Pex size - whats the current rage?

[RTcat]

Talked to a local HVAC guy last evening about radiant heat in my new shop. He suggested going with 5/8" pex. Less loops on the manifold he said.

Everything I read pretty much talks about 1/2" pex concrete slab. I see they make all different sizes of PEX.

There will be two zones in the 1600 square foot shop, basically 1,000 sqft and 800sqft. separated by an interior wall. Spray foam on the walls (R21) and Cellouse on the ceiliing (R50). Walls are 10' high. 6 windows and two garage doors. Whenever I put in the heat source it will be a condensing boiler.

Any conerns/thoughts on using 5/8 vs 1/2 pex tubing???

 

[Jackfre]

While 1/2" is most common, Pex is manuf in many sizes. I've sold up to 4" for some projects. In my bathroom floors I used Uponor's Quik-trak and I think it was 5/16" tubing. There's more than one way to skin a cat. Rule of thumb is 1 ft/sq ft of 1/2". I just sized up a friends house floor with 1/2". We needed 1400' at 12"c-c and 1700' @ 9"c-c. This being the fellows house we are going with 9" to ensure better response and more even heating. I'd ask him to figure it both with 1/2 and 5/8 and see what the difference is. You get to decide. You just want him to inform you thoroughly. Good luck with your project

 

[rburke65]

What does that mean..."Rule of thumb is 1 ft/sq ft of 1/2". ?????

 

[mrobins297aaa]

yeah what is that?

 

[Jackfre]

That is an incomplete sentence modified by an incomplete thought. My apologies. I was just meeting with the Rehau regional mgr the other day laying out a friends first floor. He offered, that with a "standard layout" you can use the "Rule of Thumb" for 1 ft of pex per sq ft of floor space at 12" spacing. His floor is about 1400 sq ft. We are going to do a 9" spacing and so will need in the area of 1700 ft of tubing. So, I'm buying 2000' of pex for this job.

 

[raspy]

I use far more 1/2" PEX than others and the only other size I use is 3/4". Just to be clear, the 1/2" PEX measures 5/8" OD and the 3/4" measures 7/8".

A couple of the considerations are the durability during the pour and the number of loops. Try to keep your 1/2" loops at no more than 300' and 3/4" loops at no more than 500'. Shorter is better and equal lengths are also good for balancing. The 3/4" PEX is way stronger than the 1/2" stuff because of the far thicker tube wall. Also, some manufacturers advertise that their PEX is more flexible. This is not a good thing because it is also softer and more vulnerable to gouging and puncturing during the pour. Tough is good!

1' spacing is OK for less severe climates, but 9" is better. If your rebar is spaced at 12" then the PEX should be also to prevent damage during the pour. 9" is about as tight a turn as you can make with 3/4". Best would be to go with 9" rebar spacing and 9" OC tube spacing with 1/2" (5/8" OD) tubing, or 12' rebar spacing and 12" tube spacing with 3/4" (7/8" OD) PEX.

With the 1' spacing I do on most systems and an extra pass at 6" near entries or in bathrooms, I usually use about 1.4 linear feet per sq. ft. of floor. I also hold the heat back 1' from walls.


John

 

[badgerboiler]

Rule of thumb is an excuse for being illiterate and/or lazy. The information is out there.

First, all good radiant floor heating designs start with a proper heat load analysis performed by an experienced designer using dedicated software.

Once you know the load and the floor covering, then, and only then can you choose the heat source, controls and the PEX tubing. Most applications will require an integral oxygen barrier. The size, length and spacing are determined by the load and application.

When designing larger slab-on-grade radiant floor heating system without floor covering (such as 1200' garages) I generally use 3/4" PEX for ease of installation in terms of loop length and smaller manifolds (reduced labor). For smaller applications such as additions or cabins 1/2" is more common.

PEX comes in three common types; Pex-A, cross-linked using a peroxide method, Pex-B, cross-linked with a saline method and Pex-C, cross-linked using an electron-beam method. All PEX tubing is specified in "Nominal" inside pipe size (even though the actual inside dimensions vary depending on manufacturer and product).

5/16, 5/8 PEX and all sizes of PEX-AL-PEX are available but professional, experienced advice should be secured before you spend good money on very special PEX.

3/8 PEX is one of my favorites and used extensively for retrofit applications below the floor, in the wall, ceiling and even in a slab if you do the math.

