I'm concerned about noise as the pex expands and rubs against either the plates, or the hangers etc. Is this a significant issue? How to avoid it? I'm now leaning toward using 1/2" pex, possibly without transfer plates. Do you tie it securely? Or better to let it move? I suppose if I used plates, I could run a lower temp, which would mean less expansion, but more places to rub. etc..... Thanks, -m

if you use heavy plates, they prevent noise for the most part.

lightweight plates are more of a noise issue. we use PAP with that, if we use them.

no plates can be quite noisey if you don't let the tubing move.

Reset control helps in all cases as well.

Thanks for the comments. Right now, I feel like just giving up and going with gas forced air. I really don't want any noise (that's one of the reasons I'm building with ICF's). I don't like furnaces, but I don't think it would run much. And there would be no (or almost none) creaking noises as things expand and contract. And, I wouldn't have to do anything. I would have had to do a lot of the labor to get the radiant system in for the same budget..

-m

You have an ICF home, Your heat load will be less than conventional. If you use a surface mount system like RHT floor panel or quick track or others and run the temperature low you will have little noise. We recently assisted in a local install of RHT floor panels in a 7,000 residence. Oak flooring is nailed directly on top. Design temp is 95 degrees, boiler is a LAARS NeoTherm condensing unit. There is no noise.
Dan

noise is a problem with bad details. Having no idea what your heat load is, I have no idea what your issues are, but I can say you are unlikely to enjoy a forced air system as much as a radiant one. Maybe, but it's not very likely.

of course, it could go the other way if you don't get the details right.

whether or not to use plates is not a noise decision: whether or not you NEED plates is a heat load and floor covering question. Just because you're ICF doesn't mean you have a low heat load. Glass is still glass. if you need plates though, using the heavy gauge plates is the right choice. and it will help make sure there is very little, if any, noise. certainly less than a FHA system.

I read that you get around 20 BTU's per sq ft with bare pex, maybe 25 with plates. I have 976 sq ft, with a heat load of about 12k BTU's per hour worst case. So bare pex should be enough...(?) The thick plates may bust my small budget..

Thanks for the input.
-m

15 BTUs without plates is a more realistic max, (140 to 145 degree Water temp under wood). 12 BTUs/hr is more like 130 degrees. depending on your heat source that might be quite acceptable: slow response, but workable.

http://www.ultra-fin.com/ 

There sure are a lot of joist penetrations in the Ultra-Fin pictures!!! http://www.ultra-fin.com/products.php Jeff

If Ultra-Fin is still claiming ridiculous outputs like 63 BTUs/sq ft or whatever, keep in mind that is totally wrong. It's a bit better than plateless suspended tube, but it's nowhere near the same ballpark as real plates with direct contact to the subfloor.

There's an article here:

Radiant-Floor Heating: When It Does—and Doesn’t—Make Sense

That raises some good  questions about whether radiant flooring is worthwhile with only a 12k BTU's heat load.

We've just installed a direct-vent wall heater in a similar sized space.  It's just about silent and, even without the fan option, it provides a pleasant even heat.

Given the high cost of installing radiant, and the low cost and simplicity of some of the other options, with a well insulated house you may want to consider the value of radiant.

We are installing radiant elsewhere in the house, but that's mainly so we can use solar for heating.

That's interesting. What product did you use? It might work for me on the main floor, where there's basically one big space. But upstairs I have two small bedrooms to heat....???

-m

We installed a Williams 22K BTU direct vent heater.  At our altitude, by the time we derate, that's about a 12K heater.  The 14K heater is just over $450 at Home Depot.  There are a number of similar products and vendors.  

The space we're heating is about 900 sq. ft. including a living room, connected kitchen and two bedrooms about 10x15 each.  Currently, the only additional heat in the bedrooms is electric space heating.  The heater heats them during the day since the doors are left open.

12K BTU (2.5KW) really is a pretty low heat load and so electric baseboards in the bedrooms may be cost effective.  Especially if all you're going to do is heat them a little in the evening and in the morning.  Feels kinda odd to be suggesting electric heating on a green building list because it's only about 40% efficient overall (vs 75%+ for a gas heater), but if you're really not using much power the efficiency becomes less important (40% of zero is the same as 75% of zero).  Seems that if your worst case heating load for the bedrooms is about 1.5KW, normal load will be about 1KW for one month and about 0.5 for another two.  You can decide if that's close enough to zero or if the economics are there (or if your local electricity is green enough for you).

