Fuel_Man

ChrisJ said:

No,

But a steam system can do it with a fraction of what you're using.

But what is your total system fuel to home efficiency? 

The point of this is, your steam system may be using less electricity....I'm sure it is especially if it's gas. But my ModCon is operating at 95% gas to water efficiency and using less than 100 watts total. 

But I burn wood in a boiler at 85%  Gas is expensive even if I'm getting 95% of its energy. 

Your steam system is likely putting 80-85%% of the energy in the gas into your home and using a negligible amount of electricity. 

So as @Jamie Hall said total system cost to operate to actually heat a space is what matters. That would include the cost of the fuel....oil, gas, coal, pellets, cord wood, and the cost of electricity and how much it uses. 

An oil burner uses a surprisingly large amount of electricity is also something. 

Of course a simple secondary burn wood stove would be the best in the electricity department or a gravity gas furnace with a thermocouple.....

hot_rod

Efficiency= output quantity ÷ necessary input quantity

Steady state which may be a very small % of the heating season = output of boiler ÷energy input
A fuel oil example:

65,000 btu/hr. ÷ .55 gal/ hr (140,000 btu/ gal.)= 84.4%

The challenge is getting accurate data for the calculations

ChrisJ

@Solid_Fuel_Man I understand.
But im taking what I can get. 

TAG

Have done a lot of deep old house rehabs ... you can make any house comfortable. Where hot water shines is in older drafty spaces .... a warm floor or nice radiator sending out heat all the time is more comfortable vs most forced air --- although the newest variable speed equipment is really nice. Same in odd spaces -- I have done both a city fire house and a small church conversion ... with high ceilings radiant really shines w/ high ceiling in a cold climate.

In my opinion is not really about efficiency as much as comfort ..... in a super insulated house w/ low BTU loads forced is both comfortable and efficent.

ChrisJ

TAG said:

Have done a lot of deep old house rehabs ... you can make any house comfortable. Where hot water shines is in older drafty spaces .... a warm floor or nice radiator sending out heat all the time is more comfortable vs most forced air --- although the newest variable speed equipment is really nice. Same in odd spaces -- I have done both a city fire house and a small church conversion ... with high ceilings radiant really shines w/ high ceiling in a cold climate.

In my opinion is not really about efficiency as much as comfort ..... in a super insulated house w/ low BTU loads forced is both comfortable and efficent.

What about radiant in super insulated houses with low load?
Wouldn't a small modcon also be comfortable and efficient?

motorman

cold air falls and hot air rises that in why you want your A/C and heating ducts separate, A/C in the ceiling and heat near the floor. i have hot water baseboard for heat and the A/C air handler in the attic with the outlets and returns in the rooms ceilings

SgtMaj

My home was built in 1920, as was the home across the street from me. Both designed by the same architect. Both homes had installed hydronic heat with cast iron radiators. My house still has a functioning hydronic system, the house across the street had the hydronic system ripped from its interior and had installed forced air. Having been in the house across the street in the dead of winter it's extremely chilly with the thermostat set above 70°. My house with its 47 windows on the main floor is extremely comfortable with thermostat set at 68°-69°. The original hot water boiler in my home was a gravity system, in the 1984 the old cast iron boiler was replaced with a Burkay labeled as A.O. Smith, 199,999 BTU in. My A/C unit is a Carrier, installed in 1949, in 2000 I had to replace the original condenser outside. No crazy ductwork the conditioned air dumps into the large living room and on really hot days we turn on a couple of fans to move the air around.

I guess my point is, if equipment is taken care of it can last more than two lifetimes, which in the end saves home owners the massive costs of of retro fitting new forced air systems. I suppose if someone had money to throw away it would cost north of $20k to install a modern HVAC system. If my Burkay boiler ever gives up the goose I would install a high efficiency boiler, but I doubt that will happen in my lifetime.

If it ain't broke don't fix it.