As for the flexibility and tensile strength, most of what you need in a slab-on-grade heated garage will not require any special PEX spec. All of the barrier PEX with familiar domestic names such as Uponor, Viega, Zurn, Rehau, and Roth conform to the German DIN 16893.

Once you know the heat load you can determine the tube spacing and design water temperature. The wider the tube spacing the higher the water temperature must be to satisfy the thermostat one the coldest day of the year. Create comfort is rarely a concern when considering a working garage and tube spacing may be 18" OC or excluded to the perimeter where low loads and warm storage needs are found.

The adjacent bathroom or office can be tightened up and another zone added for a room isolated by walls. With more window area per square foot and a higher inside design temperature the closer tube spacing may be all you need for perfect comfort. A room-by-room heat load analysis will tell for sure.

Some PEX tube is more flexible than others depending on the method by which it is made. Whether you want "soft" or "hard" pipe is a matter of application and cost.

When it is cold or I am trying to bend a short radius between floor joists, the more flexible "Ingles" A-Pex is my first choice and 3/8" size makes it even easier to use. When I am installing last minute (leaves falling 50° and below) radiant slab or snow melting jobs and the tube goes to ¾” or 1” PEX I reach for an A-Pex every time, which reminds me, if you must use anti-freeze ¾” PEX is usually used (must do math) as is will make moving the must less efficient mixture around the building. Do not use automotive anti-freeze in a hydronic heating system. Propylene glycol inhibited and made for the purpose is the only logical choice if it is required at all (rare).

Unless you are driving a cement truck over it the tensile or crush strength is of no concern.

The stiffer - and cheaper - Saline B-Pex is often and properly used for commercial applications again in a ¾” or ½” nominal size.

 

[raspy]

Designing strictly by a computer program, with the intent of satisfying a thermostat on the coldest day, is a very non human way of providing humans with the best possible experience.

People report to me, over and over, that their radiant heating system is their favorite part of their home.

If done well it can range from completely unnoticed to a greeting when you enter, to warm in one area at a certain time while cooler in another, etc, etc.

Since humans are the ones sensing it's operation, we want them to not notice it's design, just it's benefits, if they notice anything at all. So, tube spacing and timing, and BTU inputs factor in in ways not necessarily described simply by crunching the numbers. For instance, as tube spacing widens to 12' and beyond, people begin to notice cold and warm as they walk around. Especially if the area is timed with the thermostat. So, we can achieve the set temp with wider spacing, but the recovery is slower and the comfort is reduced. The same is true for where the tube is placed. Placing the tube only around the perimeter of a room will heat it, probably, but that's not where people walk.

We need heat where people step and where they sit at the time they will be there. Then, often, no heat when they are not there. Simply matching the BTU loss on the worst day misses the point. Not only do we have to match the BTU loss of the building, but we must also change the temperature of many tons of concrete and, often but not always, change the temperature of the walls and furnishings as well.

Another huge factor is the difference between night and day as far as heating is concerned. Sleeping in a dark house at night, in a warm bed, often means lower stat settings. But in the morning the sun comes in the window, cooking commences, lights go on, lots of human activity, etc. So, if the floor was too warm during the night, the house overheats during the day. But we want a warm bathroom when they get up. These factors are why we need close tube spacing, relatively high BTU inputs, numerous thermostat zones, somewhat higher input water temperatures, and less regard for simply matching the calculated worst case exterior temperature.

Then you have the guy who wants to work on his car in the garage and the only place the floor needs to be warn in where the car sits. That too will satisfy the garage thermostat, but the heat needs to be where he is.

Designing goes on and on. But never forget the human factor and try to make it so they only notice how nice it is if they notice it at all. Don't try to simply satisfy a worst case heat load, add enough headroom to liven it up. Yes, rules of thumb, knowing your area, understanding the clients lifestyle, and some guesswork all factor into an excellent design. Sooner or later, for a given area, the heat calcs are so redundant that they become just another factor that you already know and can include automatically.

 

[Teken]

Rule of thumb is an excuse for being illiterate and/or lazy. The information is out there.

First, all good radiant floor heating designs start with a proper heat load analysis performed by an experienced designer using dedicated software.

Once you know the load and the floor covering, then, and only then can you choose the heat source, controls and the PEX tubing. Most applications will require an integral oxygen barrier. The size, length and spacing are determined by the load and application.

