Under Floor Hydronic Heating: Money Saver and Comfort?

[velvetfoot]

...or is it mostly comfort?

I guess I could retrofit it in my 2 story house; I'd like to put in hardwood floors upstairs and I bet there's some product or system to do that, and the downstairs has basement access.

I bet it would be really comfortable to walk around, and I realize lower circulating temperature water could be used. But, what is the economic impact? Can a setback thermostat be used, even if only for the upstairs, which isn't used too much during the day? My wife isn't working anymore, so it's not a question of turning it down while we're both at work. How much of a lead time to get things back up to temp?

Just wondering if it would be for me. I know my wife would like the warm floors.

Thanks.

 

[91LMS]

i used ultra fins, snake hangers and 3/4" pex on my application. absolutely love it. however i did double up and used two runs per bay (16 oc joist) in my family room where its a cathedral ceiling and lots of glass. there is a noticeable differance trying to push the heat through just subfloor or hardwood on top of the subfloor. i feel its more efficient where you mix water temp down and actually loop return water back into the floor. seems to heat much easier that the baseboard portion on my house. how it's insulated in the bays has a big impact on performance as well.

 

[peakbagger]

Let me start by IMHO - My observations on radiant are as follows.

On new construction it is probably a no brainer if the house is occupied 24/7, if its vacant during the day and some weekends, there may be some debate. I havent seen many radiant systems that work well with setback thermostats. So going radiant is commiting to keeping the house at the same temp 24/7.

I know folks do retrofits of radiant to older homes and some even pay contractors to do it, but I expect the hassle and cost is pretty high. As for a second floor retrofit, if you have high ceiling and dont mind cutting the doors and reworking the trim to install a signficiantly thicker floor it can be done but with a standard 8' ceiling it does eat into headroom a bit. If you have access from underneath, its probably a lot easier but few folks have that luxury unless they want to replace the fisrt floor ceiling.

Most radiant goes in new construction or major retrofits so the benefits are hard to split off from the benefits of generally more energy efficient construction or upgrade of existing systems.

Utlimately the efficiency of a system is related to how low the circulating liquid or air can go to maintain the space. Standard baseboard requires higher temps than radiant so radiant wins unless the baseboard type and area is increased significantly to handle lower temps. If you have storage on a wood boiler, lower required temps equals much larger storage capacity. Some folks with baseboard and storage advocate just going 24/7 temp setting and run the baseboard temps lower, I dont think they can get near radiant supply temps but can definitely run lower temps throgh a baseboard if it doent need to deal with a setback.

Conventional baseboard relies on convection through a radiator and free air flow into the base of the radiator and out the top. If these paths are blocked, the heat output is lower and frequently the heat is forced up against the cold wall. Radiant doesnt really care about where furniture sits.

Some people claim that they can run a lower temp with radiant than baseboard. I am not sure of this one. Its hard to split off the benefits associated with 24/7 temp setting from the typical baseboard concept of set back thermostats. When a setback thermostat raise the room air temp it takes quite awhile for the surfaces and furniture to get up to the setpoint so during this transition, radiant feels warmer as everything is already at the setpoint.

I also have seen many radiant systems where the pumps run 24/7. This is a large phantom load for power. Depends on the design but assume 200 watts continuous is 4.8 KW per day for the entire heating season.

Fast response to changes in temp is a function of temperature and most wood floors usually have temp limits that limit the change in temp/hour. I expect some floating laminates are less fussy.

In some of the low/no energy homes designs, the designers dispense with radiant and just go with split units. If you dont already have AC and want it, I expect the savings and benefits of some split heat pumps would be equal to or better than a radiant retrofit. They are now good down to -10 degree for heating.

I expect other folks have their opinions so it will be interesting to follow this thread.

 

[Downeast Farmer]

"I also have seen many radiant systems where the pumps run 24/7. This is a large phantom load for power. Depends on the design but assume 200 watts continuous is 4.8 KW per day for the entire heating season."

I would have thought the pumps ran continuously in all radiant systems, though I'm just now learning about this. If you were contemplating a retrofit from scratch of a heating system for a large old home (which will never be as tight as new construction) in Maine, and supposing your design intention didn't allow for fossil fuel use, what would your system include?: gassifier, storage, and radiant heat?

