correct supply line sizing

bbb

I installed approx. 700 lineal feet of pex tubing into 6 different equal lengths a few years ago and my supply and return lines are 3/4". Here in Colorado when the temps drop down into the 20's the supply line doesn't seem to keep up with the heat demand. Did I undersize the supply line and should this be a 1" supply? The pex tube is 3/8" and rests in a pre-formed grooved layout that was designed in a piece together design. Can't remember the manufacturer of the board that accepts the pex tube. Just wondering if I should increase the copper tube supply line? Thanks much

Harvey Ramer

Would you happen to know the difference in temperature between the supply and return line?

Also, what kind architecture are we looking at, vaulted ceilings, lot's of windows, etc.?

Ironman

Was a heat loss calculation ever done? That is the foundation for determining the sizing of everything in the system.

Normally, a 3/4" line is sufficient for feeding six 3/8" lines as they carry about .4 gpm and the 3/4" line will carry 4 gpm.

It could be your water temp is too low, there's not enough tubing in the floor, not proper insulation of the floor, too much R value in the floor covering or the floor is simply not a large enough emitter to heat the area without some supplemental heating on colder days.

bbb

Thought someone might ask something I know nothing about. The 3/4" pipe was already installed to the same area where the infloor pex was installed but was used for a supply for water base radiators in this same room. The floor rads have been removed and in-floor pex lines installed. I did a heat loss awhile back. I have been oversizing all wall hung radiators in the house in preparation of a new boiler system one day. the water temp where the pex tube is can only be 125 degrees under the wood floor per specs from the wood floor supplier. One thing I noticed is that the temp drop between inlet and outlet of the 700 lineal foot of 3/8" pex is only approx. 10 degrees. I was anticipating a bigger drop. I was thinking maybe a slower pump would allow water to dissipate more heat. Another thing in this heating system is that there is only one pump for the whole 1800 square foot house. Until I purchase a new boiler system, this is what will have to be. I'm in the process of enclosing the supply/return pipes with drywall, and thought I'd install 1" pipes incase I would need these down the line. I know I have a lot of scenarios right now. I just need to know if I should add these pipes for future use--just in case. Thanks for your input.

bbb

Harvey--Yes--the temp difference between inlet/outlet is approx. 10 degrees. This is why a slower pump may dissipate more heat from the pex tube. In a reply to Ironmean I tried to explain my situation further. Thanks for your reply. We do use a pellet stove as a backup on colder days here.

Jason_13

You have enough flow, slowing down the flow will give you less heat. The problem is either tubing size, not getting to the correct water temperature or not enough floor space to heat with radiant only.
What was the heat loss and size of the flor you are trying to heat?

Rich_49

The 3/4 line was probably quite sufficient before since you had the ability to deliver the same energy with much less flow . That system may have had a 30 - 40 * Delta where as now you must maintain a 10* . The radiators worked fine with less flow and they had mass .

4 GPM at a 10* Delta can deliver app . 20K BTUh whereas 4 GPM at 30* Delta can deliver 60K BTUh or at 40* Delta / 80K BTUh .

Radiant floor usually is kept at around 10* Delta to keep an even floor temp

SWEI

bbb said:

the water temp where the pex tube is can only be 125 degrees under the wood floor per specs from the wood floor supplier.

Is this a laminate floor, or solid planking?

What kind of boiler is installed? Is it running on outdoor reset?

Rich_49

Surface temps are more whats important than supply water temp . Humidity is actually more important . Many problems arise with wood products and radiant because latent is not handled properly . Someone in certain situations may require higher tha 125 SWT to get a hardwood surface to an 80* temp to heat the room . I have seen required SWTs of 140*+ to achieve a 75* surface temp . Their recommendations are to generalized and never take into account the type of construction nor the outdoor conditions .

bbb

Rich--I went and looked up the flooring system that was installed in our main level floor. It's called Thermal Floor. It fit together really well and leveled out some imperfections in the plywood subfloor. I always wondered about the 125 degree requirement and haven't increased the temp because of this restriction on the finished wood flooring. Another reason for using this lower temp is because we want to get rid of our current Crown boiler that has a 12" flue that runs thru our master bed closet. We will be installing maybe a Triangle Tube boiler down the line and use it for lower temps. We also doubled the size of every wall radiator in all bedrooms to use this lower temp. water. Winter/spring is in it's finishing stages for now so can't experiment too much. The air is pretty dry here so maybe increasing the floor temp would be alright. Thanks for your input.

bbb

SWEI--thanks for your question. The floor is solid planking. We are old school here with a Crown boiler and a 12" flue that runs thru our master bed closet. Need to upgrade to a condensing boiler soon. We have been considering a Triangle Tube but have heard about problems with this manufacturer also. I'll consider any boiler with a proven record but as you all know--It's what is in stock or available that the salesman will try selling to you. Thanks again.

bbb

Rich--so a delta T of 10 degrees is good huh? I was told that when we install a condensing boiler we need a wider delta T so the boiler will condense. I guess this is where a mixing valve comes in. Thanks for your input again.

bbb

Jason--thanks for your input. We installed a product called Thermal Floor. These boards have channels grooved out to accept pex tubing and made this installation a lot simper. We saturated the whole 700 square foot floor with pex tubing. There is one thing I failed to mention and that is that we have cathederal ceilings. A 24 foot span has 8 foot ceiling at one end and 12 foot ceiling at the other end. We have wired the ceiling now for a fan. Not sure if this addition will work for radiated heat though. We love in-floor heat because of the consistent temps--being warm or not so warm. One thing I notice is that we need to set the thermostat at 75 degrees to get 68 degree heat, The thermostat is correctly placed in the center of the room. I might turn up the boiler temp which i have been hesitant to do. For our new future system i thought about variable speed pumps. Seems like it would be fun to monitor the difference in water velocity. Again--thanks for your input.

icesailor

What is the Inside Air Temperature at the 12' ceiling and at the 8' ceiling part?

