dumb question

DaveGateway

What will happen if I run 160 deg. water through pex that is imbeded in a slab? I expect overshoot at first, but will it damage anything?

Tony_8

Why ?

would you want to run water that hot ? Not enough tubing ? Or don't want to spend $ on tempering controls ?

kevin coppinger_4

what temp. are...

you starting from? It depends on how fast it comes up.It also depends on the concrete. Worse case it could very well crack the slab... You say overshoot, you don't understand...it will take days to get down to the set temp... not hours...kpc

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DaveGateway

I'm trying to design a low cost system for a neighbor.
He thinks that I know how to do this as I designed & installed one in my own house 3 yrs. ago.
I'm using a HTP Voyager with a heat exchanger built in.
Works pretty well, mostly because I insulated my house really well (r35 walls, r65 ceilings, & tripple pane windows).

I have read Dan Holohan's book 'Hydronic Radiant Heating'& am re-reading John Seigenthaler's book 'Modern Hydronic Heating'
It is stated that slab supply temp. should be low 100-105 deg. But why??
Thanks

lchmb

keep reading

a number of thing's need to be taken into consideration. The depth of the pex in the slab...What is on top of the concrete...i/e rug, wood or tile.. something to keep in mind is if you make it to hot then when you walk on the surface you burn yourself..not nice..you need the floor temp at a comfortable level..Pex has a book out that give's recommended temp's for surface used...good luck

btw..the only dumb question is the one not asked

Mark Eatherton1

If the floor surface exceeds 85 deg F...

your feet will start sweating when you walk across it. That is the reason that surfaces that you can come into contact with are limited to 85 degrees F. That is what your typical skin surface temperature is. If you exceed that, your skin goes into cooling mode, A.K.A. sweating...

Run that high of water temp into a slab and you will find the true meaning of Mean Radiant Temperature:-)

Stick to proven principles.

ME

Robert O'Connor_7

TOO HOT!

Having supply @ that high a temp is not good. How are you feeding the manifolds? I did one 25yrs. ago using a couple of thermometers, (1 in the supply & 1 in the return) a couple of tees & ball valves to balance the water temp between the floor & the supply & return. When I got the temp just right, I removed the handles. WhaLa instant mixing valve. Ask all the questions you like. I'm doin it almost 30yrs & I learn everyday. Robert O'Connor (the Jersey one).

DaveGateway

overshoot?

Well if the pex can handle the stress, I guess my question becomes: Will an airstat combined with a thermocouple in the slab and a Tekmar 512, control the rooms temp. within reason, or will the room temp. constantly overshoot?
Whats wrong with relatively short periods of high temp water followed by long periods of no circulation?

Mark Eatherton1

Why...

would you want to do that? I mean, I understand the KISS principle, but that is TOO simple.

It' so easy to do it right, and there really is no right way to do it wrong... The overshoot you speak to would be a waste of energy, and cause major discomfort from over heat conditions.

Inquiring minds want to know..

I could whip a drawing on you in 5 minutes to show you the simplest, easy way to do it.

And to reiterate what lchmb said, ther are no stupid questions.

ME

DaveGateway

dumb questions continued

Thanks for the input guys!

It's a pleasure to get response from someone I've just been reading about!

This my 1st chat ever!

Well am planning to heat DHW also, thus the high temp. requirement.
I just wondered why temper the water temp. down for the mud? if on/off control would work.

curiosity & KISS & $$ I guess

Thanks

lchmb

ok. slightly confused.. you want to run the boiler at 160 for domestic water consideration. and do not want to use mixing valve's to your radiant. Question, will you also be running baseboard from this boiler??

Mark Hunt

My partner and I

were in a home not too long ago that had Pex tubing in the basement slab.

The installation company had NEVER touched a raidant job before, which is why WE were there, and they made NO attempt at controling water temps to the system. NONE.

Walking in the basement was interesting. At first my partner thought he had oil on his boots, but we realized that it was actually the soles starting to melt! It was the most uncomfortable basement I have ever been in.

Another instance of almost the same thing, a home where no flow check was ever installed for the basement zone as well as no temp control. It was like walking on hot coals. Floor temp of 135*.

A simple Taco 3-way mixing valve will set you back about $60. In the big scheme of things, that isn't very much money is it?

