efficiency of hydronic vs forced air?

Wellness

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

ChrisJ

Wellness said:

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

You're not really trying to heat or cool air with radiant.
You're primarily cooling objects in the room via IR.

Voyager

Wellness said:

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

Current residential hydronic systems are heat only so they are 0% efficient at cooling and air conditioning as they can’t provide outside air exchange or humidity control. An FA system can do all of those.

Radiant cooling can be done and is done commercially on a small scale, but it also requires very sophisticated humidity control systems which generally require some amount of ductwork.

Radiant isn’t as concerned about heated air rising as the primary heat transfer mechanism is radiation rather than convection.

Jamie Hall

It is quite true that if you actually need air conditioning -- which you don't in most of the US (you must carefully distinguish between what you need and what you want) the forced air systems definitely have significant advantages, particularly when they can be powered with heat pumps.

However, that has absolutely nothing to do with efficiency. That is entirely a matter of comfort in most areas of the country -- and, i would also point out that in the areas of the country where air conditioning is actually needed, heat is not.

If you want to talk efficiency, talk efficiency. If you want to talk comfort, talk comfort. Don't mix them up.

Voyager

ChrisJ said:

Wellness said:

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

You're not really trying to heat or cool air with radiant.
You're primarily cooling objects in the room via IR.

I don’t follow your logic here. At room temperature, IR wavelengths are significant heat transfer mechanisms. So, heating or cooling with IR is what is happening in general at room temperatures. Now, at different temperatures, the dominant heat transfer wavelengths change.

ChrisJ

Voyager said:

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

You're not really trying to heat or cool air with radiant. You're primarily cooling objects in the room via IR.

I don’t follow your logic here. At room temperature, IR wavelengths are significant heat transfer mechanisms. So, heating or cooling with IR is what is happening in general at room temperatures. Now, at different temperatures, the dominant heat transfer wavelengths change.

I said you don't heat or cool air with radiant.

I said IR is primarily what you're using to heat or cool objects.


I'm not sure how else to say it? 

Voyager

ChrisJ said:

Voyager said:

ChrisJ said:

Wellness said:

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

You're not really trying to heat or cool air with radiant.
You're primarily cooling objects in the room via IR.

I don’t follow your logic here. At room temperature, IR wavelengths are significant heat transfer mechanisms. So, heating or cooling with IR is what is happening in general at room temperatures. Now, at different temperatures, the dominant heat transfer wavelengths change.

I said you don't heat or cool air with radiant.

I said IR is primarily what you're using to heat or cool objects.


I'm not sure how else to say it? 

You said heat or cool with radiant and then said only cool with IR as thought radiant and IR were different mechanisms and only one applied to cooling. That was the confusion.

ChrisJ

Voyager said:

Voyager said:

The discussion here seems mostly focused on heat and as a hydronics fan, I buy into most of the advantages cited above. But what about when you factor in AC? Doesn't that tip the balance to forced air? I can't imagine radiant cooling (at least if the radiators are in the floor or CI) is more efficient that FA, given that heat rises and cooler air falls.

You're not really trying to heat or cool air with radiant. You're primarily cooling objects in the room via IR.

I don’t follow your logic here. At room temperature, IR wavelengths are significant heat transfer mechanisms. So, heating or cooling with IR is what is happening in general at room temperatures. Now, at different temperatures, the dominant heat transfer wavelengths change.

I said you don't heat or cool air with radiant.

I said IR is primarily what you're using to heat or cool objects.


I'm not sure how else to say it? 

You said heat or cool with radiant and then said only cool with IR as thought radiant and IR were different mechanisms and only one applied to cooling. That was the confusion.

I should've put heat or cool on both.

My mistake

The Steam Whisperer

IN my view, comfort is integral to the concept of efficiency. I don't care what the thermostat says, I aim for the system that provides human comfort at the least amount of energy or resources used. A space heated to 72F with little humidity is not comfortable. A space heated to 70F with proper humidity is comfortable. Systems that create more air leakage are going to use more energy, require additional energy and resources for humidification than one that keeps air leakage to a minimum and doesn't require humidification.

Voyager

I view them as being separate because they really are. You can have a comfortable system that is inefficient or that is efficient. You can have an uncomfortable system that is inefficient or that is efficient. I think comfort should be considered first, and then efficiency and cost need to be considered next as there are trade-offs there as well. There is no one size fits all. It depends on the needs of the homeowner as well as their location, budget, etc.

