In floor heating vs. radiant vs. forced air in shop??

[Raspy]

wedge,

You're right.

Sometimes design theory and construction realities don't match up very well. Interesting how contractors personalities can affect the outcome on projects. Each owner has their own set of concerns or biases. All parties have their own set of responsibilities.

I agree that it may be inappropriate to venture off the actual mechanical design aspect, however, it seems necessary to work through these very questions on every project. As I mentioned in an earlier post, I interview the homeowners and the architects to find out just what it is they want and what their particular needs are. I'm also looking for some misconceptions they may have that can lead to disappointment later, or can lead to something better than they may expect. I can serve them the best when I know the most.

As shown in this entire thread, many have preconceived notions about the operation of radiant heat. Such as it must always be left on or that you cannot use setback thermostats or that it should not go into a structural slab, etc.

I certainly don't intend to offend anyone. Just cut to the bottom line and deal with the realities I see. I'm big on getting past the myths that can affect designs in a negative way. Get it all out on the table, so to speak.

Again, no offense intended. Now we can get back to the actual hardware. Whew! :laughing:

 

[mjncad]

guys guys.. getting political. Not that I dont enjoy a good debate, but I was learning a lot and hope we can continue with the original intent of the thread.

Wedge

Good point Wedge. I replied to Raspy via PM to keep this thread on track and unlocked.

 

[patrick_g]

I'm trying to understand if the PRC is so wonderful why anyone would be so gleeful about exiting it for Nevada. (Yes, I also try to put out brush fires by smothering them in gasoline!)

Having lived in California TWICE ('63-'64 Pomona and '67-'00 San Diego) I feel I am authorized to comment on the way things were in the PRC ( I still get reports from friends and relatives.) Since we retired ten years ago my wife has never been back and I was back to SOCAL one time a few years ago on business. Instead friends and relatives in California look forward to their visits out here in Oklahoma. Although this summer we will be in San Diego briefly going to and returning from Kauai I can't imagine being enthusiastic about wanting to return to the PRC.

The PRC is obviously (even to the most casual observer) over regulated. What may have been intended (or started) as benevolent paternalism went awry.

The above, like gravity, is not subject to individual choice, it is just the way things are and are continuing to get worse. (See also Feinstein and or Boxer)

Just wait until there are more voters on the dole than remuneratively employed and lookout as the "underclasses" vote themselves pay raises. Ditto regarding the Hispanic hordes, legal and illegal... motor voter, what a great idea. One of the stated goals of the Viva la Raza chanting mob is to retake California through all means necessary and so far so good for their cause.
//SOAPBOX MODE = OFF//

(Warning, thread topic content follows.)

Sufficient rebar to get the required reinforcing after accounting for the REAL not IMAGINED reduction in effectivity due to running conduit, chases, PEX or whatever adjacent to the rebar runs is not difficult to achieve and I never claimed it was. I tend to over design and tend to use way more rebar than the minimum engineering standards call for so even if I did tie PEX adjacent to rebar it would not be a likely source of failure. As a mater of fact, I do not run PEX along rebar but do tie it to rebar with the crossings at or near 90 degrees (least strength reduction.)fr Current house's in-slab hydronics has PEX tied to rebar. I have three rooms (two zones) with radiant ceilings vice floors and the time constant of those radiant panel installations allows setback strategies to work nicely.

Just one example of in-slab radiant: My great room has in-slab hydronics and most of the time gives excellent performance but... in the shoulder seasons especially you can easily get over heating when along comes a day or two of mild temps compared to previous days. The slab has been heated until it sheds the required Btu's to maintain stasis at the setpoint on the 'stat. Then the mild day and SHAZAM the space can be considerably overheated. The thermal time constant of the slab is such that it just won't cool very fast and there is little you can do about it but grin and bear it, open the windows, or run the A/C if you only have in-slab heat.

I have pairs of stats in several of my zones. One of the stats of a pair controls the hydronic heating of the slab and the other stat is for hot or cold forced air. In the shoulder seasons I run the hydronic stat a few degrees lower and use setback strategies with the air stat. So overnight the great room temp drops quickly to the setpoint of the hydronic stat and the next morning the air stat acts to bring the temp up to the desired room temp. If we experience a warm day the air stat has little or no activation and the room temp stays much closer to the desired temp. Of course in the middle of the winter I run the floor as THE heat source and set the air stat a few degrees lower than the hydronic control stat. If say there is a party or whatever causing lots of outer door openings and the room is cooled... well then, the air stat calls for hot air and the temp is rapidly restored and then the hot air shuts off until next time. Ditto if a "blue norther" (or other sudden temp plunging phenomena) hits and the slab can't react quickly enough then the hot air comes on and comfort is maintained. The record in these parts for maximum temp drop in a 24 hour period is 80 degrees F. My system will keep you comfortable. Pure unassisted in slab hydronics would not stand a chance.