When designing larger slab-on-grade radiant floor heating system without floor covering (such as 1200' garages) I generally use 3/4" PEX for ease of installation in terms of loop length and smaller manifolds (reduced labor). For smaller applications such as additions or cabins 1/2" is more common.

PEX comes in three common types; Pex-A, cross-linked using a peroxide method, Pex-B, cross-linked with a saline method and Pex-C, cross-linked using an electron-beam method. All PEX tubing is specified in "Nominal" inside pipe size (even though the actual inside dimensions vary depending on manufacturer and product).

5/16, 5/8 PEX and all sizes of PEX-AL-PEX are available but professional, experienced advice should be secured before you spend good money on very special PEX.

3/8 PEX is one of my favorites and used extensively for retrofit applications below the floor, in the wall, ceiling and even in a slab if you do the math.

As for the flexibility and tensile strength, most of what you need in a slab-on-grade heated garage will not require any special PEX spec. All of the barrier PEX with familiar domestic names such as Uponor, Viega, Zurn, Rehau, and Roth conform to the German DIN 16893.

Once you know the heat load you can determine the tube spacing and design water temperature. The wider the tube spacing the higher the water temperature must be to satisfy the thermostat one the coldest day of the year. Create comfort is rarely a concern when considering a working garage and tube spacing may be 18" OC or excluded to the perimeter where low loads and warm storage needs are found.

The adjacent bathroom or office can be tightened up and another zone added for a room isolated by walls. With more window area per square foot and a higher inside design temperature the closer tube spacing may be all you need for perfect comfort. A room-by-room heat load analysis will tell for sure.

Some PEX tube is more flexible than others depending on the method by which it is made. Whether you want "soft" or "hard" pipe is a matter of application and cost.

When it is cold or I am trying to bend a short radius between floor joists, the more flexible "Ingles" A-Pex is my first choice and 3/8" size makes it even easier to use. When I am installing last minute (leaves falling 50° and below) radiant slab or snow melting jobs and the tube goes to ¾” or 1” PEX I reach for an A-Pex every time, which reminds me, if you must use anti-freeze ¾” PEX is usually used (must do math) as is will make moving the must less efficient mixture around the building. Do not use automotive anti-freeze in a hydronic heating system. Propylene glycol inhibited and made for the purpose is the only logical choice if it is required at all (rare).

Unless you are driving a cement truck over it the tensile or crush strength is of no concern.

The stiffer - and cheaper - Saline B-Pex is often and properly used for commercial applications again in a ¾” or ½” nominal size.

Designing strictly by a computer program, with the intent of satisfying a thermostat on the coldest day, is a very non human way of providing humans with the best possible experience.

People report to me, over and over, that their radiant heating system is their favorite part of their home.

If done well it can range from completely unnoticed to a greeting when you enter, to warm in one area at a certain time while cooler in another, etc, etc.

Since humans are the ones sensing it's operation, we want them to not notice it's design, just it's benefits, if they notice anything at all. So, tube spacing and timing, and BTU inputs factor in in ways not necessarily described simply by crunching the numbers. For instance, as tube spacing widens to 12' and beyond, people begin to notice cold and warm as they walk around. Especially if the area is timed with the thermostat. So, we can achieve the set temp with wider spacing, but the recovery is slower and the comfort is reduced. The same is true for where the tube is placed. Placing the tube only around the perimeter of a room will heat it, probably, but that's not where people walk.

We need heat where people step and where they sit at the time they will be there. Then, often, no heat when they are not there. Simply matching the BTU loss on the worst day misses the point. Not only do we have to match the BTU loss of the building, but we must also change the temperature of many tons of concrete and, often but not always, change the temperature of the walls and furnishings as well.

Another huge factor is the difference between night and day as far as heating is concerned. Sleeping in a dark house at night, in a warm bed, often means lower stat settings. But in the morning the sun comes in the window, cooking commences, lights go on, lots of human activity, etc. So, if the floor was too warm during the night, the house overheats during the day. But we want a warm bathroom when they get up. These factors are why we need close tube spacing, relatively high BTU inputs, numerous thermostat zones, somewhat higher input water temperatures, and less regard for simply matching the calculated worst case exterior temperature.