 

[Paver56]

I put radiant in when I built my house. I love it. It is definately comfortable. I notice it when I go up my steps-when I walk up that steps I can feel a temp drop since I am getting away from the heat. My pumps do not run 24/7. I have a lot of tile and hardwood- be sure that your wood can handle the temp swings. I used an engineered wood made for radiant heat. I ran down and back between every joist. I used alluminum plates in our bathroom, laundry and kitchen. I wish I would have done the whole house with them.
If I was to do it over again, I would seriously consider using jip-crete or another lightweight concrete.

 

[Nofossil]

Aside from comfort, one advantage of radiant is that it allows you to get effective heat out of storage at much lower storage temperatures. This can dramatically increase your effective storage capacity. For example, assume 1000 gallons at 170 degrees to start:

Baseboards, lowest usable water temp = 140 degrees. Usable range: 170 to 140, or 30 degrees. At 8345 pounds of water, that's 250,000 usable BTU.
If your radiant allows you to use water down to 100 degrees (not untypical, though different designs give different results) that's 70 degrees range or 584,000 BTU from the same storage tank.

There's also no law against having baseboards AND radiant....

 

[VT_Bubba]

This is a very interesting thread for me. I had personally romanced about the comfort advantages of Radiant Floors and was very interested in the potential efficiency advantages.

As part of my Solar DHW research and installation, I had hoped to super size my solar design to help heat my house, and had seriously considered adding some low temp radiant to my 1st Floor where I had access for the radiant installation from the basement After some very long, deep, soul searching, and some calculations I concluded :

1) Solar Heating did not make sense for an existing Low Mass, High Temp, Base Board house.
2) Here in VT, during Dec\Jan\Feb we have VERY Large BTU needs, with very little available Sun (BTU's).
3) Because it's only me and my wife, using set-back T-stat's is a major part of our life style, which offers real potential energy savings for us.
4) I could not convince myself of any large efficiency gains (energy savings) inherent to Radiant Heating, and certainly nothing to match the potential energy savings that I get from my set-back T-Stats with BB High-Temp Heating. If we heated the whole house 24hrs a day then any potential Radiant Efficiency advantages might make more sense. For our life style and existing BB heating system (pellet boiler, with Oil Back-up), I concluded that Radiant Heat and heating 24hrs a day, would actually use more energy than using my set-back T-Stats.
5) I concluded that Set-Back T-Stats do NOT work well with Radiant Heat.
6) Radiant Heat makes a ton of sense if you have a High-Mass System Design (Solar, Geo, Boiler with Storage, etc...). But my entire heating system design (Both pellet boiler and Oil Boiler) is based on very low mass, high temp, which works well with set-back T-Stats.
7) I concluded Radiant Floor is primarily for comfort and did not have any large inherent efficiency gains, unless you had some type of High Mass, low temp, heating system to go with it.

Just My Humble Opinion here, based on my personal situation and research. I'm hoping some Heating Professionals will join the conversation and discuss the "Inherent Efficiency Gains\Losses of Radiant Heat" in general. Very Interesting Topic !

VT_Bubba

 

[BoilerMan]

As I sit in a chair on a radiant slab covered with porcelain tile. The storage point that NoFo made can be done with H.O. (read low temp) baseboard, oversized CI radiators, or panel radiators like they use in Europe.
Radiant comfort is excellant, but to make a true scientific energy audit we'd ahve to heat the same building with both types of radiation systems and see lower uses. Any low temp system will win with the same type of heating appliance, as the lower operating temps will increase efficiency slightly, staying above condensation point in non-condensing equiptment. This said, if you were going to use gas (Nat or LP) a modcon boiler connected directly to a low temp system (any of the above mentioned heat emitters) will condense all the time and get the most heat out of the gas. With a wood fired system, and storage, same as NoFo said less physical volume can store more useable BTUs. Radiant-retro is a big job and depending on the type and scope of the renovation, I'd opt for a low temp emitter first. Anyone who builds new would be foolish IMHO to not use some type of low temp system. Conventional fin-tube heat emitters in new construction mean (to me) they cheaped out or didn't do their reasearch on modern hydronics.

