In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.

Member Posts: 42
Hello All,
I'm in the process of calculating head loss for a radiant floor in my house. Why is it that everywhere I look I get a different result for head loss? It is frustrating the \$**** out of me. I checked uponor's manual like 15 times. They gave me a high head. I thought it might be a mistake in their manual so I went online and found a different copy of their manual which listed different numbers which resulted in different answers. I used the pex manual, system syzer, Dan's books, my own pencil and paper calculations...All different. I'm in the radiant twilight zone. I'm using Everhot radiant barrier 1/2" which has the same i.d as uponor hePex. My longest run is 211' . The active loop is 147ft. I need 6k BTU for 190sf. I want to supply 35btu at 140-150 per sf. For 1.7gpm with 10^T Uponor gives me 58ft head loss while Everhot gives me 3.5psi which I calculate to be about 8ft head loss. Can someone help?
Tagged:

• Member Posts: 7,903
Everhot is a lot closer. The Uponor value has something wrong with it; double check all your work. I'm not going to specify more than that, as I don't know how many bends there are or how sharp they are, or how many other fittings you have.
Jamie

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 1,912
Are you sure you need 35btu/sq foot?
steve
• Member Posts: 7,779
I seem to remember a problem with some uponor tables.

8.5 feet sounds more accurate.
• Member Posts: 297
when I take a look at the math, 6000 BTUs I found the flow rate to be at 1.2 gpm (6000/(10*500))

Looking at the Uponor CDAM, the head loss of 1/2" pex at a flow of 1.2 gpm = .01823 per foot of pipe for 130F

.01823 x 211' = 3.8 foot of head

Dave H
Dave H
• Member Posts: 7,803
1.7 gpm in a 1/2" pex loop? Typical flow rates are .50- .75 gpm. I think that 35 but/ sq ft load needs to be checked, confirmed, and lowered if possible.
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 2,930
35 BTU-sq ft, wow that's a lot of heat jumping off the floor.
Gary Wilson
Wilson Services, Inc
Northampton, MA
www.wilsonph.com
[email protected]
• Member Posts: 42
> @Dave H said:
> when I take a look at the math, 6000 BTUs I found the flow rate to be at 1.2 gpm (6000/(10*500))
>
> Looking at the Uponor CDAM, the head loss of 1/2" pex at a flow of 1.2 gpm = .01823 per foot of pipe for 130F
>
> .01823 x 211' = 3.8 foot of head
>
> Dave H

My CDAM didn't get that memo..

And the 1.7 was a number I pulled to test the math. There are more pieces to my radiant puzzle. I didn't give you guys the whole picture. However the upward load is 32 degrees. The room is like the worst design possible as far as heating and cooling go. I originally spoke about it in another post. The floor actually requires 31.5 btu . 350sf room 190 sf radiant floor. 80 degree wood floor. Mucho caliente?
• Member Posts: 7,803
The RadPad is a handy tool for those quick calc. it is amazingly accurate and not biased by manufacturers wishful thinking or changing fuzzy math..

The RadPad predicts to get a 31.5 but/sq. ft output in a 70° room temperature, with an R1 floor covering would require a average floor temperature over 85°.

With a supply temperature around 100° you would have even higher temperatures directly over the tube.

A term I have heard to describe a design like this is "technical insanity"

Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 42
Your like the Crazy Eddie of radiant. Your slashing btu's because this radiant is insaaaaane. But I'm listening. I calculated Average floor temp 80. That's the worst case..what do you recommend? If I use 31.5 i was worried that would be too low for that room. Not to mention I made an oopsie because even though my floor is 190sf i was only able to install pipe in 170sf. Actually i'll fill you guys in on the project. Let me know what you think...
• Member Posts: 42
> This is the room i'm working on in my recently moved into house: Walk about 4 feet up from the first floor
>
>
> Up the stairs is the lofted area which is the 2nd floor. The wall separates room from apt heated with baseboard. The Master bedroom is directly underneath the loft on the first floor. Below the first floor is the garage. I am installing radiant in the garage cieling/ this room's first floor. There is forced hot air in master bedroom and rest of the house. There is baseboard on the second floor on the other side of the common wall. Window to the front of me, on my right, and to my back. 16ft ceiling.
>

>
> opposite view window and 10ft cieling no subfloor. Half of the radiant floor is 3/4" thick pine tongue groove with no subfloor... the other half is subfloor with no pine tongue and groove; which is addition built out over garage.