It will be a heck of a lot easier to do this "right" now than it will be to fix it later.

Mark H

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lchmb

and it would also save on the cost of the boot's..j/k..have seen a similiar situation where the home owner couldn't control they system because of the up/down temp's and it would freeze on every cold spell..h/o put the system in himself and didnt' think the install was the problem.....

hr

Plenty of ways

to mix down temperature. Yeah you could simply pulse a zone valve, or a 3 way zone valve. manual, multiple hand valves.

Equally important is that whatever method you use, you MUST protect the boiler from cold, extended return temperatures!

Sometimes, often times, the slam dunk simple controls or homemade mixers will not adequatly do this. Very important with high mass slab applications! Don't be tempted to go too "dumb" with your mix device. It will catch up with you someday.

hot rod

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lchmb

ok

ok..since hot rod opened the subject I'll be the first to ask. I have alway's used a constant circ loop whenever I am running radiant..specially if it involve's slab's.I pull all of my feed's off the loop for each zone.This way I do not have to worry about a low return temp to the boiler.. I recently came across a job where the header dead ended...the hot fed the high temp side of the mixing valve...The cold was from the return and the mix fed back on the return for the boiler..I'll attach a pic..what is your opinion as to the best way to do a radiant job?

DaveGateway

dumb questions continued

Still in design stage here, lots of questions to figure out, cost vs. benifit etc.

We want to use condensing boiler, lowest cost design & propane costs spread over 10 yrs. Thus low return temp. is not a problem, I hope!

As 160+ deg. is required for DHW indirects,
and water boils at about 193 deg. at this altitude, 8500'
in southern Colorado, there are some design points.

We may use heat transfer plates in most of the house, as my neighbor wants hardwood floors on the main level.
My heat loss estimate says about 20 btuh & about 135 deg. water required there.
OR we may hang the pex under the subfloor & have to run high temp, maybe 180 deg.

I have not made a desision here.

The walkout basement only needs about 8-12 btuh, thus
multiple temp. requirements & questions.

As it took me about 1/2 hr to hunt&peck this reply,
while enjoying a very nice Rosemont Estate Shiraz,
I'm behind the timeline of responses.

Thanks again!

GEO_3

meltdown

Had a very old radiant system fed by a gas waterheater. Gas Co showed up for a service call and said here's the problem and pegged the thermostat, about 160, by the next morning the furniture had sunk into the flooring.

DaveGateway

still dumd questions!

Mark, I would love to have your input as to the simple & easy way to to do the tempering.

My curiosity remains, would an on/off zone valve control provide a steady room temp. within reason +/- 1 deg.?
If so why temper?

Would the the mud even out the short hot input temp. pulses & the long periods of no circulation?

I think maby it would overshoot.

Thanks

lchmb

here's two cents

I may be way off board here but..if you inject 160 degree water into a slab..with a t-stat saying it need's to run...the concrete will warm rather quickly..now by the time the t-stat realizes that it's all set that concrete is HOT...real hot...so it shut's off the circ and the slab keep's cooking..why because concrete love's to hold heat...so for awhile that floor is cooking and the house shoot's way past temp...so then it start's to cool...from the bottom up...suddenly that concrete is COLD...and so is the room...so the circ come's on...crank's the heat way up..and we start this cycle all over..hot/cold/hot/cold..not something I would want in my house
Now if you run mixing valves..you can control each zone to comfort..if you have one zone a little hot..turn it down..one a little cold..turn it up..get's nice and cozy and everyone smile's..:)

Cosmo_2

Some advice

I remember when I was first intrigued about how radiant heat works. After doing a few simple jobs designed by the supply house salesman I wanted to do the designs myself and ten years later I am still learning. I love it. The best thing I did was get training offered by Wirsbo, along with reading a lot of books. Some of the best books available you can buy right here on this site, Dan's books- "Hydronic Radiant heating", and "Pumping Away" belong on your desk or nightstand. Also Siggy's books are must haves. Have fun........

Cosmo

Boilerpro_3

> you starting from? It depends on how fast it

> comes up.It also depends on the concrete. Worse

> case it could very well crack the slab... You say

> overshoot, you don't understand...it will take

> days to get down to the set temp... not

> hours...kpc

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 323&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_

Boilerpro_3

The American Concrete Institute (Chicago) says....

an absolute max of 150F, 140 F preferred. Go above this its all your baby.

