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Old 12-07-2011, 01:46 PM   #1
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Installing radiant heating in a basement and general basement questions...


Hey gang,

So after thinking over my options I have decided to get a radiant heat system for my basement renovation.

First question... I've talked to some people who said that when their basement radiant heat runs they rarely if ever have to have their existing forced air system come on (even in the upstairs. they say the radiant heats up the whole house). Is this possible? Are we talking about a system that needs to be run at a VERY hot temperature? I ask because the efficiency of my current HVAC system is piss poor.

Second question... The existing concrete has a thick paint over it and I need to jack hammer much of the floor to get to drains/plumbing lines anyways. Does it make sense to just jackhammer it all up and install the radiant there? Or is this a big can of worms and I should just clean off the paint, apply a bonding agent for the new concrete pad, and be ok with losing 3" of head room in the basement?

Third question... This may link up with the first question but... are there any good websites that I can use to help calculate if I need a new hot water heater to support the radiant floor AS WELL as my normal home loads?

Fourth question... Can the basement rooms JUST use the radiant floor system? Do I NEED to run HVAC to these rooms as well (supply and return ducts)? Even thou they would be comfortable as is without the forced air heat?

I know this is a long post but I'd rather be specific than vague on what I am asking.

Also I have not done ANY work or spoken with ANY contractors or the city yet.. I am still in the data gathering phase here.

Thanks guys!

Chris

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Old 12-08-2011, 12:38 AM   #2
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Installing radiant heating in a basement and general basement questions...


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First question... I've talked to some people who said that when their basement radiant heat runs they rarely... Absolutely possible. FIRST AND FOREMOST, you NEED to do a heat loss analysis, at least by yourself using one of the online heat loss calculators. They are easy to use. You just input your areas, R values, and heating degree days for your climate. People heat all sorts of stuff w/ radiant floor. It is all in the numbers above. Without an accurate heat loss analysis, you are peeing in the wind and hoping.

Second question... The existing concrete has a thick paint over it and I need to jack hammer... I sure would get the whole damn floor out of the way while you are at it, and install everything correctly and efficiently. I can only see major PITAs any other way.

Third question... This may link up with the first question but... are there any good websites... See above comment, and/or a qualified person to do the calcs for you. IMHO, you can do it accurately enough if you feed in good info.

Fourth question... Can the basement rooms JUST use the radiant floor system? Depends on the heat loss analysis, but very likely you will only need to supply fresh air and exhaust stale air in addition to the in-floor heat. INSULATE LIKE HELL under your new slab. If anyone tells you "No insulation. The earth will be a good heat sink", then you study yourself and come to your own conclusion. That BS has been debunked 75,000 times. Keep the heat IN the house; trying to heat up China is purely a waste of YOUR money. BTW: You should not run over 120 degree water into concrete, and unless you have really poor insulation, you won't need water that hot. It is not a cake walk, necessarily, to figure out your water temp, water velocity, PEX size and spacing, etc, so either study like hell or hire a competent contractor/engineer. You will possibly do fine if you "just do what the guy next door did", but you can also screw yourself up. Mistakes embedded in concrete are rather permanent.
See after the bullets above. John Seiliger has a great book on all this. "Modern Hydronic Heating". There are also others, I am sure. Buildingscience.com will keep your reading all winter.

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Old 12-08-2011, 07:31 AM   #3
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Installing radiant heating in a basement and general basement questions...


Exactly the information I was looking for! Thanks!

GAH!!!!! That is an expensive book..... F**K it if I have to redo ANYTHING that book will pay for itself 10x over. Done and ordered
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Old 12-08-2011, 02:09 PM   #4
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Installing radiant heating in a basement and general basement questions...


Ok here is a question...

So say i demo the slab to put in the radiant floor.... won't that undermine the structure of the home until the new slab is in? :-x
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Old 12-09-2011, 12:06 AM   #5
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Installing radiant heating in a basement and general basement questions...


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Ok here is a question...
Good point. Is the house sitting on the slab, which sits on a foundation (stem) wall, or is the slab floating? If the slab is not floating, I can not see how jack hammering the floor near the wall could disturb anything. That said, a more cautious approach would be to get a concrete saw and cut the slab near the wall, then jack hammer the rest. Whether or not you pin the new floor to the old is something you and an engineer out to figure out. I don't see the need to attach them, but I'm not there looking at the job, nor do I know the age of the house, soil type, etc (nor am I an engineer). BTW: Since you are still planning, you can buy plywood that is pre-slotted to accept PEX. Installing that over foam may be an alternative.
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Old 12-09-2011, 12:14 AM   #6
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Installing radiant heating in a basement and general basement questions...


I'll talk to a structural engineer (/civil) buddy of mine and ask. The home itself is a one story ranch home that consists of a poured cement floor and walls and a main central beam across the basement ceiling (3 posts supporting it). I'll see what he has to say on the structure. I would LOVE to dig down to get an extra 2' of space but that seems... dangerous. So I'll consult with him and then go from there.

Regarding the plywood... that sounds nice but with my floor plan I'm not sure how much that would help me. It is a big irregular as you can see.

Time to pay my Civil Engineer buddy in beer and find out what he has to say about this project!!!

(BTW the white is existing and everything else is proposed work)
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Old 12-09-2011, 01:32 AM   #7
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Installing radiant heating in a basement and general basement questions...


Digging down 2' is very dangerous, yes. I see no reason to not use the plywood, but it would lessen the height of the room, and it sounds like you need more, not less. Do see the engineer, and post back what he says if you don't mind.

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