Hey, anybody out there familiar with infloor/underfloor radiant heating using a high efficiency water heater as the heat source? I am in the process of a remodel of a 1930s home in South Dakota, which will include new heat. Total square footage of the main floor 900 sq ft., partial basement about 600 sq ft. I already have poured a new basement floor, with Wirsbo pex piping installed, and plan to run it between the floor joists of the main floor. I had a heat loss done, and have had a very expensive but small wall mounted boiler recommended, with a hot water storage tank attached for domestic hot water. About 7 grand for this system. Seems a bit steep. Any ideas on less expensive alternatives for a heat/domestic hot water source?
Thanks, Norsky
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jt8
"A tree is known by its fruit; a man by his deeds. A good deed is never lost; he who sows courtesy reaps friendship, and he who plants kindness gathers love." -- Saint Basil
There have been a number of discussions of this on Breaktime over the years. Some strong opinions pro and con (don't remember any flames over the topic, however, unlike some other areas...) David Thomas, in particular, gave some cogent insights on using a high efficiency water heater. Try using the advanced search feature of Breaktime with some variation on "water heater radiant floor" - some people prefer hydronic heat, so you might also stick that in there for one of your searches.
For a small space, water heaters seem to be a good deal. Here's an article you will find interesting from November 1998 issue of Journal of Light Construction. It's free online:
Using Water Heaters for Radiant Heat
If the load is in the right range....15K - 25K BTU/H at design temperature, which is probably in the 10° range for your climate, a water heater will work just fine. The simplest way to do this is buy TWO water heaters, one for domestic and one for radiant heat. You should separate the systems.
You also can use one water heater with enough output for both radiant and domestic and heat the radiant side via a heat exchanger.
There is a problem within the industry here in that there simply are not very many, if any at all, bonafide boilers that will modulate down far enough to match the season-long load variations of small foot-print, low-loss dwellings like the one you describe.
Remember that heat loss calculations are generally designed to make sure you are able to supply enough BTUs to the space for the COLDEST stretches of weather, which in midwestern USA is maybe only 10 - 20 % of the time. The rest of the time you can heat most economically with a source that can modulate way down into the low 1000s of BTUs....which a water heater (although not truly "modulating") can accomplish just fine.
what's the heat loss?
A "high efficiency" water heater is not going to be cheap either.
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Norsky
There are companies who help people like you. Radiantec is one. They will sell you everything you need and help you do the calculations..
Water heaters are particularly efficent compared to boilers due to their lower operating temps.. Using a boiler usually requires adding cool water to bring the operating temps in line. Somehow that seems counter productive, why heat water up much higher than needed only to cool it down to run it thru the tubing.. My 5000 sq ft house will be heated by one 80 gallon high efficency water heater with a 50 gallon back up from a domestic water heater..
(It's super insulated)
If you do the calculations yourself you can go to places Like Home Depot and buy most of the stuff yourself, However you will only save a little bit compared to buying it from Radiantec though..
MY Brother-in-law bought the manifold made up by Radiantec, bought the Pex's from them as well amd even bought their aluminum and formed it himself..
I've bought their manifold, pump etc. but the pex (tubing) I bought from a local big box store and I made my own aluminum plates because I own a bead roller.
It is easier for me to install mine since my flooring is three inches thick. I just used a roofing nailer and popped a nail straight in.. My brother in law working with 3/4 inch flooring had to staple things in and at that angled the staples..
