radiant floor heat not supplying enough heat

[stealman]

I just finished up my hydronic system about a week ago and the system does not supply enough heat. I am hoping that someone may be able to offer some advice. In all fairness the insulation is not 100% yet and we are having really cold weather, but I thought the system would perform better.

I paid a professional to do a heat loss calc. and design the system and I assembled the system. I have 1400 sq. feet and 12' plate height and 17' to the ridge.
3" ridged foam under 4" concrete, the pex is stapled to the foam at 12" centers. 4" ridged on stem walls with a 45* at the top and 8 inches of stem wall uninsulated above that. R 42 s.i.p. walls. R 30 fiberglass batts in the ceiling, I will add another 3" of ridged foam to the bottom of the truss, but have not done it yet. The building has no sheet rock yet.
The heat system is a 100,000 btu high efficiency condensing water heater with a Taco x pump block to control the system.
I have the thermostat set at 55* and the system runs all night none stop and the temp only gets to 53* {I cant imagine how much propane that uses}. As soon as the sun comes up the temp come up to 55 or higher and the heater does not run all day until about sunset ant the the system run all night again.
Night time lows are -5 to -10 normal is more like 10 to 15 and the highs are like 10 and normal is like high 30's.
Does anyone have any ideas? Is this normal or how I can improve the performance? How much difference will the 3" ridged on the ceiling make? The inside temps don't bother me much, but I am worried about how much it will cost to run. I have done every thing I could think of to build a efficient building and I am a bit bummed at the moment.
Thanks for listening.

 

[socapots]

Most of the heat loss is always through the roof.
Everything I've always seen had lots in the roof. And not as much in the walls.
So maybe more R in the roof will help.

 

[Randy in Maine]

How hot is the water going to and coming back from the floor?

When it is cold and windy outside and you don't have adequate insulation, it will require some BTUs to heat up the slab and to keep it at 55º.

 

[stealman]

I am really hoping that the extra r20 in the ceiling in the will make the difference.
The supply temps are 105* and the return is 82*.

 

[Dick in Wisconsin]

Are those the temps in the morning after its been running all night long? What is the surface temp of the concrete floor? (shoot it with an infrared gun) Do you have spots that are much colder than other? is there a "dead zone" in the tubing that isn't getting the hot water?

How many square feet of floor space? How many loops? How long are the loops? Are there any valves on the manifold that might not be completely open?

Do you know the temp of the water coming off each zone? Maybe a zone or two isn't working.

 

[anthony666]

lets see a picture of you near boiler piping

 

[stealman]

The temps I listed are the temps at the time I posted. I dont think they are much different in the a.m. The valves on the manifold are all the way open. I have flow guages on the manifold and they are all the way open. Although the max flow that they are showing is about 2.75 L.P.M. I have 5 loops and 1400 sq.' The surface temp on the floor at the present is 55*. I can take pictures in the morning and try and post them. I have not posted pictures before so I might have trouble with that one.
Thanks for the interest. This is my first experience with hydronics so I know little about it.

 

[KenB]

There are a lot of variables, but I think you need a higher delta-t, the difference between supply and return temps. Increasing your supply temp to around 120 degrees should help a lot. After that, restricting flow to decrease return temp to about 75 will squeeze much better efficiency from the system.

Ken

 

[Sureshot]

First thing I would try is slowing the water down to give it time to drop its energy.

 

[wedge40]

Which pump are you using?

 

[stealman]

I am using a Taco x pump block. It is a heat exchanger pump and mixing valve in one. I am using the outdoor reset mode, which calculates supply temp based on outside air temp. It also has a delta t mode which I dont really understand. I am not sure if I can manually adjust the supply temp.
I have been speeding up the flow through the loops thinking that it might hepl. So you think I should slow it down? How much drop in temp between supply and return should I be looking for?

 

[theoldwizard1]

3" ridged foam under 4" concrete, the pex is stapled to the foam at 12" centers. 4" ridged on stem walls with a 45* at the top and 8 inches of stem wall uninsulated above that.
...
Night time lows are -5 to -10 normal is more like 10 to 15 ...

Too late now, but I would have gone with at least 4" under the concrete.

What is the temperature of the uninsulated stem wall and how do you plan on insulating it ?

 

[Blk88GT]

First thing I would try is slowing the water down to give it time to drop its energy.

Agreed.

 

[ReneJK]

How much drop in temp between supply and return should I be looking for?

Where we are (Europe) delta T we're looking for should be at least 20 degrees but preferably 30-35 degrees

slowing the water flow (letting the pump run slower) ensures that the water gets time to release its energy and get cooler

you also said that the system has only been running for a week ? , might take 'a bit' longer than that for the slab to heat up. Typically we're being advised to up temp by 5 degrees per week to prevent problems with the concrete

 

[stealman]

Too late now, but I would have gone with at least 4" under the concrete.