ChrisJ

I'm not positive but in theory the Ecosteam increases both comfort and efficiency by decreasing overshoot and temperature swing.

TAG

hot_rod said:

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

Jamie Hall said:

It is quite true that if you actually need air conditioning -- which you don't in most of the US (you must carefully distinguish between what you need and what you want) the forced air systems definitely have significant advantages, particularly when they can be powered with heat pumps.

However, that has absolutely nothing to do with efficiency. That is entirely a matter of comfort in most areas of the country -- and, i would also point out that in the areas of the country where air conditioning is actually needed, heat is not.

If you want to talk efficiency, talk efficiency. If you want to talk comfort, talk comfort. Don't mix them up.

I think you need AC in most of the country .... the way we use AC.

They don't use AC in many parts of norther Europe the same way .... Mini splits rule now

TAG

Many people here seem to be in the north east .... where hot water is still popular. People grew up with it and like it ... we pay a bit more for it.

It would be interesting to know the number of installs (hot water) over time --- of all types. Copper baseboard took over ... cast was used in nicer houses. I used some cast in one project. It was all less and less common over time .... Pex sort of brought hot water back for new installs in higher end homes.

I'm just not seeing it in as many new builds where my weekend place is. The newest ducted system are really good and seem to be the norm ... electric floors in the bathrooms.

Jamie Hall

If the ambient air temperature is below about 85 F you don't need air conditioning. Granted, you may want it. But you don't need it. A lot of people demand it and want it -- but they don't need it.

ChrisJ

Jamie Hall said:

If the ambient air temperature is below about 85 F you don't need air conditioning. Granted, you may want it. But you don't need it. A lot of people demand it and want it -- but they don't need it.

Well.
I guess technically no one needs central heating, ever. A single wood stove will heat most houses enough to make them safe in all rooms at least if the building is laid out half way decent.

At what point do you actually need some form of heat in a building?

I guess you could argue that you need to keep it above freezing for plumbing, but, do you really need indoor plumbing?

Voyager

Jamie Hall said:

If the ambient air temperature is below about 85 F you don't need air conditioning. Granted, you may want it. But you don't need it. A lot of people demand it and want it -- but they don't need it.

And it the temperature is above freezing, you don’t need heating either. Water won’t freeze so you can still drink it and food won’t freeze so you can still eat it and it isn’t hard to dress for 35 degrees. So, heating is unnecessary most of the year in most of the US, right?

TAG

Jamie Hall said:

If the ambient air temperature is below about 85 F you don't need air conditioning. Granted, you may want it. But you don't need it. A lot of people demand it and want it -- but they don't need it.

You sound like my long departed grandmother telling my father back in the 70's it was foolish to have AC in the house he was building in Maine.

Jamie Hall

Voyager said:

Jamie Hall said:

If the ambient air temperature is below about 85 F you don't need air conditioning. Granted, you may want it. But you don't need it. A lot of people demand it and want it -- but they don't need it.

And it the temperature is above freezing, you don’t need heating either. Water won’t freeze so you can still drink it and food won’t freeze so you can still eat it and it isn’t hard to dress for 35 degrees. So, heating is unnecessary most of the year in most of the US, right?

I wasn't going there -- but it brings up an interesting point. How and why (calling @DanHolohan !!!) did the "normal" temperature for heating come about? What is normal about 72 or so? If you are wearing a loin cloth -- or Daisy Dukes and a crop top -- you won't really be warm enough. On the other hand if you are wearing warm clothes including long johns (remember those?) you will be too hot if you are doing anything at all.

I have no intention of going into Abraham Maslow's theory of the hierarchy of needs -- although it's worth looking at, if one is so inclined -- but one of his major points is worth keeping in mind: there are certain basic physiological needs and second and third tier psychological needs which he argues (I think correctly) must be met if an organism -- such as it might be a human -- is to be free from anxiety at all; if those are not met, even though other wants and desires are met, there will be anxiety and stress. But all that gets well off into the weeds, however valuable it may to contemplate.

