Warmboard install advice
Howdy all,
Seriously considering a warmboard install for about 460SF of floor area in my own house. Priced out the board, and it ain’t cheap, but all-in-all it looks like it gives value for money.
My question has to do with how to most cost-effectively heat the water. We’ve icynened the space, and the windows are new, so it stays pretty warm with very little effort. I know that with Warmboard, the water doesn’t have to get as hot as with some products, so I’m thinking perhaps a small electric water heater?
We don’t have a gas line in the house. So no gas boiler. We heat with oil.
I’m also wondering what componants would be required. I had an old sub of mine quote me for just the pex install, thermostats, valves etc and it was like 2400 beans. That’s NOT including the water heater! Seemed pricey and I know his rates are fair. Wondering if there’s a way to save a few greenbacks without giving up too much in performance.
Hoping NRTRob or some other pros might be lurking that could make a recommendation as to best course.
I’m just outside Boston, climate-wise.
Thanks,
Brian
_____________________________
HomeBase______________ LLC
Replies
There is a problem in that there are no really efficient oil or gas fired boilers that modulate down to what you'll be needing for BTUs for that space...probably under 10K BTU/hr for most of the winter. So your next option is, in fact, a water heater.
There are three or four manufacturers/distributors of electric boilers that get down to that range...google on "electric boilers" for a sampling. Is your wiring up to snuff for the additional load, and what is your electric rate?
You say you heat with oil...is it forced air or a boiler? What currently supplies your domestic hot water?
Interesting.
Forced hot air furnace, and we're running an electric water heater to supply DHW. It's pricey to run... get's my meter spinning like a fan!!
Have you found an electric boiler to be more cost effective than a water heater?_____________________________HomeBase______________ LLC
at the load you're probably looking at, I'd look for cheap. worrying about efficiency or fuel/electrical rates is probably a waste of time for you. Of course if you have big windows or cathedral ceilings, that may start to shift things a little bit, but if you're icynened and its a small space, I doubt cost of operation will be much of a concern in any case.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
also, electric boilers can be cheap. However an electric water heater is probably the cheapest and simplest way to go. Do you know what water temps you are expecting to run?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Can't imagine we'd get much over 90 -100 degrees for water temp, Rob. Seems like even a small water heater can handle the BTU loads.
What about modulation/distribution? What kind of set-up am I looking at to get the water to the right place at the right time/temp?
I've heard that a floor and an outdoor stat were minimums. Any kind of thermostatic valves required? Is a closed loop system possible that recycles the water that's moving through the pex so it's not being heated from 50 degrees all the time?
Thanks for the great spreadsheet, Johnny. I'll have closer look when I get back to the home office, but that's teriffic.
Brian_____________________________HomeBase______________ LLC
One of the nicer things about using a water heater is that it is designed to maintain a relatively low water temperature in storage, so when used as a hydronic heat source, kind of just views the tubing as an extension of its tank. The water in the tubes looses its heat to the floor and comes back to the tank cooler than when it left. Ultimately the WH senses the difference and turns its elements/burner on to maintain the temperature. A lower setting will approximate the temp you'll need for your floor, and that can be fine tuned with a thermometer in the supply plumbing.
You do, of course, have to rely on the WH's built-in temperature range, but I haven't had a problem with that in my applications.
I get by with $12 Honeywell thermo-couple thermostats measuring and reacting to inside air temperature, one for each of five zones, that send a call for heat to a Taco zone valve controller that relays the calls on to both the zone valves and a relay for the circulator pump. Do you think you will need more than one zone in your area? If not, all you'll need is a relay for the circulator and some way to get a heat call to the relay. I haven't found outdoor reset to be necessary. But I'm only heating 1600 sq feet of really well insulated and sealed space.
With your 460 sq ft of area, you may want a floor sensor, because I'm assuming the area will get SOME heat from the forced air system, so maybe an air temperature thermostat won't work so well. But that is a straight-forward thing to do. I also wouldn't worry about temperature mixing valves...thier purpose is to protect non-condensing boilers from too-cool return water, or showers from too-hot supply water, or to send varying water temperatures to different areas.