What is the temperature of the uninsulated stem wall and how do you plan on insulating it ?

I'm sure the 8" of exposed stem wall is very cold. I am not sure how I should go about insulating it. Seems like 2" of ridged on the exterior would be good, but I haven't seen a good detail. How do you keep the ants from eating it. The easier method seems like 1" on the inside. Thoughts?
Thats funny you say to put 4" under the slab. Seems like everyone goes with 2". I do 3" and still not enough.

I slowed down the flow at the floor loops and will monitor to see if it helps.
The system has only been running one week. The slab temp comes up all night long until the system turns off when the sun comes up and then the floor cools off all day and the cycle starts again in the evening

 

[Blk88GT]

Where is your thermostat? Do you have a slab sensor?

 

[stealman]

Where is your thermostat? Do you have a slab sensor?

I don't have a slab sensor, but I am open to installing one. What is the benefit of it.

I have tried the thermostat in different locations. The exterior north wall seemed too cold. Right next to the heating controls stayed too warm. Presently it is on a interior wall at the north end. I think this is the best so far.

 

[jlckmj]

I have 2 inch foam board on the outside of my slab and the slab is 5 to 10 degrees colder at the outside perimeter than the rest of the slab.

It looks like you are fighting the cold without it, I would bet that your slab is colder much farther in. Like suggested above, pick up an infrared thermometer and check the temp of the whole slab.

For your other question;
On the outside of my slab, I used aluminum flashing over the insulation to protect it where it is exposed, I actually went over the insulation down to a couple of inches under the ground, bent it over the top of the foam (exposed 2 inches), then went in and up a few inches under the siding.

Jim

 

[custom1]

I never hooked my floor up yet and I'm not a heating guy. These are just some questions that came to mind.

What is your heating source? Edit...Never mind this one. I must have missed that the first time through.

How does the outside reset thing work?

What is the outside temp during the day when it shuts down? Does it stay off all day?
I guess there is an outside sensor, if so where is it located? In the sun?

Where are you located?

I looked up that Taco pump.

Why the need for the heat exchanger as part of the pump? Why not just a pump. Are you running antifreeze in the floor and water in the heater or is there some other reason?

When you read the supply and return temp, is that on the heater or floor side of the exchanger?

If it is shutting down all day it probably never got up to operating temp yet. You might have to do away with the outside reset thing. It sounds like it is starting up for the first time everyday.

Just a guess. If you run it on the delta-T setting it probably adjusts it own speed to get that temp difference.

A couple of pics would probably help spot a problem.

Also I think you are loosing a lot of heat to the outside if your floor is not separated from the outside wall on the inside of the wall.

 

[Highbeam]

Your insulation and construction methods are not your problem. Sure, you might have an improvement or two you could make but you have another issue. You will discover that you are not wasting energy. It is not that your system can't keep up, it is that your system thinks it is keeping up.

You have a mod/con boiler that is designed to use less energy but burn longer. The most efficient way to run a boiler is all the time at low output and that's what it is doing.

You set the stat for 55 and you are getting 53. That's prety close, within the standard variance of a stat. Try bumping the stat up to 60 and see what you get, I'm guessing you'll get 57.

 

[stealman]

I don't have a boiler. It is a water heater 50 gal. 100,000 btu. The way I see it is it is like a on demand with 50 gal. of storage.

Let me try and explain the situation as I see it and hopefully I can find answers to solve the issue. It is 11* outside right now and sunny. Unusually cold. The air in the shop is 58* the floor temp is 53*. The heater has not run since around 8:00 a.m. It is comfortable in here. When the sun sets The temps. drop fast outside and it takes a little while to cool off in the shop. The heater kicks on and runs non stop until 8:00 a.m. Mean while the temperature inside drops slowly all night until the sunrise.

Remember the system has only been running for a week. I ran the heat nonstop for 2 days until the slab and air temp got to 58*. And then set the thermostat to 58*. Thats when this cycle started of heat off all day and on all night. And a cooling of the building all night.

It seems like the slab is not getting enough heat. Or loosing too much. A combination of the two most likely. Or I still have not brought the mass of the floor fully up to temp. I thought That when I got the floor to 58* and the air was the same that things had equalized and I was good to go.

 

[Highbeam]

A 100,000 btu water heater is the same as a 100,000 btu boiler as far as I'm concerned. Both make 100,000 btu for your floor.

You have a wall stat and are comparing that setting to the floor temps? How are you measuring floor temp? Is your wall stat programmable or do you leave it on one setting?

The operation you describe is exactly how I would expect floor heat to run. There is a huge lag between the time when the thermostat calls for heat and when the stat is satisfied. The floor temp is likely overshooting in the morning, shutting off, and then must recover in the evening. You will get temp swings with such a large thermal mass.