Then the weather is warmer but has the occasional cold snap, hydronics only can't respond quickly enough and you will have an uncomfortably cool space. In the spaces with pairs of stats there is no problem. If the outside temps take a dip the air stat does what is needed to maintain the setpoint. The time constant of the slab is just too great to allow the room to be sufficiently heated in time to maintain comfort when the outside temps change too quickly.

The above scenarios are not theoretical conjecture but are observed fact. Along these lines a very competent geothermal sales and installation guy I interviewed but didn't select avoids in-slab hydronics due to over/under heating issues based on immutable laws of physics. I selected another HVAC contractor and in collaboration we designed my system. My system is not the cheapest design BUT it works well.

I have three heat pumps in this house and two propane furnaces (and 4 direct vent gas logs), one of the heat pumps is geothermal. It supplies all the hot water for the hydronics and preheats the DHW in a 50 gal storage tank which feeds a 40 gal propane fired DWH tank. It is not prudent to try to get more than about 115 degrees F out of the Water Furnace brand geo unit so the propane is used to "top off" the temp of the DHW to appropriate sanitation temps . Should there be a problem with the geo unit DHW consumers will not know as the propane unit will just do the whole water heating job just fine.

I typically have as low or lower heating and cooling monthly costs than friends and neighbors with smaller homes ranging in size from about 1/5 of our floor footage to about 1/2 or so. My metal and wood working shops are attached to and part of the house but not counted in the floor footage comment above BUT are counted in the heating and cooling costs. The metal shop is about 21x50 or a tad over and the wood shop is 24x36 (less a 6x12 section "donated" to the attached garage by a wall with a "bump out" and then another 175 sq ft in the shop where it makes a 45 degree attachment to the house proper.

Pat

 

[Raspy]

There are a number of factors and strategies that help radiant to keep up during cold snaps and to help stabalize interior temps.

I've found that a weather cold snap has little if any affect on the interior comfort if the system is set up properly and designed properly.

In my setups I am always trying to make them work so well that people forget the thermostat completely. This is a good measure of performance. People will sometimes call after 3-5 years, when the heat stops, and I'll simply ask them to replace the t-stst batteries and call me if that does not fix it. Most oftem it does. Once I found a home where the woman didn't even know they had a thermostat. That house was worth studying to find out why!

First you have to start out with enough BTU supply to really make a difference in slab temps without being ridiculous. In a multi t-stat system this is about 25 BTU/sq ft. The magic of this number is that you can heat the whole house well, or you can heat half the house twice as fast, or 1/4 the house really fast. This BTU delivery rate can be adjusted on a given boiler by setting the high limit and the differential. This way the boiler throttles back at higher temps and reduces it's affective output.

The radiant surface should always be the floor. Always. Some exceptions may apply, but just make that a rule.

Windows, trees, insulation and orientation of the house are huge issues. If you have a choice when building, you should factor these in for sure. The same floor plan with the sun on the bedroom side instead of the kitchen side, for instance will have a different character.

Heat infiltration from the sun seriously affects the performance of the house. Imagine that the temp in the house is stabalized during the night from the radiant system. All is well and the inside temp is, say, 68*. Now morning comes. Lights go on, cooking begins, humans are walking around, hot water and showers begin, and finally the sun begins to heat the place. Now you have all these heat sources combined with a warm floor and you get over heating of 10 - 15 degrees. The radiant stays off all day because of this and, finally the sun goes down and the air temp begins to fall. After a while the inside air temp reaches a point where the t-stat comes on again. By this time the slab is cooler and the inside air temp is dropping. The recovery takes time and so you get a drop in interior temp that gradually, over a couple hours, is correccted by the radiant. By the time you go to bed all is well again and the cycle starts over.

This whole scenario is typical and must be corrected for best comfort and best economy. Enter the magical setback thermostat!


More in a minute......................

