Radiant floor performance troubleshooting

Leonc

Hi All,
I installed radiant heating for my first floor (stapled with aluminum plates directly to subfloor from basement) back in summer of 2021.
Both in winter of 2021 and winter of 2022, things worked just fine. We had adequate heat throughout the winter, our coldest high temps were about 10 degrees.

This week, we are getting our first week of sub freezing highs in the mid 20s, and my system does not seem to be keeping up.
No changes were made since install.
I would understand if we got a sudden cold snap, and it took some time for the floors to recover, but the circulator was running all day yesterday, and never satisfied the thermostat.
Not a particularly cold day: Outside is 29, low last night was 25, thermostat air temp is 66, set to 69. As I said earlier, we kept the house at about 69 degrees for the last two years with no problems.
Most of the basement has a finished ceiling (installed in 2021 as well), but for the parts that are still exposed, I can peel back some insulation and I see nothing visually different about the installed pex/plates.
The thermostat shows a floor temp of 87, from the sensor embedded into the subfloor around the middle of one loop.
The past two years I would occasionally check the floor temp, and sometimes it would get to 95ish degrees on days that it was sub 10 degrees outside. The floor still felt fine standing with bare feet; noticeably warmer but not uncomfortable.

When I look at the hot side of the manifold, I'm seeing 120 degrees (sometimes more) leaving to the loops, and I'm getting about 100 degrees coming back.
Second floor zone convectors are working just fine, I can get any temp I want.
DHW has had no issues (heatflo indirect tank)

Question is what would cause a decline in system performance in such a short time frame?

System details:
Honeywell T6 pro hydronic thermostat controlling the first floor zone
300ft loops cover the first floor, stapled up with aluminum plates and R19 insulation underneath
Everhot 6 Radiant manifold
Taco Setpoint 3 way smart mixing valve
Caleffi ZSR104 controls
https://forum.heatinghelp.com/discussion/183631/dual-temp-hydronic-heat-piping-plans

Is there something I'm missing? Has the tubing degraded?
Are there other troubleshooting steps I can take?
I'm getting worried that my heat loss calculations were just completely off base two years ago and I'll have to go back to using convectors on my first floor, but that still doesn't explain why it worked so well the last two winters...

Thank you all for your input!

GGross

Honestly if your floor temp is 87 right now, and was 95 last year and its not keeping up this implies you have a very high heat loss in the space. I am sure you are aware that the maximum recommended floor temp for a radiant floor in a residential space is 85 and most will consider that uncomfortable. Since we know we are transferring heat well, and the floor is cookin, what else could change? I would start looking at infiltration, no doubt if your floor required a 95 degree temp to satisfy last year you have some high ceilings and large windows in the space, perhaps some seal has given up and is letting in more cold air?

Air can act as an insulator in the boiler system as well impeding heat transfer, but if you have a good air separator this should probably not be an issue

Leonc

Thanks for the input, GGross!
I'll take my temp gun around and look into any new drafty leaks either from windows or what not. Nothing feels different from last winter and I always thought I was pretty sensitive to those things when just sitting in the room.

As for this comment:
"Air can act as an insulator in the boiler system as well impeding heat transfer, but if you have a good air separator this should probably not be an issue"

Are you saying it is possible that air is in my pex? I do have a Taco air separator (https://www.supplyhouse.com/Taco-TTK-100T-ADV-1-Advanced-Near-Boiler-Trim-Kit-Air-Separator-Combination-Boiler-Feed-Valve-Backflow-Preventer-4-1-2-Gal-Expansion-Tank) as my main separator, and my manifold also has an air vent.
If somehow there is air trapped in my pex, is there a more manual way I can get it out, as opposed to just running the system and let it bleed out the separator and vent?

Thanks.

GGross

entrained air should work itself out through your air separator relatively quickly. You will introduce more air into the system whenever you need to fill the system. I wouldn't expect the air to be the problem, but its just a thought.

hot_rod

What type of floor coverings?
was a load calculation performed?

Leonc

Floors are hardwood, with some area rugs.

Yes, we did a load calc when we installed in 2021, about 11k BTU loss over 460 square feet.

The math seemed to be fine, which is why we went forward with the install. I would think if the heat loss was done wrong, I would have seen a performance issue the first time we hit a cold temp in winter 2021, and add additional heating. We had no issues keeping the first floor at 69 degrees even with 10 degree temperatures outside the last two years. This week I can't get past 66 degrees with just a 29 degree day.
Like I said, I'm going to check the envelope, but I feel like something has to have gone wrong for such a drop in performance.

Thanks.

hot_rod

Simple to do, roll up the area rugs for a day or to. They can really reduce output when you need it most. Feel how hot the bottom side of the rug is when you roll them!