Interesting stuff, anyway...if your up to it, you might want to consider building your own facsimile of WarmBoard with plywood sleepers and aluminum plates. Lots of info both here and in other sites on how to do this.
There are two ways to approach this, from my POV.One is to go super simple. If your max water temp is low enough, then outdoor reset isn't going to do all that much for you; no big deal if you can only get a 20 degree temp spread across the season. In that case, I would use PWM thermostats (like Tekmars) to keep the floor more consistently heated than with normal differential thermostats, and I would *consider* floor sensors as an additional measure. Between the two, you're only talking about $80/zone more for a rather dramatic comfort differential.The other is to shoot for perfection. Slap a motorized mixing valve on there with outdoor reset and indoor feedback sensor.. such as you might get using, say, a Tekmar 362 w/063 RTU. This will add several hundred dollars to the system. However, then for a single zone you have constant circulation, with indoor feedback modulating that water temperature to just what you need, consistently, 100% of the time. The floor may not always feel warm (that depends on your load), but you'll always be comfortable and the floor will never be cold. All depends on how picky you are and what kind of a budget you're working with. Either one will be an excellent system. Constant circulation would just be a perfect one.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
This is great advice, guys. I really appreciate it. Seem like we can do a pretty straightforward system here with a minimum of controls. Rob, cost is somewhat of a factor, and it sounds like the simpler system will give pretty good performance. It's a relatively small space to heat, and Johnny is right, there will be some warm air from the furnace during heating season, so the load on the system shouldn't be too much.
Out of curiosity, have you seen any sites out there that provide a "typical" diagram for a water heater baseed RH system?
I understand conceptually but am having trouble visualising the partculars.
Thanks again,
Brian_____________________________HomeBase______________ LLC
For a simple system, pretty easy. One pipe out to your radiant manifold, one pipe back. I would use the standard closed system components: air seperator, fill valve/backflow preventer, thermometers, drains. Not sure if you can use a cast iron pump with all water heaters.. non ferrous would be safe though. This assumes you are not doing domestic hot water from the water heater: if you are, you need to add a heat exchanger and an additional pump (cast iron, on the closed side of the HE).-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Did I misread that spreadsheet that johnnyd posted. It seemed to indicate that an electric boiler was cheaper to operate than propane at the prices indicated.
If you use a conventional boiler, it appears that way. However the 78% efficiency assumption there applies only to conventional boilers. A modulating/condensor, for example, would exceed that by a good 15% if matched to a low-temp system.For a very small load though, that 15% might be negligable enough to never pay back the difference in cost between an electric water heater vs a condensing boiler. Just discussing the use of the sheet a little there ;)-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Careful, I think I saved that .xls with $.04/KWH pricing...you need to change the numbers to fit your situation.
As to the diagram....these are pretty good diagrams:
http://www.radiantec.com/230/index.html
You do need to question some of thier methods, however, chief among them being "open" systems, use of sand between sleepers, and they don't mention a "sandwich" system that is basically what warmboard, quiktrack, etc are as well as many DIY sandwiches that emulate them.
BUT, thier diagrams and their pre-plumbed systems are pretty good.
Careful, the second diagram is a REALLY BAD way to pipe a boiler.
Thanks Johnny, this is exactly what I had in mind. Makes a great case for the WH, too. Looks like that's the way to go.
I was leaning toward a closed system at the start (to keep it outside the potable system)l and am wondering now if there is any 'loss' factor in a closed system, and if so how to deal with replenishment. I can't see how there would be, conceptually, but I have the vague sense that I'd need to 'top off' the system from time to time, or at a minimum clean it.
Am I completely off base in that assumption?_____________________________HomeBase______________ LLC
As long as there are no leaks, you'll be good to go without any replenishment.