 

[AHNC]

John,

Less chance of damage by the concrete crew that way ?

What I always did with a pour is to take a little oil or wintergreen or peppermint, pour it into the tube. Put just a bit of air pressure to the tubing, give all the laborers on the concrete crew a whiff and tell them to sing out if they smell it during the pour. You then sit on their shoulders while the pour is under way. You will know if someone punctures your tubing .

 

[Raspy]

Just to review and to clarify what, I'm sure, you guys already know. But to makes sure we're all on the same page with this, let me say what I think about thermostats and why it's important.

This issue has come up several times in this thread and I don't think stats are being used correctly in all cases. Some preconceived notions or habits with forced air may be causing this.

These stats do have their limitations, but they are excellent little helpers. Just imagine if you had a little friend standing by somewhere in the house with a clock and a switch for the boiler. He could also take a message and refer to it. Every time he was cool he'd turn on the boiler switch. When warm off it would go. If you told him when you would get up he could turn on the boiler in advance. This would mean he could let the house cool more at night and anticipate your needs in the morning. He could also turn it off BEFORE the house was warm.

So now let's put a thermostat in the master bedroom/master bath zone. We'll decide we want to sleep in a cool room, but wake to comfort at 7:00 AM. We have anticipated this need when building the system, so there are two loops of tubing in the sleeping area and one in the bath. The sleeping area has a tube spacing of 1' OC and the bath has a tube spacing of 6" OC We have the ability to run those three loops and the boiler without any of the others in the house. We also have a manifold with balancing valves to adjust the flow in each loop. In the bedroom example I like to turn down the bedroom loop's flow rate while keeping the bath flow high. This flow rate difference and the closer tube spacing make the bath respond faster than the sleeping area.

Since we don't use the bedroom except to sleep at night we'll keep it cooler during the day, evening and night. In the morning we want to get up and walk into the bathroom.

Now, for just a moment, let me talk about what "comfort" means with respect to radiant. First is a cold slab. Step on it and "ouch" that's not inviting. Next is "invisible". Step on that and you don't notice it at all. It doesn't do anything to get your attention. Next is "warm". Step on this and a smile appears. It greets you, it welcomes you. And finally, maybe, very warm where it feels nice but you can't stay in there very long without feeling uncomfortable.

So, back to the bedroom setting. All night the t-stat was set at what we've determined to be to coolest comfortable temp. Since we will be getting up at 7:00 AM we'll turn on the heat at about 6:00 AM by calling for 75* or so. This means the heat will come on absolutely. Then at 7:00 AM we go back to the previous setting and the heat goes back off. This is important, off at the time we get up. We get out of bed in a cool room that has not heated much and step into a warm bath that greets us with a warm floor. This floor begins to coast down and remains comfortable as long as needed until we are off on our day. It also did not significantly add to the overall house temp and so the mid day overheating I described does not happen. Also it's only about 1/4 the overall area of the house so the boiler was four times the size needed to heat the area and the response was vigorous.

Bottom line is we can use this type of scenario in all the zones and only heat as needed without overshooting. This is quite simple and can be enhanced with other controls if needed. Never leave the system on continuously and only use simple, non setback stats in special cases.

The indicated thermometer temperature is of little value and I don't like folks comparing a thermometer with the boiler or the t-stat too much. Remember, it's radiant heat. That means we are heating objects and bodies, not air, or at least not heating air directly. We don't want it to act like forced air, that's the point of going with radiant in the first place. It's better than forced air. Overheating and different temperature days are of no consequence and, if they are it's beacause the delivery temp, the BTU rating or the settings are not right.

Sometimes this method does not work completely. In the case of solar heating or with a very small heat source we have to leave it running for a much longer time per day to accumulate the required floor temp for the worst cold we may see. In that case a compromise is made and temperature swings must be tolerated to get another benefit. With solar, sometimes we have to store some energy in the floor and that means heating when the sun is out. If heating from overhead (a bad idea), the thermostat can get satisfied, but the floor is cold and our heads feel hot. Sleeping gets very uncomfortable in these systems and tile floors are awful.

I spend a lot of energy trying to dispell myths about radiant heating with prospective customers and those considering the purchase of a radiant home. Many come from a forced air or steam radiator home and expect something other than what they get. In the long run everyone is happier with radiant and I'm often told it is their favorite thing about the house. Even neighbors can have horror stories about the same design house next door, where they raised children in cold bedrooms or had wild temp swings in houses with too much glass and no insulation. I come along and simply open a closed balancing valve and they get heat where it's been cold for twenty years. A set back thermostat goes in, in spite of the local folklore, and presto, the heat bill drop $150. per month and they are more comfortable.