Roger

This is an interesting topic, and I did some research on distribution efficiency several years ago. As housing stock does not turn over that quickly, much of this is likely still relevant. Here are some key findings from Department of Energy Energy Efficiency and Renewable Energy (EERE) publications:

• A wide body of literature has found that distribution system conduction and air leakage can cause 30-40% energy losses before cooling and heating air reaches the conditioned space. LBL Building Technologies & Urban Systems Division
  
• Typical systems with ducts in attics or crawl spaces lose from 25% to 40% of the heating or cooling energy that passes through them. EERE Building Technologies Program
  
• Poor-quality HVAC design and installation can reduce the overall HVAC system energy efficiency up to 30%. HVAC routing is much less flexible than plumbing and electrical, and a final framing plan with ducts must be set early in the design. Keep the duct layout short, straight, and simple for best performance. EERE Building Technologies program.
  
• This study of duct work installed in conditioned space resulted in average duct efficiency of 84% to 85% (15% to 16% losses with best practices). LBNL/UT Austin: Integrating Ducts Into the Conditioned Space Successes and Challenges
  
• Residential HVAC Practices, Duct leakage is the most common source of performance degradation of HVAC systems, with most studies finding 90-100% of systems tested needing sealing or repairs to the supply or return air ducts. EERE, NIST, and others.
  
• And of course for fellow Wet Heads: For houses with hydronic space-heating systems, a distribution efficiency of 95% shall be applied to the appliance efficiency, representing a small amount of energy loss through the pipes. EERE Building Technologies Program
  
• I'll add that thermal purge further increases distribution efficiency in hydronic systems as it captures heat left in the piping, and distributes it more effectively to areas with heat emitters like fin tube baseboard and radiators.
  

And for your viewing pleasure, here is a typical house where the builder "saved space" by installing ducts and registers in outside walls. Of course there's not much room for insulation when a duct branch is in the stud bay, so more heat is lost when the system is running and when it's off. Apparently there's not much insulation on the basement walls or rim joists, either.


Best,
Roger

Camdo

Impossible to stop sound transmission thru the ductwork of a forced hot air system, but easy to do with hydronic systems. Think of kids playing video games or small apartment buildings. Sound isolation between rooms is a very important consideration. On the other hand forced hot air is so simple compared to hydronics, and never a worry about freezing.

mrlarson

While I drink my coffee, what will cool the fastest? A cup of steam, hot water, or air poured at the opportune temp to equal the normal btu per square ft. requirement. Knowing it will take longer for steam and water to heat up from the same fuel source than air with an equal fuel input. Also knowing the air temp will cool quickly, the steam will condensate almost immediately, while the water will slowly drop in temp. The equipment material and design used would be important to understand a fair comparison, so in this case for those inquisitive engineers who have three pressure canners, and time on their hands, let me know what you come up with.

JR3_Home_Performance

It's so simple, as to hydronics (steam systems excluded):

Advantages:
1)far more efficient energy distribution
2)raises mean radiant temperature in rooms
3) They are better suited for minimizing interior temperature swings, the delta T you experience when the house thermostat is set at one temperature. This is a whole topic in itself and dependendent on several factors. Newer multistage/variable forced air systems with communicating thermostats can perform as well as hydronics but it takes more tech to do it with forced air. Hydronics can decouple btu's at the boiler with btu's delivered to house via outdoor reset controls that modulate water temperature. An old boiler can be setup to perform as well as a super modern forced air system.
4) Quieter. (Albeit a well setup maybe even slightly oversized insulated flex duct system can also be so quiet most people can't hear them running)

Disadvantages:
1) No practical cooling (except for very advanced systems)
2) No air filtration ( Rising concern with real health costs)(MERV 13+ recommended to all my clients)
3) No air exchange (Co2 and VOC dilution not possible)
4) Not able to increase/decrease absolute humidity as forced air can with a humidifier or dehumidifier built into system

Because of the practical aspects of air quality I would choose a variable forced air system over hydronics in normal budget applications. If money is no object multiple systems can be in place for ultimate control and benefits

Jamie Hall

And why, good sir, did you exclude steam? It has all the advantages of hydronic, plus lower distribution losses (no pumps). The only serious disadvantage is that it's difficult to zone.