If you want to heat the bedrooms more efficiently, there are some double-sided gas wall heaters that you could put in the wall between the two bedrooms.  Williams has a top-vent unit but it's not a direct vent and if your house is well sealed (probably) a direct vent unit might be a better choice.

I suspect that two heaters would provide you with a good solution at a lower cost than forced air, but I'm not an HVAC expert so others may disagree.

It would be good to have some proponents of radiant comment on why you might be happier with the heating provided by a radiant solution.

Hmm. Electric heating is 100% efficient, not 40% efficient. It is the cost of the electricity that makes it expensive, not its efficiency. There are some places where cheap electricty (4 cents / kwh) can make it a viable alternative to gas, if the price differential is to be trusted.

Jeff

Yes, I also thought that electric heaters were more or less 100% efficient. But maybe stonecaveman is referring to the initial production and transmission etc being less efficient. Whatever the case, it's still too expensive here (12 cents/kwh and going up) to use as thr main source. But I do use a small electric oil-filled radiator ($35 at Walmart) to heat an extra bedroom in the basement in my current home.

I will look into the possibility of using a direct vent gas wall heater for the main area. I wonder if it might make sense to use a smaller one in the upstairs bedrooms. Although I'd hate to have too many penetrations through the outside walls for vents (might be a source of oustside noise?).

Thanks,
-m

Jeff,


The heater is 100% efficient however, if you consider the loss from generation and transmission you seem to come up with about 40% according to this article from Wikipedia: Electric Heating

So, for 100 therms of gas, if you generate electricity about 40 therms will end up heating your house, vs 75+ if you burn the gas directly in a furnace.  So if the electricity is generated from fossil fuels, you're increasing your carbon footprint as well as (possibly) paying more for the heating.

If you live in an area where a significant portion of your energy is generated from renewable resources, for example, Quebec is cited in the article as getting 90% of their energy from hydro, then your carbon footprint may be lower if you use electricity vs. burning gas.  Here, we can pay extra (about 2c more per KWh) for electricity from "green" generation.

With the type of house described, well insulated and sealed, unless you're living in an area of very high electrical costs, the savings in installing electric baseboard, which is low cost to buy and install, may offset the extra cost of heating for a good number of years.  Especially since we're considering only the bedrooms, if one's a guest room it may get heated only occasionally, if they're not used during the day (or can get most of their heat from downstairs) and you spend $100 on a warm comforter (quilt) they might need very little heat.

this is a good article, but I will note that in spite of my advice to people with very low loads that radiant makes less sense, a significant portion of my clients with loads like that notice a difference with radiant and are glad they have it.. I suspect mostly in areas that are unheated below, in which a neutral floor is a big improvement over a cold one.

40% net efficiency from the source fuel BTUs across the grid to the load is the optimistic view. Most analysts put it between 28% & 33% in the real world.

But local grids matter.  If you live next door to the nuke and you use off peak power you're using energy that would have otherwise been dumped in the cooling system to keep from having to turn the nuke down overnight (they turn down slowly, but come back up even MORE slowly- far to slowly to respond to demand curves, so operators typically dump power all night, heating up the rivers & atmosphere.)   Even coal plants are often power dumping to keep from shutting down. Peak space heating loads have good correlation with off-peak rates- it can be a good fit even in not-so-green power country, if done right.

I keep hoping they'll scale down the boiler coupled with the NG-fired cogen in the hydronic Freewatt system to match it to more modest heat loads. (The min-mod on the boiler by itself is ~3x my design-day heat load.)  They have propane-fired versions in the works too.  The thermal output of the Honda by itself would support about half my seasonal load, so the total fuel utilization for the ~1.2kw of power generation would be more like 85-90%, not the ~30% (40% for the optimists) in a grid-sourced power scenario.  (I'm not sure what the altitude limit on the Honda would be.) See: http://www.freewatt.com/hydronic.pdf  and http://www.freewatt.com/warmair.pdf

I have a friend that brokers electricity in the Seattle area, we were having a discussion one day about fuel efficiency, and sadly we us our electrical plants (nuke, coal, oil) at about %35 tops.
The forward looking days of co-gen, PV, and more will serve all us better the sooner they arrive in mass.
Our dependence on grid will be minimized to some degree, perhaps looking forward a decade when there are mass electrical outages the neighbor down the road may have ample power to run the well and provide water to you.
These systems are barley out now.
I best get to work and stop rambling,
Dan