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Old 10-25-2008, 07:51 PM   #1
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using forced air for radiant heating


Our house has been plagued by rats, cockroaches, water bugs and a horrible musty smell for several years that I knew was being caused by the crawlspace ductwork being eaten up by rats (Cockroaches were crawling up from the floor vents). If I seal up the vents in the foundation wall and the floor vents, I can eliminate the bugs and smell and heat the house with a makeshift radiant heating system (visa vis my forced air heat pump via the leaky ductwork. I would have to go down and detach some of the floor vent ducts since a few of them still deliver heat).

I don't understand why this system isn't being used in radiant heating homes as it seems perfectly viable to me. Does anyone have experience with this? HVAC people like to tout that old BS about foundation venting required to alleviate moisture buildup, but modern research has indicated that it is not nearly necessary as previously thought. It does help sell those expensive hydroponic systems though. I say we end this hydroponic hegemony now and retrofit our older homes with forced air radiant heat systems... and they're already 3/4 installed :-).

Dave

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Old 10-25-2008, 11:38 PM   #2
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using forced air for radiant heating


Actually. many of us have known for years, that vented crawlspaces are more harm then anything.

A heat pump won't be able to heat the crawlspace warm enough to get enough radiant heat to heat a home at normal design temp.

Most heat pumps won't last long with return air temps above 80F.
The compressor will over heat and die. Even before that happens.
It will lose capacity as the crawlspace warms. So you would be using your electric aux heat mostly.

Code restricts air temp to less then 120 in wood joist bays/cavities.
Code as prohibits Romex/NM cable.
All your wiring would have to be rire rated/MC, or in conduit to be in a plenum cavity.

Next, how will you cool your house without those ducts.

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Old 10-26-2008, 02:39 PM   #3
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using forced air for radiant heating


Good point about the 80 degrees on return duct. That's why I will install a thermostat w/ remote sensor located right at the return duct on the heat pump. At 80 degrees it shuts off. The only remaining problem I'm worried about is short cycling. I would cool the house the same way. In summer, the leaky ducts were cooling off the floors so much (w/o much coming in in the way of direct air) that our house was still getting cooled (I blocked off a few of the larger man sized holes last summer. I figure if I go around and block them all off, it'll be reasonably efficient). I think that 80 degrees will be well sufficient to heat the flloor with from below. We have very little floor insulation and the floors are pretty thin to begin with.

What do you mean by the heat pump losing capacity as the crawl space heats? Why is heating a crawl space so dramatically different from heating the living space? I don't think you fully understand that that's all that's been getting heated for several years due to leaky ducts. Some of the larger 14" have ducts have fallen off (according to the HVAC guy we recently hired to inspect it).
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Old 10-26-2008, 05:16 PM   #4
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using forced air for radiant heating


By losing capacity as the crawlspace heats up.

It takes more then an 80 temp in the crawlspace to get enough heat to heat the occupied area(when its at design outdoor temp).
So it will lose capacity. HPs lose efficiency and capacity the warmer the return air is.

Trying to do raidant floor cooling only. You will end up sweating the floors, and with high humidity in all of the occupied areas.
Good way to grow mold.

Even with holes in the ducts. You had an air exchange.
The returns drew air from the occupied area into the air handler, and what ever air it drew out, had to be replaced with air from somewhere else.

The few homes with radiant floor cooling and commercial buildings with radiant floor cooling. Do use the radiant until the humidity is down, so they can prevent sweating walls, floors, and mold growth.

A carpeted floor over a crawlspace heated to 90F to try and heat the occupied floor to 70F, would only give you a heat transfer of 4.4BTUs per square foot per hour.
A hardwood would give you 6.2 BTUs per sq ft per hour.


You would still have to address the drying out of the wood. And your electrical wiring in the crawlspace.

You would also have to insulate the crawlspace floor.

by the time you did all the work required to do what you want, and still not have good heating or cooling.
You could have invested that time and money into replacing your duct work. And heating and cooling for half what it currently cost you with your current leaking duct ystem.
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Old 10-26-2008, 11:43 PM   #5
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using forced air for radiant heating


I've was down there looking around today and the only thing that really concerns me is the filthy air (very fine, dry dirt that kicks up dust very easily). I'd have to change the return air filter(s) pretty frequently as covering the floor doesn't look do-able... stuff sticking out of the ground (like a gas line). That might make it more hassle than it's worth right there.

At 80-90 degrees, I don't see the drying out of the wood as a problem, and I'm sure romex can handle 80 or even 90 dry degrees. It's been surviving 100 degree summers (with high humidity) for over a decade.
And with all the A/C cooling leakage, I would have expected to see mold but it was dry as a bone.

