efficiency of hydronic vs forced air?

Voyager

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 😒 

Minisplits are certainly convenient for adding AC after the fact. Our church has four of them and they work pretty well, but they are very drafty compared to the ducted AC in my home (the ladies complain all summer about that) and they are ugly as sin both inside and outside. My three compressors are on the back side of my house clustered on one concrete slab where they aren’t visible and the noise is not very noticeable. The church has compressors on two of the four sides of the building and you can see them and hear them from almost anywhere outside the church. And when a condensate drain line gets plugged, they run water down the inside of the walls leaving ugly stains. This has happened to two of the four units. And they are a pain to clean and maintain as they are located near the top of our 14’ ceiling.

When my condensate drain got plugged, I had a damp basement floor with no damage to finished walls or ceilings. I would never put a minisplit in new construction.

Jamie Hall

There are plans afoot (don't have a heart attack, folks) to supplement (NOT replace!) Cedric with two heat pump systems. One will be mini-splits, and the purpose is two fold: some supplemental heat in an apartment which is occupied by an elder person, and air conditioning in the same apartment. They will be mini-splits, as the necessary cabling and pipe runs can be placed on the exterior of the building in question with relatively little interference -- and duct work is not possible. The other will be a central, ducted system for much the same purposes in another portion of the structure which originally had a gravity hot air furnace (not in use since 1960), and for which it appears that some of the needed ductwork is still quite usable, limiting new ductwork to where it can, in fact, reasonably be installed. Neither one will be intended to carry the full heating load, especially down near design temperatures -- Cedric does that very nicely, thank you, and in any event there are parts of this structure which don't lend themselves to mini-split heads and in which ductwork is not an option.

BennyV

For a gas or pellet-fired system, a properly installed hydronic system will be more efficient than a properly installed scorched air system, due to not needing to turn it up as much, as well as not having duct loss, and the hydronic system will be more comfortable. Gas-fired scorched air will be the least comfortable, hydro air marginally better, SDHV hydro air a little bit less bad, baseboard convectors better than that, high-mass radiators better yet, and in-floor radiant the ultimate where the floor surfaces are right for it.

The problem is, this is only a tiny part of the equation. If you're firing with gas or wood pellets, and have no A/C in the building, then hydronics wins. But that's not reality in most cases. For most applications, if you've got combined heat/cool ducting, or want to put A/C in with mini splits, then a heat pump will be far more efficient, and air-to-water heat pumps just aren't as efficient as air-to-air, even when the air-to-air needs to be turned up a bit higher (but probably won't, as the inverter will just drive it constantly all day long). The same is true for water-to-water not being as efficient as water-to-air heat pumps.

From a cost perspective, mini splits are just unbeatable, especially when ducting doesn't already exist, or isn't set up properly for A/C. They're also about the least obtrusive way you can put heating and cooling in a building, other than maybe SDHV or in-floor radiant or something like that which costs several times more. They're basically silent, and just do their thing, usually running at a small fraction of their capacity. For new construction, they can handle the entire heating and cooling load, as design loads can be brought down in the low-single digit BTU/sq.ft. range. For additions and remodels they are great as well, as you don't have to dedicate space to ductwork and air handlers, everything just uses dead space hanging on the interior and exterior of the walls.

In a large majority of US houses that already have ductwork that can be sealed up and balanced so that it will work properly, then a ducted heat pump probably makes the most sense, even though they aren't like to be as efficient, even when they have higher efficiency ratings then mini-splits, due to ducting, zoning, and usage losses that mini splits avoid entirely.

TAG

Modern modulating forced air heating equipment is very comfortable. Have been using the Carrier Infinity system for about 20 years in my projects. The variable speed rotary compressors that came out in 2014 really bumped up the AC comfort -- obviously they come in heat pump versions as well. I always zone my projects and the Infinity system is one of the best.

My new project has floor radiant throughout .... being in the Mid Atlantic it needs AC as well. Getting a properly designed duct system takes a contractor willing to put some time into the design. Mine has the zoned Infinity VS heat-pump .... I don't have natural gas but do have propane. I also installed the matching Infinity propane modulating furnace. This project is a converted church and getting duct work to some locations was impossible -- so I also did three mini-splits to provide AC to those odd areas (heat as well when the radiant would be off). As you may imagine this was a very expensive system -- more than the vast majority of people would be willing to spend.

