Help with electric boiler and rehau floor system

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Old 01-16-17, 05:46 PM
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Help with electric boiler and rehau floor system

Hi , everybody

i have a new home that is running a 23 KW lion electric boiler, the house has
Rehau in floor heat, the home is 2800 sq ft of living area and 1600 ft of attached garage. The system comprises of ( main level ) 12 -300 ft of 1/2 in pex runs > the second floor is 800 sq ft and it only has 3 -300 ft runs also 1/2 inch. and finall the garage has 5-300 ft runs of the same 1/2 inch runs.

The circ pumps are Grundfos 3 speed units NRF-25 . and i also have pro balance manifolds at all 3 zones.

My question is what speed do i run these in? they are currently all running .5 gal a min/ run. the heat performance is not great , and the heating bills are crazy.... can some one help ? thanks sean........oh boiler temp is set a 110 f out and i do for the most part get the 20.f difference in return temps.
 

Last edited by seank; 01-16-17 at 05:48 PM. Reason: adding info
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Old 01-16-17, 07:20 PM
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Welcome to the forums.

I am NOT the pro in this forum. Just thinking out loud.

If this is a new house.... who designed the system and why aren't they balancing it ?
20 differential is about perfect which means your pump speeds are good.
It's going to be very costly to run a 23k electric boiler. That's almost a 100A load.
 
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Old 01-16-17, 07:54 PM
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re electric

hi

thanks for your reply, Well, its a long story, it eats energy to no end ..not happy... and no support here at all i really am on my own i just know its not running correct ,,,, any and all replies are appreciated, thx s
 
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Old 01-16-17, 09:14 PM
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In floor radiant is not noted for being quick to respond. What do you have for floor covering? Foam pad under carpet can be a major insulator.
 
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Old 01-16-17, 09:28 PM
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Hi

Tile in lower level 2000 sq ft
Engineered hardwood in bonus room 800 sq ft
Garage is concrete. How do I calculate head loss for this system? Each loop is 300 ft
 
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Old 01-17-17, 01:40 AM
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The saying is that radiant is easy to do and even easier to do wrong. The bad thing about radiant, and this is especially true with radiant embedded in a slab, is that it is difficult to impossible to correct any mistakes.

Your boiler has an output of about 78,500 BTUs per hour. With you heating 4,400 square feet that gives you about 17.8 BTUs per square foot, a bit low considering you live in Canada. I would prefer to see it closer to 23-25 BTUs per square foot. Also, 300 feet of PEX is a bit long for 1/2 inch, I would rather see less than 200 feet OR going to 5/8 or 3/4 inch diameter. I would prefer a lower temperature drop as well depending on just how the loops are laid out.

Do you know anything about the construction of the slab? Was it made with a drainage area beneath as well as sufficient insulation? My feeling is that no less than two inches of polyisocyanurate (about R-14) is minimum and I would prefer to see four inches under the slab. The perimeter of the slab needs even more insulation or a significant amount of heat will be lost. This perimeter insulation should be installed to provide a thermal break from the walls surfaces as well.

How about the upper floor(s)? Was the tubing embedded in a lightweight concrete, in channels (Warmboard) or perhaps fastened underneath the subfloor? Any insulation under the floor and around the perimeter?

Are you attempting to use a night/away setback thermostat? High mass thermal sinks such as concrete respond VERY slowly to changes in temperature and require an almost constant temperature setting. The positive is that with the high thermal mass it is also slow to cool off.
 
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Old 01-17-17, 06:21 AM
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re slab

hi,

thank you for your reply, the house is sitting on a crawl space, the floor under the garage was insulated with a lot of insulation a thick ( white foam, and a thinner pink insulation foam as well) as for the house the main level had the pex pipe attached to the wood floor then a thin layer of crete was poured on.
the bonus room above the garage was done the same way but it has bats of insulation installed between the floor joists to deaden sound as its above my garage area. The main level of the house however had NOTHING under the floor joists to retain heat. my crawl space which has no heat source at all is 3-4 *celcius warmer than my main area , i know im loseing heat down here and i am slowly installing reflective foil to the underside of the floor joists to reflect the IR energy back up,( were i have installed it there is a major difference in upstairs floor temp?)

how do i calculate head loss for this system? im running my lil grundfos pumps in full speed , but im not sure its right .

According to the flow guages it says .5 gal per loop per min main level (12)
garage is set to .75 gal per loop per min (5)
bonus is wide open at 1 gpm per loop per min (3)

does this sound correct? also if i upsize the boiler will that not consume even more energy? thx sean

ps we have had bout 2 weeks or so of -30-34*c with the wind chill its been in the -40's....the poor boiler hardley ever shut off, this month hydro bill is gonna be bad.
 
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Old 01-17-17, 12:51 PM
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I haven't done any design on radiant systems since several years prior to retirement and that was eleven years ago. Sorry to say but I don't remember how to calculate system head loss.

I will say that you are simply not moving enough heat through the tubing. As I previously stated in my opinion 300 feet is way too long when using 1/2 inch tubing; the head loss on this is going to be high. The contained volume of water is fairly low and this means less heat content. You ARE transferring heat as is evidenced by the 20 degree differential but again I feel that is excessive for a radiant floor system.

Can you increase the flow through the main level loops or are the flow limiters/flowmeters already wide open?

I am NOT advocating a larger boiler, at least not yet. Without knowing all the details of the house construction as well as the radiant construction it would be foolish to simply increase the size of the boiler.

Do you also have air conditioning in this house?
 
