Welcome to the Solar Collector
Brainstorming and Development Page!



Hot Air Collector

Hot Water Project 1

Hot Water & Space Heating

Solar Electric

Solar Construction 101


Best Collectors

Simply Solar
Sign up Calendar Latest Topics

  Author   Comment   Page 2 of 2      Prev   1   2

Avatar / Picture

Posts: 2,890
Reply with quote  #11 
I was thinking more about HEATING the crawl space and that will take a LOT more than 1cfm/50sq ft. Exhausting all that air to the outside would totally defeat the idea. Some compromise would have to be made.

I live on a slab so it was just a thought. You have a CS, what do you suggest?

Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay


Posts: 269
Reply with quote  #12 
My parents have pex stapled to a wood subfloor that is covered by carpet and tile as the heating source for their home.  The pex is covered with aluminum spreaders but compared to the fins built for the solar collectors they are thin and barely touch the pex.

When the system is running you can really feel the difference when you step on the tile compared to the carpet as the tile is warm to the touch but the carpet doesn't feel like much.  There is a long lag between them turning the system on and the room getting warm but it does work.
   They use a boiler that gets the water temp up to close to 180F I believe.  I'm not sure how well the system would work if solar heated.

Avatar / Picture

Posts: 2,240
Reply with quote  #13 

Exhausting all that air to the outside would totally defeat the idea

Not necessarily.

A lot of  homes have CMV, and *THAT* also exhausts air to the outside ! without totally defeating the idea of heating the home...

Also, many folks that heat their homes, open a door every so often, to let the cat out, without this defeating the idea of heating...

In effect, heating requires VENTILATION also...
Warm air holds more water vapor than cold air (I am not telling a Floridian anything new...), and warm air has bad bugs etc. so it needs to be blown out...

The 1 CFM per 50 square foot is not my figure - I found it in the article, and it comes from "building code" (whose ?).

In any case, it looks pretty modest to me - imagining a 1600 sq.ft home, we are looking at perhaps ? 400 sq.ft of crawlspace (depending on the shape of the home and the number of floors).

So that would come out at 8 CFM of extraction.
You would have a hard time finding even a PC case fan that would go THAT slow !
(I have one that does 19 CFM).

I have a bathroom extractor that pulls 57 CFM; the bathroom is "slightly smaller" than the 400 sq.ft of my CS...  However, this wild level of extraction is needed to get rid of the excess humidity after the shower is turned off...

My fear would be that heating a CS might actually increase the RH.
Therefore venting some CS air to the exterior might not be such a bad idea...

Also, (particularly if the heating is "free" anyhow (solar)), then it might be a good investment, to vent, in order to maintain a good air environment in the CS.

Otherwise, heating a CS (provided it is insulated and moisture-sealed) (note that I did not say air-sealed...) has got to be a good idea, like Mike said before, the heat  has got to go somewhere...

If you don't heat your CS, and it is damp to boot, then it certainly will be sucking heat from the house...

So I want a conditioned, heated CS.
The conditioning will be based on the 1 CFM law, and it requires works (penetration to get the air in from the house); I already have a penetration that will get the air OUT, just have to get the duct into the CS (through a 20-cm solid-block wall loadbearing wall...).

The heating will (eventually) be solar hydronic (and a small infrared radiant backup).

I am also using the CS to house my whole house fan, which drags house air from upstairs, through the CS (in a duct) then dumps it in the Lobby - this is for stack-effect mitigation, which is my "other" problem.

So working on the WHF fan ducts this week !

And so finally, to answer your question,
to sort out Terry, I'd suggest that he installs Crawlspace Radiant Heating; this would require first insulating the periphery walls like U said, then insulating the floor (2 inch of XPS) then laying the PEX directly on the floor, then dumping sacks of gravel over the PEX,
and if there is any room left, pouring a liquid screed (LIME SLURRY), over the gravel, to form a slab.
There ought be be enough room to get that in, even if it means (temporarily) lifting some floor to get into the CS from above.