With a tight house (especially foam) -- radiant floor heat is IMO going to have a harder and harder time being used in my area. The benefits for most people are just not there and the cost very high. Some of the super insulated houses have such a low heat load it seems impossible to use floor radiant. May partial floor? Also -- I could have done hydro air off of my boiler to provide heat to my ducted system vs putting in the furnace. I did not for two reasons: 1. The cost of the furnace was not much more than running the pipes and other items needed to get that hot water to the existing air handler location 2. Controls -- how do you control the hydroair system? Answer -- you don't ..... it's a dumb on off system vs having a fully integrated modulating system controlled through the Infinity thermostat.

As far as mini-splits ..... they are great problem solvers. For most people in the USA having a properly designed duct system is still going to be the norm for most. I wish there had the modulating ones 20 years ago when I did my small modern house on a river in PA. It was radiant heated and doing the duct work for the AC was a pain and I know that mini-splits would have been the answer today. I have used them now in the last three rehab projects ... done correctly they are great and if you give some thought to the placement ... they disappear. No one ever mentions them.

I would never rip out an old hot water system ..... especially since all are going to be in an older house with less of a tight building envelope. That where hot water shines .... I have added hot water to an old house just for this reason .... nothing is going to give you the same comfort in a less than perfect house.

Another problem with hot water or radiant -- speed. In my area of the mid-atlantic/ lower new england the shoulder seasons are large and it's often nice to interject heat early in the morning .... or maybe a bit in the evening. Radiant fails here and it's why I did the heat in the ductwork. Turning on the radiant is not going to be comfortable when the sun comes up or efficient .... most often the heat-pump will be used with great results. No different when I was in Boston and we were cold in the morning and the big old cast system took 1/2 hour to get up to temp and then was heating for too long.

Voyager

TAG said:

Modern modulating forced air heating equipment is very comfortable. Have been using the Carrier Infinity system for about 20 years in my projects. The variable speed rotary compressors that came out in 2014 really bumped up the AC comfort -- obviously they come in heat pump versions as well. I always zone my projects and the Infinity system is one of the best.

I agree. However, this is a forum heavily biased towards hydronics so it isn’t surprising that knowledge of FA systems seems to be 40 years out of date. The clearest of giveaways is when someone uses “scorched air” rather than forced air. That shows not only their bias, but their level of ignorance.

There is no one best system and each has its advantages and disadvantages. I am quite happy with the FA system in my house and I like being able to do rapid setbacks for sleeping at night and waking up in the morning. And I like not having to mess with water quality, worry about leaks or freezing if I am away on a trip and the heating source fails.

I am also quite happy with the slab hydronic in my workshop. A concrete floor building is far more comfortable when the heat comes from the slab and not the air. And with the slab, I probably have 3 days or so of time should the boiler fail before the water in the pex freezes and cracks my slab. However, I am often away from home in the winter for weeks at a time so if I can’t get someone to either fix my boiler or blow the water out of my pex tubing in the slab, I could be in for a very expensive repair should the boiler fail midwinter.

It is entertaining though to read all of the uninformed comments about forced air here. 😁

ChrisJ

I feel my comments were accurate.

Jamie Hall

I response to @Voyager , I feel that your comments do the professionals among us a serious disservice; I'd almost say insulting. First, most of not all of them have as their primary objective a desire to give the customer the best system they can at a reasonable price. Most if not all of them have specific technoligies with which they are very familiar, and others with which they are less so. Most if not all of them will be quite willing to suggest various technologies to the customer -- and sometimes even suggest other companies -- if they feel it is in the customer's best interest.

I will grant that there are a few of us who are one note Johnnies. That is unfortunate, as there is no one technology -- in heating or any other engineering or construction discipline -- which is always the best.

Voyager

Jamie Hall said:

I response to @Voyager , I feel that your comments do the professionals among us a serious disservice; I'd almost say insulting. First, most of not all of them have as their primary objective a desire to give the customer the best system they can at a reasonable price. Most if not all of them have specific technoligies with which they are very familiar, and others with which they are less so. Most if not all of them will be quite willing to suggest various technologies to the customer -- and sometimes even suggest other companies -- if they feel it is in the customer's best interest.

I will grant that there are a few of us who are one note Johnnies. That is unfortunate, as there is no one technology -- in heating or any other engineering or construction discipline -- which is always the best.