Boilerpro

DaveGateway

still dumd questions!

Hello,

Iv'e got the books, read em, didn't see the answer!

I don't think that on/off control would control the room temp. though.

Thanks for any input

Dave Palmer_3

could

you do one for me?????????? thanks Dave Palmer

hr

Primary secondary will not

in itself protect you boiler from cold return temperatures on every system. You still need a control of some sort to watch the temperature at the boiler return connection, and respond accordingly.

This can be a electronic control, a mechanical thermostatic mix valve, or a combo of electro mechanical devices. Unless of course the boiler is designed to run CONTINOUSLY at low return temperatures.

All these temperatures within the boiler, piping loop, and distribution can be calculated, by the way. Either long hand with formulas in Dan's books or with Design Software.

If you are not running the numbers, you are wild guessing as to the ability of the heating device to supply not only the accurate, needed mix down temperatures, but also protect itself.

Trust me a non condensing boiler connected directly to a high mass concrete slab will have problems!

It may not present for a few, maybe 5 or 7 years, but it will compromise the HX of cast or copper boilers.

Get some design criteria together and have someone help you through a design that accomplishes all your, the homeowner, and the system component, goals. There are dozens of ways to do it "right" and tailored to you customers budget.

I have seen, and walked on some 1950 vintage 180° copper tube systems. Someone installed hands full of 3/8" copper tube systems around here before I was born. Copper refrigeration tube, a boiler at 180, expansion tank,and a series 100 B&G pump. Period!

Generally the homeowners have very thick slippers they wear around the house. And the pets prefer the outside, regardless of the weather conditions:)

hot rod

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hr

Primary secondary will not

in itself protect you boiler from cold return temperatures on every system. You still need a control of some sort to watch the temperature at the boiler return connection, and respond accordingly.

This can be a electronic control, a mechanical thermostatic mix valve, or a combo of electro mechanical devices. Unless of course the boiler is designed to run CONTINOUSLY at low return temperatures.

All these temperatures within the boiler, piping loop, and distribution can be calculated, by the way. Either long hand with formulas in Dan's books or with Design Software.

If you are not running the numbers, you are wild guessing as to the ability of the heating device to supply not only the accurate, needed mix down temperatures, but also protect itself.

Trust me a non condensing boiler connected directly to a high mass concrete slab will have problems!

It may not present for a few, maybe 5 or 7 years, but it will compromise the HX of cast or copper boilers.

Get some design criteria together and have someone help you through a design that accomplishes all your, the homeowner, and the system component, goals. There are dozens of ways to do it "right" and tailored to you customers budget.

I have seen, and walked on some 1950 vintage 180° copper tube systems. Someone installed hands full of 3/8" copper tube systems around here before I was born. Copper refrigeration tube, a boiler at 180, expansion tank,and a series 100 B&G pump. Period!

Generally the homeowners have very thick slippers they wear around the house. And the pets prefer the outside, regardless of the weather conditions:)

hot rod

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Mark Eatherton1

If all things were equal...

which they're not, your idea "might" have a snowballs chance to work. What your thinking doesn't take into consideration is the time lag between the time the heat is pumped into the bottom of the slab, and the time it starts jumping out of the top of the slab to let the air sensing, and even the slab sensing thermostats know of it's presence. The room stat will say "Whoa, Ive got enough heat to make me satisfied", and the slab is saying "You ain't seen NOTHING yet, there's a WHOLE bunch of btu's stored up in me that are headed in your direction, and unless you throw some kind of BIG blanket on me, you ARE going to meet them, like it or not!" The room over heats. You need to feed low temp btu's to the slab gradually in order to avoid overshoot/overkill.

Attached is a simple design using a condensing boiler. Remember, simple some times can lead to discomfort. This design is based on using the highest temperature setting zones and having them prioritized. Until the high temp load is satisfied, the low temp load will not be seeing any energy input.

As for the best below floor application, I try and design every system I install as if I'M responsible for paying the utlity bills. Whenever possible, stick with conductive methods of heat transfer. The plates will pay for themselve many times over in immediate comfort, and energy savings.

