Radiant heating settings - basic questions


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Old 12-11-14, 08:05 PM
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Radiant heating settings - basic questions

Hello, thanks in advance as I am new to this forum. I have a closed radiant system consisting of 3 loops of red Pex tubing (looks like 3/8 or 1/2 inch) for a 550SqFt room, embedded in grooves within a plywood subfloor over slab (no basement under this room), with quite a few stamped metal heat plates, and covered with 3/4 inch wide-plank eastern white pine. The system includes a stainless manifold (unknown brand but looks similar to Rifeng brand pics), with a Grunfoss pump, and a water heater. Room has a high ceiling (16FT+), lots of large windows (I estimate 40% of total wall surface area) and one standard sized solid door. We also have a large ceiling fan which we were told can be reversed in winter to circulate hot air that may concentrate higher in the room. We are in central New Jersey, where typical lowest temps are 10-15F, but mostly around 20-30F. Weíd like the room at about 68-70F.

I am having good success keeping that temperature but donít know what the optimal settings are. I can control heater temp, pump speed (Hi-Med-Lo), and flow (through either supply or return valves?). I donít have flow meters on the supply line but rather simple allen valves which I turn with an allen key. Each valve turns about 1 full turn max. The return lines have white plastic caps and manual actuators.

Currently I have all supply and return lines fully open. I have the pump at medium, temperature from heater entering system at about 130F. Outside temp is 30-32F. Room thermostat at 70F, and the system and heater run on and off throughout the day and keep temp between 65-70. The return water temp however is usually about the same or only up to 5 degrees below the supply temp, even though I read it should be 15-25 degrees lower.

My general question is: is the goal for an efficient radiant system a constant running flow at higher speed and lower temp, or like now an intermittent but larger flow at higher temp, (and I would assume lower speed?).

My specific questions are:
How do I control the temp differential between supply and return? how do I control flow? should I adjust the supply valves or the return valves? which should be fully open or not?
Whatís better: hi or low pump speed?, high vs. low flow?, high vs. low heater temp? (e.g. 110 vs. 140)
Even if current settings are working, are they the most efficient?
How should I adjust the system when temps drop into teens?
Also, can my allen valves be replaced by flow meters that I can somehow use to adjust the system?

I donít have a heat load analysis nor do I know the heat output of my system, but absent these design specs, are there some general guidelines on the basic questions above?

I researched quite a bit online before posting and couldn't get a clear perspective. I am just starting to educate myself on this. Thanks in advance for any guidance.
 
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Old 12-12-14, 11:13 AM
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Hi and welcome to the forums,

This system is only the one room you mentioned? Rest of home has another heat source?

You said 'water heater', so I presume that you mean just that, a domestic water heater as heat source for the radiant system?

The return water temp however is usually about the same or only up to 5 degrees below the supply temp, even though I read it should be 15-25 degrees lower.
Radiant delta T is often less than other types of hydronic heating. What you are seeing (5į) might be a little too little though.

How do I control the temp differential between supply and return? how do I control flow? should I adjust the supply valves or the return valves? which should be fully open or not?
Low delta T usually means too much flow. If you run the pump on LOW speed, do you see a wider delta T between in and out?

I wouldn't bother fooling with trying to adjust flow at the valves on the manifold, nor would I be too concerned about it either.

high vs. low heater temp? (e.g. 110 vs. 140) Even if current settings are working, are they the most efficient?
Radiant floors should never be above 85F. This probably means that the water going into the system should not be more than 120F or so.

How should I adjust the system when temps drop into teens?
You shouldn't have to adjust anything. Set it and forget it. It should be designed so that it can properly heat the room on a 'design day'.

can my allen valves be replaced by flow meters that I can somehow use to adjust the system?
Perhaps, but without knowing whose manifolds they are, you might not find something that 'fits'.

Again though, lots of expense for very little (if any) gain in performance.
 
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Old 12-12-14, 01:34 PM
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Thanks for your response.
Yes, the system is only in this room, which is a fairly recent addition adjacent to the dining room (access through double glass doors which we keep closed). Rest of house is heated by a gas furnace. The radiant system controls are in the basement right below the wall between the dining room and the addition (which does not have a basement). I have what seems like a regular Bradford & White "Defender" dedicated water heater.
I just set the pump to low and will let it run a few hours to see if/how the delta T evolves.
Thanks for the other feedback.
 
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Old 12-12-14, 06:16 PM
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At 550 sq ft, and the windows at 40% of the wall space... and I'm thinking that three walls are exposed to the weather?