My comments should not have insulted any professionals. Professionals don’t use pejorative terms like “scorched air” which is completely inaccurate in addition. So, no professional should have been at all bothered by my comments. Now, those less than professional may be bothered…

ChrisJ

Voyager said:

Jamie Hall said:

I response to @Voyager , I feel that your comments do the professionals among us a serious disservice; I'd almost say insulting. First, most of not all of them have as their primary objective a desire to give the customer the best system they can at a reasonable price. Most if not all of them have specific technoligies with which they are very familiar, and others with which they are less so. Most if not all of them will be quite willing to suggest various technologies to the customer -- and sometimes even suggest other companies -- if they feel it is in the customer's best interest.

I will grant that there are a few of us who are one note Johnnies. That is unfortunate, as there is no one technology -- in heating or any other engineering or construction discipline -- which is always the best.

My comments should not have insulted any professionals. Professionals don’t use pejorative terms like “scorched air” which is completely inaccurate in addition. So, no professional should have been at all bothered by my comments. Now, those less than professional may be bothered…

There's plenty of professionals that use terms like that and it doesn't make them any less professional especially when they're on a public forum helping others for free in their own time.

pecmsg

Voyager said:

TAG said:

Modern modulating forced air heating equipment is very comfortable. Have been using the Carrier Infinity system for about 20 years in my projects. The variable speed rotary compressors that came out in 2014 really bumped up the AC comfort -- obviously they come in heat pump versions as well. I always zone my projects and the Infinity system is one of the best.

I agree. However, this is a forum heavily biased towards hydronics so it isn’t surprising that knowledge of FA systems seems to be 40 years out of date. The clearest of giveaways is when someone uses “scorched air” rather than forced air. That shows not only their bias, but their level of ignorance.

There is no one best system and each has its advantages and disadvantages. I am quite happy with the FA system in my house and I like being able to do rapid setbacks for sleeping at night and waking up in the morning. And I like not having to mess with water quality, worry about leaks or freezing if I am away on a trip and the heating source fails.

I am also quite happy with the slab hydronic in my workshop. A concrete floor building is far more comfortable when the heat comes from the slab and not the air. And with the slab, I probably have 3 days or so of time should the boiler fail before the water in the pex freezes and cracks my slab. However, I am often away from home in the winter for weeks at a time so if I can’t get someone to either fix my boiler or blow the water out of my pex tubing in the slab, I could be in for a very expensive repair should the boiler fail midwinter.

It is entertaining though to read all of the uninformed comments about forced air here. 😁

Try keeping the responses to the question............Whats more efficient!

And I prefer Cast Iron Hot Water

BennyV

Old-school bang-bang gas furnaces are properly described as "scorched air". Modern inverter-driven variable speed heat pumps with or without a variable speed 97%+ gas furnace as backup/hybrid are something rather different, and don't deserve the "scorched air" label.

ChrisJ

BennyV said:

Old-school bang-bang gas furnaces are properly described as "scorched air". Modern inverter-driven variable speed heat pumps with or without a variable speed 97%+ gas furnace as backup/hybrid are something rather different, and don't deserve the "scorched air" label.

The Steam Whisperer

If you want to dig into this topic, extensive studies were done by the DOE in the 1990's and despite forced air being the most powerful political force in the HVAC industry, multiple DOE studies found huge inefficiencies in typical forced air systems. In addition, the Gas Technology Institute ( the research arm for the Natural Gas industry in the US) believe that there are significant problems with the efficinecy ratings currently applied to forced air equipment that inflate the efficiency of furnaces versus boilers. Remember these are systems, so how they interact with the building and occupants ultimately effects thier efficiency. This is why the saying "a Btu is a Btu" is false when looking at systems. I.E. from one of the DOE studies, When typical ductwork is installed in a building, the building air leakage increases about 10% when not in use. When the ductwork is put into use with a blower, air leakage of the structure doubles. Using systems that don't increase the air leakage of a structure are clearly more efficient systems at delivering and holding btu's that the building needs to maintain occupant comfort. That's why btu's delivered by some types of systems are much more efficiently used than others.