Frenchy, NO water heater on the market... none... can rival the efficiency of a modulating/condensing boiler on a radiant system. Mod/cons are built to not only operate at low water temperatures, but to use the low temperatures to condense additional energy out of the flue gases.For a similar price as a Polaris "High Efficiency" water heater, I might add, and if you add a storage tank to the mod/con, the heat exchanger you MUST add to the Polaris just about evens out that extra cost as well. Not exactly, but it's not that different either.Plus the mod/con will be silent, the Polaris roars like a bear. The Polaris will not gain its listed efficiency because you'll run it at high temperature, or you'll short out your igniters every year. The mod/con will EXCEED its listed efficiency in a low temp system, absolutely.Using a lesser water heater could save you a couple of grand. You'll pay for it in fuel costs in a relatively short period of time though, if you chose it instead of a mod/con. Plus, the action of your radiant system will be substandard as you'll be lacking outdoor reset water temperature control (though you can add that to the water heater to heat exchanger injection pump for a few hundred dollars and if you go that route you absolutely should).I've done plenty of water heater systems over the years, especially before mod/cons were brought around, and plenty of conventional boiler systems and now plenty of mod/con systems. If the choice is conventional boiler vs water heater, I might consider the water heater. Conventional boilers are not as efficient as listed and water heaters are more efficient than rated, typically, so they are in about the same league, unless you add the boiler controls you should be adding AND you have a load that is well sized for a particular conventional boiler. For my typical 30/40kBTU house a water heater could make sense vs a CONVENTIONAL boiler. But I will *always* go for a mod/con boiler if at all possible because after I've run the numbers, I've seen that nothing else makes sense, no matter how charitable you want to be for water heater efficiency.The fact is, if you have a real load (greater than 30kBTUs/hr) in a climate with real winters (significant Degree Days), it's quite plainly a bad choice to use a water heater instead of a modulating condensing boiler. Bad choice, and bad advice if you are advised to go that route. Period. I generally try to be more diplomatic than this, but frankly this is a very important subject with a lot of misinformation surrounding it out there, and I want no chance at a misunderstanding. Do not waste money on an overpriced water heater, and do not waste money on skyrocketing fuel unnecessarily. Design a low temperature (under 130) system, and use a mod/con boiler. And if you can get the temps even lower, well that's that many more options you have on how to heat water down the road should energy prices continue to climb as they have been.Finally if you are expecting a total el cheapo dual use water heater system without a heat exchanger, anyone telling you to do that is quite simply just trying to sell you pipe and doesn't care about you, your home, or your system. Never mix heating and potable water. Another very bad idea that I myself fell prey to for many years. Now I know better.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
You make extremely interesting reading. Somewhat at odds with what I've read from a variety of other sources. (that doesn't make you wrong, simply a request for further information.)..
Minnesota has a modest cost base for electricity. Our cost per therm is the same as for natural gas..
Right now we have many, many wind generators not on line.. (over 50% of them) as those come on line when powerlines are built to them the cost for electricity will be under even more pressure while natural gas costs will be under increasing demand.
Thus I choose to use simple electric high efficency water heaters.. Radiantec recommends water heaters as do several other sources..
If I should be mistaken in my calculations ( nobody seems to have good figures for SIP's, the ones I've found very all over the board) I was forced to extrapolate my calculations since nobody does them for 12 inch thick walls.. I did provide myself a fall back position in that the original forced air furnace will serve in a standby position and I've added two natural gas fireplaces with (supposedly) 80% efficency.
Frenchy, go to heatinghelp.com's "the wall", or the RPA forum at radiantpanelassociation.orgif you poke around their forums with the search feature.. I suggest searching for "open systems" or "water heater radiant".. you'll get lots of discussions about why this is a bad idea. You'll find a couple of proponents as well. But I think you'll find there is a pretty good consensus among real professionals.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
Thank you I will.
I do have a tendancy to question authority, Too often in my life I've seen highly opinionated people assume a position with no real basis in fact .. Too bad boilers aren't a hot topic over at Consumers Reports.
Agreed, however for what it's worth, I do not sell boilers. You are wise to fact-check.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Frenchy,
This statement "Water heaters are particularly efficent compared to boilers due to their lower operating temps.. Using a boiler usually requires adding cool water to bring the operating temps in line." is about as wrong as can be.
IF water heaters, the cheap ones like you advocate using for heat, were rated in terms of AFUE, they would be in the 40 to 50% range. The energy factro as is, is on the order of 0.6. Even high temperature boilers do better, and do so for much, much longer. The best gas water heaters acheive efficiencies in the 90% range with a 70 deg temperature rise. At the ranges that a heating system operates, as in 15 to 30 degree temperature difference, the best is at 75% or less, and those are commercial versiions that cost as much as residential boiler.