ChrisJ

Jamie Hall said:

And why, good sir, did you exclude steam? It has all the advantages of hydronic, plus lower distribution losses (no pumps). The only serious disadvantage is that it's difficult to zone.

I also disagree with those who claim forced air systems filter the air.

They never seem to filter the air in a building to any useful extent. If anything, they tend to stir up dust around a room more than anything but I've never noticed them actually reduce dust. Vacuum cleaners seem to do well at this task.

@Jamie Hall Steam's main disadvantage is no modern systems exist.
We could use some modern examples rather than 100+ year old ones. There's plenty of tricks that can be done with it that would out perform hot water.

PEvans

Yes, there are all these factors bundled in "efficiency."

One of the great things we first learned about in the early 1970s was miles per gallon. You don't have to be an automotive engineer -- everyone knows that a 10 mpg car is less efficient than a 30 mpg car. The vehicle's weight, combustion system, fuel system, driver habits, weather, etc., etc. are factors, but at some level the details don't matter. MPG is enough to inform consumer choices and identify very efficient and very inefficient outliers.

So what about buildings? Us building energy geeks have so far failed to disseminate metrics that are as accessible as MPG for everyday consumers.

In a prior life I worked on developing and exploring metrics for building efficiency like kWh/yr/sf for overall electricity use, or kBtu/sf/HDD for heating. I think in a given climate zone comparing buildings of similar size and use, measures like these can, as the sample size grows, at least help identify very efficient and very inefficient examples.

(One of the challenges at least in the west is separating the heating portion of curb nat gas use. A logging thermostat like a Nest can tell you how many hours a day a given heating system ran, which is super granular and useful; however, Nest does not make it easy at all to routinely collect that data.)

I also suspect that for a given building, it is pretty hard to move these measurements much unless you are changing everything -- the heat source, heat distribution, and building skin thermal properties, and it is all engineered as an integrated system (in the west, for residential HVAC there is no real project-specific engineering unless the owner demands it). Anyway you guys who have done many retrofits would know.

BradHotNCold

From efficiency standpoint, for hydronic heating, I (a homeowner) just discovered the ECM circulator pump. https://www.efficiencymaine.com/docs/Introduction-to-ECM-Circulator-Pumps.pdf
With this installed on a hydronic system, one uses less electricity. Is the blower on a forced air system adaptable to differing speeds?

Thermo

Can't help but put my 2 cents in. Learning some HVAC principles in 1977, the first question to the class was asked is, outdoor temp. 16F, a person sitting at a desk with a window behind them complains about being cold in a room that's 72F,the window is good quality a sealed tight, no drafts , normal humidity, persons not sick, etc, WHY?
Answer is radiant heat being removed directly from the persons warm body to the colder outdoor air. The radiant heat flows through all materials and does not need air as a conductor.
I experienced this many years later. I went to steel supplier on a cold day, and as the person was searching for my steel, he said don't stand so close to the steel it will draw the heat from your body. Although he may not have know how radiant heat works, he knew to stay away from the steel when it was cold
Years later I renovated my house removing hydronic cast iron "radiators", and installed baseboard "convectors" for a more modern look. Although the convectors could satisfy the room thermostat, the house always felt cooler than before on very cold days because you did not have the heat mass that would radiate heat to you body rather than you body radiating heat to the outdoors.
So ignoring which system cost more, heating air may satisfy a thermostat but will not help on those very cold winter nights where your body temperature is proportionately much higher than the outdoor temperatures.
Matt

Jamie Hall

Good points there, @PEvans . Your single broad metric idea is a very good one (although vehicle MPG ratings are cautionary there -- a surprising number of people actually expect their vehicle to get the numbers on the sticker -- which they may or may not get -- and then get annoyed when they don't). More to the point, the data don't have to be all that granular, although in warmer climates splitting off the energy used for cooking and hot water is needed, and, for electric systems splitting off the rest of the household loads). A simple BTU (or KWh -- both energy) per degree day per square foot is all that is needed. That is not hard to compute! I'd suggest that the energy usage should include cooling usage as well as heating.