Whether it is a radiant floor or radiant ceiling, cathedral ceilings still get hot and need fans to push the convected heat back down.

SWEI

You can design to a 15°F ΔT if that helps any of your numbers. Much more than that and things may get a bit uneven depending on the tube layout.

bbb

Icesailor--thanks for your input. I never measure the temp on the ceiling. The only reason we don't already have a fan is because my 94 year young mom lives with us and she doesn't like wind. Someday.

bbb

SWEI--the tube layout was really close. The runs were 112-115 feet long. Can't get any better than that. So, after all this input I've had is there any reason to have 1" copper pipe instead of the 3/4" now installed? Doesn't sound like it but am ready to drywall pipes in forever. Thanks again

RobG

Is there insulation under the floor? Are you using area rugs in the space?

bbb

RobG--thanks for your input. We have insulation on about half of the underneath of the heated floor. I removed the half under the kitchen when we installed all the piping etc to the in- floor. I was going to install the silver insulated liner stuff that is about 1/4" thick but never got around to it. The room under the heated area is all 4' tall crawl space. I believe some of the heat that should be heating the living space is heating this crawl space. The crawl space walls are all underground and have 2" of rigid insulation. My wife likes her throw rugs also. A lot of the wood floor is exposed. Thanks again.

RobG

You need to install as much fiberglass insulation under the heated area as possible, make sure and hit the band-boards too. I did not re-read the post, did you use aluminum plates? If you did, you do not need an air gap in between the insulation and the plates, if you did suspended tube you need to leave an air gap between the insulation and the subfloor. Without insulation under the floor you are heating more of the crawlspace than the room above. Do NOT use bubble foil as the insulation, use fiberglass. Throw rugs are just keeping the heat out of the room as well.

Rich_49

If the crawl is of the ventilated type I would suggest Mineral wool over fibreglass

tbrooks

I'm new here and new to this type of heating, but with radiant heat it will be going down as much as up. With that floor uninsulated you will be losing a lot of heat.

Zman

I am not familiar with thermal floor.
Is there aluminum in the panel or just wood?
Do you have any output specs?

Rich_49

tbrooks said:

I'm new here and new to this type of heating, but with radiant heat it will be going down as much as up. With that floor uninsulated you will be losing a lot of heat.

Any radiant floor will go more down than up without insulation .
Resistance is needed . The higher the R the more resistance on that side . Remember also that with radiant , a floor is a wall is a ceiling . They all need Resistance behind the panel . Don't think it is not needed on an interior wall either unless you want the room behind it receiving heat also

Tinman

Once you determine GPM required >
Square root of (GPM x 1.24) = pipe size

Tinman

Correction:
Square root of (GPM X .124)
Not enough caffeine yet.

icesailor

bbb said:

Icesailor--thanks for your input. I never measure the temp on the ceiling. The only reason we don't already have a fan is because my 94 year young mom lives with us and she doesn't like wind. Someday.

Its not supposed to blow like a Northeaster Gale of wind in the winter time. Just a warm breeze in the summer time.

Most paddle

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Another partial message from the HH.com lock-ups, just found.

Something must have been done because HH.com is much more stable now.

bbb

RobG said:

You need to install as much fiberglass insulation under the heated area as possible, make sure and hit the band-boards too. I did not re-read the post, did you use aluminum plates? If you did, you do not need an air gap in between the insulation and the plates, if you did suspended tube you need to leave an air gap between the insulation and the subfloor. Without insulation under the floor you are heating more of the crawlspace than the room above. Do NOT use bubble foil as the insulation, use fiberglass. Throw rugs are just keeping the heat out of the room as well.

bbb

Thanks everybody--Been real busy lately and haven't been able to read my responses here.. ROB G--I was going to use the foil bubble wrap stuff eventually but will probably be using fiberglass to insulate under the heating system. Rich--the crawl space is not vented and is insulated around the whole perimeter with 2" rigid insulation. Z MAN--The flooring system that incorporates the pex tubing is called thermal board. The boards are grooved out to accept pex tubing, and they fit together like a puzzle. The top of the board is covered with aluminum foil to radiate heat upward, I like the simplicity of installing this system. I didn't op for the tubing under the floor boards because I liked this system better. Anyway, guess I will insulate this summer underneath floor that is lacking insulation now. I guess my question is: Why isn't the bubble foil recommended? The specs say that all radiated heat will be pushed upward if used below the in floor tubing. Thanks again everyone.

RobG

Bubble foil has an "equivalent" R-value which is junk science. Do a search on this site for it and you will see the reviews. Something either has an R-value or it doesn't. And as for the foil reflecting heat, how long do you think it will take for dust to settle on it and have it lose any reflective properties it may have had?

bbb

RobG--thanks for your input about bubble foil. Never thought about the dust.

RobG

bbb said:

RobG--thanks for your input about bubble foil. Never thought about the dust.

It's just like the saying "I read it on the internet, it must be true!" I'm glad that we caught you before you trusted it. Manufactures can say anything they want as long as their lawyers word it correctly. You have to read the fine print. If bubble foil could equal other insulations why would we still be using the others?