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Old 01-17-17, 04:03 PM
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re specs

hi,

i aquired the heating plans today, they are as follows,

main level 12 Loops

shortest loop is 270 ft , longest is 300 for a grand total of 3206 ft of 1/2 inch pex on main level . pex lines are installed on 8 inch centers.

garage 5 loops 290 ft each on 8 inch centers 1450 ft total pex 1/2 inch

bonus room 3 loops 295 ft each 8 inch centers 884 ft total 1/2 inch pex


Yes the house has ac but it is a ductless style , not connected any way to the heat unit. I use the floor system for heat only.

Can any one tell me are my 3 speed Grundfos NRF -25 pumps big enough to circ this? what speeds should i be looking at? If i speed the pumps up the temp diff between out going and retun water changes , at slowest speed i get about 20f diff, the faster it goes the diff will close down to 15-10f.

tho i cant really test now , weather warmed up to melting outside, tho im sure it will not last , thx sean

oh the main floor is currently running at .5 gal per loop per min. garage is at .75 bonus is at .9
 
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Old 01-17-17, 07:13 PM
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Please check the make & model of the circulators. I can't find any NRF circulators made by Grundfos. I found some made by Bell & Gossett.
 
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Old 01-17-17, 07:35 PM
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correction

oops my bad, you are correct sir. they are Bell and Gossett


sigh ....im having a terrible day
 
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Old 01-17-17, 09:09 PM
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The manual for your circulators is here: http://documentlibrary.xylemappliedw...07/P86203F.pdf

Figures 6 & 7 on page 14 are pump curves with & without internal check valves.

My suggestion is to finish the insulation ASAP. Far better for that heat to be forced up & not be allowed to go down heating the crawl instead of the living area. If the crawl space walls are not insulated, they should be.
 
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Old 03-11-17, 06:45 PM
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hi again...

hi

i have been trying for the last month to contact the guy who designed this floor system for me to no avail.

With the info that i have provided can someone please shed a little lite on what pump speeds and flow do in relation to heat trans fer? should i slow this thing right down? .5 gal per loop enough? should i put the pumps in high? and restrict the flow down? aggggrrraahhhh im at a complete loss.... they sure knew to sell it but it has never ever worked right,

I am considering a bigger boiler but i already have on average 600 buck a month heating bills... would speed or volume be cheaper and help ... thx sean
 
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Old 03-11-17, 07:43 PM
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Yes.... I mentioned you would have high electric bills. This is certainly not an efficient way to heat a home.

You said the system is not working. What is not working ?
Does one zone have a problem or is it all zones ?

You wouldn't increase the boiler size unless it's not maintaining its set temperature.
Previously you mentioned the boiler was set to 110f. Is it holding that temperature ?

If it is holding that temperature then the loops are not emitting enough heat. Increasing the water speed will cause the loop to run warmer and give off more heat. By now you should have tried different speeds and charted the effects.
 
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Old 03-11-17, 08:16 PM
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re reply

Hi

thank you for your reply,

it will about keep 100 f in high speed ( flow adjuster set to .5 GPM ) if i increase it any more than that the boiler temp will fall.

i have done some searches that show increasing pump speed for some has shown drastic reduction in power usage.... i can only hope this will make a improvement.

May i ask , why does increasing the pump speed allow more heat transfer ?

i have 3 zones

zone 1 is 2000 sq ft
zone 2 is 800 sq ft
zone 3 is 1600 sq ft

so should i set the circ pumps to high speed and adjust the flow to .5 per loop for all?

thanks, looking forward to your reply, sean
 
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Old 03-11-17, 10:32 PM
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Since your boiler can't maintain heat it is demonstrating that it is too small for your application.

Faster moving water supplies hotter water to more of the pipe quicker.

You can play with the water speed but that isn't going to change how many BTU's are needed to heat the house.

In theory..... you heat the floor requiring a large amount of heat but once it's heated it only should need to be maintained. If your losses are too high you will not be able to maintain heat.

I have a question that's been bugging me..... why are you heating the garage ?

There are guys that specialize in these types of systems. I am not one of them.
 
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Old 03-12-17, 10:22 AM
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re

hi,

I heat the garage because i store a few muscle cars in there , etc the garage was finished in full exactly as the house was. And it has the infloor heat system why would i not use it after all the cost of installing it.

Interesting note, as of this am i put all the circ pumps in low speed, i adjusted the flow meters for exactly .5 GPM per loop, the boiler out put temp interestingly rose to the 110 * setting on the aquastat. Im not sure what is going on but , this seems to be the most progress i have ever made on this system, its cold here today so i should have a better idea on how things are looking by tonite.

what really gets me is why did the original designer of the system choose the 23 kw boiler? there must be a reason, as it was designed by a reputable company , and used the loop cad program to design it.

ah i only wish i could understand why.........sean
 
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Old 03-12-17, 10:25 AM
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Sure boiler temperature will rise..... you're putting less heat into the loops.

If it gets cold out the residence will also cool down.
 
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Old 03-12-17, 10:38 AM
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actually , since doing this change this am the house temp has risen .5 degree c

tho im not sure if this is related to my change or the day just getting warmer
 
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Old 11-09-17, 08:58 PM
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hello again,

hi folks

well winter is back, and so am i i have made some progress on this boiler radiant heat trouble of mine..... i discovered that the rehau
manifolds were not balanced, now i have done that the comfort level is much better.

can some one please explain how do i calculate head in this system? and pump speeds? thanks sean
 
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