The risk, of course, is also similar to MPG ratings: target values may get set in stone (well, regulation, amounts to the same thing), which can have perverse effects -- and consumers may expect to get certain results, and get annoy ed when they don't.

scott w.

Hydronic heat is the Cadillac of heating systems. Forced air is kinda like the lower end Chevy. It will get you where you want to go but not as comfy as that Cadillac. Was first introduced to in floor heat in my great aunt and uncle's home (two story) that had all poured concrete floors built in 1949. Should have seen all the steel that went into that home. The heating system at that time was the talk of the town. As a little kid what a great house to play on the floor as it was toasty warm. Would have loved to have seen all that black iron pipe in the floor before the concrete was poured. I remember the boiler room was kinda scary looking as it had this huge boiler with lots of big pipes with valves coming out of the boiler and going in many directions.

Had heated floors installed in my house during a renovation and it is wonderful to feel those warm floors in the bathroom (master bath has three outside walls) and kitchen (three outside walls) during an early winter morning. Can turn down the heat to 72 degrees in winter and still feel very comfortable. With another house that had forced air had to turn up the thermostat to 76 or 77 on cold winter days to be comfortable. Would be warm while the heat was blowing air but the house would start to chill until the furnace started up again.....If I was building a new house today would not scrimp on the heating system in a cold climate........ hydronic heating is a very quiet and comfy system. A luxury I would not do with out. It is more expensive to install but you will soon forget about that on cold winter days. It was a hefty expense during the renovation. Very happy now with money well spent.

Voyager

psb75 said:

In a room with forced-air heating, think of "wind chill": air moving past a person's skin makes them feel several degrees colder than the actual prevailing temperature. Now...what if things in the room (most especially the entire floor) were all nice and warm, and there was very little convective air movement--almost like the warming rays of the sun on a calm day. This condition is the opposite of "wind chill." This is a bit of an exaggeration put the basic principles hold. Radiant, hydronic/steam heat is better than heat provided by moving hot air. If done right, it is much more comfortable, quieter and more efficient.

Wind chill isn’t a factor when the moving air is warmer than skin temperature. For most people, skin temp is in the 90-92 F range and the temperature of air from a forced air system is generally at least that warm and often warmer. And a well-designed forced air system will have air velocities so low that drafts will be imperceptible. If anything, the moving air from a forced air system will heat a person up faster than if the are was not moving as the air can transfer more heat when it is moving past a cooler object.

There is a reason that wind chill tables don’t go above 50 degrees nor have wind speeds below 3 MPH generally, and that is because wind chill is negligible at temps above 50 and wind speeds below 3 MPH.

ChrisJ

Voyager said:

psb75 said:

In a room with forced-air heating, think of "wind chill": air moving past a person's skin makes them feel several degrees colder than the actual prevailing temperature. Now...what if things in the room (most especially the entire floor) were all nice and warm, and there was very little convective air movement--almost like the warming rays of the sun on a calm day. This condition is the opposite of "wind chill." This is a bit of an exaggeration put the basic principles hold. Radiant, hydronic/steam heat is better than heat provided by moving hot air. If done right, it is much more comfortable, quieter and more efficient.

Wind chill isn’t a factor when the moving air is warmer than skin temperature. For most people, skin temp is in the 90-92 F range and the temperature of air from a forced air system is generally at least that warm and often warmer. And a well-designed forced air system will have air velocities so low that drafts will be imperceptible. If anything, the moving air from a forced air system will heat a person up faster than if the are was not moving as the air can transfer more heat when it is moving past a cooler object.

There is a reason that wind chill tables don’t go above 50 degrees nor have wind speeds below 3 MPH generally, and that is because wind chill is negligee at temps above 50 and wind speeds below 3 MPH.