Then you have the guy who wants to work on his car in the garage and the only place the floor needs to be warn in where the car sits. That too will satisfy the garage thermostat, but the heat needs to be where he is.

Designing goes on and on. But never forget the human factor and try to make it so they only notice how nice it is if they notice it at all. Don't try to simply satisfy a worst case heat load, add enough headroom to liven it up. Yes, rules of thumb, knowing your area, understanding the clients lifestyle, and some guesswork all factor into an excellent design. Sooner or later, for a given area, the heat calcs are so redundant that they become just another factor that you already know and can include automatically.

Both of you . . .

 

[badgerboiler]

"Yes, rules of thumb, knowing your area, understanding the clients lifestyle, and some guesswork all factor into an excellent design. Sooner or later, for a given area, the heat calcs are so redundant that they become just another factor that you already know and can include automatically."

Uncle!

You can't argue with that logic. Most of my clients say their last contractor didn't need no stinking heat loss program either.

To think, I spent 25 years learning how to design and install radiant floor heating systems and all I needed to do, was guess!

"These factors are why we need close tube spacing, relatively high BTU inputs, numerous thermostat zones, somewhat higher input water temperatures, and less regard for simply matching the calculated worst case exterior temperature."

For those who might be mislead; none of these "factors" can be determined without an accurate heat load, which includes outdoor design conditions and indoor design temperatures as prescribed by Manual 'J'. It is not uncommon for the layman and professional alike to guess at heating and cooling design, kind of like gambling with another's money.

 

[raspy]

You may consider my over 30 years experience in hydronic heating and running a successful company, simply, "gambling with others money" But your response simply points out a very sophomoric method of only relying on a program and not seeing the many other factors that might be involved. Your approach certainly has merit as part of the story, but it's only part of it. And it also points out why it's been fairly easy to become highly regarded in an industry with competitors that can't see the larger picture.

As an example, I have done a lot of work for many years in a certain neighborhood of 756 homes with radiant heating. These were all built at minimum cost between 1956 and 1961. Long before your program was written. There are only 5 floor plans and all the systems are designed the same. All the same tubing layout, same boiler output, etc. There are tremendous differences in how they work, the cost of operation, the satisfaction of the occupants and the general heating performance. Mostly due to outside influences and lifestyles. But also due to poor installation methods.

Your factors seem to give little importance to the slab thickness, as you seem to be fixated on outside temperatures. But I design systems around slabs that range in thickness from 1 1/2 inches to 24 inches and I can assure you the response is far different between the two. Response time is one of the most important considerations. And outside temperature has little to do with one aspect of the system operation. That is giving a warm floor in the bathroom in the morning. People like that summer or winter and outside temp doesn't have much to do with it.

I'm not saying calculations are not important, or your program is not important. But I am saying that the programs I've seen are a good starting point for someone that has no experience and wants to design a system. Or someone working in a new area. Or someone trying to cut costs to the bone. Or someone that doesn't want to take responsibility. But they don't take into account the human factor, and if you leave that out, you are doing your customers a disservice. You may not understand that or know how to get there, and that's fine for your competition, but it leaves you with thinking you know it all and depriving paying customers of having their best system. I'm afraid you're the one operating in a bubble and unable to see the larger picture. It's the numbers AND the adjustments for other factors that provides the complete picture.

I recently designed a system for the parents of a prominent solar home designer. The son was absolutely proud of all his knowledge and his dogmatic way of simply declaring "facts" that had no basis except in programs he used. Like common underground temperatures for geothermal and how to gather and store energy in large mass slabs. We went round and round as I called him on issues that were simply not true and he was insisting be built. Items that ran the cost up, delayed construction and gave nothing. I asked him over and over how he came up with ideas that could so easily be proven wrong, but he went blissfully on. Unfortunately, he was only able to see the value in what a professor had said or a program had said, but unable to actually measure anything or rely on very experienced folks trying to help both him and his parents.

