Radiant floor heat cant keep up

schtoink44

I've seen alot of similar post but I haven't found a solution yet.  I built a 2 story addition to my house, living room downstairs amd bedroom upstairs.  Both floors have radiant floor heat, pec stapled under the floor with aluminum plates to disperse heat.  That side of the house heats fine.  On the old side of the house, I did the same thing.  Stapled pex to underside of the floor in basement.  Insulated with the silver bubble wrap like insulation.  System works great until the temperature outside drops below 20°F.  The old side of house, the radiant keep up.  I have it set at 69° and that zone will drop to 66 and when my furnace will kick on (I kept the furnace and duct work installed).  I've insulated crawl spaces on 2nd floor(old original house is 1 1/2 floors with loft area looking down to kitchen/dining room).  I've opened up cieling on 2nd floor and insulated there as well.  I've slowed the circulating pumps down to first setting.  All windows replaced prior to this, plywood and insulation was replaced as necessary to exterior walls as needed before siding was done. 
Any help would be greatly appreciated.

Thank you 

Alan (California Radiant) Forbes

Why did you slow your pump down? Up to as point, you will get better heat transfer at more flow. You're looking for 4-8 gpm.

Is the old part of the house zoned separately from the new part?

Dave H_2

There are alot of variables when it comes to troubleshooting a heating system.

The first thing typically needed with a radiant floor system is the heat loss and design. The design will tell us the flowrate and also the water temperature needed based upon that heat loss.

Sometimes turning the water temperature up works, but without knowing all we are doing is guessing.

I personally don't like bubble foil as the insulation under a floor; with plates, I prefer fiberglass insulation pushed up against the plates. We are looking for conduction here (transfer heat from the pex to the plate to the floor) we don't want any convection (heating air pocket).
Conduction is going to transfer that heat with out losses, if heating an air pocket, you need to make sure none of that heated air has any chance at all to leak out.

Dave H.

schtoink44

Alan, from what I read on other post and online.  Slowing down the flow on water allows the heat to transfer better 

schtoink44

David H, I am working on figuring out heat loss.  Also I do agree about the insulation.  I am going to put up fiberglass soon.

Jamie Hall

schtoink44 said:

Alan, from what I read on other post and online.  Slowing down the flow on water allows the heat to transfer better 

Oh dear. No. Slowing down the flow may -- usually will -- produce a greater delta T from supply to return. That's quite true. However... The heat transfer at any given point depends only the fluid temperature in the pipe and the temperature of the receiving material -- in this case the plates and floor. Flow has absolutely nothing to do with the heat transfer rate (well, at any normal velocity that is). What does happen with less flow is greater delta T. What also happens is that for a given supply temperature, you will get less heat transfer, as the overall heat transfer in the floor is related to the average water temperature in the system -- and if the delta T is greater the average is less.

Thermodynamics is not subject to wishful thinking...

Zman

Does the section you are having trouble with have heat transfer plates?
Slowing the flow rate will not increase output. It will make the heat feel less even and will likely reduce the output slightly.
I have heard the flow rate claim before and believe that in the case of radiant heat it is pure nonsense. The extra turbulence should help the transfer unless of course, the BTUs are too scared to jump off such a fast-moving train.

schtoink44

Alan, and yes the old side of the house is zoned separate.  

schtoink44

Zman,  yes there is heat transfer plates

neilc

did I miss it /
what water temps are you running,
what hw reset schedule are you following?

schtoink44

@neilc the outdoor temp sensor is on so that controls the temp.  Other than that I dont know if there is another setting or adjustment for that 

Zman

The outdoor reset needs to be adjusted, every home is different.
What model is your boiler?

hcpatel78

By the way, I have the same setup at my home. I have 4 loops of HEPEX installed in extruded plates (screwed on the ceiling in between joist) in well-insulated (walls) basement ceiling for my first floor colonial house.
I have a similar situation like OP when outside is below 20f. So I played with 3 things.
* I have set the highest flow rate with speed setting 3 on my alpha 2 pump that gives me 1.25GPM/loop (total 5GPM in 4 loops)
* Custom reset ODR curve from the default (80 f to 120 F) to 90-120F.
* Insulation definitely helps...I tested in one area and I see a big difference in the temperature (BTU) output of that area.
* I have Noritz combi CB199 and I can set the custom SWT with the respect to running time. e.g. I set that if the burner runs 30 minutes continuously then SWT will increase 10F more than the default SWT.
* These tricks worked for me, but I don't have the basement ceiling insulated because I have the basement wall insulated (R25). Basement heat stays in the basement for a longer period of time so heat loss is very minimal once basement temp reaches to equilibrium.
* So I am also gaining 72-degree basement temperature here in NJ while radiant will heat my upstairs living space.
* But when the outside temp. dips below 10 and single-digit this happens in the early morning my living room temp drops from 69-70 to 64-65. But in that case, I just turn on my air furnace to bring room temp to 70 in the morning and then Radiant takeovers to keep up that temperature the whole day and until 11 pm at night. In all scenarios my basement temp swings between 70 to 75 f.
* I don't want to insulate the ceiling of the basement because I can use my basement as an office. I am enjoying as a "radiant ceiling" there.

schtoink44

@Zman it's a ruud ultra series professional, I don't have the model # at the moment 

Ironman

As mentioned, there are many factors that go into designing a radiant floor that will work right. The first is an accurate heat loss calculation; it’s the foundation. 