The issue I've always had with forced air heat was it feeling like it's warmer when the system is running.

I've never heard of the moving air cooling people.

Voyager

This is an interesting topic, but one that probably has no answer as energy efficiency isn’t the same as comfort and different people have vastly different “comfortable” environments.

I own both a forced air heated home (4,000 sq. ft. with a very well-designed forced air system) and a large workshop (32’x48’) heated hydronically with a radiant concrete slab. I also am a deacon at a church that has a hydronic baseboard system.

Of the three, the church is by far the least comfortable. Then again, it is the oldest building with the poorest insulation and the most air infiltration. My feet are always cold in that building.

My home is probably the most comfortable overall, but I do wear slippers in the winter as the floors are on the cool side, particularly the kitchen and dining room which are above a basement garage that is essentially unheated. I keep thinking about adding hydronic heat under those floors, but it is easier to wear slippers.

The workshop is the most comfortable at times when the outside air is fairly stable, but can be quite uncomfortable when the outside air is changing rapidly as the slab simply can’t respond quickly enough. For example, it was 18 degrees last night, but today warmed up rapidly to 50 degrees. My workshop thermostat is set at 65 and I just checked and it is 73 in the shop right now which is uncomfortably warm for the work I do there. My house is set at 72 and the temp is 72 as it never varies from the setpoint. The shop always lags when the temp outside drops quickly and overshoots when it warms outside quickly. And there is nothing you can do about that as the physics of a 5” concrete slab determine how fast it can be heated and cooled. My house, on the other hand, is always dead nuts on temperature, except for a couple hours at night when it is cooling to the 65 setback and 30 minutes in the morning when it is warming back to 72.

If I were to build another house, I would probably put in hydronic floor heat capable of heating the house up to about 60 degrees outside temperature and then supplement with heat pump forced air systems to actually control the inside temp to the ranges I like, which is 72 in the day and 65 at night. And I’d also have AC from the heat pumps as I have AC now on my forced air furnaces. From what I have learned over the years, that would be the most comfortable for me as I don’t sleep well in a warm room and need to be able to set back at night, and this is nearly impossible with hydronic heat alone. And I also want AC.

So, if you ask me what is most efficient or most comfortable, my answer would be a hybrid of both. Radiant floor heat for foot comfort and to help keep a more nearly ideal temperature gradient from floor to ceiling, and forced air to allow me to “trim” the temperature to accommodate rapid changes in outdoor temps and also to allow fast setbacks at night for sleeping comfort.

And I have to continue to laugh at the comments about forced air systems being drafty and drying the air. A well designed forced air system does neither. If you come to my house, you will not be able to tell when the furnace is running unless it is super quiet and you hear it fire up. And, since the main furnace is in the basement, it is pretty hard to hear. The only way I can tell it is on is to put my hand pretty close to a register as the airflow rate is very slow. My system was designed by a commercial HVAC company that knew what they were doing. I have probably twice the number of heating registers as most homes I have seen and every room has at least one air return and all rooms were balanced individually. I have two furnaces in attics as log houses are a challenge for ductwork. And I have to HRVs, one in the basement and one in the attic to control outside air exchange. This system is very efficient and very comfortable and has worked well for 21 years now.

I believe the quality of the system design and installation is a greater factor than is the type of heating system. I have stayed at places that had poorly design steam systems and poorly designed baseboard and panel rad systems. And all were very uncomfortable, generally far too warm with no way to control them. I grew up in mobile homes so I am quite familiar with poor forced air systems which are noisy and which do have drafts that will move wall hangings.

I’ve also seen well designed forced air and hydronic systems and both can be very comfortable and very energy efficient. My experience is that you are far better off worrying about the competence of your system designer and installer than you are worrying about forced air vs. hydronic.