In another example, there is a company near here that charges a fortune to design systems. They get lots of customers because they produce something that look official and they do the legwork to introduce themselves to architects. Unknown to the customers is how they actually do the work. I made a point of going to their office and seeing what they do. And I think they are stealing and misrepresenting themselves. Here's why: They simply take a nicely drawn and official looking schematic (everyone gets the same one or a simple variant) that they got from an equipment supplier that they are friends with. They include that drawing with a reprint of the floor plans that has serpentine lines printed on in to represent loops. This overlay of loops is simply a program that is reduced or expanded to fit and area and printed. The whole operation takes, maybe five minutes and they charge thousands for the service. When the installer arrives he has to redo most of it to make it work and that leads to a lot of angry homeowners that thought they were getting top notch design work from a computer program that was designing around their needs. Nope. There's no variation in tube spacing for different areas, there's no consideration for how tube runs get to the manifolds, there's no consideration for loop length. The installer is expected to simply order all the equipment from the supplier that drew the schematic and call it a day.

Another "designer" sent all the precut lengths of tubing to a job and the owner expected us to simply lay them out, throughout the house and hook them up to the manifold with no cutting. After all, he'd paid good money for those cut lengths and the layout. Sheesh. It never ends. We started over with full rolls of tubing and gave them a good system that made sense, and they love it. The cut lengths got thrown out.

My final example is of a supplier in the radiant field that I've known for 25 years or so. He promotes and sells equipment. Unfortunately, his motivation is way different than mine. To sum it up in a nutshell, if something sells, it's a good product. If he can't sell it, it's a bad product. He gets together with manufacturers and helps design products based on that criteria. Then He contracts with them for exclusive rights and promotes the stuff to architects who don't know better and they spec it in their designs. Consequently, there have been numerous disasters with poor, unproven products that fit the computer program, but were not right for the job or the end user.

Again, there is more to this than crunching numbers. Sorry you can't yet see it. I've had a number of plumbers and others tell me my job is simple and they could easily do it. I encourage them to go ahead and even give them a bit of information. And in cases like yours, where you declare me to be illiterate or lazy, I just smile. It's tiresome to listen to someone who knows it all, but it's easy to compete with them.

 

[badgerboiler]

All that without one number! Impressive.

Show me the numbers...if you have them.

I have been to Levittown and worked on many old copper radiant floor and ceiling systems here in the Minneapolis area and elsewhere (Frank Lloyd Wright was a big fan). They can be improved with outdoor reset, proper circulators, air eliminators and condensing boilers, but this experience has virtually nothing to do with Modern hydronic heating.

I see your 30 years and add 25 since I installed my first "Modern" radiant floor using polybutylene tubing, Glowcore boiler and indirect. A short stint on the Radiant Panel Association board of directors (charter member) and I set on the technical committee that wrote the first US standard. Interested parties should get a copy of "RPA Guidelines".

I simply stated that you can't start without an accurate heat load. You can do it in the sand with a stick, but you won't convince smart people that you learned radiant floor heating from your granddad and you just have the "thumb".

What separates the professional radiant floor heating contractor from the also-ran is an accurate heat load.

Anecdotes, don't a good argument make. And "I" am the know it all.

 

[raspy]

Too bad you fell for the Glowcore scam. I avoided it because the design looked suspect. Sure enough. Back in those days I used miles of polybutalene and still think it was pretty good stuff. Sounds like while you were sitting in meetings trying to tell others what to do, I was designing and installing new ones and repairing poorly built systems. One of the biggest problems that has faced the industry is corrosion. Either from the wrong kind of tubing, like steel, or non oxygen barrier tubing. This has been one of my main issues and I've saved hundreds of systems, with my products, that were declared dead. I've spent a lot of time with building officials pointing out why steel tubing should not be allowed. Oh well, some sit and try to regulate, while others go out and do.

I've always started with heat load calcs, but then calculated in the rest of the story to come up with the final design. Sounds like you don't see the value in meeting your customers. Kind of a "my way or the highway" method. And I've always taken a pure numbers design only as far as it made sense to. It has always amazed me that so many architects and mechanical engineers can be paid well to come up with designs that make no sense. They often proudly put their stamp on systems that are just nuts. Not always, of course, but it always pays to look at the theory and the numbers. That's what I do and I've been successful doing it. If I put it in, it will do as expected and I guarantee it.

Obviously, you don't need to learn anything, but I hear a lot of comments and complaints from people that have radiant. And I listen. Often it's the same old tired stories about 48 hour recovery times, having to leave it on all the time, too hot during the day, wanting to run the forced air to get a head start on the heating after being away, etc. Or equipment failures from certain boilers and some brands of tubing (does Munchkin ring a bell?) Modern, yes, but "modern" is only good if it's better.