Voyager

The Steam Whisperer said:

If you want to dig into this topic, extensive studies were done by the DOE in the 1990's and despite forced air being the most powerful political force in the HVAC industry, multiple DOE studies found huge inefficiencies in typical forced air systems. In addition, the Gas Technology Institute ( the research arm for the Natural Gas industry in the US) believe that there are significant problems with the efficinecy ratings currently applied to forced air equipment that inflate the efficiency of furnaces versus boilers. Remember these are systems, so how they interact with the building and occupants ultimately effects thier efficiency. This is why the saying "a Btu is a Btu" is false when looking at systems. I.E. from one of the DOE studies, When typical ductwork is installed in a building, the building air leakage increases about 10% when not in use. When the ductwork is put into use with a blower, air leakage of the structure doubles. Using systems that don't increase the air leakage of a structure are clearly more efficient systems at delivering and holding btu's that the building needs to maintain occupant comfort. That's why btu's delivered by some types of systems are much more efficiently used than others.

Do you have references to these studies? I remember reading a report done, if memory serves, by a university where they built two identical houses and heated them different ways to make a head to head comparison. I have searched and searched and can’t find it now. My recollection is that HWBB and FA were nearly identical when FA used a setback at night which most do. In slab hydronic was slightly better, mainly due to its superior vertical temp gradient, but the difference wasn’t as much as one might expect.

I’d love to find this report again, but it has eluded me thus far.

hot_rod

The vast majority of owners say their HVAC systems are uncomfortable. The main reason has to do with how heat transfers to and from a body.

Remember the Holohan parable about cold 70? Walk in the frozen food isle of the store, while it reads 70F air temperature, you feel cold due to heat being pulled away by the cold surfaces, glass, stainless, etc.

Well the opposite is also true. A 65F room with warm, body temperature, radiant surfaces feels warm/ comfortable.

Match the bodies heat loss and you have a comfort system.

What FA brings is filtration, humidity or de humidify, air movement for order removal, etc.

While efficiency is not to be ignored, what people really want, and would pay dearly for, is comfort.

Thanks to Robert Bean healthyheating.com for the graphic

BennyV

Voyager said:

Do you have references to these studies? I remember reading a report done, if memory serves, by a university where they built two identical houses and heated them different ways to make a head to head comparison. I have searched and searched and can’t find it now. My recollection is that HWBB and FA were nearly identical when FA used a setback at night which most do. In slab hydronic was slightly better, mainly due to its superior vertical temp gradient, but the difference wasn’t as much as one might expect.

I’d love to find this report again, but it has eluded me thus far.

Both could easily be correct. The study showing FHA is less efficient is probably studying a *typical* FHA system with a lot of duct leakage, whereas the one showing that a BTU is a BTU (although comfort still isn't exactly the same) was probably an ideal hydronic system and an ideal FHA system with properly designed sealed air ducts with < 3% leakage or even lower. That's one claim of the SDHV systems is that they get < 1% leakage and near ideal air mixing/aspiration.

The Steam Whisperer

I believe the studies looked at a typical 1990's ductwork installation... pretty much like most today. Sealing ductwork is a huge upgrade and would bring the overall system efficiencies and comfort levels probably much closer. The studies were DOE... probably Oak Ridge National Lab. I've' looked to find them again on occasion and they seem to have been disappeared.

However, there are still the problems of smoke spread, flame spread, and dirty ductwork that just are inherent in the system. I just spoke to another person that nearly died in a multi-unit building were the smoke from another apartment fire poured into thier unit through the ductwork. Obviously, firecodes where not followed ( there's no way smoke should have been able to enter the ductwork from another uint), but I've seen the same problem in detached single family homes.

There's a reason why none of the developed world uses forced air outside the US (except for a bit in Austrail, IIRC) for heating or A/C anymore.

Voyager

I think the reason is more historical than fire safety related. There is no reason that ducts provide a dwelling to dwelling fire hazard. That is just poor design.

I think the difference is related to the US leading the world in air condition adoption. Since ductwork is generally needed for both (prior to minisplits anyway), FA made a lot more sense than hot water as the ductwork was already needed for the AC. I suspect FA would not have become as popular had AC not taken off so quickly or had it not used centralized compressor/evaporator configurations.

ChrisJ

I'm just laying here in the livingroom looking at a 1 1/4" pipe that carries 14,400 btu/h via steam and wondering how much bigger that would be for forced Air

TAG

The Steam Whisperer said:

I believe the studies looked at a typical 1990's ductwork installation... pretty much like most today. Sealing ductwork is a huge upgrade and would bring the overall system efficiencies and comfort levels probably much closer. The studies were DOE... probably Oak Ridge National Lab. I've' looked to find them again on occasion and they seem to have been disappeared.