I also have developed ways to keep older systems with metal tubing alive. After seeing all this I'm a big fan of PEX. Whatever you do, don't rule out PEX tubing.

 

[patrick_g]

"There are a number of factors and strategies that help radiant to keep up during cold snaps and to help stabalize interior temps."

Reduce or eliminate windows would be one option but not to my liking. Please mention a strategy to which you refer. That would certainly stabilize the heat loss under conditions of variable ambient temps, given sufficient R-values. Also define what you call a cold snap. We have WILD variations in temps.

"25 BTU/sq ft. The magic of this number is that you can heat the whole house well, or you can heat half the house twice as fast, or 1/4 the house really fast."

I assume you do not SIGNIFICANTLY pressurize your hydronic loops to permit temps greater than the boiling point of your heat transfer fluid (water/glycol?) under normal pressures. Water Furnace advises static system pressures in the hydronic lines well under an additional atmosphere. As I stated in my last post my heat source is a geothermal heat pump with a practical upper limit in hot water temp of about 115F. To deliver twice the Btu would require doubling the delta T. I can't get there with a heat pump, especially geo thermal heat pumps of this genre. Please give me a little more detail on how you get water that is not significantly pressurized hot enough to transfer 4 times the Btu. ??? Or do you run the PEX under significant pressure?

"The radiant surface should always be the floor. Always. Some exceptions may apply, but just make that a rule"

WHY? My shower has radiant in the floor and the walls and would have the ceiling also if I had it to do over as I woiuild have overridden my radiant expert on that issue (we don't hang pix in the shower.) My master bed room has radiant ceiling and a much smaller thermal time constant. It easily tracks demand. It is IMPOSSIBLE to notice that when you leave the great room with its radiant floor and enter the master bedroom with radiant ceiling that the source of the heat has changed.

Our large walk-in closets do not have standard provision for heat and cooling. The corner of the closet farthest from the wall shared with the bedroom has an exhaust duct Y'ed into the suction side plenum of the ERV. Conditioned air is being exhausted via the closet so the closet gets what the bedroom got. I put a grill on the wall to facilitate air passage and not rely on an undercut door. There is a furnace filter in this grill to filter dust (previous house had a problem with dust accumulation on hanging clothes due to make up air passing through.)

The floors of the master bedroom have pads and carpet. I did not wish to limit carpet and pad selection due to considerations for the effects of floor covering R-value on thermal performance/comfort of the room. Again with 115 degree or cooler water the R-value of the floor coverings are a distinct consideration. Another issue in the bedroom is the significant percentage of the floor covered in furniture including a Cal King captain's platform bed. This would significantly limit Btu delivery. There are aluminum heat sinks snapped around the PEX in the ceiling to help transfer heat to the ceiling's sheetrock.

I have wide wrap around porches with full coverage on the south side. There is only one window on the west side of the house, a small decorative octagon upstairs. The east end of the house is shielded from the morning sun by the two workshops and an attached 3 car garage with 12:12 pitch cathedral (vaulted) ceiling going up to 30 ft in height. There is a sun room at the Southeast corner of the house that gets morning sun.

During winter there is considerable solar gain in the house as the sun angle gets light in under the porch. In summer there is no direct solar gain in the house. There is a problem on hot shoulder season days due to fenestration high on the south side of the great room. I will be installing interior reflective solar shade to address that. On cold shoulder season days the direct gain is very nice and of course in winter too. Short of mimicking Thomas Alva Edison and putting the house on a turn table I did OK on the solar aspects.

I have a powerful variable speed range hood that also has a variable speed make up air blower that has its exit as a 3/4 inch slot across the front of the hood to make an air curtain. There is little effect on the house from cooking with this efficient exhaust system and little conditioned air is lost.

Given the volumes involved, the Btu of normal occupants has little effect on the larger spaces (great room ceiling is 28 ft above floor.) Of course the master suite being of ICF construction with a full 8 inches of concrete and 2 1/2 inches of Styrofoam on both sides of the walls can be heated with a candle or cooled with an ice cube so a couple occupants makes a significant contribution to heating it.