This is not a hot air furnace. That funky outdoor reset, mixing valve, scenario might also be making things worse.

 

[ejk52d]

What type of perimeter slab insulation do you have? what model water heater do you have? I have heated 10000 sq ft with 145,000 btu in N IL somethings not right.
If your picking up a large amount of passive solar during the day then your outdoor reset should be compensating for the gain. where do you have the outdoor sensor? It should be on the north outside surface isolated from the building. You may also need to tweek the settings on the reset.
As far as flow if anything your to low with that high of delta t across the circuit. Low flow loops in europe are in series a slab is parallel and should have around 15* delta t or temp drop.
What appears to be happening is that it runs all night and overshoots by morning and shuts down. the sun then warms it all day allowing the slab to cool down.

 

[hidollartoys]

Install a slab thermo sensor. Let it overide the air stat on call for heat.

 

[stealman]

Thanks for all the ideas and thoughts. I am kind of getting confused. Some are saying speed up flow others are saying slow down.

I have a programmable thermo, but I have been over riding the program and just setting a temp. For measuring slab temp I just have a thermo laying on the floor out of the sun. The out door reset thing I don't really understand. The sensor for that is on the exterior North wall. My cystem has a delta t mode as well. Should I try that? How does that work?

I kind of like the idea of a floor sensor. Would I just use a temp prop. drilled into the conc. connected to the thermo?

I bumped up the temp on the therm to 60* a couple of hrs. ago. The floor temp cam up quick from 54 to 61 and the indoor air temp rose to 60* for a bit, but now the indoor temp is falling the pump is circulating, the heater is turning on and off and the temp in the building is falling. It is down to 58* and the floor is 61.5. It seems like a case of just not enough insulation? What do you think? The thing is, is that the building is insulated very well except for the ceiling. And it is r30 which is not bad. Maybe the 3" ridged on the ceiling will make all the difference?

 

[Highbeam]

Your "problem" is that your measured temperatures are not exactly the same as your stat setpoints, right? They are within a couple of degrees though. I would not try too hard to fix this problem. Don't you think that this is just the flywheel effect of a huge thermal mass heater?

 

[Highbeam]

Try bumping the stat up to 60 and see what you get, I'm guessing you'll get 57.

Do I get a prize? Pick what temperature you want and adjust accordingly.

 

[Dick in Wisconsin]

is the inside of the building comfortable?

"but now the indoor temp is falling the pump " What is the outside temp? That is really, really important every time you talk about how your system and building are behaving.

When you had the heat calcs done, how many BTUs was the breaken between outside air temp and 100,000BTU water heater you have?

For example, if the building will leak 105,000 BTU at 18*F and you have a 100,000BTU water heater, as the outside temp goes below 18*F the water heater will run full blast, the pump will continuously circulate water, and the temp inside will slowly fall. The BTUs escaping are greater than the BTUs being put into the building, plain and simple. This is the assumption at night with NO help from any solar gain.

The day time on a sunny day might be different (a little bit better) with some solar gain.

As you add insulation (reduce the BTU leaking out the building) and reduce air infiltration, the performance of your heating system will improve.

Keep us posted.

 

[stealman]

The problem is I have the thermostat set to 60 and the temp came to that for a little while, but now it is getting colder and the temp in the building continues to drop. Is that the way this radiant works. I thought radiant floors where the most comfortable and at night it gets cold in here and wont warm up. If I could turn the thermostat to 60 and get 58 that would be great, but the temp just drops as the night goes And the heat system runs full tilt.

The heat loss calcs. show 38,000 btu. required, but that is with the 3" ridged foam yet to be installed. I would think that my 100,000 btu. heater would still do it.

 

[Dick in Wisconsin]

When the sun goes down, turn the termo stat to 70 and see what happens. (I expect the water heater will run continuously, the pump will run continuously, and the temp will go down.)

I think your building is leaking at night, with the current outside temperatures, more than 100,000BTUs (the output of the water heater) per hour.

Regardless of the type of heater you have, if the building is leaking MORE heat (measured by BTUs) than your heat source puts in ... then the temp in the building will drop. I don't think it gets any simpler than that.

I live in Grafton, WI; about 25 miles north of Milwaukee. When I build my 1,000sf race shop in the spring I'll put radiant in the slab with what I expect (and hope) is enough insulation under the slab, in the walls, around the stub wall, in the ceiling and try my best to seal the building up. I have an unused, existing (no cost to me) residential natural gas water heater that will heat the water for the radiant heat. I have resigned myself to the fact that because of the limits of the water heater I will having the following limitations:

1. Moving the temp from say 40 to 60 will take a while.
2. Once the temp gets in the teens (maybe single digits if I'm lucky), I won't be able to hold 60 or 55. As the O/S temp goes down below zero I will be stuck in the 40's and maybe high 30's.