I'm sure you know a lot about what you do, and that's as it should be, but I've been around long enough to know how to produce good efficient systems, that I can proudly stand behind, and people love. I know the theory and what equipment works and why. That's why I'm successful and why I think it's comical when people that sit on boards and yell out their credentials, call me lazy.

Carry on. This conversation is getting tiresome.

 

[rburke65]

All this just makes the average guy just want to walk away from it all and say the hell with it.

 

[tool whore]

Talked to a local HVAC guy last evening about radiant heat in my new shop. He suggested going with 5/8" pex. Less loops on the manifold he said.

Everything I read pretty much talks about 1/2" pex concrete slab. I see they make all different sizes of PEX.

There will be two zones in the 1600 square foot shop, basically 1,000 sqft and 800sqft. separated by an interior wall. Spray foam on the walls (R21) and Cellouse on the ceiliing (R50). Walls are 10' high. 6 windows and two garage doors. Whenever I put in the heat source it will be a condensing boiler.

Any conerns/thoughts on using 5/8 vs 1/2 pex tubing???

RTCat,

I appreciate your time here at the GJ (2005). I also appreciate your time to ask a very 'specific' question. Unfortunately, I can only add my .02 as my work has been in plumbing and not radiant flooring. I have done 'some research' but that is about all I can add honestly to the conversation here.

Regarding PEX, the biggest issue I can see (and I do NOT disagree with what you have been told by your contractor regarding loops) is the cost of the pex and associated fittings. Real 5/8" PEX is a specialty item many places as 1/2" and 3/4" are much more common. Before someone attacks back, just call a couple of parts houses in your area and ask them if they have 2000' of 5/8" PEX. In addition to the actual PEX pipe, the fittings are another animal altogether. A radiant flooring contractor 'may' have everything you need, but Lowes and HomeDepot will not. The uncommon sizes will be substantially more IF you can find them. That's my .02

That is an incomplete sentence modified by an incomplete thought. My apologies. I was just meeting with the Rehau regional mgr the other day laying out a friends first floor. He offered, that with a "standard layout" you can use the "Rule of Thumb" for 1 ft of pex per sq ft of floor space at 12" spacing.

I have also heard this rule of thumb many times from many different people.

Rule of thumb is an excuse for being illiterate and/or lazy. The information is out there.

First, all good radiant floor heating designs start with a proper heat load analysis performed by an experienced designer using dedicated software.

Once you know the load and the floor covering, then, and only then can you choose the heat source, controls and the PEX tubing. Most applications will require an integral oxygen barrier. The size, length and spacing are determined by the load and application.

Rules of thumb are in effect, to make estimation easier. They are not for lazy people or illiterates. Badger, you mention all of this heat load and dedicated software, several times, but you dont mention any details about it beyond you need one. It's also not relevant to the OPs question regarding 5/8" vs. 1/2".

Uncle!

You can't argue with that logic. Most of my clients say their last contractor didn't need no stinking heat loss program either.

To think, I spent 25 years learning how to design and install radiant floor heating systems and all I needed to do, was guess!

For those who might be mislead; none of these "factors" can be determined without an accurate heat load, which includes outdoor design conditions and indoor design temperatures as prescribed by Manual 'J'. It is not uncommon for the layman and professional alike to guess at heating and cooling design, kind of like gambling with another's money.

Uncle would indicate your willingness to 'give up'. Will you please?
Also, nobody asked about past contractors. OP stated a contractor told him he could use 1/2" to reduce quantity of loops. Perhaps a heat load has been done and either pipe will do. Is it possible? It could be, but you dont reflect that, you just piss on everyone elses comments. Other Peoples' Kids~ I tell ya!

Manual J? Cahooter Valve? If you are an expert and I have no doubt you are, site your sources even if its just Google. Simple enough. If you're one of those professionals that are just guessing, please stop.

All this just makes the average guy just want to walk away from it all and say the hell with it.

You are absolutely correct. I'm no expert, but I am afraid to ask a question on here because all of the so-called experts who are going to flog me with erroneous information. It's unnecessary and if a 'real' contractor did that to me, I would tell him to get screwed and hire another one. Real experts do NOT need to spout useless information to be recognized. I am however, no expert so I am free to spout. Hopefully, I have added something to this diatribe.

