Radiant Floor Not Keeping Up

[Mralalex]

Good evening,

I am a new user but have used your site for reference for years. There are some very knowledgeable people on here. I am now able to officially thank you for all the help in the past.

On to the question that finally stumped me and made me sign up. I recently bought a new to me home in Wisconsin. 2700SF heated solely with infloor radiant heat in concrete. 3/4” Grey pex tubing. 8 zones. I have no idea if under the slab is insulated or of the pex spacing in concrete. The house is 30 years old with all original windows, doors, etc. 2x6 exterior walls and there is decent fiberglass insulation in the attic, but I can feel drafts from the windows and doors. The temps have been in the single digits here lately. The house slowly loses heat throughout the night with temps around 65 in the morning and thermostats set to 70. House normally catches back up during the day and the boiler cycles. The furnace runs non stop throughout the night. The radiant in floor system is original to the house but the boiler has been replaced approximately 3-4 years ago with a HydroSmart unit from Menards. My outgoing water temperature is 120° and return is around 90° (Plus or minus 5°). Boiler readout says 2.7GPM. There are two pumps on the system. One fixed and one variable speed with it set on speed 3. I know the previous homeowner installed the system himself. Boiler systems are new (and confusing) to me. I am unconfident the system is sized correctly for the house and/or hooked up correctly. Any advice is appreciated.

 

[Mralalex]

Picture for reference.

 

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[Fitter30]

For your windows to get u by for the winter there is a film that is put over the windows inside and will cut the drafts. There are other brands hardware and box stores carry them.

Amazon.com

Doors cold coming from the bottom put a towel down weather stripping at the hardware and box stores but with your temperature id wait till it gets above freezing. Radiate floor heat temps vary on type of floor coverings. Wood floor temp not over 85° carpet or ceramic little higher. Call ur utility companies see if they offer a energy audit that includes a blower door test( tell how tight the house is). Boiler piping looks correct.

 

[Mralalex]

Thanks for info. I am aware of the different solutions for drafty windows and doors. I apologize for the mountain of text on the original post but I wanted to give a little context to the situation. All floors have ceramic tile. I appreciate the insight on the boiler piping. The different connected loops seem incorrect for someone with little radiant system knowledge.

 

[Fitter30]

Boiler is piped in a primary/ secondary loop configuration. Bottom pump look right see there are two tees next ot each other they are the primary loop that is part of the boiler piping. Secondary loop goes out to the floor loops. Boiler piping bottom left supply , right boiler return. Top radiate manifold supply to the floor, bottom manifold return. Follow the piping from return manifold black y fitting is a strainer. The two tees back to back is for hydraulic separation. Grey tank left of boiler expansion tank and the brass fitting it's connected to air eliminaator. Can't read the gauge what are the readings?

 

[Mralalex]

Gauges read pressure and temperature. Upper gauge reads 120° when operating. With pressure usually around 28 psi when operating. I have seen the pressure as low as 5 psi.

Lower gauge is the same design. Temperature usually reads 85-90 while operating with psi around 30.

It does make me feel better knowing everything is piped correctly. I’m now leaning towards the house not being sealed up well enough for the cold winter nights.

 

[Mralalex]

When looking at the lower pump. Just to the right where the two T’s are piped in, there is a ball valve in between them. Right below the green corrosion. Should this be closed to prevent a “short circuit” or is being open correct?

 

[John Gayewski]

I think I'd turn the temp up. Concrete slabs can go to 150 degrees F safely.

What is thr total heating load for the house?

 

[Fitter30]

Surprise that the boiler relief valve isn't dripping or blowing since it's factort set at 30 lbs. The expansion tank has either lost part of its air charge or has failed. To check the charge need a 0-50 lb tire air guage that is straight and tire pump. With a cool system 80-90° boiler and pumps off take the cap off bottom of tank depress the valve if water comes out tank is bad little or no air pump it up to system pressure. Pressure should be around 10 psi. Your floor heat is all one zone.