Voyager

I don’t know the history either and it would be a great Dan topic. 😁

I suspect it isn’t any one major event, but a gradual progression as we moved from a hunter/gather society to farming to industry. When everyone had to work outside all day to survive, I doubt there was a lot of consideration as to the temperature in the cave or whatever shelter was used. Once more and more of the population could pursue intellectual pursuits such as writing and such where you aren’t doing heavy exertion and you really need bare hands, having a warmer environment becomes more useful. I suspect the correlation was strongest with the move from an outdoor work environment to an indoor work environment.

This topic is far broader than heating and AC as one can argue that we don’t need 90% of what we have today.

DanHolohan

@Jamie Hall I can offer this:https://heatinghelp.com/blog/whats-the-right-temperature/

The Carbon Club also was involved with this in 1899 when they declared that a house must be able to be made 72F with not more than 2 psig steam or 180-degree water. The contractor had to prove it before getting paid. They published a chart, which I don't have at hand, that showed the temp the house had to be on any give day of the year. Do the job in July and you might have to get the house up to 140F or so to prove it would go to 70 in January.

It's just people in authority sitting around making it up. Some things never change.

Jamie Hall

That blog post is it, exactly!

The Steam Whisperer

I think what is called comfort varies from person to person. However, the most accurate way to define comfort is wet bulb black body temperature. This gets you closest to how the actual interaction of the skin surface of human beings interacts with the environment. As the humidity level drops, people start to feel cooler because evaporation from the skin increases. If the radiant temperature drops...even with the same air temperature, people start to feel cooler due to radiant transfer from the skin surface to the colder room surfaces( "cold 70"). This is why I insist that a "btu is a btu" is false, because a system providing higher radiant temperatures and higher humidity levels will provide comfort at lower air temperatures. Less air leakage equals higher humidity, (neither of my homes ever need humidfication in the winter... we maintain about 35% at below zero outdoor), higher radiant temperatures from radiators increase radiant temperature, and less hot air stratification keep ceilings cooler to reduce heat transfer through ceilings.
With truly thermally efficient homes with low air leakage, well insulated warm walls, floor and ceilings, the type of system used should not have nearly the impact of fuel usage as with most typically built homes and older building stock. Air leakage is low and radiant temperatures are higher, so the advantages of radiant systems begin to diminish with really efficient homes.

Jamie Hall

In terms of providing comfort, perhaps I could agree that "a BTU is a BTU" might be seen as being false -- but I would say that more accurately it is misleading. The problem is that one is confounding comfort, which is a sensation, with space or object temperature, which is not. If, for example, one finds that for a particular person wearing particular clothing engaged in a particular task the space temperature needs to be 65 F and the relative humidity 55%, then the objective of the climate control system is to achieve and hold that pair of conditions -- and that will take a certain power to accomplish in a specific setting.

This, of course, is also the problem with "wind chill" so beloved of the weather people. It is perfectly true that if the wind is howling the wind chill -- which takes into account convective heat transfer by the wind -- will be lower than if it is a still day. However, while the object -- such as our shivering peasant -- will cool much faster, he or she will still arrive at a final temperature which is NOT controlled by the wind.

In the instance which was mentioned above -- in which relative humidity plays a factor -- if evaporation is present the equilibrium temperature will be lower than if it is not.

The entire topic is remarkably complex, but for practical purposes if one has established what the space and object conditions are to be and the power required to achieve them, it makes no difference as to how that power is transmitted into the space or onto the object.

JakeCK

Jamie Hall said:

If the ambient air temperature is below about 85 F you don't need air conditioning. Granted, you may want it. But you don't need it. A lot of people demand it and want it -- but they don't need it.

I'd argue cooling is actually more important than heating when you get right down too it. I've got winter gear that could keep me warm down to -20 easily. 
Ever sit motionless in the dead of winter hunting? But in the summer I can only take so much clothing off.

The ambient temperature at which it becomes thermodynamically impossible for the human body to cool it's self is largely affect by humidity, air flow, and metabolism. And that temperature isn't as high as most people would think. 90% RH, 85f on a still day and people will eventually start to experience heat exhaustion sitting still. Given enough time absent some form of intervention such as swimming, sitting in front of a fan, artificially cooling, etc it will advance to heat stroke. The young and elderly are especially vulnerable.

hot_rod

Some info here on hydronic cooling. Chilled beams are one way to handle some cooling load.
I think part of Taco building in RI is cooked with a chilled ceiling system

https://www.caleffi.com/sites/default/files/file/idronics_28_na.pdf

delcrossv

Jamie Hall said:

...snip....