However, there are still the problems of smoke spread, flame spread, and dirty ductwork that just are inherent in the system. I just spoke to another person that nearly died in a multi-unit building were the smoke from another apartment fire poured into thier unit through the ductwork. Obviously, firecodes where not followed ( there's no way smoke should have been able to enter the ductwork from another uint), but I've seen the same problem in detached single family homes.

There's a reason why none of the developed world uses forced air outside the US (except for a bit in Austrail, IIRC) for heating or A/C anymore.

Having lived all over the world -- it's mostly economic. We had widespread AC decades earlier than the rest of the world .. that was ductwork. It was natural for heat to be with it.

We also built with wood in north America .. not the case in the first world 40+ years ago. Masonry based construction was cold and hot water was the only way to heat them. Japan used wood in housing -- but the construction was so different as was most of Asia. We lived outside Osaka for almost two years when I was 10 in 1970 ... we had an early mini-split for AC. It was so rare ... people would come over to see it.

When I lived in Germany -- everything is masonry and many of the buildings old. Hot water is the only way to heat them ... It's still true that electric rates in the world are very high. Minisplits rule

Voyager

CFM = BTU per Hour / (1.085 X DELTA T)
CFM = 14,400 / (1.085 x 40)
= 332

A = Q / V
= 332 CFM / 1500 FPM
= 0.22 ft^2
= 32 in^2

So, a 5.66” square duct would do or a 6.38” circular duct, which means a 6” square duct or a 7” circular duct, if my calculations are correct. 😁

ChrisJ

Voyager said:

CFM = BTU per Hour / (1.085 X DELTA T) CFM = 14,400 / (1.085 x 40) = 332 A = Q / V = 332 CFM / 1500 FPM = 0.22 ft^2 = 32 in^2 So, a 5.66” square duct would do or a 6.38” circular duct, which means a 6” square duct or a 7” circular duct, if my calculations are correct. 😁

300 cfm is a 10" duct according to my info.

Voyager

ChrisJ said:

Voyager said:

CFM = BTU per Hour / (1.085 X DELTA T)
CFM = 14,400 / (1.085 x 40)
= 332

A = Q / V
= 332 CFM / 1500 FPM
= 0.22 ft^2
= 32 in^2

So, a 5.66” square duct would do or a 6.38” circular duct, which means a 6” square duct or a 7” circular duct, if my calculations are correct. 😁

300 cfm is a 10" duct according to my info.




It depends on the velocity you are willing to accept. For transport purposes, I used 1500 FPM as shown in the calculations. If this is for distribution out a register, you would want much slower speed and would need a larger duct, but in a residential application you would never try to push 14,400 BTUH through a single register. It also depends on the length of the duct, the pressure capability of the fan, etc. There is no one answer.

ChrisJ

Voyager said:

Voyager said:

CFM = BTU per Hour / (1.085 X DELTA T) CFM = 14,400 / (1.085 x 40) = 332 A = Q / V = 332 CFM / 1500 FPM = 0.22 ft^2 = 32 in^2 So, a 5.66” square duct would do or a 6.38” circular duct, which means a 6” square duct or a 7” circular duct, if my calculations are correct. 😁

300 cfm is a 10" duct according to my info.

It depends on the velocity you are willing to accept. For transport purposes, I used 1500 FPM as shown in the calculations. If this is for distribution out a register, you would want much slower speed and would need a larger duct, but in a residential application you would never try to push 14,400 BTUH through a single register. It also depends on the length of the duct, the pressure capability of the fan, etc. There is no one answer.

For a residential installation there's most certainly an answer and it's not 1500 rpm.  Ever.


Off the top of my head and it's been a few years you want less than 800 fpm in the duct work and you want 300 fpm from the register or diffuser but I can't guarantee those numbers.  But I bet I'm close.

You also need to keep your static pressure reasonable.

You could do a single 10" into a 10x10 or 12x12 diffuser.

Or three 7" ducts.

Yes there are many options but you need to be at least in the ball park and a single 7" wasn't it.

ChrisJ

Remember @Voyager by far the biggest issue with most forced air systems is grossly undersized ductwork.

pecmsg

ChrisJ said:

Remember @Voyager by far the biggest issue with most forced air systems is grossly undersized ductwork.

The Biggest issue is Oversized equipment on Undersized ducts!

The Steam Whisperer

Voyager said:

I think the reason is more historical than fire safety related. There is no reason that ducts provide a dwelling to dwelling fire hazard. That is just poor design.

