View Full Version : looking for information on radiant heat source
09-13-2010, 07:23 PM
I have been looking around here on and off for a year or so and it seems you guys know what you are talking about.
I have a question for you. I am planning on installing a hw floor radiant heat in my 50's brick ranch.
1) First phase is about 1000sqft , original house. New windows, R-19+original insulation(R-13?) in attic, unsure of wall insulation.
2) Second phase will be about 400sqft in slab in basement, creating a master bedroom/bath down stairs. Walls 3/4 buried in soil will be isulated with 1" blue board and R-13 studded out and dry walled.
3) 3rd phase will be an additional 600sqft addition, above garage to be done in the future. Addition is there but heated with wood stove for now. Walls insulated with R-19 ceiling w/R-32, floors with R-19.
I know get a heat survey done.
Could anybody give a ballpark recomendation on boiler/heat source for me? I would like one to be big enough to include all three phases. They will all be done, just need the first phase done before winter this year.
I don't get to check the computer untill 9pm ,family life, so please be patient with me if I don't respond until late and only once a day.
Thank you in advance.
09-13-2010, 07:34 PM
Forgot to mention it will be natural gas for feul.
How much gas did you use last year (or at least September through May), and what are the BTU in/out ratings of the furnace or boiler, and what type? If it's a hydronic boiler in reasonable shape, you may already have the boiler in place, since they're typically 2-5x oversized for the peak loads anyway, but we can determine that from your fuel use, output ratings, and climate data.
Also, with only ~25% of the R-value in the basement being in foam you might be on the edge of winter condensation issues in the studwall at the above-grade portion of the foundation in your climate. The average temp in January in Pittsburgh is ~ 25F (that's average, not average high or average low). If you keep the interior relative humidity to the recommended 30% minimum, and the basement room temp to 68F the dew point of your interior air occurs at ~37F- any portion of the wood that averages 37F or lower in the same vapor-or air pressure environment as the interior will accumulate water. The cold edge of the studs are ~ 3/4 of the way through the R at the above-grade portion, and will average about 36F in January- you're right on the margin. Half the hours it'll be condensing, half will be drying, but during cold snaps it could be days or even a week of all-condensing, with potential for liquid water dripping down the face of the XPS to the studwall's bottom plate. If the dew point temp occurs inside the foam layer, no condensation occurs, since there isn't any air inside the foam from which to draw the moisture.
In an above grade studwall you can raise the vapor retardency of the interior to let it dry toward the exterior, but the foundation wall needs to dry toward the interior to keep sill-rot potential low due to ground moisture wicking issues. Under no circumstances should you use rigid board with facers (poly or foil or vinyl) or batts with facers (kraft or foil), or the moisture content of the foundation will rise, risking rot conditions at the foundation sill as well as efflorescence & spalling on the exterior of the above-grade portion of the foundation wall.
Doubling up the XPS board to R10 and going with a 2x3 studwall and UNFACED R8 batts would be safer for about the same R18. If cost of the insulation is an issue, using 2 unfaced EPS (bead-board- usually white) and unfaced R8 in a 2x3 studwall delivers a similar but slightly lower R as your 1" XPS + unfaced R13. (R16 vs. R18), while giving the foundation wall much better drying capacity. If you're dedicated to the full R18, if you can tolerate an extra half-inch of wall thickness going to 2.5" of EPS would get you there.
09-14-2010, 06:14 PM
I did not use that much gas as we used the wood stove. I have a very old forced air furnace that only comes on in emergency or when we go away. The wood stove kept the living spaces comfortable. Our bed room was the farthest from the heat and it was cooler but good for sleeping.
This year we have a baby and must keep the old section warmer. The reason for radiant instead of replacing the forced air is a matter of comfort. Our house is all hard wood floors and we like warm feet.
So I need some sort of idea of how big and what type of boiler/water heater to install.
Considered a 50 gal Polaris hot water tank but not sure it would be large enough. Would like the most efficent boiler/heater I could get for my budget.
I am very handy, was a pipe fitter for years and now in industrial maintenance now so the project doesn't scare me I just need information.
Thank you very much for the insulation information. It is a future project so I will keep your recomendations for when I start. I knew that I needed at least 1" foam board so increasing that to 2.5" will not be a problem.
On the foam-board- don't go to 2.5" if it's XPS (pink or blue)- keep it to 1.5-2" max or it won't allow sufficient drying for the foundation wall. Up to 4" is OK if it's EPS (beadboard) without facers.