Otherwise, as an ex-spelunker, I would be game for doing it in situ, it would mean getting some GOOD LIGHTING (not to mention VENTILATION...) down there first...

Laying the PEX would require an assistant or two - for the uncoiling.  It can be softened by dipping in HOT water...).

Sorry this was a bit long (Crawlspace stories usually ARE !)


(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
terry j

Posts: 29
Reply with quote  #14 
thanks for the discussion

figured it all out last night unable to sleep-not the coffee I might add!

Had a read of the second link before bed, and it will be a snap (still a pita tho)

Guess I should expand slightly, initially I was just questioning the rightness or wrongness of that guys rigid stance.

As mentioned, it is a (nearly) 200 year old house, and SOLID. It is also heritage listed so all of what I do in this vein is 'stealth', running heating pipes etc are invisible. that has meant pulling up floors to run pipes etc, none of this 'just cut a hole in the wall and run pipes looks be damned' stuff. Luckily in the main rooms the house is so old that it is not tongue and groove, just sawn floor planks. makes it easy to pull up.

We installed a wood boiler five years or so ago, which circulates water to the different rooms for individual heating using radiators. Installed it all myself which I imagine saved a bit of dough (esp given the work done on the 'stealth' aspect). As such there is a large radiator already installed in the kitchen. When I finally get to reno-ing the kitchen I have to (you guessed it) remove bad cement render finishes and re-lime it all. Additionally we will also be doing an extension which comes off the kitchen and so at that stage we cpould do drastic things like pull up the floor and tie it in to the extension if needs be.

Yes, the kitchen does get warm, but to me that warmth 'feels unsatisfactory' somehow. Not to mention how unsatisfactory it feels to pull up and waste a perfectly good floor I might add. All of which led to my idle wonderings about saving the floor, heating with this method by plumbing it into the existing heating network. Which led to my meeting with this local pex guy.

Whilst I do have a solar hot water panel of my new design to test, realistically this would not be heated by solar but my existing wood boiler. The amount of wood we go thru in this huge house sadly makes it unrealistic to believe solar space heating would make much of a dent.

I am looking forward to my tests on my design tho, if successful then I'll start a build thread soon. (I truly believe this has not been done before. Time will tell if it is as good as I hope. Suffice to say, if it works and is better than the 'standard' design I'll start a thread, if not it will sink without a trace and hopefully none of you will remember this guy crowing about some marvellous breakthrough design!)

Anyhoos, back to the topic and the solution for me.

[I always find it interesting how 'our initial thoughts/conclusions colour a topic ever after'. Our OWN considerations tend to corral and herd our thinking down the one path initially decided upon, and it is often very hard to break that and come up with better solutions. When we do, if we do, those are the 'ah-HAH! moments. When we break out of that corral]

In this case I managed an ah hah moment, and turned a very difficult job into a snap.

In the best of worlds i would have had tons of space to work from below-I don't. With the help of friends etc I could pull thru and loop all of the pex and easily staple it up. In this very small space the pulling through and looping is THE major problem.

My solution is found on page 26 (and the following) of this link http://www.radiantcompany.com/wp-content/uploads/radiantcompanymanual.pdf

Rather than pulling thru a single length of pex which loops into each of the  (many) joist spaces, by using headers and connectors I run 'small' pieces of pex in EACH joist space (or pair, up one and back the next door) to the inlet and outlet headers. So the difficulty of pulling thru a 300 foot length (say) in one piece thru all of the joists in a foot and a half crawlspace is gone, replaced by 'many' short runs each to it's own joist cavity, each with it's own connection.

Yep, many more connections (which equals greater cost, those sort of things always seem inordinately expensive don't they) and more fiddling with many joints, but suddenly a job that seemed insurmountable on the face of it suddenly becomes quite easy.

I love those ah-HAH! moments.