As for the circulation issue.... In Europe they use almost exclusivly constant circulation with full outdoor reset. This lowers water temps as the outdoor temp goes up and in theory the heatloss of the building also lowers. This does not take wind into account or solar gain. I set up most systems with a partial-reset meaning a heatloss calculation, and slightly higher temps for margin and installing a conventional wall thermostat. Full reset has no thermostat and indoor temp is a direct function of water temp. 200watts is a good number unless smart circulators are used. If VS circs are used the total wattage from all associated (constant circulation part) would more likely be in the <100 watt range. I do not like a circulator running 24/7 no matter how low the wattage, but that is just me.

My $0.02

TS

 

[dogwood]

Velvetfoot or anyone, considering the amount of construction work needed to put in underfloor radiant, might panel radiators be a better way to go for you? I would think you'd have almost all the advantages of underfloor with lower operating temps and increased storage capacity, plus the advantage of easier installation, less construction and construction related costs, and less of the inevitable household disruption, not having to leave the system on 24/7, and easy regulation of temps room by room with trv's.

Before I decided to not put in-floor radiant in my own home during construction, one of the deciding factors was not wanting to have a 3/4 inch sub-floor and 3/4 inch oak flooring between the heat emitter and the space being heated upstairs. Downstairs was less of a concern since it is a slab, originally intended for radiant, before I decided against going that way. I never did figure how I could install a hardwood floor over the slab with radiant without creating a messed up situation.

I'm no expert on this, so I'd be interested in any thoughts on underfloor radiant vs. panel radiators for your situation.

Mike

 

[bmblank]

Radiant floor can be done two ways, and the conversation is bouncing back and forth with much confusion. One way is to staple it to the bottom of the sub floor between the floor joists. Very easy to do. Watch it if you still have nails/screws to put in. I stapled my pex to some spacers so the floor staples had no chance of hitting it. Another way I'd to put it on top of the sub floor. Many ways to do that. I've seen it stapled down and concrete poured over it. Very good way of doing it, but hard to retrofit. You sort of need to plan for that beforehand. That way would also be way better for the passive solar thing. I've also seen a track system that has aluminum track for the pex to fit into spaced apart with some sort of plywood. Basically the flooring is applied directly on top of that, but stapled into the plywood spacers.

 

[maple1]

Pex in the floor joists also doesn't have to be up tight to the subfloor. It can be 'suspended' a little bit, then insulated.

 

[JP11]

wirsbo has an expensive.. but great stapler. It won't fire unless the two "ears" on each side are touching subfloor.. AND... pipe is in the built in U. No chance of stapling the pipe.

my plumber let me use his stapler.. and I did the whole house myself. Staples are about 1,5 deep.. and about 2 wide, so pipe can move laterally, but held tight to the floor.

Using this.. I used no aluminum transfer plates. I left an inch of air space.. then used 1.5 inch foil faced hard foam between trusses. Each truss bay is about 2', and has 3 pipes in it. Leaving the floor above with a pipe every 8"

JP

 

[bmblank]

Pex in the floor joists also doesn't have to be up tight to the subfloor. It can be 'suspended' a little bit, then insulated.

Indeed. Bottom line is, the closer to your feet you can get it the better, but there are tradeoffs to get there.

 

[Downeast Farmer]

There's research out of Kansas State University that shows that those expensive heat transfer plates make a big difference, but they sure do add to the cost and complexity of installation (if retrofitting to the underside of an old floor with cut nails poking through from the hardwood floor installation above). Are you satisfied with your installation without plates, JP? Is yours a really tight home? What size pex are you using?

 

[Downeast Farmer]

And I imagine without heat transfer plates, you'd have to run your radiant floor at a high temperature. What temperature does anyone here run their radiant floor pex? With or without heat transfer plates?

 

[BoilerMan]

A staple up or suspended system is referred to as a dry system. A wet system is when the tubing is buried in a concrete or gypsum slab. This slab can be a thin (gypsum or gypcrete) pouring over a wooden subfloor, this weight needs to be accounted for as bmblanc pointed out. A wet system has the lowest operating temps per but given due to the surface area of the pex being in full contact. Thin slabs, pour-overs, or gypcrete slabs are all the same thing for the scope of our conversation here. Thin slabs are much more conducive to setback thermostats due to lower mass.