This house is a piss poor design for forced air heat. 1 1/2 floors with cathedral ceilings. All the hot air collects in the 2nd floor bedroom). As far as I'm concerned, forced air heat in the living space is not an option. It doesn't work and is too liable to spread filth and pathogens from the crawl space. I may convert over to hydroponic radiant if it can cool too.
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Old 10-27-2008, 06:55 AM   #6
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Forced air from teh crawlspace, only draws in dirt, or pathogens from the crawlspace, if the duct work is poorly installed, or damaged.

60% of your natural air infiltration is from your crawlspace, with out the forced air system.
Are you going to seal it from your first floor.

A 100 attic in the summer, has more moisture in it, then what your basement would have at 100 in the winter.

You need a lot warmer basement then 90, to heat your house.

You need a way to get the humdity down in the occupied area, to use radiant cooling. Other wise, you'll get sweating walls, and mold.

Romex/NM, is not allowed in a plenum for fire concerns. It puts off toxic fumes when burned.
Gas, lines are not allowed in the air stream either.

Forced air heat, with cathederal ceilings, does take special considerations. But is working well in 1000's of homes.

Hydronic radiant, will require you to insulate your floor joist from teh crawlspace, or you will be paying a lot to heat your crawlspace.
That is a mistake that has been made by many already.

Is you crawlspace high enough for a boiler, or will you install it on the first floor somewhere.
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Old 10-27-2008, 10:46 AM   #7
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using forced air for radiant heating


I would seal all the vents on the first floor from above, and probably remove all the ductwork on the 2nd floor and seal from below. After spending an hour down there yesterday, the filthy air is a real showstopper. That'll clog any filter i put on the return duct in no time. I'd have to cover the floor for that reason alone. But all the ductwork and other obstacles will make that more than a one man job. Moisture doesn't appear to be a problem down there at all. We've had heavy rains for the last 6 months and it was dry as a bone. The soil is very fine and sandy consistency and kicks up dust very easily.

>>You need a lot warmer basement then 90, to heat your house.
1/2 of the floor space has no insulation and the insulation is falling down in other parts. The floorboards are pretty thin and I bet we'd get a decent result at 80 degrees. At that temp, drying of the wood and heating of gas lines and/or romex is not a problem.

Humidity is bad in summer and it doesn't seem to have caused any problems with mold down there so far and there was plenty of cooling leakage going on. I would say the problem is not as bad as commonly thought.

>>Forced air heat, with cathederal ceilings, does take special >>onsiderations.
I'd have to route another duct between 1st and 2nd floor w/ tempeature differential sensor to have it pull the air back down to 1st floor when needed. Radiant has none of those problems to begin with.

>>But is working well in 1000's of homes.
Sounds like you have a vested interest in keeping forced air alive and well.
I'm going to add cheesecloth filters to all the floor vents since I'll be stuck with forced air this week during the the cold snap. I was able to re-attach one of the ducts that had fallen yesterday, but I'm sure it's filthy disgusting inside and that stuff'll be coming right in the living space if I don't filter it.

>>Hydronic radiant, will require you to insulate your floor joist from teh >>crawlspace, or you will be paying a lot to heat your crawlspace.
>>That is a mistake that has been made by many already.
Heat rises, so that doesn't seem like a huge problem but if one was going to go to all that trouble to put in the water lines, I'd think they could easily insulate while they were at it.

>>Is you crawlspace high enough for a boiler, or will you install it on the >>first floor somewhere.[/quote]
I'd put it on the 1st floor in the sun room I'm building so it could absorb solar rays while sitting there. In fall and spring, it could be a solar powered hot water heater for showers.
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Old 10-27-2008, 03:38 PM   #8
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using forced air for radiant heating


I'm not concerned weather people use forced air, hot water baseboard, or radiant heat.
I sell and install all of them.

The humidity currently in your crawlspace, may now be ok.
Cool that crawlspace in the summer when its 90 outside, and it changes quickly.

Its sounds more like you have your mind made up. And won't change it until you run into the problems I have been trying to help you avoid.

You don't understand radiant cooling.

You don't understand radiant heat either.

Using hydronic radiant. You need to insulate the joist bays, or you have to increase the size of the boiler, and the amount of pex tubing you install to heat with.

In an unconditioned crawlspace, it takes more insulation then you may think.

Fire code, no matter weather you think drying of the Romex is a problem or not. Does NOT allow Romex to be in a ceiling plenum.
Not does it a llow a gas line to be in it.