 

[CARS]

Isn't it funny how someone from Nevada can argue about heating with a guy from MN??

 

[CARS]

OK, that last post was kinda "a $mart a$$ one", but seriously...

What difference does it matter if you use "grandfathers formula" or a computer program? Heat loss is heat loss. Forced air, radiant, or futuristic alien radiation??

I used 1/2" pex. It's what the guy sold me. According to the "old guy" and my future calculations, I still have the same heat loss/needs.

Is bigger pex better?? I don't know... ask my wife if size matters

 

[CARS]

If you are an expert and I have no doubt you are, site your sources even if its just Google. Simple enough. If you're one of those professionals that are just guessing, please stop.

Ya, he has some time in...

http://radnet.groupee.net/eve/forums/a/frm/f/4771065301

Google before you bash........

 

[skiingman]

These factors are why we need close tube spacing, relatively high BTU inputs, numerous thermostat zones, somewhat higher input water temperatures, and less regard for simply matching the calculated worst case exterior temperature.

That doesn't sound expensive to build, operate, and keep reliable for a hundred years at all.

Hopefully, I have added something to this diatribe

Good luck with that. BTW, I'm not an expert either, but I'm pretty sure you can find Manual J from ASHRAE or one of its spinoffs. You can Google that if you like. You fail to understand why the poster took issue with the offer of "rules of thumb" as something helpful to the OP. Rules of thumb are useful for experienced designers; for everyone else they are excellent incentives to do things wrong. Period.

Nothing as important and expensive as a heating system is worth letting a contractor estimate with rules of thumb. Let the contractor estimate things that are easy and that they own the risks of for a defined time, like how much material to buy. If you must, let them estimate things you can change eventually like how big of an electrical service to install. Let them estimate exactly how to install permanent heat exchangers whose design details are critical to comfort and cost for decades to come? Be my guest, I won't.

I'll now let you all return to your regularly scheduled arguments about how to spend far too much money building complex and dubiously durable heating systems. "Hey, that stuff we used ten years ago was junk, buy this new stuff, it'll be good at least twice that long!"

 

[badgerboiler]

Raspy is right...except for using his thumb for heat loads.

I probably wouldn't do a heat load on all 756 homes either.

.

 

[IGOTWUD]

If we could get back to the original post, RTcat was heating a shop. I am also in the prosess doing a 48x16 shop with 3/4 pex so I can space the tubing farther apart because I have equipment I will be bolting to the concrete. I'm using 2" insulation around the block walls and 2" in the floor, I plan to space the pex 14" OC. I am also probably going to install a hydronic unit on the cieling to do the 2nd floor mezz area. This may not be scientific but it works for me!

 

[jrhaines2]

What thickness and material is recommended for floor insulation?

A few contractors in this area were using foil bubble wrap and now are getting away from that.I was thinking there would not be many bubbles left after all the traffic of installing the pex and with the concrete being poured.

 

[IGOTWUD]

Here is a post on this tread.
http://www.lowes.com/pd_96554-46086-...7C1&facetInfo=

I am using 2" insulation over 4" 3/4 clean stone compacted with 2 layers of 4mil poly, with 6 to 7" concrete. I think alot has to with soil type. My area is heavy clay, when it gets wet it takes for ever to dry out, so I need good drainage under the concrete.

 

[Frank The Plumber]

So why would a DIY ish guy not contact an engineer or a tech from one or more boiler manufacturing companies to get the for certain logistics of this whole thing per the unit manufacturers specs?

If I was going to do this project and invest my time and money into a well performing system I would as a fail safe contact the manufacturer.

I would of course read the expert opinions and search through all of the pertinent information and high light any questions I thought mat arise, but respectfully I would substansiate all of the info and research it thoroughly.

Keep in mind that you are installing a system, change a part here or there and you must be certain they all gel together as a system.
You need all factors present and need to follow them after you present your system for design.

As you can see there will be some varying opinions.

And personally, I would not be asking the guy working at the desk at the big box store, I would contact the unit manufacturer or several.

 

[IGOTWUD]

I currently have a 150,000BTU coal fired stoker boiler, so my hot water is already in place. With the house and shop my figures indicate that I will consume approx. 105,000 of them, the left over BTU's I plan to use for snow melt. I hate snow removal.
Other than that I'm just plain CHEAP. IGOTWUD but I heat with coal!