I would ball park the heat loss in that room at perhaps 15K - 18K BTUH on a design day. This is just a wild azz guess though... so going with that then...

Is most of the floor space open? or is there a lot of furniture placed around? You can't really count floor space under a sofa for example as radiator in a radiant system.

So let's keep guessing... Let's say that you have maybe 450 sq ft of floor radiator with 100 SF being under furnishings.

If there is no carpeting, only the board flooring, and the floor system is WELL INSULATED below the tubing, you might get say 30 BTUH/ SQ FT... maybe even 35 if you're lucky... we'll go with 30 for now.

450 sq ft of radiator at 30 BTUH/SF = 13.5K BTUH ... that room might get chilly when temps are at design.

Raising the water temp would be the only workaround for that problem, but the floors might get uncomfortably warm, and some materials are damaged by excessive temperature over long periods of time...

What size is the water heater? (model number?)

Do you know the tube spacing under the floor? How many loops are run?

Do you know if they used a tighter (closer) spacing under the window area?
 
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Old 12-13-14, 07:46 AM
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Yes, 3 walls exposed. Mostly open space, no sofas or carpets, just chairs, some tables and desk.
My concern is exactly what you say, whether in very cold days the system can keep up and/or how to adjust. Last year it didn't work well, but we had issues with air in the system which I now learned how to purge. We do have a Mitsubishi Mr Slim hot/cold split system which is sized for the room and heats it well and quickly when needed, but I'd rather minimize its use in the winter if the properly adjusted radiant is sufficient. Currently with thermostat at 70 it is keeping room at 66-69 (outdoor temp about 32). I reduced the pump speed to low as you suggested, and the delta T is in fact wider, this morning it was about 140 supply and 126 return, and despite the high supply temp the floor (3/4 inch solid pine) was comfortably warm.
On your other questions:
Heater is Bradford White 40 gals, model M1TW40S6FBN
We have 3 loops. Not sure about the tube spacing, but here are some pics of construction. Spacing seems even throughout.



 
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Old 12-13-14, 10:18 AM
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Is
the floor system is WELL INSULATED below
?

Bradford White 40 gals, model M1TW40S6FBN
That's a 40K BTUH unit. Should be capable.

and despite the high supply temp the floor (3/4 inch solid pine) was comfortably warm.
OK, but the issue is UNcomfortably warm. Spend any considerable time on a floor surface that is above 85F and you will have hot feet... and as I said, some materials don't like living at that temperature. The solid wood flooring may dry out and crack even, and the finish you use could be damaged too. If it's pre-finished flooring, check manufacturer specs. If you finish the floor yourself, check specs on the finishing material. Should probably also check specs on the insulation below the floor also.
 

Last edited by NJT; 12-13-14 at 10:46 AM.
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Old 12-13-14, 10:49 AM
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Regarding the insulation, here are some more pics of the construction: plastic and some light blue insulation under the slab, then the concrete slab, then the grooved plywood, then the tubing which rests over the slab in the plywood grooves, and finally the wide-plank pine floor. Great to know the heater is OK. Thanks.







 
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Old 12-13-14, 04:31 PM
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I'll keep an eye on the floor temp, and will try to keep supply temp below 130 or 120. I did the finish myself, just 5 coats of waterlox Tung-based oil over the pine.
 

Last edited by NJT; 12-13-14 at 05:53 PM.
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Old 12-13-14, 04:57 PM
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Probably some duplicates now, I'll weed them out later.

Did you get a 'pop up' that said your posts were waiting for moderator approval? If you didn't I would like to know so I can tell the web ppl that there's a problem. If a poster doesn't see his post, and no message that it's waiting approval, he's gonna try again... and again...

More later...
 
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Old 12-13-14, 08:12 PM
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I did see a brief notice pop-up but it showed literally only about 3 secs, then disappeared, and couldn't read it all. Then I waited a few hours and thought there was an error, as I searched for "pending posts" or something to that effect under my name and could not find my post anywhere. Sorry if I inundated the inbox as I may have sent almost the same post 3 times.
 
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Old 12-13-14, 08:24 PM
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Sorry if I inundated the inbox as I may have sent almost the same post 3 times.
Not your fault! I need to talk to them about displaying that pop up a little bit longer... or maybe they can set it up somehow that you have to click an "OK" button or something.
 
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Old 01-02-15, 10:56 PM
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New hear and need to post a new thread question on radiant heat but can't find where
 
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Old 01-03-15, 06:29 AM
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Welcome to the forums! You are in the right forum. Click on Boilers ... and note the +Post New Thread box. Click on that and give it a title and post in the body
 
 

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