>
> tearing apart garage for radiant piping and insulation

>
> This is where all the magic happens...or maybe not. Its about 32 feet to the loop and and about 50 years on that boiler. 1968 Utica. Notice the epoxy on the 1962 Taco 195 Perfecta circulator. Its still capable of delivering 50 gpm at 8ft. of head. And I hear every gallon of it going through the pipes to the the 66ft of baseboard in my mother in laws upstairs apartment.
>

> Welcome to the garage..Straight ahead the top of the knee wall is the basement cieling. On the other side of that wall is the master bedroom. If you look up you can see the loft room with no subfloor. After I finish the radiant I'm getting cellulose blown into the common walls and ceiling.
>
>
> So now you can see what i'm dealing with. My heat loss is 6,000btu p/h. I was hoping to get that out of 190sf since my initial calculation gave me 31.5 btu per square foot so I figured since 35btu is the max that this was doable. If you guys think i'm going to burn the floor then I may run a gas pipe and install a rinnai wall furnace to supplement. However, I wasnt sure how that would work with a radiant floor since the Rinnai furnace monitors the floor....hm? That room gets no heat from the two forced air registers that were in there. Whoever designed this is an idiot. As you can see someone told the previous owner they could fix it by adding 15 feet of electric baseboard. So now if you think about it I have 4 different methods of heat in my house. Forced hot air, hydronic baseboard, electric baseboard, and soon to be radiant. I want to eventually get rid of the furnace and boiler and install a reverse cycle chiller(s) which I think would be perfect for my situation since that loft room needs AC now anyway.
• Member Posts: 7,803
Some designers will suggest supplemental heat if the load is too great for radiant surfaces. I'm assuming there may be furnishings in that room that will also limit the output of the floor?

A radiant wall for example 110°AWT, 70° air temperature = 32 btu/ sq. ft.

.08 (110-70) = 32

Radiant ceilings use a .71 factor .71 (110-70) = 28.4.

Of course if you are comfortable with lower room temperatures, maybe 68°, outputs increase, it's always about the ∆T. As we age we tend to be more comfortable at 70- 72F, regardless of the heat emitter type.

My personal feeling is radiant floors are good for outputs in the mid to high 20's (btu/sq. ft.) Beyond that you may have unhappy customers, call backs and customers slamming radiant heat as not viable.

We are just trying to warn you of pitfalls with high load designs, the folks offering advice have years of first hand experience with under-performing systems.
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 42
• Member Posts: 42
hot rod said:

Some designers will suggest supplemental heat if the load is too great for radiant surfaces. I'm assuming there may be furnishings in that room that will also limit the output of the floor?

A radiant wall for example 110°AWT, 70° air temperature = 32 btu/ sq. ft.

.08 (110-70) = 32

Radiant ceilings use a .71 factor .71 (110-70) = 28.4.

Of course if you are comfortable with lower room temperatures, maybe 68°, outputs increase, it's always about the ∆T. As we age we tend to be more comfortable at 70- 72F, regardless of the heat emitter type.

My personal feeling is radiant floors are good for outputs in the mid to high 20's (btu/sq. ft.) Beyond that you may have unhappy customers, call backs and customers slamming radiant heat as not viable.

We are just trying to warn you of pitfalls with high load designs, the folks offering advice have years of first hand experience with under-performing systems.

You think once I insulate and being that the bedroom underneath the loft has forced hot air and the common wall has forced hot air and baseboard on the other side. I could get away with 28btu/170sf. 4760 btus.?
• Member Posts: 7,803
The loads are never 100% predictable, most any load calculation or software has some fudge factor with that in mind. The toughest room is the small square footage to act as the emitter with high loads.

