Convert baseboard to radiant floor
Last Post 28 Dec 2009 08:26 AM by NRT.Rob. 8 Replies.
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losttrailUser is Offline
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06 Nov 2009 10:55 AM
Hello, just found this forum and have looked through for ideas. Good place to be it appears. We are looking to buy a house after several years of renting. Long, sad story. There are homes in our area, Colorado, that have hydronic baseboard heat, better than forced air, but we really want radiant floors. How difficult would it be to convert and existing hydronic baseboard to radiant floor? Thinking of 1/2" PEX, 8"OC using 5/8" OSB strips on top of existing subfloor & concrete basement floors, with alum reflectors. Finished flooring will be hardwood (stapled?) and tile. Most likely, basement will be finished, so access to joists would be nonexistant. However, if it made more sense to tear down the ceiling and attach the PEX to the bottom of subfloor, I'm not opposed. I used PEX for plumbing in a new construction in 2005 in TX and really like working with it. Suggestions? Thanks. P.S. I should add that most of the homes we are looking at have a majority of carpet, which we will want to get rid of. Thus my idea of radiant floor on top of existing subfloor.
thehabitatgroupUser is Offline
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08 Nov 2009 10:03 PM
You might want to consider using Magnesiacore http://www.magnesiacore.com/solutions.html (see their radiant floor installation) or similar Magnesium Oxide board such as Dragonboard asIt's lightweight and probably easier and less expensive than pouring gypcrete over pex or buying the expensive prefabricated radiant panels. I am strongly considering using the MgO board as a quick and cheap way to get the thermal mass needed on the floor for a new home construction project of mine in the Northwest. Good luck with your search and eventual project.
Loren J. Lobbestael
http://thehabitatgroup.blogspot.com
http://www.google.com/profiles/lorenjl
losttrailUser is Offline
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09 Nov 2009 08:44 AM
Thanks for the info. Looks like an interesting product. I'll get more info the closer we get. Has anyone done a conversion from baseboards to floor?
Dana1User is Online
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09 Nov 2009 10:50 AM
Posted By losttrail on 11/09/2009 8:44 AM
Thanks for the info. Looks like an interesting product. I'll get more info the closer we get. Has anyone done a conversion from baseboards to floor?

It's a fairly common retrofit. The above-subfloor solution you're proposing has been commercialized by folks like Warmboard ( http://www.warmboard.com/ ) and is fairly responsive compared to slabs & staple-ups (under-subfloor installation.)  And above the subfloor is the preferable retrofit if you're ripping up the rugs to install hardwood/tile/etc.

You'll still need to insulate under the subfloor to keep heat losses from radiating downward, and don't get sucked into thinking reflective insulation (radiant-barrier)  is either necessary or sufficient for that  function (most of the time it's neither.)  R15-R19 is usually sufficient between conditioned spaces, R19+ would usually be called for above unconditioned space.

The hydronic water temps of radiant are dramatically lower than most baseboard designs call for (you'll likely be looking at 110-140F vs. 160-200F), and if you don't have a high-efficiency condensing boiler you'll need to protect the boiler from excessively cool water or it's lifespan will be drastically reduced. Return-water temps entering oil-fired boilers needs to be above 140F, but with gas/propane you can usually tolerate return temps as low as 130F, provided the flues are lined & properly sized. (Flue condensation/corrosion can be an issue otherwise.)  But since that's often above the output temps delivered to the floor, there will be some plumbing tweaks necessary (primary/secondary loops, boiler-bypass, etc) to keep both the radiant floor and the boiler happy.  The specifics will vary depending on the particulars at hand.

You may need to add water-mass to the system to keep an old-skool boiler from efficiency-robbing short-cycle burns as well (particularly if the system is broken up into several micro-zones.)  Since most are 2-4x oversized for the coldest-hours-of-the-year heat load anyway, micro-loads start to look RIDICULOUSLY undersized for the heat output.

Done right, dropping from 180F temps to 130F temps will by-itself yield ~15% in fuel savings, assuming you stick with the same boiler.   But with a modulating or modulating-condensing boiler utilizing "outdoor reset" control (changing the boiler's water temp in response to outdoor temps) you'll reap much more (30-50% savings isn't unusual.) 

It's a hefty chunk o' change up front, but with radiant you can typically run much of the season well below 120F water temps, where real 90%+ efficiencies kick in with mod-con boilers:

http://www.csemag.com/photo/167/167345-boiler_efficiency_vs_temp_2.jpg

If your system design indicates mid-winter water temps predominantly higher than 130F it's harder to rationalize the cost of retiring  functional boiler for a mod-con at current fuel prices.

Note, if you're running a 4x oversized short-cycling high-mass boiler your true AFUE is going to be in the 55-65% range, even if the specs say 78-83%.  This can sometimes be mitigated by adding thermal mass (big buffer tanks) to the system, but for the money you may be better off retiring the beast early and installing a "right-sized" mod-con or modulating low-mass copper-tube boiler.

In the end, it's usually more than just swapping baseboards for radiant- there is some system design to be done, but if you plan to live there awhile it's worth it from a comfort & cush-factor point of view. There may be some home resale-value aspects, but don't count on ever making it back in fuel cost savings. (It's easier to calculate/rationalize for new-construction than with retrofits.)


losttrailUser is Offline
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09 Nov 2009 11:40 AM
Dana1,
Thanks for that detailed reply. Just what I was hoping for.