A Polaris is probably 2-3x oversized for just the space heating load (I have a 2000'+ antique of a house not including the full basement in central MA with known insulation deficiencies that comes in at around 30KBTU/hr for peak heating load with a simlar or slightly lower outdoor design temp)- you could probably heat it with a less efficient & much cheaper Bradford White Combi-2 or even a standard HW heater (with a heat exchanger, if you're using it for both HW and space heating.) The Polaris more than enough burner, but is it the most-efficient or best fit?
But you have several design issues beyond boiler-sizing. If you're trying to do it all with one water temp (which saves a lot on mixing valves & plumbing) for both the slab zone and the wood floors you'll probably have to go with tubing above the subfloor WarmBoard(tm) style. If you do that your space heating water temps will be well below domestic hot water temps, and you can go from the high-80s for efficiency (the likely best as-used efficiency of the Polaris with 125F water) to the mid-90s using a low-mass mod-con of simliar or cheaper price such as Munchkin Contender 50 or 80. Even if you add the cost of an indirect tank for your hot water needs it'll be less hardware cost up front, and use 10% less fuel than a Polaris.
The only way to get a real handle on the zone-by-zone heat loads & required water temps is to do a Manual-J type heat load, and work from there to find a tubing & heat-spreader plate configuration that works. If you're going staple-up under the existing floors rather than an above-the-subfloor system, use only EXTRUDED aluminum plates for the heat distribution, which will knock a significant number of degress of your temp requirements. If you don't have a large fraction of glazed in those rooms with extruded plates you may never need more than 110F water, whereas with the cheapo sheet-metal plates you could be looking at 130F+ (or 150F+, if suspended-tube). You have to kind of work backwards- your worst-case room determines the max temp requirement.
When looking at mod-cons, the lowest modulated fire is often a more important consideration than the highest-fire rating. An 80K unit may be oversized for your peak load, but may still deliver the same efficiency as an 50K unit if their lowest-modulation numbers are similar, and if using it for domestic hot water can be as-good or better than a tankless on-demand.
You really do need to do a heat loss calc to get very far with this though, since that will determine whether and what type of radiant flooring might work for you. You're not going to get 50 BTU per square foot out of any radiant system without burning your feet, but 20-25 is realistic on a staple-up with extruded plates at reasonble water & floor temps. Read up as much as you can on radiant system design- it's not something that's typically a "design-by-web-forum" sort of thing- too many particulars to juggle. Then come up with a design for the web-pundits to pick apart & clean up.
Before then, see if you can't get a handle on your wall insulation. If it's sagging deteriorating R11 batts, a blown-cellulose retrofit will likely do more for comfort than radiant floors. (And it'll lower your peak heat load & water temp requirements for max boiler efficiency.)
09-15-2010, 06:30 PM
Thank you for taking the time to give me more information.
I was not looking for a domestic hot water out of the system for now. I imagine it could be an option for the future.
The slab work is 2 years off so I have some time to come up with the piping and anything else I need. I just want to know what I get now will have enough heat capacity to do what I want in the future.
Is there any books, websites, or othe sources of information on designing a radiant system and how would I go about doing/getting a Manual-J type heat load test done?
What do you mean by this " If you don't have a large fraction of glazed in those rooms"? If you are talking about windows, well they are small so shouldn't be much of a factor.
The wall isulation, while I would like more, I am not sure how I would go about it. All my access points are difficult if not impossible to get into.
Again, thank you very much for your time and information it is giving me lots of bits that I would not have thought about.
You might browse John Siegenthaler's material on hydronic design. He also has regular column postings on some websites, eg: http://www.esmagazine.com/Articles/Feature_Article/7b961898eeda8010VgnVCM100000f932a8c0____ (http://www.esmagazine.com/Articles/Feature_Article/7b961898eeda8010VgnVCM100000f932a8c0____)
There's an IBR-method heat loss freebie/cheapie developed by a (now retired IIRC) hydronics academic/professional that would be similar to Manual-J: http://www.heatpro.us/ (http://www.heatpro.us/) or you could do the $59 Comfort Calc package (http://www.comfort-calc.net/price.html).