EDIT: And I should add that my forced air systems have been far less maintenance and trouble than either of my hydronic systems. I change filters a couple of times a year and that is all. Of my three Lennox furnaces, one has had zero issues in 21 years of operation. One had a control board go bad when it was two years old and nothing since then. And the large main furnace required a new blower motor about 5 years ago. All still have their original igniters, gas valves, and pressure sensors.

Our church boiler is constant trouble and generally needs attention at least once a year.

My Triangle Tube shop boiler has been trouble free, but there is still at least annual water quality testing and the heat exchanger is supposed to be opened up and cleaned every year. I have not done that yet, but it is ending its third season so I probably will do that this summer. Looks to be at least an hours worth of work, maybe two the first time. I am not sure I have spent two hours total time changing filters on my forced air furnaces in the 21 years I’ve operated them.

Solid_Fuel_Man

Some disadvantages I see with steam @Jamie Hall

*Difficult to zone
*Open system, corrosion
*Not able to use copper or pex for distribution 
*Must rely on gravity and pipe pitch or multiple condensate pumps 
*Boiler must be the lowest point in the system, or condensate pumps again
*Difficulty in achieving fuel efficiency, no modulation or condensation w/o extreme circumstances 
*Limited emitters 
*Steam traps, venting, knuckle heading
*Limitation of alternative energy boilers
*Larger pipe diameters 
*Steam traps are hideously expensive 

OK, flame suit on. 

These would be in comparison to a radiant slab, or properly sized panel rads with a mod/con running at say 105 supply temp. 
We always talk about advantages, this is just some of the things I see. 

Jamie Hall

Some of your points I agree with, @Solid_Fuel_Man . Some are differences, not disadvantages. And some I just plain disagree with. The two biggest disadvantages for steam in the 21st century you don't mention, however -- so I will. First, and perhaps biggest, is that there seem to be precious few people who can figure out how to make it work properly. This is also true of hot water or forced air, too -- but those can be knuckleheaded with the property owner or manager not being aware of the problem, accepting the poor performance as normal (which, sadly, it is). Steam, while remarkably forgiving, will let you know if the installer has messed up. The other you do mention in a way -- so far, at least, although they are technically feasible, no one has made heat pump steam boilers. This is going to be a tremendous problem if and when retrofitting the vast stock of existing buildings begins to be addressed.

If I were building a residence from scratch today, it would be none of the above -- true passive solar would be my choice. (not some Rube Goldberg arrangement of collectors and pumps and controllers and tanks -- truly passive solar) The only problem with passive solar is that it's somewhat less forgiving of architectural and siting blunders and poor construction practices than powered systems. Also, it doesn't work all that well north of say 60 degrees latitude...

Labenaqui

There is little argument that FHA is less efficient than FHW, from energy creation through distribution ..... just open your Physics Book. What is less apparent is contemporary hydronic application methods and their effect upon theoretical efficiencies.
For our part we have revisited natural hydronic convection and moved it into contemporary heating practices. Emulating the old "gravities" of a century ago and applying delta-t distribution to a perimeter baseboard system moves hydronic heating efficiency to a new level.
Operating a high-mass boiler at lower Delta-T ECM circulator managed distribution temperatures with low head, passive piping and radiation provides virtually seamless, lowered profile natural convection heating. To date all of our patented appliance-based systems are using only 8-13 watts of distribution energy with over 40 system-years and 125,000 hours of operation.
"Low & slow" seems to be the way to go ..... hydronically speaking, at least.

TAG

Ductwork does leak ..... But, where is the ductwork? Using a house where the ducts are located in an unconditioned attic or vented crawlspace is not the same as one where it's all within the building envelope. Any leaks are still going to the building. Sealing the ductwork and wrapping with some insulation is the norm today. I remember watching one of the TV shows where they used a spray product to seal the ductwork from the inside ... then cut holes for vents in the crawl space. The practical score of that operation would depend on the cost of the spray being applied and what that really yields. My guess is it's not cheap.

My new project is all metal ductwork with the joints externally sealed and the ducts wrapped with bubble. The spray foam sealed crawl is filled with ducts as the project is zoned. I don't find the space to be showing signs of excessive leaks --- it's under the main space temp target be it winter or summer.