The entire topic is remarkably complex, but for practical purposes if one has established what the space and object conditions are to be and the power required to achieve them, it makes no difference as to how that power is transmitted into the space or onto the object.

Instantaneously, I'd agree with you. But as soon as you integrate over time, how much thermal mass the emitter into the space has makes a lot of difference. I take note as to how thermostats have high CPH settings for forced air, as air has minimal heat capacity compared to most solids (walls, radiators etc.).

Voyager

hot_rod said:

Some info here on hydronic cooling. Chilled beams are one way to handle some cooling load.
I think part of Taco building in RI is cooked with a chilled ceiling system

https://www.caleffi.com/sites/default/files/file/idronics_28_na.pdf

Radiant cooling can be very effective, but it requires very good humidity control in many climates so you end up with forced air systems in conjunction with the radiant cooling beams/panels. And if you lose humidity control for long, you will have serious problems with condensation and then mold.

Voyager

delcrossv said:

Jamie Hall said:

...snip....

The entire topic is remarkably complex, but for practical purposes if one has established what the space and object conditions are to be and the power required to achieve them, it makes no difference as to how that power is transmitted into the space or onto the object.

Instantaneously, I'd agree with you. But as soon as you integrate over time, how much thermal mass the emitter into the space has makes a lot of difference. I take note as to how thermostats have high CPH settings for forced air, as air has minimal heat capacity compared to most solids (walls, radiators etc.).

Yes, that is part of a good FA design. If memory serves, my thermostat is programmed for 6 CPH and often runs for only a couple of minutes at a time. Keep in mind, that unlike a boiler than has to heat up several gallons of water before it can distribute useful amounts of heat, an FA furnace can distribute heat almost immediately, again due to the low thermal mass of air so this difference works both ways.

One of the problem with early FA designs is that they were set to run once or twice an hour like boilers and this causes wide temp swings. My house never moves off the setpoint temperature other than during my daily setbacks. I think the Honeywell t-stat cheats a little and allows a =/- 0.7 degree swing before it actually shows a change on the display, however, even a 1.4 degree swing is pretty small and not noticeable. My FA house is more comfortable than the HWBB, which probably is more accurately called “unforced air”, heat at my church. Both buildings have cold floors leading to cold feet on really cold days. My radiant floor heated shop eliminates that problem and is thus more comfortable much of the time, but its weakness is when the outdoor temp changes quickly as it can’t keep up due to the very large heat capacity of the 5” slab. It will undershoot for several degrees for several hours when the temp drops at more than about 2 degrees/hour and will overshoot for several hours when the temp rises faster than about 2 degrees/hour.

Each system has different limitations imposed by physics and it is very hard to get around them. ODR helps, but it can’t remove heat that is already in a slab so when the outside air warms up quickly, the slab is going to keep radiating its heat and you simply can’t stop it. Now, if money was no object, you could install a chiller and run chilled water through the slab, but that adds even more cost to an already fairly expensive system.

ChrisJ

Fast is actually forced air's biggest issue.

We notice when things change fast, but slow changes we do not notice.
A system that responds very slowly and can still maintain a somewhat narrow temperature swing will be the most comfortable.

Every house I've ever been in with forced air was always incredibly noticeable when the system was on or off. With heat it feels cool when the system is off and too warm when it's on, always. Same with my air conditioning, it feels cooler when it's on than when it's off, even in low stage.

You're going to say that it's a benefit that air conditioning feels cooler when it's on, and that's true, if it's never off. But in the real world, it will very often be off and that will result in people either feeling too warm when it's off or too cool when it's on.


Forced air is also really efficient at spreading smell through a building.
I suppose that could be good, but it's very often bad. Radiant forms of heat do not spread smells.

If a family member is rocking their bedroom due to something they ate, I'd rather isolate it to that room.

Jamie Hall

All of which sort of brings us back around to the top! Pretty much any climate control system can be made to work well and provide very good comfort -- if it is properly designed and installed with attention paid to the requirements and the situation. Doesn't that mean that our job isn't really selecting boiler X and piping Y or compressor Z and ducting Q, but analysing what the customer's requirements are and what other structural and climate constraints there may be, and engineering and installing a system -- any system -- which will do the job?

Voyager

ChrisJ said:

Fast is actually forced air's biggest issue.