Crusty old-schools would eyeball the house, and depending on age/condition throw out a number like "35btu per square foot" or "25btu per square foot", install the next size up boiler and NEVER get the 4am call from the shivering irate customer, but the boiler would be typically 2-3x oversized for reality and running less than efficiently. In your case (2000 square feet of heated area) those methods would call for 50-70KBTU, and be 2x oversized. The smallest mod-cons out there are in the 50K range, and would deliver 43-45K running flat out even at non-condensing return water temps, so unless you live in a leaky uninsulated barn, odds are that's the size boiler you should be looking at, and the lowest-fire modulation is the more important number (lower is better, to limit cycling losses.)
Contact some cellulose installers and have them assess your place for "dense packing" the walls, and any other spot-insulation that would be cost effective. You may be surprised at how easy it can be. Foam can sometimes be retrofitted behind existing old stuff, but it's 3-5x the cost and only marginally better than dense packed cellulose.
You might also look into air-sealing services (usually offered by insulation contractors- often spray-foam guys.) A grand or two spent on air-sealing, with blower-door test verifcation can have HUGE financial return.
[edited to add] And yes, "glazed area" means all windows, glass sliding doors, skylights, etc. An average double-glass window runs ~ R3, and an "Energy Star" triple-glazed version is still under R5. From a heat loss point of view an ~ R2 window in an ~R20 insulated wall has 10x the heat loss per square foot as the rest of the wall. In other terms, a 10 square foot window loses as much heat as a 10'x10' section of blank wall. If the windows are 9% of the wall area, they're literally half the heat loss out of that wall. Small windows==good!
Also- here's a popular $50 Manual-J type heat loss tool: http://www.hvaccomputer.com/gtarget1.asp?kwx=0&adx=0&gclid=CK_KlZTdjKQCFYp_5QodSyGPLA (http://www.hvaccomputer.com/gtarget1.asp?kwx=0&adx=0&gclid=CK_KlZTdjKQCFYp_5QodSyGPLA)
10-17-2010, 06:10 PM
Well, I finally got the heat loss done. Looks like around 37,000 for my complete project.
So the boilers I was considering are the Burnham Alpine ALP080 or the Lochinvar Knight KBN081 both modulate down to 14,000 to 16,000. Any thoughts or suggestions? The one thing that was different was the location each manufacture called out for the expansion/air seperator. One was on the return to the boiler the other on the supply, what would cause the difference?
Still working on my piping layout.
10-17-2010, 08:14 PM
You might also look at a Buderus. I've been happy with mine. Bought it on recommendations, plus, their US headquarters is only about 15-miles away, so parts and expertise isn't far. Did need it once, the installer messed up, but it got quickly sorted out with their help.
Burnham Alpines and Lochinvar Knights both have good reputations. The most important aspect of buying a mod-con is the installer/system-designer, followed by the degree of local support by the manufacturer. There are lots of good ones out there- the Peerless Pinnacle PI -T50(or 80), Peerless Purefire PF50(or 80) or Triangle Tube Prestige Solo 60 would also be good candidates, with good reputations. Triangle Tube Solos are VERY popular among radiant-installers, and they're built in NJ. Peerless is a Boyertown PA company. The newer Munchkins look like re-badged Peerless Pinnacles, with identical specs- if Munchkin local support is better than Peerless go with them. Figure out some models that you like, find out who the local distributors are, and ask THEM for recommendations for installers.
If you're looking for a "deal" the Munchkin Contender series give good performance with good reliability, but are a bit spartan on the control end (unless you spring for their add-ons), with a noticeably lower sticker-price.
The location of the expansion tank & air scoop is relative to whether the circulator is pumping TOWARD the boiler or pumping AWAY. If the boiler comes with an internal circulator pumping toward the boiler (or if that's the recommendation from the manufacturer), the expansion tank would be located at the input side, on the low-pressure side of the pump. As I understand it, the reason some mod-cons pump toward the boiler is that with low mass high head (=more restrictive) heat exchangers, pumping away could reduce the pressure in the heat exchanger enough to get some micro-bubble sizzle, reducing the efficiency of the heat exchange. Lower-head boilers typically recommend pumping away, since the pressure drop across the boiler is minimal, and pumping toward could cause spittin' & sputterin' at the pressure relief valves. In either configuration, pumping away from the expansion tank & air scoop is necessary for more reliable purging of air from the system.
10-21-2010, 01:18 PM
Keep troubleshooting and repair in mind, if there is such a thing for floor heating.