 

[Mralalex]

My expansion tank had only 2-3 psi. I added more air. Time will tell if it’s holding. I did not get any water out of it. After continuing my research on this. I’m wondering if my circulator pump is too small? I have a delta T of 30-35 degrees as return temp is 85-90°. My floors never feel toasty warm, just warmish. Would a bigger pump push the water quicker therefore getting warmer water to areas for a warmer floor? My understanding is you want a delta T of 10-20. Is this correct? Is my 30-35 degree difference unusual? I have never read the floor temp with an infrared thermostat but could do that this weekend.

 

[Jadnashua]

In a concrete slab, you can likely raise the outlet temperature some. You might also check to see if the boiler can support an outdoor reset controller. This would raise the temperature of the boiler when the outside temperature drops to provide more heat to the floors, and lower it when it's warmer outside. Having the boiler run constantly isn't an issue as that will provide the best comfort.

Radiant floor heating normally won't make the floors 'hot', but generally, they would not feel 'cold'.

You probably don't want to put in a larger pump, but I'm not positive on that. I'd bump the outlet temp in say 5-degree increments until it can maintain the room temperature you want.

 

[John Gayewski]

My expansion tank had only 2-3 psi. I added more air. Time will tell if it’s holding. I did not get any water out of it. After continuing my research on this. I’m wondering if my circulator pump is too small? I have a delta T of 30-35 degrees as return temp is 85-90°. My floors never feel toasty warm, just warmish. Would a bigger pump push the water quicker therefore getting warmer water to areas for a warmer floor? My understanding is you want a delta T of 10-20. Is this correct? Is my 30-35 degree difference unusual? I have never read the floor temp with an infrared thermostat but could do that this weekend.

You should have a delta t of 10 to 15 degrees on a radiant floor in a living space. Even lower depending on the situation. One side of a room shouldn't be 20 degrees colder than the other. The reason I asked for the heating load is because that's a major ingredient in pump size.

 

[John Gayewski]

Even with an outdoor reset a concrete floor can't respond if there's a large temperature change that happens pretty quickly. It would take all day.

I have read about some predictive thermostats that use weather forecasts and correct themselves accordingly for high mass floors. But I don't know much about it.

 

[Mralalex]

I am not an expert on heating load. After googling and using a crude calculator it said I should require 48,000 BTU. I entered square footage, average amount of windows, average insulation, ceiling height, region (blue) and a couple others.

 

[John Gayewski]

I am not an expert on heating load. After googling and using a crude calculator it said I should require 48,000 BTU. I entered square footage, average amount of windows, average insulation, ceiling height, region (blue) and a couple others.

Need to know the longest loop length. Are there lengths written on them anywhere?

 

[Fitter30]

Boiler temp difference is only one reading need to know the loop readings and manifolds. Any rooms warmer than the others? Could cut the flow down to individual loops. Looks like ur pumps are grundfoswhat are the model numbers?

 

[John Gayewski]

Assuming that load is correct. With 10 degree delta. You need 9.5 gpm.

If the longest loop is 300ft. You have 18 ft of head (using a standard estimation multiplier).

You need to look up thre pump curve for your pump and see if the pump can do that. Looking at it I'm gonna guess it can't.

You could have shorter loops and the 18 ft of head would drop significantly. A 200 ft loop would be 12 ft of head. So the tube length would be nice to find out.

 

[Mralalex]

Unfortunately there arnt any markings, writing or indicators of tube length. Seeing as this is all buried in concrete I don’t see any way or finding this information out. I did realize the pex size is 5/8” (not 3/4” as I mentioned earlier). The upper pump is a Grundfros - one speed and the lower pump is a Steibel Eltron - 3speed (set on speed three). I found the pump curve chart for the Grundfros (which is discontinued) which I believe shows this pump to be inadequate. Pictures and chart are attached below.

 

[Fitter30]

That pump curve is for 9 different pumps. Need the model numbers. How are you measuring the pex od? There is a lot of difference between 1/2, 5/8, 3/4 loop maximum is 300', 400', 500'.

 

[Mralalex]

I have found another pump curve chart with just the pump I have. Grundfros UP 15-42 F. As for pex size, I found factory applied writing on the tubes stating the pex is 5/8”.