Avatar / Picture

Posts: 2,240
Reply with quote  #15 

Hi again, Terry,

Interesting document !

The header theory looks nice on paper, but I am not sure how well the random headers (in particular) would work, from the circulation viewpoint...  In my admittedly non-specialist view, the 1st header would take most of the pressure, and the last one would hardly get any... This could result in uneven temps in the floor...  Successive headers suffer from (and generate...) all sorts of complex flow phenomena, Gary Resa talks about this elsewhere on here...

Updated for link...

The arguments (Item 14) relate to a vertical panel, not to an horizontal floor, but I suspect the problem is analogous...)
See if Gary or any other specialists respond on this point...


Otherwise, I had another think about your underfloor: provided you insulate the CS walls (a must...),  and also the floor (just as must...), then you *could* put ANY type of heating in your CS, and get the benefit of it...

I am thinking in particular of electric storage heater (with bricks or oil etc.)  Or just an uninsulated water tank (our main upstairs heating at home in UK, many decades ago !).

This might sound like anathema on a "simply solar" site, but it is "simply" suggesting helping out the solar as you would rarely get 100% solar fraction in any case, for heating.  (look at it as the equivalent of having solar DHW, but using an immersion tank as backup, for the off days...).

(I'd be careful installing infrared radiant under your wood floor...)

Maybe a few 100-watt lamps might just do the trick...

In any case, without flogging a dead horse, I would highly recommend insulating the CS outer walls, as a first step.

read this !  http://homeguides.sfgate.com/install-rigid-foam-board-walls-crawl-space-66641.html

  • Adding rigid foam insulation to your crawlspace is one of the smartest things you can do to your house.
  • The advantages are multiple: Floors running atop will feel warmer to bare feet in the winter. Pipes running through the area are protected from busting in freezing temperatures. The crawl space stays dryer, which discourages the growth of dangerous mold and rot.
  • Not to mention your pocketbook will thank you as your heating and cooling bills lower.
  • The only drawback to insulating the space is you have to crawl around underneath a house…

Second thing that intrigues me, is why does your kitchen heat feel so poor...

Any drafts in the kitchen ? what type of windows, and walls ? Insulation levels ?  Ceiling height ?  Do you have a ceiling fan in there, if not, perhaps try one...  Lack of thermal mass maybe ?

Maybe a plan of the house might help - what is the aspect of the kitchen anyhow ? not dead south, I imagine...  Maybe you just (simply...) need a CONSERVATORY !

(Are you in Tasmania by any chance ?)



(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
terry j

Posts: 29
Reply with quote  #16 
hi GH, yep quite comprehensive actually that little PDF.

I too don't know about the random header, have not put much thought into it because the one that grabbed me was the the diagram of parallel headers, page 27. That was the instant solution to my threading problem in next to no space. that pciture is almost an exact representation of my current thinking, except it shows each loop going thru four joist spaces (up, back, up back) when I expect I'll do each 'loop' across two joist spaces (up and back only).

If I am honest, I would not expect too much pressure variation between any of the loops, I guess that is a possibility in a huuuge room with (say) fifty 'loops', I'd imagine ten separate 'loops' at the most in my case. (which equates to twenty joist cavities, each at 450 mm centres. That easily exceeds my requirements)

It is always easy (and perhaps safer) to err on the side of caution, in which case you would run the headers to start in the centre of the room, and the three or four each side fall off in temp at a gradient as opposed to 'hot at one end' (a kitchen cabinet?) and coldest at the other, with the middle 'most used' not as hot as it could be. Starting in the middle would give you the heat in the middle and it drops off at each opposite wall.

It would be one less thing to wonder 'what if' at night I guess, even if my gut feel tells me it would not be a problem. (I view all of this in an 'electrical theory' way with current flows and resistance. To me the inlet header is full pos volts, the outlet is ground. I cannot see a difference in potential between the first and last loop of either header. I could obviously be wrong)

Might as well use the heating system already installed and paid for, the water boiler. I need to start doing more research (for example, how would I control it thermostatically? Where would I put the sensor? that type of stuff) but-pending actually DOING it-an awful lot of my misgivings have gone ranging from the initial question posed to the HOW of it given the circumstances.