A radiant floor is in essence a radiator. A heating designer must know the amount of heat that’s needed to meet the heat loss of the room on the coldest night of the year (design temp). He must then select a heat emitter (radiator) that has sufficient capacity to meet that need.

There are many variables that will determine the output of a radiant floor: average water temperature; tubing size, length and spacing; flow rate; heat transfer material; R-value of the floor covering; insulation value; etc just to name some. If all these things aren’t  factored, then the output of the floor may not be sufficient. That’s appears to be where you’re at now.

If you could supply us with some of these details, then suggestions could be made to help.

What’s the square footage of the radiant floor?
What’s the calculated heat loss of the area using a scientific method like a Manual J? What’s the length, size and spacing of the tubing? What’s the R-value of the floor covering? What’s the AVERAGE water temp in the floor? What kind of plates were used, extruded or beer can?

You may be able to make some modifications or adjustments to some of these factors or you may need to add some from of supplemental heat depending upon these factors.

Alan (California Radiant) Forbes

@hcpatel78 *

I have set the highest flow rate with speed setting 3 on my alpha 2 pump that gives me 1.25GPM/loop (total 5GPM in 4 loops)

Wow! That's 15 feet of head per 300 foot loop. No wonder you need an Alpha2.

Zman

Ruud seems to keep its I&O manuals top secret and unavailable online.
If you can find your manual, there will be instructions on how the read the target and actual temp and how to adjust the outdoor reset curve.
You need to turn up the boiler temps and your problem will be solved.

schtoink44

@Zman I have the manual and went through all the settings.  One was for heat type, it was set on finned tubing.  I changed it to low mass radiant heat.  I dont understand what or how but we'll see what difference that makes.  Already I can tell it's been running less and the furnace hasnt kicked on.  Hopefully finish up insulating the basement cieling and go from there.

schtoink44

@Ironman being honest I dont know the answer to all those question.  Hvac isnt my thing.  But I will do my research and figure it out.  I do know its half inch pex with aluminum heat transfer plates, each about 36" long.  Two runs per bay ( supply and return I'm assuming), with I think 3 or 4 zones on that side of house. No loop or zone is more than 300 if anything def under.  I did rough measure so I can figure out adjusting flow if needed.  Heat loss and r value of floor I'm working on figuring out.  Rest of info as well.  Thank you 

Zman

I have never seen one that does not allow a custom curve. There may be a service menu that you need to access.
Is there a way to temporarily disable the outdoor reset? What happens if you disconnect the sensor?

schtoink44

@Zman There is an option for custom, I'm not 100% certain but I think I have it set to low mass radiant (d.LrF) according to book.  But what I notice now after changing that setting earlier,  is there is the call for heat, the external pumps are running the water temp is at 112 on LCD but the burner is not on.

Alan (California Radiant) Forbes

I think you want to be careful with the water temperature if you have hardwood floors and not go over 120°.

Zman

Low mass radiant should be close to the right temp range.
How do the pipes feel? Do you have an IR gun or another way to measure temp?
Posting some pictures might help, there could be an issue with the way the new loops are piped.

schtoink44

@Zman I do have a temp gun, usually the temp in the pipes is close to what temp is at manifold.  What would you l like pics of?

Zman

Pictures of the boiler room piping from a distance would help.
I would also help to know what the manifold supply and return temps are as well as the outdoor temps on the days you are having issues.

Zman

The G.CUS setting will let you enter whatever temp you want. I am a little surprised that the one you are set to is not working, 80-140 should be plenty of heat for your system. Where is the outdoor sensor located? Northside out of the sun? Does it appear to be accurate most of the time? A sensor too close to a heat source or in direct sunlight will screw the whole thing up.

Ironman

This is very generalized, but a radiant floor with tubing at 8-9” OC and good heat transfer plates will produce about 20 btus per square foot @ 120* SWT. Floor covering and insulation will play a larger part of that.

As mentioned, you generally don’t wanna send more than 120* SWT to a hardwood floor, but there can be some wiggle room there, particularly if you have Advantech sub flooring.

So, your simplest solutions are:
1. Increase the SWT IF the flooring can take it.
2. Add proper batt insulation under the plates. At least R-19.
3. Reduce floor coverings to less than an R-2 value. That includes the sub floor which is probably about an R-1 by itself.

SlantFin has a free app from which you can do a fairly accurate heat loss calculation. There’s a link to it somewhere on site or you can google it.

If your heat loss calculates substantially higher than 20 btus per square foot, then you’ll know that you’re gonna have to add some form of supplemental heat.

schtoink44

@Zman @Ironman talked to a local hvac company today.  May have identified a few issues over the phone.  One being something stupid I overlooked is a tall cieling in one of the zones.  Scheduled apt is the 15th for them to look over the system.  Also sounds like a few settings may need to be adjusted accordingly.   I will update