I hope that helps you understand what is going on with your building.

You could get an infrared camera to show you where your heat is leaking out of the building. Or you could use an infrared temp gun (I use a Sears one with the race car and am happy with it) to shoot the surfaces ... floors all over (especially around the outside perimeter), outside on the walls, door, windows, stub wall, etc. which will help you further understand where you're leaking the heat. Even a remote thermometer in the attic above the insulation with the master readout in the shop and/or house will allow you to compare the outside air (with a sensor outside) and the attic. The warmer the attic of the shop is compared to the outside air temp ... the more heat you have leaking from shop to the attic; hence insulation will help.

Believe it or not, I've had friends who have spent money on insulating attics or this or that and have seen ONLY marginal improvement ... all because the existing insullation was adequate and anything beyond was "diminishing returns".

Keep posting. You're making me think about my upcoming build.

 

[HoosierBuddy]

I agree with **** from WI.

Forget about the delta T, etc. Your water heater is running flat out with 100,000 BTU/hour input and can't keep up. That means you are losing more heat than that.

Solution?

First check for drafts. If you're leaking air that will kill you. Drafts are much worse than just "under insulated".

Second, insulate what needs insulated. Sounds like you know what needs done, you just haven't gotten to it yet?

Your water heater will be burning through a bit more than a gallon an hour if the burner is on all the time. Figure what? 12 gallons a day? Is that about $10 per day at current prices?

Fix any drafts. Insulate.

Phil

 

[Fastback]

My .02
Stop dicking with it until your inside insulation and wall board is up and sealed.

Also, I cant tell from your initial post but did you provide a thermal break between the slab and the foundation walls?

Also, we dont know what your system pressure is yet, or if you have the air out of the system and we dont know how you are taking heated fluid from the tank and returning it etc... Post a pic.

 

[Sureshot]

A temp gun is a necessity not an option if you use infloor heat. My mixing valve takes its cue from the return line. I found it to be much better that way.

I don't know how you are getting an air temp that is higher than the slab. It should be a few degrees less in winter and especially if you are losing heat as other suspect.

You may also be worrying too much. Set the indoor temp and give it 24 hrs to acclimate.

 

[stealman]

Lets see if this works. Here is a picture.

 

[jlckmj]

Stealman,
I am definitely not an expert, It looks like you have plenty of insulation, (other than possibly your stem walls) R30 in the ceiling is about what I have, so that is probably not your problem.

If you are worried about the cost, turn it down to 55* and let it be. In fact, I would be turning it down until I found a temp that it maintained with the heater running fairly equally both day and night, then work out the bugs. Like others have mentioned, it may very well be working the way it should be, but modulated down so it is not running full bore.

What are you going to do in the garage? I have mine set at 55* and I was in there working today with only a flannel shirt on and I was sweating. You normally do not need it as warm as a garage with forced air.

You seem to have tried everything other than the Delta T setting instead of the outdoor reset. I would read up on how that works with your system and try to get that working instead of the outdoor reset and see what happens.

Buy an infrared thermometer ($30) so you can check the floor for cold spots, and around doors and windows for air infiltration. In my garage, if the floor temp is 55*, then the air temp is about the same or a few degrees lower, and the inside of the walls and the underside of the ceiling is the same as the air temp, Everything is very close in temperature throughout the garage.

Jim

 

[Shop Specialties]

Are you sure you got all the air out ?

 

[theoldwizard1]

Thanks for all the ideas and thoughts. I am kind of getting confused. Some are saying speed up flow others are saying slow down.

The only way you will really know which is correct is to install a thermometer at the outlet of the water heater and at the return from the floor.

I bumped up the temp on the therm to 60* a couple of hrs. ago. The floor temp cam up quick from 54 to 61 and the indoor air temp rose to 60* for a bit, but now the indoor temp is falling the pump is circulating, the heater is turning on and off and the temp in the building is falling.

So why is the burner turning on and off while the pump is still running ?

This is why you are cold !

I am no expert, but there could be an overtemp in the water heater burner shutting it down. (I actually have that problem with my horizontal flow forced air furnace when it is extremely cold out; The burner can not run more than 10 minutes without tripping the overheat sensor)

 

[theoldwizard1]

Forget about the delta T, etc. Your water heater is running flat out with 100,000 BTU/hour input and can't keep up.

It can't keep up because the OP stated that the burner was cycling. Got to figure that out first !

 

[bams50]

No idea what the problem is, but I want to learn before I build mine. Keep at it, and keep us posted with what you do and the ultimate solution. I am subscribed!

 

[philjafo]

Can't tell from the pics what direction is the water flowing in the system, supply coming from the hot side and return going into the cold side of the tank? Tank type heaters don't work very well if you try to run them backwards.