We notice when things change fast, but slow changes we do not notice.
A system that responds very slowly and can still maintain a somewhat narrow temperature swing will be the most comfortable.

Every house I've ever been in with forced air was always incredibly noticeable when the system was on or off. With heat it feels cool when the system is off and too warm when it's on, always. Same with my air conditioning, it feels cooler when it's on than when it's off, even in low stage.

You're going to say that it's a benefit that air conditioning feels cooler when it's on, and that's true, if it's never off. But in the real world, it will very often be off and that will result in people either feeling too warm when it's off or too cool when it's on.


Forced air is also really efficient at spreading smell through a building.
I suppose that could be good, but it's very often bad. Radiant forms of heat do not spread smells.

If a family member is rocking their bedroom due to something they ate, I'd rather isolate it to that room.

Fast has nothing to do with forced air. Fast has to do with poor design. My house does not change temperature fast, except when recovering from setback in the morning and that is a very good thing. Maintenance of setpoint is simply not noticeable. Then again, I have a very well-designed FA system by a company that knows what they are doing. It is clear from your comments that you have never experienced a well-designed FA system, and, sadly, this is true of most hydronic heating folks.

I guarantee you that if you came into my house blindfolded and never saw the registers, you could sit in my house and never know it was FA heated or cooled.

Voyager

Jamie Hall said:

All of which sort of brings us back around to the top! Pretty much any climate control system can be made to work well and provide very good comfort -- if it is properly designed and installed with attention paid to the requirements and the situation. Doesn't that mean that our job isn't really selecting boiler X and piping Y or compressor Z and ducting Q, but analysing what the customer's requirements are and what other structural and climate constraints there may be, and engineering and installing a system -- any system -- which will do the job?

I agree 100%. Understanding the occupants needs/wants and understanding how to meet those needs with a variety of technologies is what separates the pros from the hacks.

If you need/want only heat and you like the same temperature around the clock, it is hard to be radiant heat under the floor. Having warm feet and a more uniform vertical temperature profile is wonderful. And if the radiant is low mass, you can still have a fairly responsive system. If high mass, be prepared to open windows now and then to vent excess heat or be chilly for a few hours when temps drop quickly outside.

If you need/want only heat, but you like it cooler at night for sleeping, then you may want to consider FA as it can more readily accommodate this. Now, you can use radiant and just keep the bedrooms cooler all the time, but that may not work for everyone. Low mass radiant may respond fast enough to allow night setback, but it may take a couple hours in the morning to get up to daytime temp as compared to 20 minutes for FA.

If you need/want air conditioning, outside fresh air and humidity control, then FA is the way too go in many cases. My FA system has HRVs and does a fantastic job of providing fresh air more efficiently than relying on infiltration and the AC is integrated and works well.

I have FA in my house because my needs there are different than in my workshop where I have in-slab radiant … although there are a few days when I wish my shop had AC …. 😁

The key to a comfortable system is to understand how the occupants define comfort as it does vary a lot as has been discussed. The key to efficiency is often the quality of the design and installation more-so than the technology. My home is about 2/3 the square footage of the church I attend and my heating costs are almost exactly 2/3 of those of the church. The church is about 1 mile from my house so it sees virtually the same weather. It has a 225K boiler and my home has 225K of furnaces (1 125K and 2 50K units). The church has HWBB and my house is FA distribution. Comfort levels are similar other than my house can use setback effectively and the church can’t. We do setback the church to 60 during the week, but it takes 6-24 hours to recover to 70 for services so it would not work well in a home. Both buildings have cool floors leading to cool feet, but the church is worse as it is over an unheated crawl space where my house is over a heated basement, which also means my duct losses are negligible as they are almost all in heated space.

If I were building another new house, I would use the same system I have now (FA with AC and HRVs), but I would add some radiant under the floors, just enough to keep the floors warm enough to prevent cold feet. I think that would be the best of all possible worlds, albeit a more costly solution.

ChrisJ

Voyager said:

ChrisJ said:

Fast is actually forced air's biggest issue.

We notice when things change fast, but slow changes we do not notice.
A system that responds very slowly and can still maintain a somewhat narrow temperature swing will be the most comfortable.

Every house I've ever been in with forced air was always incredibly noticeable when the system was on or off. With heat it feels cool when the system is off and too warm when it's on, always. Same with my air conditioning, it feels cooler when it's on than when it's off, even in low stage.