TBH it probably would not have occurred to me to insulate the subfloor walls, and with very good insulation under the pex under the floor (try saying that quickly) I struggle to see what difference it might make, BUT as i would be down there anyway that would definitely fall into the category of 'may as well do it whilst here' so good idea, thanks.

Just checked, yeah I did not say the heating was 'poor', rather 'unsatisfactory somehow'. It definitely IS good heating, trust me without it......I guess I feel like my legs below the knees are cold. It feels like 'warm air' rather than an all over comfortable temp. All very fuzzy, and it might turn out not to be an improvement in 'feel', but there ya go. It WILL however get the radiator off the wall for what that is worth in an old heritage home that never had one. (We aim for authentic-as possible-restoration. Not to the extreme of 'it originally did not have electricity so we will remove that, but you get the idea)

The windows do face north, but they are TINY! Good in summer of course, but bad in winter. In any case, that is an example of a thing that would not be changed, the original fabric of the house above all needs to be retained. Likewise (as good as it might be in an infinity of other applications) concepts like a conservatory built on to it won't happen. Probably would not be approved by council anyway (rightly so in my opinion, we have so little 'history' in aus in my view it is worth keeping)

Nope, in NSW, a place called bathurst. I've got some pictures on the net somewhere, one of those picture sharing sites. But for the life of me I cannot remember which haha, if it comes to me (and firefox remembers my password) I might post a link if anyone is interested.

On a sidenote, got some time to nearly finish getting ready for my prototype test, when the rain clears (yeah! rain!) I can get started testing. Fingers crossed it is successful.

terry j

Posts: 29
Reply with quote  #17 
ah, it was photobucket! firefox didnot help, but my memory was not as bad as I feared.

It was mainly stereo gear stuff, but a few photos of the house that will at least give some sort of 'feel', certainly nothing specific of the kitchen.

And if i can work it out forum software wise.......


Somewhat of an optical illusion photo, A view from way up the hill behind our place, with the barn in the foreground and the house behind. that chimney on the far left is in the kitchen. Interesting strobe effect on the barn roof. You can get an idea of how small the windows in the kitchen are by the one in the laundry, just behind the car and under the left hand chimney. there are two of about that size in the kitchen, one each side of the fireplace belonging to that chimeny.


Ignore my speaker (the original reason for posting the picture), in the background is the other side of the barn than the earlier picture. If you look you can see how 'bad' the bottom three feet or so of the walls are. Some bright spark had decided the best way to fix the rising damp was to concrete-and I mean concrete, not sand and cement-the bottom meter or so. Of course it just pushed the damp up HIGHER and destroyed the mortar above it. I had to jackhammer the bloody lot off and will re mortar it with lime putty. We fixed the rising damp anyway, and it was easy if YOU LOOKED MORON!

(sorry about that, most of my work is undoing what others have been paid for grrrrrrrrrr)

As it turns out, not too many other pictures useful to this thread, hope that was at least a little bit interesting for some. (dunno about you guys, but one of the things I really enjoy when seeing peoples build pictures is the house, surroundings and neighbourhood, the feel and vibe of different places around the world.)

Avatar / Picture

Posts: 2,240
Reply with quote  #18 
Nice speaker !

the house looks OK too [biggrin]
Do you know its history any ?
Looks like a flanders farmstead to me, those roof pitches, tall stacks, brick entablatures... dead give-away !


See what you mean about the small kitchen windows - looks like you are stuck with them - have you thought of inviting your building-control officer to a barbecue [rolleyes]


(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
Previous Topic | Next Topic

Quick Navigation:

Easily create a Forum Website with Website Toolbox.


web statistics