I think the difference is related to the US leading the world in air condition adoption. Since ductwork is generally needed for both (prior to minisplits anyway), FA made a lot more sense than hot water as the ductwork was already needed for the AC. I suspect FA would not have become as popular had AC not taken off so quickly or had it not used centralized compressor/evaporator configurations.

Ducts provide a single dwelling smoke/ fire hazard. Seen it.... A/C ductwork sizing and vent placement for optimum operation is completely different than for heating..... it's just been a cheap way to "give something" ( "its a bargain") more while ignoring the ultimate goal....comfort at lowest cost.
There also has to be some reason why in new construction even the Europeans are not using forced air.

ChrisJ

The Steam Whisperer said:

Voyager said:

I think the reason is more historical than fire safety related. There is no reason that ducts provide a dwelling to dwelling fire hazard. That is just poor design.

I think the difference is related to the US leading the world in air condition adoption. Since ductwork is generally needed for both (prior to minisplits anyway), FA made a lot more sense than hot water as the ductwork was already needed for the AC. I suspect FA would not have become as popular had AC not taken off so quickly or had it not used centralized compressor/evaporator configurations.

Ducts provide a single dwelling smoke/ fire hazard. Seen it.... A/C ductwork sizing and vent placement for optimum operation is completely different than for heating..... it's just been a cheap way to "give something" ( "its a bargain") more while ignoring the ultimate goal....comfort at lowest cost.
There also has to be some reason why in new construction even the Europeans are not using forced air.

The house I grew up in was forced hot air since it was built in 1958.
My grandfather's house built in the early 60s, also forced hot air.

Neither had air conditioning.

Most older houses I've been in had forced hot air without air conditioning.

Forced air was taking over here long before central air became popular.

pecmsg

Old Thermo Pride belt drive were comfortable when sized right. 

Solid_Fuel_Man

ChrisJ said:

I'm just laying here in the livingroom looking at a 1 1/4" pipe that carries 14,400 btu/h via steam and wondering how much bigger that would be for forced Air

My man cave....er.....boiler room. I look at a pair of 3/4" copper pipes which heat my entire house, all 3200 square feet of it when it's -40F outside. 

High temp injection loop to low temp slab. 

RichinTenn

psb75 said:

I really like converting houses from old forced air systems to hydronic heat--pulling out all the old duct work and showing the owners all of the recovered space and having them see all of the dirt and pet hair inside the ducts. I then use the duct pathways to run the pex lines for the panel radiators. They can't quite believe the lack of noise when the system is operating. Of course they also enjoy the superior comfort and control of the heat delivery--cooler bedrooms, warmer common areas and bathrooms.

The only thing I have not seen in these comments is ... What does one do for cooling? When a house is in a temperate zone with cold winters and hot and humid summers? I like the idea of Hydronic heated floors but in order to get cooling I will need an AC unit and I despise the look of some Hotel looking Boxy thing hanging on the wall (ah yeah... those things called "Mini Splits")

So yes... I will need a Forced Air System with duct-work and Hydronic Heated Floors, so I am going to want to have both!

ChrisJ

RichinTenn said:

I really like converting houses from old forced air systems to hydronic heat--pulling out all the old duct work and showing the owners all of the recovered space and having them see all of the dirt and pet hair inside the ducts. I then use the duct pathways to run the pex lines for the panel radiators. They can't quite believe the lack of noise when the system is operating. Of course they also enjoy the superior comfort and control of the heat delivery--cooler bedrooms, warmer common areas and bathrooms.

The only thing I have not seen in these comments is ... What does one do for cooling? When a house is in a temperate zone with cold winters and hot and humid summers? I like the idea of Hydronic heated floors but in order to get cooling I will need an AC unit and I despise the look of some Hotel looking Boxy thing hanging on the wall (ah yeah... those things called "Splits") So yes... I will need a Forced Air System with duct-work and Hydronic Heated Floors, so I am going to want to have both!

A split is what's used with ductwork.
A minisplit often hangs on the wall but can be ducted, or hidden above the ceiling or in a wall.