And PLEASE stop referring to your questions as being dumb. They're not, and I guarantee you that there are more people learning from this experience than you think...not just yourself. Keep reading and learning, and soon it will all make sense.

I await your next questions.

ME

DaveGateway

getting smarter, I hope

Hello Mark

Thanks for the input, what you say about lack of temp. control makes sense to me.
& I REALLY appreciate the diagram.

Is there any way to do this with the 3 way mixing valves,
but useing only 1 pump in the system that runs only when a tstat tells a zone valve that it needs heat?

I have read the Raypak technical report on the costs that go along with running the main loop pump constantly, "quite a price for the home owner"

Next question, in order to make enough DHW using an indirectly fired hot water heater (IFHWH ?)
that will keep up with 2 showers, dishwasher, washing machine, sinks etc.
I think that I need to add an even higher temp.(180deg) & highest priority ckt.???

Condensing boilers like low temps. for high efficency
BUT IFHWH's need high temps.
I have read about the Munchkin Vision & Monitors version of priority DHW, & others
But when they are putting out really hot water & the return temp. is high, their efficency drops by at least 10%
maby more!

Is there anything new & eligant in this area of what seems like a dichotomy of requirements???

Thanks again, Bill Patrick

looks like I don't have this posting sequence thing figured out yet! sorry

Mark Eatherton1

It depends...

The only reason I incorporated a 3 way mixer is because I was under the impression that you neede 105 deg F water for a slab application and 140+ degree water for below floor application. Generally, if the waters are within 20 degrees of each other, I don't bother segregating them. But in your case, 35 degree difference requires mix down. The only way that you could do it would be to make sure that all floors required approximatley the same temp, which would require more tube on top of the floor poured in a cementitious material. Not the least expensive way to go.

When it comes to DHW, you will HAVE to go with a second pump for the DHW load.

In all honesty, the original drawing I produced would require a third pump. You need one for the boiler primary, one for the hi temp secondary, and one for the low temp secondary, and if you add DHW you'd need a fourth pump.

Sometimes in trying to KISS, I forget critical issues... My bad:-(

Your statement about the DHW loads is fairly accurate. In my own house, I have an 80 gallon tank with the DHW coil immersed in the TOP of the tank. I keep the water in the tank stored at 140 degrees F, and under normal operating conditions we have PLENTY of hot water. The tank is a protype tank manufactured by Amtrol that a great friend of mine got for me to experiment with. By keeping the tank at temps below 140 degrees F, it causes my condensing boiler to stay in the sweet zone for condensing appliances.

Although not inexpensive, you might want to consider one of the Max tanks (Ergo or Thermo). They have a low storage volume, but put out 98% of what is put into them. With a Vision 1 control package, the boiler goes immediately to its maximum output, thereby satisfying the DHW call on a priority basis. IMHO, this is the way to do DHW with a condesnsing boiler. Otherwise, you have to take it out of its condensing range to produce hot water, which while not as efficient as it could be, is still more efficient than most atmospheric boilers.

Heres a modified drawing showing the correct way of piping a Munchkin boiler.

ME

DaveGateway

still frugle

Mark,

thanks for the diagram.

I'm starting to get the idea, I hope!

Are all 3 load takeoffs from the main loop closely spaced T's?

Could DHW be placed directly in the main loop? so that anytime the condens heat source fires up & turns on the main loop circ., assuming the DHW was selected with 1 1/4"
HX, the hot water flows 1st through it? purpose being to elemonate that pump?

Thanks again Bill Patrick

Mark Eatherton1

Nice try but...

if your needing water at a temperature of less than the highest temps minimum, you'd be taking heat FROM the DHW tank and putting it back in the system. Then your DHW would be playing catchup.

ME

DaveGateway

still frugile

Hello Mark,

What I was thinking was:

By puting the IFHWH (is there a real acronym for this?), as the 1st load directly in the main loop, that it would act as a buffer to extend burn times, thus efficency?
AND eliminate the cost of the IFHWH pump?

What do you think of a Dunkirk Quantum Leap set at 160deg. for this system? Do you think that would make enough DHW?

We could use a high temp. (160deg) emitter that would provide the 20 btuh required for the main levels oak floors, such as hanging the pex under the subfloor?

Thanks Bill Patrick