The master suite slab has (dare I say it???) the aluminum coated bubble wrap style insulation/vapor barrier under the slab as do my shops. Sorry to hear the stuff for whatever reason doesn't work for you but it works fine for me and according to the guy who did it he is successful using it in many applications. I did opt for 2 1/4 inches of rigid foam plastic under my basement floor on top of the 16 inches of washed (septic) gravel and under the HD Stego Wrap vapor/radon barrier. I did this before the slab was poured for the master suite or it may have got the aluminum coated bubble wrap too.

The great room floor has integral beams (concrete) about 16 inches in vertical extent with pairs of 1 inch rebar on 24 inch centers near the bottom of the beams. Connecting the top of the beams is a more or less standard garden variety slab floor with NS and EW rebar mat located as if the integral beams and their 1 inch rebar were not there. This is one monolithic pour. Maybe my thermal time constant is a bit longer than you are accustomed to having. My time constant is too long to get the "magic tuning" effect you claim to observe.

Given a longer thermal time constant and water no hotter than 115 degrees (usually less given the mixing at the 3 port storage tank) I can't get ACCELERATED heating as you report and due to my time constant I sure can't track well when outside temps are falling really fast. I'm sure we would be comfortable enough without the forced air supplement, especially considering the gas log fireplaces in the great room, sitting room, sun porch, and basement but with the forced air supplement we get extremely comfortable results.

Since forced air for cooling was our best option we have air ducts to most of the spaces in the house. Since the Water Furnace brand geothermal heat pump can supply hot air, hot water, or both simultaneously (or cold air but not cold water) it was easy to see the advantages of the strategy we use.

I elected not to use radiant slabs in the shops due to the intermittent nature of their occupancy. If I had it to do over I might put in just a little hydronic heat to keep things definitely above freezing in the coldest part of winter. A side benefit of that would be more comfortable floor temps. My floor temps are not so bad as is since the slab tends to average out the fluctuations between occupied and empty, i.e. heat on and off. (Don't forget the miraculous aluminum coated bubble wrap under the slab!!!)

Pat

 

[Raspy]

What I always did with a pour is to take a little oil or wintergreen or peppermint, pour it into the tube. Put just a bit of air pressure to the tubing, give all the laborers on the concrete crew a whiff and tell them to sing out if they smell it during the pour. You then sit on their shoulders while the pour is under way. You will know if someone punctures your tubing .

I pour all slabs with 100 PSI in them. If the tube breaks, it's not subtle! A small amount of pressure is not good because if a nail goes into the tube it can seal just fine for months or years.

I watch like a hawk unless I really trust the guys and have experience with them. No throwing shovels or floats, watch that pulsating pump hose, don't step there, etc.

 

[patrick_g]

I pour all slabs with 100 PSI in them. If the tube breaks, it's not subtle! A small amount of pressure is not good because if a nail goes into the tube it can seal just fine for months or years.

I watch like a hawk unless I really trust the guys and have experience with them. No throwing shovels or floats, watch that pulsating pump hose, don't step there, etc.

Oil of winter green? I'd be tempted to use cadaverine or putricine as they would get plenty of attention. The high pressure thing would certainly be noticed too.

We only had two problems... the finish carpenters drilled a hole in the PEX to put in a concrete screw. We didn't look at the drawing... we didn't think the tubing went there... Demo hammer it out put in fittings anda short piece of PEX. I hate putting metal PEX fittings in concrete.

Other booboo was HVAC guys tagging a recirc line to the master shower were the plumber's PEX went through a large plenum chase in the floor between ground floor and basement. Luckily we could just run the recirc line to the bathroom sink, the farthest one from the water heater.

Pat

 

[Raspy]

patrick,

Once again, I'm afraid you are injecting too much personal politics into this discussion and your terminology is off. The PRC is the People's Republic of China. Sometimes geography can be confusing. I've been there a number of times and done extensive research on various subjects. They have next to zero radiant heating though. Climate varies from tropical to cold and barren. These days there are a lot of personal freedoms, it's capitalism, private property and a legal system following the US example. Special economic zones allow for different governmental systems in different provinces and even cities. People are generally very happy and upbeat. Unfortuantely, unlike many here.

As far as fixing cut PEX in a slab, the best fittings are brass barbs with copper crimp rings compressed with a calibrated tool. Then wrap the repair with electrical tape. These never fail.