There's options but they cost more and often have more issues

Roger

Many points and perspectives here. Regarding the OP, my prior post summarized many Department of Energy Lab studies that indicate distribution losses in ductwork are very substantial, and hydronic distribution losses are about 5%. One study had homes specifically built with all ductwork inside the conditioned space at the direction of the Department of Energy. My recollection is that the average duct losses were 16%, and ranged from 9% to near 30%. All had "regain" as the ductwork is in the conditioned space (which means that the heating/cooling did not go where intended but remained in the conditioned space).
Not common residentially, radiant cooling in the Infosys building in India was built with two halves mirror imaged. Half radiant, with a dedicated outdoor air (DOAS) system, compared to the other half with a state of the art air source variable air volume (VAV) system.
The radiant half saved 34% energy with improved comfort (based on surveys of occupant satisfaction).
Here is the ASHRAE article for reference.
Best,
Roger

Jamie Hall

At the risk of chucking a wrench into the works -- a few considerations, without thought about heat source or heat transfer mechanism.

First, we all need to be very careful in separating considerations of efficiency from considerations of comfort. Not that the two can be easily separated sometimes; depending on the actual heat transfer to the target person or thing space temperatures can be quite different and accomplish the purpose. In fact, taking that aspect of the problem into consideration, it may be that two different heat transfer mechanisms may have widely different BTUh requirements -- but this is not an efficiency question, except in the broadest possible terms.

As an example, consider an outdoor dining area with the ambient air temperature at, let's say, 35 F. It could be heated by individual overhead radiant heaters at each table. It could be heated by having the deck nice and warm. It could be heated by blowing hot air into the area. Any of these three will keep the patrons warm enough to drink their beer -- but the power requirements (BTUh) will be very different. This is not an efficiency question, but a comfort one.

In another area, we must be rather careful to be sure that when we discuss actual efficiency -- that is power in vs. usable heat (or cooling) out -- we consider whether we are talking about a specific piece of equipment -- a boiler or furnace, perhaps -- or the transfer system -- the piping or ductwork and any blowers or pumps -- or the system as a whole, and also careful to remember that any energy used within the heated or cooled space is only a loss if it is somewhere not needed -- or in the case of cooling, if it works against the objective of the system.

This can get complicated, but it's worth being careful with our words and our thinking.

Paul Pollets

This argument has been on the table for over 25 years. It was proposed that two identical houses be built side by side and one would have radiant installed, and the other with forced air. Each house would be loaded with sensors and occupied with the same size and age of family. DHW production and cost would also be tracked. This was never accomplished, despite major manufacturers being part of the discussion. Here we are 25 years later.

Voyager

Paul Pollets said:

This argument has been on the table for over 25 years. It was proposed that two identical houses be built side by side and one would have radiant installed, and the other with forced air. Each house would be loaded with sensors and occupied with the same size and age of family. DHW production and cost would also be tracked. This was never accomplished, despite major manufacturers being part of the discussion. Here we are 25 years later.

It has been done many times, but the data seems very hard to obtain. Not sure why.

https://www.pruefstellen.ibp.fraunhofer.de/en/energyefficiencyandindoorclimate/twin-houses.html

hot_rod

it would be all but impossible to have each occupied and used exactly the same, cooking, laundry, doors opening and closing ,etc. So how accurate would the results be?

It kind of a dumb argument, the efficiency one. Pick the system that suits you best. Comfort will always win over efficiency if they are at all close to the same operating cost. I'd say properly designed and installed there would be a small % difference.

Jamie Hall

Completely agree with @hot_rod above. We have developed an obsession with numbers -- particularly efficiency in the HVAC trade, but in other areas as well. And there are too many variables for such numbers to have any practical meaning at all. Seems to me we need to pay much more attention to what works well, and select the best system we can for the budget we have available and the comfort of the customer. Which means, among other things, for the trades, becoming adequately familiar with the advantages and disadvantages of as many different approaches to the fundamental problem as possible -- and being willing to say when we think a system we don't particularly do ourselves will do the best job, and even sometimes recommend that the customer talk to Joe Smith over in Bugscuffle who does a really good job on whatever.

Paul Pollets

It kind of a dumb argument, the efficiency one. Pick the system that suits you best. Comfort will always win over efficiency if they are at all close to the same operating cost. I'd say properly designed and installed there would be a small % difference.

I agree with HR except that radiant systems have a higher cost than forced air when designed and installed properly. The cost seems to be the focus rather than efficiency. That cooling is not easily done with radiant is a larger part of the argument.

ChrisJ

SO basically.

Is forced air as efficient than radiant? NO
Is forced air as comfortable as radiant? NO
Is forced air cheaper than radiant? YES
Is forced air cheaper to maintain than radiant? YES

If homeowners need to choose between a quality HVAC system or granite counter tops which one will win? Granite, every time.