You're going to say that it's a benefit that air conditioning feels cooler when it's on, and that's true, if it's never off. But in the real world, it will very often be off and that will result in people either feeling too warm when it's off or too cool when it's on.


Forced air is also really efficient at spreading smell through a building.
I suppose that could be good, but it's very often bad. Radiant forms of heat do not spread smells.

If a family member is rocking their bedroom due to something they ate, I'd rather isolate it to that room.

Fast has nothing to do with forced air. Fast has to do with poor design. My house does not change temperature fast, except when recovering from setback in the morning and that is a very good thing. Maintenance of setpoint is simply not noticeable. Then again, I have a very well-designed FA system by a company that knows what they are doing. It is clear from your comments that you have never experienced a well-designed FA system, and, sadly, this is true of most hydronic heating folks.

I guarantee you that if you came into my house blindfolded and never saw the registers, you could sit in my house and never know it was FA heated or cooled.

But keep in mind, I spent over a year designing and changing my forced air cooling system with a lot of help from people I consider to be some of the best in the business. And then after I installed it I spent the next year tweaking and changing things I wasn't happy with. I used aluminum diffusers in the ceilings though, not registers.

So, I'd take that bet.


I also noticed you never commented on smells.
You know, smells are a part of real life. I know I know, yours smells like roses, right?

Heating systems in bathrooms.
We never put returns in bathrooms, BUT, they do get a supply or two and those supplies need to push air back to the system. It doesn't matter if a return is put in the room or not, that air (with scent) is coming back.

Basically, forced air STINKS.

Voyager

ChrisJ said:

But keep in mind, I spent over a year designing and changing my forced air cooling system with a lot of help from people I consider to be some of the best in the business. And then after I installed it I spent the next year tweaking and changing things I wasn't happy with. I used aluminum diffusers in the ceilings though, not registers.

So, I'd take that bet.


I also noticed you never commented on smells.
You know, smells are a part of real life. I know I know, yours smells like roses, right?

Heating systems in bathrooms.
We never put returns in bathrooms, BUT, they do get a supply or two and those supplies need to push air back to the system. It doesn't matter if a return is put in the room or not, that air (with scent) is coming back.

Basically, forced air STINKS.

Never had an issue with smells. I would have to check, but the air return ducts go by the HRVs as I recall so some portion of the air is exhausted outside and replaced with fresh air. Then it goes through a 5” filter before going through the furnace and back into the entire house. So, any smells get diluted first by outside fresh air and again by being distributed through a 4,000 ft^2 house. We don’t cook Indian food or similar, but normal smells have never been an issue. I am sure a strong enough smell would get distributed through the house, but with two HRVs running continuously, they are quickly diluted and exhausted.

If your forced air stinks, then I will argue you have a poorly designed system problem lacking adequate HRV/ERV capability.

My bathrooms have air returns that go directly to the HRVs so all bathroom smells and humidity get exhausted directly. Again, this is all part of proper design. Anything less is poor design and I will be the first to admit that a poorly designed FA system is bad as is a poorly designed hydronic system.

ChrisJ

Voyager said:

ChrisJ said:

But keep in mind, I spent over a year designing and changing my forced air cooling system with a lot of help from people I consider to be some of the best in the business. And then after I installed it I spent the next year tweaking and changing things I wasn't happy with. I used aluminum diffusers in the ceilings though, not registers.

So, I'd take that bet.


I also noticed you never commented on smells.
You know, smells are a part of real life. I know I know, yours smells like roses, right?

Heating systems in bathrooms.
We never put returns in bathrooms, BUT, they do get a supply or two and those supplies need to push air back to the system. It doesn't matter if a return is put in the room or not, that air (with scent) is coming back.

Basically, forced air STINKS.

Never had an issue with smells. I would have to check, but the air return ducts go by the HRVs as I recall so some portion of the air is exhausted outside and replaced with fresh air. Then it goes through a 5” filter before going through the furnace and back into the entire house. So, any smells get diluted first by outside fresh air and again by being distributed through a 4,000 ft^2 house. We don’t cook Indian food or similar, but normal smells have never been an issue. I am sure a strong enough smell would get distributed through the house, but with two HRVs running continuously, they are quickly diluted and exhausted.

If your forced air stinks, then I will argue you have a poorly designed system problem lacking adequate HRV/ERV capability.