Leonc

Thanks for the suggestion Hot Rod. Your comment about the rugs had me thinking we just rearranged the furniture a few months ago. The room with the thermostat actually used to have two rugs, and now it has none. Would the rugs have actually helped keep thermal mass in the room?

hot_rod

At this point the rugs are more a liability than asset. If they have foam pads under them, you have a double whammy

neilc

so the thermostat, no rug room is heating up faster than the room with the carpeting,
like throwing a blanket over a cast iron steam radiator

Leonc

Sorry I'm really confused now. We have two main rooms on the first floor. For the last two years, the room with the thermostat had rugs in it, and the heat performed just fine (+60 degrees). This year, we rearranged, and now that room no longer has any rugs in it at all, and the heat in that room (and as far as I can tell, the rest of the first floor) has gotten worse, (can't get +40 degrees). No carpeting in the house at all.
Are we saying the rugs were making my heat worse last year, and are some how the cause of the heating issues I'm having this year? No foam pads.

hot_rod

Your best indication of heat being delivered is the supply and return temperature. Expect a radiant to be operating anywhere between 10- 20 degree differential. Measuring a warm floor surface everywhere would eliminate an air locked loop. If so it doesn’t sound like a flow issue.

Two missing numbers are what is the heatload of the space that is falling behind. And if you knew the gpm flowing into that zone you could calculate how many btus are going there. Then compare the calculated. Heat load to what the floor is actually doing.

It doesn’t make sense that the floor is warm, but the ambient keeps dropping. Especially if it worked in the past.

Actually the colder the room, the higher the floor output as the temperature delta increases, so does heat transfer.

Really floor should be able to cover the load at a maximum 82 surface temperature.

I was looking for any change in the room that prevents heat from the floor getting to the space. Furniture, carpet, built in.

psb75

It sounds like your system is able and presently IS delivering heat. The question is, IS your house able to
retain that heat efficiently? The floor is MORE able to deliver heat with the carpets gone. Are there new, unknown places that you are LOSING heat? Put your hand on the manifold that is sending heat out and the other hand on the manifold with the water coming back. Is there a nice temperature differential of 10 to 20 degrees? If "yes', that means your system is working. The OTHER system...is the house envelope itself-- that RETAINS the heat that is delivered. Is THATworking well?

Leonc

Thank you all for the comments! I'll go back and double check the heat load calculations, and try to remember if any other changes to the house could have an effect. Seems like things are not so bad, as today we are even colder, and we are able to keep the first floor warm.
I'm seeing a 20deg drop in the exit and return for the manifold. I'll have to get out my temp gun to get the surface temp of the floor.

hot_rod

The main reason that residential radiant floors design around a 10- 15 delta is for comfort. You want the floor temperature to be a consistent as possible.

If you run in that 10- 15 range when you reach thermal equilibrium ( supply and return temperature stabilizes) , all is good.

This shows what a 300' loop would look like running 3 different delta Ts. Same 110 supply temperature in 3 examples.

neilc

Leonc said:

Sorry I'm really confused now. We have two main rooms on the first floor. For the last two years, the room with the thermostat had rugs in it, and the heat performed just fine (+60 degrees). This year, we rearranged, and now that room no longer has any rugs in it at all, and the heat in that room (and as far as I can tell, the rest of the first floor) has gotten worse, (can't get +40 degrees). No carpeting in the house at all.
Are we saying the rugs were making my heat worse last year, and are some how the cause of the heating issues I'm having this year? No foam pads.

ok, so, now no carpet,
but last year there was, in the room with the stat, was the carpet being the blanket on the Rad(Floor), and keeping the thermostat on more?
and now the rest of the house is the heat sink?

what temp are you running? and are you doing OA reset?

Leonc

hot_rod said:

The main reason that residential radiant floors design around a 10- 15 delta is for comfort. You want the floor temperature to be a consistent as possible.

If you run in that 10- 15 range when you reach thermal equilibrium ( supply and return temperature stabilizes) , all is good.

This shows what a 300' loop would look like running 3 different delta Ts. Same 110 supply temperature in 3 examples.

Thanks for this diagram hot rod! I also just want to say thanks for all of the info you have provided in your videos and on this forum, I wouldn't have been able to get half of this system put together.

I did a bunch of checks last night, I'm getting a 15-20 degree temp drop throughout the zone, and my floor surface temp is measuring in the 80-83 range. My initial post was two days ago (with temps from 27-30) , and yesterday was even colder (19-25) and I didn't see a performance drop, so I'm no longer on the edge of the cliff that my system "doesn't work".

I really appreciate the comments from everyone to help me make sure things are working as designed and I think they are. My old windows and doors probably just got just slightly worse to make me feel like this, and that is for sure the next "heating" investment I'll be making.

Leonc

neilc said:

ok, so, now no carpet,
but last year there was, in the room with the stat, was the carpet being the blanket on the Rad(Floor), and keeping the thermostat on more?
and now the rest of the house is the heat sink?
what temp are you running? and are you doing OA reset?

I really doubt the rugs were actually making any difference, just throwing around wild theories since hot rod said to remove the rugs, but was likely not aware of the actual rug configuration in the rooms.

I'm running 180 from the boiler to DHW and 2nd floor zone convectors, and a setpoint mixing valve to drop the temp to 120 for the radiant floor.