Remember too, on the plus side, maybe 10-20% of the heating season are you at or below design conditions, that data is out there for your area. Worse case you plug in an electric portable heater for those days. Comes down to what you and your families expectations are.

The older remodel or retro fits are the hardest to design and implement some times, as you are discovering.

Sure, any upgrades to the structure or means to lower the load by heating the space around that room are to your advantage.
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 42
If I were to be conservative and figure 6000btu/350sf instead of 350/170 I would get 17btusf. I'll raise it to 20btu w/10^T and get 4110btu per square foot. Then either use the wall which I didnt really want to do or supplement with a small rinnai direct vent furnace installed on the loft where heat will rise or the ground floor which will be radiant? I thought 35 btu's was a max industry standard for radiant and that standard implied that it was viable. I dont doubt what your saying but up until this point I based my floor on the max I thought I could safely get away with. Why do 35 btu systems get call backs?
• Member Posts: 7,803
edited October 2017
All sorts of thumbs and rules of in our industry. As for 35 btu industry standard, not sure where you got that number? Sounds more like a manufacturers projection?

My go to for unbiased info has been the RPA and the work and research Siggy has done in 40 years of design and teaching as well as forensic work.

As I showed above with the Radpad formulated by Larry Drake the father of the RPA, the issue with trying to drive 30- 35 btu/ sq ft becomes the floor surface temperatures required to get there.

If you use an R1 for the 3/4 flooring, to get 35 output in a room with 70° air temperature requires 104° surface temperature 30 btu needs 99° surface temperature.

For a residential application many agree surface temperature should be limited to around 82° which in a 70° air temperature space = 25 btu/sq. ft. That is where my belief in the mid to high 20's comes from.

The 82° surface temperature has a bit to do with typical skin temperature. Robert Beans Healthy Heating site has excellent info on that topic. Bare feet, or other body parts exposed to surface temperature above that tend to get sweaty and uncomfortable. Dogs hate it also.

Where that 30- 35 "industry" number can and does work is in a shop slab application for example where folks don't tend to be barefooted so surface temperature could be above 82° And or where the air temperature could be maintained lower, at 65° or so.

Bare concrete with 0 r-value covering :
65° air temperature, surface of 82° = 35 btu/ sq. ft.output. See RadPad example attached.

35 to me is a snowmelt load number

Yeah, probably there is some fudge factor in the Radpad, the disclaimer printed in blue indicates that. Using the RadPad projections keeps you out of trouble, why tempt fate?

The back side of the Pad does tube size calculations, flow rate suggestions, pressure drop, etc. It allows you to see al the various "what if" scenarios.

At the end of the day, you get to do whatever you want with your home and system.

Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 42
Thanks for the help. I'm going to lower my btu's and order a radpad. Also I plan to use an iseries valve with outdoor reset to help control it.
• Member Posts: 60
i believe honeywell issued a recall on that WW1 gas valve some 20-30 years ago, im all for keeping the old stuff alive but that boiler really needs to be evaluated.
jmho
• Member Posts: 42
> @HydroNiCK said:
> > This is the room i'm working on in my recently moved into house: Walk about 4 feet up from the first floor
> >
> >
> > Up the stairs is the lofted area which is the 2nd floor. The wall separates room from apt heated with baseboard. The Master bedroom is directly underneath the loft on the first floor. Below the first floor is the garage. I am installing radiant in the garage cieling/ this room's first floor. There is forced hot air in master bedroom and rest of the house. There is baseboard on the second floor on the other side of the common wall. Window to the front of me, on my right, and to my back. 16ft ceiling.
> >
>
> >
> > opposite view window and 10ft cieling no subfloor. Half of the radiant floor is 3/4" thick pine tongue groove with no subfloor... the other half is subfloor with no pine tongue and groove; which is addition built out over garage.
>
>
> >
> > tearing apart garage for radiant piping and insulation
>
>
>
> >
> > This is where all the magic happens...or maybe not. Its about 32 feet to the loop and and about 50 years on that boiler. 1968 Utica. Notice the epoxy on the 1962 Taco 195 Perfecta circulator. Its still capable of delivering 50 gpm at 8ft. of head. And I hear every gallon of it going through the pipes to the the 66ft of baseboard in my mother in laws upstairs apartment.
> >
>
>
>
> > Welcome to the garage..Straight ahead the top of the knee wall is the basement cieling. On the other side of that wall is the master bedroom. If you look up you can see the loft room with no subfloor. After I finish the radiant I'm getting cellulose blown into the common walls and ceiling.
> >
> >
> > So now you can see what i'm dealing with. My heat loss is 6,000btu p/h. I was hoping to get that out of 190sf since my initial calculation gave me 31.5 btu per square foot so I figured since 35btu is the max that this was doable. If you guys think i'm going to burn the floor then I may run a gas pipe and install a rinnai wall furnace to supplement. However, I wasnt sure how that would work with a radiant floor since the Rinnai furnace monitors the floor....hm? That room gets no heat from the two forced air registers that were in there. Whoever designed this is an idiot. As you can see someone told the previous owner they could fix it by adding 15 feet of electric baseboard. So now if you think about it I have 4 different methods of heat in my house. Forced hot air, hydronic baseboard, electric baseboard, and soon to be radiant. I want to eventually get rid of the furnace and boiler and install a reverse cycle chiller(s) which I think would be perfect for my situation since that loft room needs AC now anyway.