Tim,
I guess unless I find credible evidence to the contrary we'll get to see this winter.. If electric water heaters abit high efficency ones with a 98% rating really are as bad as you claim then my heating bills will be over the $500 dollars a month they used tobe.. (december and January) If they are I will quickly do the math and a boiler will be in place.
Actually I may not have the in floor radiant fully up by december. So I may use the furnace for one more winter and see next winter..
Stay tuned!
Frenchy,
I thought that you were comparing a gas fired domestic water heater to a gas fired heating boiler. In that case, the numbers I quoted apply.
As you well know, (cost of electricity, present or future, exclusive;p) electric resistence heat is practically 100% efficient.
BTW, What do you pay for electricity and who is your provider? If you don't mind sharing this info, I'd be curious as to how cheap it is.
Tim
Excel energy. I'll have to wait for she who must be obeyed to get home to find out the rates.. I do know that our monthly bills now are under $35.00 a month and that in spite of building a timberframe home and using every single power tool known to man.. Our stove and oven etc. are electric because my wife is a stubborn sweed and it took her decades to learn how not to burn food.. A gas stove would be a terrible thing to inflict on me..
I am aware of the sliding scale that Excel has and the rates will drop a bit once they are informed of my conversion to electric heat..
Why anyone would settle for the mere "100% efficiency" of electric resistance heating is beyond me. The fuel to heat efficiency of such a heating system is TERRIBLE! Electricity is high-grade energy- thermodynamically, it's "work on tap"- it can be readily converted to work, like operating an electric motor etc., with minimal losses. It's tough to make- and there are lots of losses in doing so. Turning high grade electric energy into low-grade comfort heat is a waste.
At least with a heat pump, even a lousy air-source heat pump, most of the winter you'll pump a few watts of heat from the outdoors into your space for every watt you put into the compressor and fan! The very worst a heat pump can do is better than the BEST a resistance heater can do! Back that up with local resistance heating to provide a little extra comfort and reduce the heat pump's size if you must, but PLEASE don't heat your house directly with resistance heating!
This is what p*sses me off most: the market for electricity is so messed up, that it sends the wrong signals to people when they make energy use decisions. If the local market is telling you that electricity is cheaper than burning a fuel, that's saying that it's more cost-effective to buy a fuel and burn it in a power plant to make steam to turn a turbine to turn an alternator to make electricity, then lose a good chunk of that in transformers and a transmission system to do what with it- turn it back into low grade heat with a resistor?! It's energetically stupid, regardless of whether or not your electricity market is subsidized or there's a nuclear power plant handy.
Yeah, I know coal is cheaper than natural gas, but burning coal by proxy is still burning coal. Everybody downwind, yourself included, is still suffering the consequences of that decision.
I'll bet you that eventually those electric market subsidies will die away and you'll end up paying something closer to the REAL price for electricity. When you do, the heat pump will really start paying for itself.
Besides venting and expressing just a little sarcasm (both I do frequently), is there a point here? Electricity use for heat, in your opinion, is good or bad? Only if used with a heat pump?
Molten, you can make electricity a large number of ways. Up here in maine, I pay about $15/month extra (not heating with electricity, of course, but still) to make sure all my usage is generated by wind and hydro.Even with a 50% transmission loss, it's still fossil fuel free. FREE. None, zero, nada. If I put in an electric boiler, I would have a fossil fuel free home.The beauty of hydronics is, you aren't tied to a particular fuel. Electricity is cheap? Go ahead and use it. Oh, it jumped? Switch to something else. The beauty of LOW TEMP hydronics, is the options that you can switch to get wider and wider. Geo, wood, solar, corn, oil, gas, electricity... whatever you like. The lower you go the more choices you have if/when the time comes that using mainstream fuel becomes cost prohibitive. Most of these choices don't have to be planned and installed right off the bat either... you have options later.All anyone can do is make decisions based on currently available information. Electricity may very well jump before long. Or, huge subsidies may be enacted to ramp up electrical production further and "get us off oil". Who knows? I don't, that's for sure. But with hydronics, you can make the decisions based on the info you have, and if you're wrong, you're out the cost of that heat source plus some installation labor. not the end of the world.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Rob: you're of course right about the benefits of low temperature hydronic heat and its flexibility toward energy input sources.