I have looked at the Warmboard before and it is still a possibility.

If however, I were to opt for staple-up under the subfloor, would the aluminum 'fins' or plate be necessary if:

1) Immediately below the PEX, install MEPS or XEPS with reflective barrier agains PEX,

and

2) Below rigid foam with reflective barrier install batt (probably natural fiber) insulation to completely fill void?

I do understand that there will be additional design, cost, install of mechanical for boiler, HW storage, etc. that is TBD.

Thanks again. Great reply.
Dana1User is Online
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09 Nov 2009 01:16 PM
In order to get the heat out of the PEX you need solid contact of significant surface area with a refractory material (like aluminum plate)- the heat is primarily CONDUCTED, not radiated (even if the heat transfer in the room above has a signficant radiated fraction.) The emissivity and surface area of the PEX itself is nowhere near sufficient to deliver the heat predominantly via radiation, even boiling temperatures. In unplated staple-ups the heat transfer out of the PEX is still largely conducted/convected from surface contact with the air. The heat transfer performance difference between plated/unplated PEX is more than 2x at any given water temp. (The difference between sheet-metal plates & extruded heavy plates is also something like 1.5x.) Unplated staple-ups probably aren't going to cut it in most homes unless you keep the water temps at about where they were for baseboards, (maybe even higher.) And with any staple up you're putting another ~R1 of subfloor between the room you're trying to heat and the PEX, which is why above-subfloor solutions are more responsive, and work well at lower temps.

Reflective barriers are of very marginal use in staple-ups (aluminum plates have exceptionally low emissivity- far lower than the PEX itself.). Adding them is an unnecessary step- it's usually less labor & more effective to bump up the density & R-value of the fiber insulation, skip the reflective stuff. If you're planning to use rigid foam board, iso is preferable to XPS (easier to cut, higher R per inch, etc), but in reality, just unfaced R19 f.g. or similar snugged right up against the tubing is sufficient- it's performance is similar to low-density R13 batts + radiant barrier at the temps we're talking. If it's over unconditioned space, consider high-density R25-R30 or similar. If the subfloor is truly nail-free and there's no gap between the spreader plate & floor you could put up a course of OSB and blow cellulose in there if you wanted (only for plated radiant.) By the time you've screwed around with setting the gap for the reflective layer and adding the fiber, you're money & performance ahead going with thicker batts and doing it as one step. With low density batts there's some benefit to adding a reflective layer to the cold side of the assembly- about half what you'd get by doing it "properly", but not enough to make it cost-effective. Reflective insulations really only belong in unconditioned attics of less-well insulated buildings in cooling dominated climates (or in the vacuum of space). At 120F radiation temps and a proper gap about the best they deliver in conjunction with low density fiberglass is an effective ~R5-6. The denser the fiber insulation (any type) the less benefit you get out of RB. At R25 and up the benefit becomes difficult to measure.

With an above-subfloor solution you could use blown insulation instead of batts and avoid needing to demo/reconstruct the ceiling below. Something light, like blown fiberglass or blown EPS beads would keep the ceiling-sag to a minimum, but if you have at least 1/2" sheet rock and 16" o.c. joists, cellulose wouldn't be too heavy. (If you're concerned, adding a second layer of sheet rock after you've blown the insulation would make it mechanically more robust.)

In the basement, unless the slab was poured over 2" of XPS you'd need to add it above the slab to keep the heat loss of the radiant to a minimum. This can subtract significantly from the available headroom. For low headroom options include adding a minimum amount of insulation (R3-R5 XPS sheathing glued to the floor) under an OSB nailer/subfloor (or variations on thinset/tile/slab), then using a radiant CEILING (between the joists) to heat the basement. It won't have quite the same cruisin' in yer socks appeal, but it is otherwise quite similar to radiant floor when wearing shoes. With a radiant ceiling you can usually limit the headroom loss to 1.5-2". (If you can stand a cooler, uninsulated floor the headroom loss can be quite low. But don't use wood on an uninsulated slab or it'll guaranteed get mold underneath. R3 and a polyethylene vapor retarder is usually enough to keep the cold underside of the wood out of the mold inducing temp & humidity zone.)

losttrailUser is Offline
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09 Nov 2009 01:48 PM
Thanks again, Dana1. Pretty much what I wat thinking. You've just helped me weed out a couple of sources that were minimizing the use of plates. We'll have to see what house we end up with. We're still about 10 months from buying, but I'm trying to get my list of preferences in order and have plans laid for when it does finally happen. Thanks.
cdmitchUser is Offline
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26 Dec 2009 07:53 PM
Would there be a money saving improvement to install radiant heat on 1st floor even though there is baseboard heat or just install a comboheater like a polaris for saving through the use of a nore efficient furnance thanks mitch
NRT.RobUser is Offline
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28 Dec 2009 08:26 AM
Mitch,

to save money step one is the envelope, always.
Step two is the heating system as a whole. you have to match an emitter to a heat source to some degree. If your baseboards can run at low temps, they could be close to as efficient as radiant. If not, radiant could help with the efficiency, especially on a condensing heat source like a mod/con boiler or a polaris.
-=Northeast Radiant Technology=-
NRTradiant.com
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