Aluminum transfer plates under a subfloor reduce the temps needed but are expensive. A staple up or suspended system is considered a medium temp heating system, but as JP said is very easy and fast (read lower job bid) to install. It still has the radiant benifits but needs higer temp water due to the lack of surface area contact with the pex. This can be accounted for with more pex runs like JP did with 8" O.C.

Radiant floors on top of the subfloor can be done with sleepers and running the pex in the voids between sleepers with plywood on top covered with the flooring. This is like the staple-up system but is on top of the subfloor, good for retrofits floors with a finished ceiling below the joists. There are also special cut boards that are precut for this purpose but I can't remember who makes them, Wirsbo/Uponor? They are wicked expensive....

Bottom line in no order:
Dry radiant
1. Staple-up
2. Suspended
3. Over subfloor installs
4. Aluminum transfer plates (also can be used as radiant wall)

Wet Radiant:
1. Tubing in concrete slab on grade
2. Tubing in gypcrete over wooden or metal subfloor (known as: pour-over, thin-slab, or light-weight-slab)

This list may not be complete as it is off the cuff.

TS

 

[91LMS]

i was nervous of the fact that i had to construct my hearth and nail down my flooring so opted to go for the ultra fin setup. it does a great job imo. also was advised that with thick hardwood flooring i might be better off with ultra fins so that i dont overtemp my floor. do the staple up plates get much noise as the pex expands and contracts? has anyone run into issues using staple up and having too high of floor temps in really cold temps?

 

[Downeast Farmer]

So, Taylor, what temp is medium temp for the suspended pex? If you can run your pex+heat transfer plates down to 110* or so, to what temp can you run the suspended pex? Over the long run, for your own system that you weren't bidding out, would you be better off going with the heat transfer plates (after having cut or ground off all those protruding nails?).

 

[BoilerMan]

Floor temp is directly related to the heatloss of the structure. This is the same with all radiant types, however there may be a more noticeable hot spots in staple-up, suspended or over the subfloor systems. The floor has to be warm enough to match the heat escaping from the building. This is why in super insulated houses radiant floors are not noticed much, they don't need to be much over room temp to keep the place warm.

TS

 

[BoilerMan]

So, Taylor, what temp is medium temp for the suspended pex? If you can run your pex+heat transfer plates down to 110* or so, to what temp can you run the suspended pex? Over the long run, for your own system that you weren't bidding out, would you be better off going with the heat transfer plates (after having cut or ground off all those protruding nails?).

All depends on the building's heatloss.

If money were no object I'd go with plates or a pour-over.

Personally I hate basements, in my line of work, I've been in way too many which were musty, flooded at random times, or had expensive radon issues, these were in new and old houses. I'd want to finish part of mine if I built one and these are all not gonna fly in a living space. This coupled with the benifits of a radinat slab-on-grade's huge mass I built my house on a slab.

TS

 

[JP11]

I did the staple up myself. My builder and the plumber both told me not to bother going with the plates, as there was a lot of cost and labor (mine) involved.

My house had a sizeable budget, so it wasn't make or break.

The idea, as I was told, was for that air space and pipes to be the whole heat source. My pipes on the staple up run about 140 to 145 degrees.

There's 3 zones upstairs (which is the main floor of the home) 1200 sf photo studio for my wife. Kitchen, Laundry/half bath, living/dining, Mudroom, all another zone probably 1400sf. Then the bedroom, master bath, walk in closet on the last. about 1000sf there.

Works well. I can't complain a bit. Toughest part of running all the loops was the figuring.. figuring where to pull the end thru and from in order to not jump the trusses more than once. I got good at it... of course about the time I was done.

 

[nate379]

I'm not a big fan becaues of the SLOW reaction times.

 

[Downeast Farmer]

By which you mean, nate379, that you have to run at desired temp all the time because it takes to long to heat up?

 

[BoilerMan]

I'm not a big fan becaues of the SLOW reaction times.

Please read post #16 that depends on the type of radiant system.

Also I've seen buildings spec'd for both a radinat floor and a supplemental fin-tube (baseboard) system for fast-response. Y'all talk like the high mass is a bad thing, it allows me to fire once a day and not have "storage" as most think of storage.

TS

 

[Downeast Farmer]

Well, I'm not part of "y'all"; I'm sold on high mass or storage--just trying to figure out what nate is referring to. I'm also sold on no set-back thermostats on radiant installations because they work best that way, according to VT_Bubba....Not the case?