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Old 08-25-2013, 10:39 AM   #1
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pex hydronic radiant


Sadly, cool weather is just around the corner. My home is over 100 years old and one of the first things I did 7 years ago when I bought the house was install hot water baseboard and a boiler. I was young and didn't quite know any better. Had I been a little smarter or not in such a rush to install a better heating system I would installed cast iron radiators (as opposed to copper tube/fin baseboard), cast iron baseboard or better yet, hydronic radiant pex.

That being said, I find my house is rather chilly (drafty perhaps) even with the heat on. I find I use a lot of gas to heat a building that doesn't get comfortable. Don't get me wrong here there is heat, the house gets warm but it's nothing like a new home with new windows, etc... As the years have gone by, I have upgraded windows, sealed any original windows (the originals never had as much as a bronze spring strip/felt stripping), better sealed doors and demo'd plaster/insulated/re-installed drywall.

While part of the house is still un-insulated because I just don't have the time and resources to demo all the plaster, I got to thinking about installing PEX radiant heat from the basement to warm the first floor and use it as a radiant convector.

Again, THAT being said, would changing my existing hot-water baseboard to a hot water radiant floor heat make sense? Even though the house is less drafty, has more insulation than it did years ago and is a little thermally tighter, would the radiant help with comfort and economy?

I'm feeling that since the basboards typically sit on the outside wall of the house, the second the boiler/circulator kicks off that pipe is cooling down. My feeling is that the radiant won't "cool down" as fast and hopefully maintain the comfort level a lot better. As I mentioned prior I can access the basement easily and install pex against the floor boards. It's relatively inexpensive and easy from a labor standpoint.

Am I crazy here or does this sound somewhat reasonable? I know a little bit about thermodynamics and heat transfer (I come from a family of engineers albeit i'm not one). Also would you run the first floor zone as a single zone (baseboard & radiant) or split the radiant into its own seperate zone keeping the baseboard in-tact in case you need a little extra heat.

I'm just curious....it's always been a thought on my mind when I step onto a 'cool' floor and how it would work.


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Old 08-25-2013, 11:08 AM   #2
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I would either series the baseboard and radiant heat. And also use an outdoor reset to control the water temp to the lowest temp safe for the boiler, and still able to heat the house.

Or have the radiant as first stage heat, and the baseboard a second stage if you can't get enough pex in for the heat loss of the first floor.

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Old 08-26-2013, 05:59 AM   #3
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Originally Posted by beenthere
I would either series the baseboard and radiant heat. And also use an outdoor reset to control the water temp to the lowest temp safe for the boiler, and still able to heat the house.

Or have the radiant as first stage heat, and the baseboard a second stage if you can't get enough pex in for the heat loss of the first floor.
How would you recommend using the radiant as first stage? My understanding is two have two zones. 1 for the radiant set at say 70*f and a second zone for the baseboard set at say 68*f ?

I could do an outdoor reset but unless it would be a huge benefit I really don't want to shell out the money for the controller. Last time I checked they were pricey. That was a few years ago so I guess I could check on an updated price.

Thanks!!!
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Old 08-26-2013, 03:32 PM   #4
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I would use a 2 stage thermostat, and circ relays. That way it would automatically bring on the baseboard if the radiant was keeping up.

Radiant is a slow heat. So if you don't use outdoor reset. the boiler heats up to limit temp every heat call, and waste fuel. An outdoor reset can save what it cost in 2 or less years.
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Old 08-27-2013, 12:09 PM   #5
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Radiant and baseboards can require two different water temperatures from your system/boiler depending on how the radiant is installed.

The radiant option is always going to give more creature comfort (if installed and controlled properly) than any other form of heating. If installed and controlled improperly you can easily just swap one type of uncomfortable for another.
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Old 08-27-2013, 12:45 PM   #6
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Radiant and baseboards can require two different water temperatures from your system/boiler depending on how the radiant is installed.

The radiant option is always going to give more creature comfort (if installed and controlled properly) than any other form of heating. If installed and controlled improperly you can easily just swap one type of uncomfortable for another.
I'm not installing anything yet but what would you consider an improper installation? just curious! Also what happens if you run 180 boiler water through pex/hydronic? again just curious...

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Old 08-28-2013, 11:15 AM   #7
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I'm not installing anything yet but what would you consider an improper installation? just curious! Also what happens if you run 180 boiler water through pex/hydronic? again just curious...

Thanks
What do I consider an improper installation........... anything that is done without the math to back it up. Hydronics is ALL about doing the math first.

The needed calculations are done to determine heating needs first. This is done for the entire area to be heated by the hot water system with all individual rooms/areas singled out separately. Once you have the "need" identified you can go about designing a delivery method that can supply the need.

Heating is all about first making the "heat" as efficiently as possible and then delivering it where it's needed in the correct quantities to maintain comfort throughout the structure.

Think of it like buying all 200 watt light bulbs for your house. You install them everywhere and then have a single switch to turn them all on. Make any sense? Shouldn't..... not to anyone. BUT, the truth is that there are a lot of heating systems in homes today that are installed by that very premise. "If just enough is good, then a lot must be better."

Can you run 180 water through pex? Yes, if it's rated for it. That's the simple answer. The real question is: Do you need to run 180 water in your hydronic system? And if you do, when?

Hydronics delivers energy by means of heat transfer. You add (transfer) heat to the fluid at the boiler, move (circulate) that "energy" to the areas it's needed and then remove (transfer) that heat to the air or objects in the space. Repeat as necessary. You transfer it to the air by baseboard or other like forms and to objects by radiant style setups.

A "good" design of a system allows for the water temperature to be varied depending on the amount of heat needed on any given day. This gains you maximum comfort by always adding as close to the exact amount of heat to the home as is being lost. A "good" design of a system allows you to control this amount of heat room by room or at least area by area. A poor design is like going back to the 200 watt light bulbs and single light switch way of doing things.

The average hydronics design I do for a new system takes anywhere from 2 - 16 hours depending on the variables. The math/software generates on average a 1/2" stack of printed pages of information..... again this depends on the variables/complexity of the system. What does this get me and the customer? A room by room assessment of how much energy each room/zone needs on any given day of the year. It gives the options of how that energy can be delivered and what it takes to do it, from how many feet of tubing to the types/size of circulators to the types of controls to be used.

The math allows me to guarantee that if the system is installed according to the math it will be as energy efficient and comfortable as possible. A poorly thought out and installed hydronics system will always be less efficient and comfortable...... that's guaranteed. How much depends on the amount of deviation from the math. It may be energy efficient, but the home will be uncomfortable. It maybe an energy hog, but the comfort is good. What I usually find, when called in to make it right, is an average of both.

Sorry for the book. If you can't tell, hydronics is my passion.

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