I'm sure there will be some loss in an exterior wall where you are forced to run a duct --- even using ridged and spray foam. There will be some loss.

I still did radiant in this house. Frankly -- with all the better building products today (windows/doors/ closed foam) in my area (mid Atlantic) I think radiant is a harder sell than jsuta few years ago. In the dead of winter it's still nicer IMO --- but, for most the cost of two systems is not worth it. Ducts for AC are a must today -- so you have heat. I'm not seeing it go into the high end stuff around me like it did years ago .... still the high end rehabs of old stone farmhouses ....not all new.

Voyager

TAG said:

Ductwork does leak ..... But, where is the ductwork? Using a house where the ducts are located in an unconditioned attic or vented crawlspace is not the same as one where it's all within the building envelope. Any leaks are still going to the building. Sealing the ductwork and wrapping with some insulation is the norm today. I remember watching one of the TV shows where they used a spray product to seal the ductwork from the inside ... then cut holes for vents in the crawl space. The practical score of that operation would depend on the cost of the spray being applied and what that really yields. My guess is it's not cheap.

My new project is all metal ductwork with the joints externally sealed and the ducts wrapped with bubble. The spray foam sealed crawl is filled with ducts as the project is zoned. I don't find the space to be showing signs of excessive leaks --- it's under the main space temp target be it winter or summer.

I'm sure there will be some loss in an exterior wall where you are forced to run a duct --- even using ridged and spray foam. There will be some loss.

I still did radiant in this house. Frankly -- with all the better building products today (windows/doors/ closed foam) in my area (mid Atlantic) I think radiant is a harder sell than jsuta few years ago. In the dead of winter it's still nicer IMO --- but, for most the cost of two systems is not worth it. Ducts for AC are a must today -- so you have heat. I'm not seeing it go into the high end stuff around me like it did years ago .... still the high end rehabs of old stone farmhouses ....not all new.

I think that a cheap and poorly done FA system is less costly than a cheap and poorly done hydronic system. And probably much less comfortable and less efficient. It is not as clear to me that a well done FA system is that much less expensive than a well done hydronic system. The FA system in my house was quite expensive as it has sell sealed fiberboard ductwork (metal isn’t really better in most cases), many registers, returns in every room, every room balanced, etc. The air flow is slow, even and quiet with no drafts and you can’t hear the system turn on unless the house is completely quiet. If the TV is on, you can’t hear the furnace and there is no air drafts to tell you it is on.

As I wrote earlier, I am convinced that the competence of the design and the quality of the installation trumps the system type every time. Most people have never experienced a well-designed and installed FA system. If you base your opinion on mobile homes and spec homes, then you really don’t know what you don’t know.

Solid_Fuel_Man

Hydronic for heating, and .......cough.....minisplits for A/C. I've installed a few ducted minisplits for customers as well. 

I've really found no cheaper A/C to operate than inverter minisplits. As much as I hate to admit that 😒 

ChrisJ

Solid_Fuel_Man said:

Hydronic for heating, and .......cough.....minisplits for A/C. I've installed a few ducted minisplits for customers as well. 

I've really found no cheaper A/C to operate than inverter minisplits. As much as I hate to admit that 😒 

My reasoning for installing duct work instead of minisplits were..


I didn't want to clean 6 evaporators in the house where its messy.  

I didn't want equipment hanging in the rooms.  The aluminum diffusers are a lot less noticeable.

I could not figure out a reasonably easy way to run all of the linesets that wouldn't look ridiculous and be easy to replace.  Most of my equipment is in the attic which is the worst place but it's the least intrusive.

Looking back on the past 5 years with it I think I'd make the same choices again.  I did a 2 stage system and I'd insist on that at a minimum.

I can't say it's the cheapest to run but it's 3 tons and costs less to run than the 2 tons of window units it replaced.   It keeps the place comfortable and the cost is reasonable for the structure.