My bathrooms have air returns that go directly to the HRVs so all bathroom smells and humidity get exhausted directly. Again, this is all part of proper design. Anything less is poor design and I will be the first to admit that a poorly designed FA system is bad as is a poorly designed hydronic system.

4000sqft house with multiple HRVs and ERVs eh.

Voyager

Yes, two story log house with finished basement. Since running ducts in log walls is a challenge, and since I have a cathedral ceiling that bisects the second story, the HVAC company suggested using three furnaces. The furnace that heats the main floor and basement is 125K BTUH and is in the basement. Each bedroom one the second floor has its own 50K BTUH furnace in the attic above it that heats that bedroom and jointly heats the upstairs library and bathroom. There are two HRVs, one in the basement and one in attic above the wing with the bathroom. It was a little expensive, but it has been a great system and works better than I could have ever imagined FA working having grown up in mobile homes and one house with a very poorly designed FA system.

ChrisJ

@Voyager


Your HVAC system costs more than a lot of houses.
Yeah, it was "a little expensive".

ChrisJ

Although I am curious how efficient that house is.
I've always heard bad things about log homes in regards to infiltration and insulation.

How does that compare in performance to a house framed from 2x6's?

Voyager

ChrisJ said:

@Voyager


Your HVAC system costs more than a lot of houses.
Yeah, it was "a little expensive".

Not exactly, and not much more than the hydronic in slab system in my workshop cost, if you exclude the AC and HRV expense.

Voyager

ChrisJ said:

Although I am curious how efficient that house is.
I've always heard bad things about log homes in regards to infiltration and insulation.

How does that compare in performance to a house framed from 2x6's?

That is an interesting question. I think it varies a lot by the log home style build and technology used.

My house used 8” machined white pine logs. They are tongue and groove top and bottom and are sealed with a layer of foam tape and also a material somewhat like plumbers putty. They are then lag screwed together. Air infiltration hasn’t been an issue.

Insulation is a trickier question. From a raw R-value perspective, log walls don’t look that good. 8” of white pine has an R value of about 10. This caused many log homes to be rejected by building codes require it R-19 walls. So, many years ago, a log home association built two structures that were identical other than one being logs and the other 2x6 studs with fiberglass insulation. They then measured them through actual day/night conditions. I wish I could find the study, but I believe it was done pre-worldwide web and I can’t find it online. I saw a paper copy the log home company showed to me back in 1999 before I committed to logs. What they found was that the thermal mass of the log home kept it comfortable using nearly the same energy as that of the R-19 stud frame home and this data convinced the US to accept log homes as meeting the energy requirements of the building code and I believe this is still the case. I know that heating my home costs about the same as similar sized homes of other construction styles.

Now, if you look at traditional round log homes made with green logs that were chinked and then shrunk and checked over the years, the difference could be substantial. Round logs have great thickness at the diameter of the log, but the walls may be only a few inches thick where the chinking is, and if the chinking isn’t well maintained, the infiltration rates can be impressive. I chose kiln-dried and machined logs to avoid those complications.

So, I would say that an 8” log wall home that is well sealed and tightly constructed and uses machined square logs such that the wall thickness is pretty well uniform, will pretty closely match a 2x6 wall fiberglass home. My basement uses precast Superior Walls that came with R-5 foam insulation and I added R-19 fiberglass for a total of R-24 and the concrete walls have effectively zero infiltration, however, our basement really doesn’t feel any warmer than the upstairs of our house even though on paper it should be better.

Energy efficiency is a tough thing as we have been discussing here. The problems are that things like R value are very useful, but they only capture part of the total system. R value measures a steady state heat flow from a constant temp on one side of the wall to a constant temp on the other. This pretty much completely ignores the transients, which in many parts of North America constitute the majority of the day/night cycle.

It is like taking a concrete wall that has the same R-value as a solid wood wall and building a fire inside. Even though the R-value is the same, you will feel heat through the wood wall much faster as it might take an hour for the fire to simply warm up the mass of the concrete wall. If you don’t wait for steady state to be achieved, you would say that the wood was much worse than the concrete because the heat was apparent more quickly. Similarly, if you let both get to steady state and then extinguish the fire, the wood wall will cool much more quickly while the concrete might emit heat for hours. This again is misleading as the transient response of a high mass wall is much different than one of low mass, even though the R values are the same.