As to your purchase of wind/solar electricity- kudos to you for being so responsible. Unfortunately, as a result of your action, the utility merely increases the proportion of coal-fired electrical production to people on the same grid who don't care to pay the extra $15/month. The fact is, your choice has increased grid demand, though perhaps it has softened the cost differential somewhat for the installation of new wind turbines.
Given you live in Maine and have no access to natural gas, I understand your selection of electricity rather than propane. But as someone who has demonstrated such an advanced knowledge and skill in hydronic heating design and installation, it shocks me that you would choose resistance heating, regardless how you pay your utility for the electricity. A heat pump would be so easy for you to implement and would reduce your bills significantly most of the year- why wouldn't you do it? The worst it could do is better than your resistance heater!
As to the OP's question about whether or not electricity is a good source of heating: all I can say is that electric heaters are inexpensive to buy, extremely reliable and very easy to control. But given the grid balance in the United States in general, from a source energy input to comfort heat output point of view, electric resistance heating is probably the least efficient means of heating a hydronic system by a long shot.
Read my post again: I'm not heating with electricity, just switched my regular electrical power over. My point is that efficiency aside, there is a flexibility of generation in electricity that is not there with any fossil fuel, and so ultimately it may be the one of the only choices we have left.In the meantime, my clients have to make economic decisions, and using an electric boiler, if it performs correctly, while electrical rates are inexpensive could very well make sense. I won't begrudge them that. And if the prices jump, well, it's not a lot of capital wasted.I'm not sure what kind of heat pump you're talking about. Geo? Air?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I assume he meant geo, not air.
jt8
"The old Quaker Meeting house is almost 300 years old and as my sawzall made its way into the pegged ancient wood, a smell emerged that told me about dried, cracked things. The ancient Quakers sitting in the well worn pocket of their silence on the darkened pine benches were whispering something to me across the years. Something about why I was here, why we're here. Lord but it was hot. I reached in to clear anything out of what was the sill, nothing but the hardened mud, lime and sand mortar, dust and shadows." -- Jer
Ground-source is fantastic, but not really a fair comparison- the capital and installation costs are very high. No, I was talking about air-sourced. Even at relatively low temperatures and using a lousy heat source like air, a heat pump will still deliver more than a watt of heat into your structure per watt of electricity you put in, which is the best you can ever do with a resistance heater!
Air-source got a black eye in this area about 20 years ago. 100+ in summer with down to possibly -40 in winter. They would do reasonably well in summer, but would have to work like a dog in winter to draw enough heat.
There has been a resurgence in them in the last couple years. Both HVAC guys I've talked to recently tried to sell me one. As far as I can tell though, the only real improvement is that they've added electrical resistance backup to them. Which is the last thing I want heating my house.
Whereas ground source in a well insulated home... you just can't do any better (assuming budget isn't an issue).
So air-source heat pump isn't a selling point in this area, but a ground source can be.jt8
""The early bird gets the worm, but the second mouse gets the cheese." --Dave Barry
I don' t know much about air heat pumps (my focus is pretty narrow, hydronics only), but from the projects I've been involved in, the air heat pumps are put in as "cheap heat" during the shoulder seasons. apparently they aren't that expensive to install.I would argue that the comfort is lesser, but I don't know enough about the performance comparison to comment on that.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Same around here, John. There was a fad for a while during the last energy crisis, but it died out due to poor durability and under-delivered performance relative to the claims made by the sales guys. Air-sourced heat pumps are a poor option for mostly-heating climates if they're your only source of heat, because you'd need an enormous one to handle the coldest days of the year, which would be massively oversized for the rest of the year. But relative to 100% electric resistance heating, adding a heat pump with resistive back-up is pretty much a no-brainer from an energy efficiency standpoint.
As to payback period, that depends how heavily your electricity is subsidized and what happens to the price in the future. My bet is that electricity prices are going up- way up- in most jurisdictions in the next 10 to 20 years, due to fuels costs, environmental/taxation costs and the need to replace existing power plants nearing the end of their design lives.
Have a look at http://www.htproducts.com
They have modulating/condensing wall mounts, and the prices are more moderate than what the Germans are charging.