> @ch4man said:
> i believe honeywell issued a recall on that WW1 gas valve some 20-30 years ago, im all for keeping the old stuff alive but that boiler really needs to be evaluated.
> jmho

Yeah..I really didn't want to mess with it too much. I plan on getting a new one next season. Originally I thought about piping an indirect in parallel to that boiler and connecting an on demand electric heater to it to feed my radiant floor. My thinking was that the boiler feeds 1 zone of 66 ft of baseboard in my mother in law's upstairs apt. She keeps her apt about 197 degrees in winter. I would add the indirect to her zone. I would piggy back off her load Everytime she calls for heat her load would heat my indirect which in turn heat the water for my radiant floor acting kind of like an aqua booster . If by some chance she hasn't called for heat in awhile and the indirect temp drops..the electric on demand would bring the indirect temp back up. All because I wanted to mess with that boiler as little as possible. I figured piping in the above way would keep the systems separate,eliminating condensing and avoid making the indirect a separate zone because Everytime she needs heat my floor would need heat anyway. You think it would work?
• Member Posts: 42
• Member Posts: 7,803
looking again, is it the room at the top of the stairs, two outside walls and windows? Looks like it would get some heat from the rooms below, especially if that has forced air. The hot air tends to rise up.

How did you run the load numbers with that room basically extension of the rooms below?

Certainly two outside walls with lots of glass and small floor square footage are a tough load, I would think it would get some, maybe a lot of heat from below.

I assume you have lived there through a heating season to see how the room behaves?

The guys here that do load calc on a daily basis may have some insight.
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 42
The room is split. One side is lofted. The lofted side shares a heated wall. I'm not overly concerned with the lofted side yet. Since it shares a baseboard heated wall and forced hot air room below it. However, the lower part is where I am installing the radiant floor. It shares a forced air heated wall however the unheated garage is below. 50% extends out leaving the shared forced air wall creating 3 exterior walls 1 of which has a window. As you can see in the pic the section with the lower floor extends over the garage. In effect that section has three exterior walls. My heat loss was done by an engineer after the extension to the lofted section of the room was built. 6000 BTU loss. I guess the previous homeowner got the extension but didn't upgrade the heating in that room to match. I have experienced heating and cooling season in that room and it does not heat during the winter nor does it cool during the summer. yikes! My intention was to install radiant under the floor over the garage area. I might supplement with a small rinnai wall furnace if need be. my only question with that is in regards to the placement. I'm taking your advice and lowering the radiant BTU's. Now, if I were to go with the wall furnace do i place it in the radiant area or the lofted are. That furnace monitors temp along the floor. So i thought it might get inaccurate readings because of the radiant. If i installed it in the loft area the heat would flow up to the 16 ft cathedral ceiling and might not heat the lower radiant area well.