The pressure tank takes care of compensating for pressure differential between cold and hot water. Seems like the rule of thumb for most domestic systems is 10 PSI, and you should have a pressure gauge plumbed in to verify that. Upon initial fill and bleeding, you'll probably use house pressure of 30 - 50 PSI, and then once you've got most of the air out, bleed pressure off until you've got ~10PSI. It should stay that way forever.
not exactly accurate. There is some evaporation over time. Generally speaking, all closed systems should have a fill valve and backflow preventer plumbed in.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
you know it's funny b/c I thought I'd heard that, Rob. I just don't get the physics. Where does the moisture go?_____________________________HomeBase______________ LLC
Nothing is 100% sealed, ever. You might be "close enough" that you wouldn't notice the loss, but someday, over time, it'll be there.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
WH's are fine for very small loads. They are really not very appropriate for larger loads where greater efficiency will save significant dollars though.You need to be careful as well; MA is strict with codes. You may not even legally be allowed to use a water heater, appropriate or not. I'm not sure how strict they are these days, but you should check if there is going to be an inspection or a house sale at any point in the future.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
good point re: codes. I've had several of my reputable builder friends and clients recommend the WH, so I know it's being done locally. I don't know what, if any, special code hoops there are to _____________________________HomeBase______________ LLC
Rob/Johnny,
Quick follow up question. How do you guys go about calculating the BTUs required to heat a space like this? (468SF, Cathedral ceilings in 1/2 the space) I'm pricing out WH options today, and seem to recall from looking awhile back that a small one would probably do the trick, but wanted to make sure the calcs were right.
Thanks again for your help.
Brian_____________________________HomeBase______________ LLC
No problem. I run a heat load calculation. Which is basically the sum total of all heat loss through all exterior faces (glass, walls, roof, floor) and via infiltration. There are free calculators out there that usually come in a little high, but your results are only as good as the info you feed it for outdoor design temp, infiltration rates, etc.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
While I also advise a step-by-step, by the numbers, heat loss calc, my seat of the pants reading indicates that heat loss is generally in the range of 15 - 30 BTU/hr/sq ft..which puts you in the 7,000 - 14,000 BTU/hr range, so you'll probably be OK with a heat source somewhere in the middle of that range.
What you're basically looking for is a source that will almost never fall behind on the coldest stretch of days/nights that you're likely to get, but at the same time is not so grossly oversized that it losses efficiency to short cycling or over-heats the space on milder days.
While the capacity of the heat source is important, I think you've already recognized that how you control the delivery is equally, if not more, important.
Kind of a dice throw these days....I'll try to attach a really good spread sheet that helps you figure out which fuel might be best for you.
In my case, my electric co-op offers dual/fuel off-peak rates of .04/KWhr, so it's a no-brainert with $1.36/gal propane. The electric boilers are typically less expensive, both in price and in installation costs than gas or oil fired.
One you might want to look into is:
http://www.energyproducts.biz/specs.htm
Johnny, I don't know if you'll pick this up, but are you really at .04/KWH total elec cost where you are? I just calc'd mine based on my bill and I'm running .20/KWH when you factor in all the charges (dist, transmission, etc etc).
Making me think I should look a little oil fired furnace or something. On the sheet you gave me it looks like it would be almost half the cost/MMBTU (even if a WH is 99% efficient... which I can't imagine)._____________________________HomeBase______________ LLC
Actually 3.8 cents is the charge for dual fuel/HW heating during the winter months. There is an additional charge I think of $8.00 a month for the second meter...basic charge or something. So I just round it up to 4.0 cents.
They call it dual fuel because they can control for up to X (depending on the program) hours at a time during peak demand, which usually happens during sudden cold snaps relatively early in the heating season. So you must have an alternate fuel back up, which in my case is a propane fired conventional water heater.
The way it turns out in my case now is that I fire up a small EPA wood stove as a matter of course during these cold snaps, so burn very little if any propane.
Here's the explanation:
Dual FuelDual Fuel Rates are:
3.8 cents/ kWh-Winter
6 cents/kWh-Summer
Back up heat system must be automatic
http://www.tec.coop/services/dual_fuel.shtml
Johnny, what would the cost/KWH be if you didn't have the back up/dual fuel system? Amazing that our cost's can differ so much by region. I have to see if we have any other options locally._____________________________HomeBase______________ LLC
Normal household service is 8 cents/KWH, plus service charge.