If, a fire does occur.
Your insurance company does not have to pay for damages.
Fires happen to those that thing it will never happen to them.

good luck
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Old 10-27-2008, 06:19 PM   #9
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using forced air for radiant heating


and you understand typical industry practices, but don't understand physics very well (if at all). The heat under the floor has to go somewhere (energy cannot be destroyed) and heat rises, so it will eventually heat the floor to 80 degrees unless it escapes some other way. If the foundation is well insulated, the heat will go through the thin wood floors long before it leaches out of the brick foundation walls. You can't snow me with your industry B.S., I have a physics degree and several decades of industry experience myself. I know what I'm doing. To be honest, I was hoping to hear from other DIY'ers, not a bunch of HVAC industry blowhards who think they know something and get on here to inflate their already huge ego's by snowing a bunch of green behind the ears newbies.

I came up with a solution to the re-circulating filthy crawl space air clogging up the heater problem: pull in outside air in the return duct instead of using crawl space air. I'd add a "mud flap" style door to a few of the foundation vents so the air pressure can escape, and put remote temp. sensors at those vicinities to shut off when the specified temp. is reached. An "industry pro" told me that heat pumps lose efficiency when the return air is at or above 80 degrees, so this will solve that problem. The only drawback I see here is that it wouldn't work for cooling in summer... but I put it out there for anyone else who's researching this topic and wants some idea.
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Old 10-27-2008, 11:56 PM   #10
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LOL...

If you have a degree in physics, then you know that heat DOESN'T rise.
Hot air being lighter rises above cold heavy air. Hot water being lighter rises above cold heavy water, heat does not rise.

Or I couldn't heat a garage with a radiant heater mounted to the ceiling.
Nor would radiant ceiling heat work in the 1000's of homes its installed in.
Higher energy flows toward lower energy.

As far as B S.
You are laying it on.
Now your going to draw in cold outdoor air to increase heat pump efficiency. LOL...

All this because a crappy duct system was installed in your home.

good luck
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Old 10-28-2008, 06:07 AM   #11
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using forced air for radiant heating


Sometimes its best to just walk away. If violating every Mechanical, Fire and Building Code is your way of justifying your " repair " to your own home...good for you...but from a safety standpoint, please reconsider.

If your system were an accepted and approved method of heating a home, we would be utilizing it, and the lack of acceptance is due to the fact that it is not...and its not, because it violates laws and codes that are designed to protect you, your property and reduce energy waste.

Have a great day.

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Old 10-28-2008, 11:08 AM   #12
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using forced air for radiant heating


If you think county codes have kept up with the latest research in building science, you have a lot of faith in your local government my man! All I've seen or heard about around here is inspectors requiring unofficial payments to do timely inspections. And they still require crawl spaces to be vented, something that is costing us millions a year in wasted heat.

I'm not talking about blasting 120 degrees of heat through my crawlspace. I'm talking about heating it to about 80 degrees. That's not significantly different than heating the living space to 80 degrees. This fear mongering is ridiculous. You people have to learn to think outside of that box that your years of experience in the HVAC industry has placed you in. The romans used to do exactly what I'm suggesting! It was the first form of radiant heat that we know of. Go ahead and google it, maybe you'll learn something!

And as far as heat transfer: In an air or liquid medium, the hot portion of it will rise since it is lighter. Simple principle, no need to split hairs. If people have installed radiant heat in the ceiling, then their attic or upstairs should get nice and warm.
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Old 10-28-2008, 01:52 PM   #13
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using forced air for radiant heating


The Romans didn't have wood floors.

Radiant ceiling heat has been installed since the early 60's that I know of.
Its not a new concept.

Heating the crawlspace to 80 to heat the house is different then setting the stat 80.

A house heated to 80 will draw teh moisture from the basement, crawlspace, or slab.

With the crawlspace at 80, and the house at 70, there is no place for the wood to draw moisture from.

Fire codes apply weather you think they should or not.
So do the electrical, and gas codes.


Splitting hairs.
I would expect someone with a degree in physics to use the correct expression if he is going to tout that he has his degree.
Heat does not rise.

Do a load calc on your house.
See how much heat your house is losing compared to how much heat you get from having the crawlspace at 80F and the living areas at 70F.

Many houses can't get enough radiant heat to heat at design temps. And have to use a second stage/aux heat.

Don't need to think outside the box.

You should see the heating bill when people try to heat their house by letting the steam pipes heat the basement to heat their house.

They were thinking outside the box, and cost themselves lots of money.
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Old 10-28-2008, 04:26 PM   #14
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using forced air for radiant heating


Quote:
Originally Posted by djsmith9 View Post
Our house has been plagued by rats, cockroaches, water bugs and a horrible musty smell for several years that I knew was being caused by the crawlspace ductwork being eaten up by rats (Cockroaches were crawling up from the floor vents). If I seal up the vents in the foundation wall and the floor vents, I can eliminate the bugs and smell and heat the house with a makeshift radiant heating system (visa vis my forced air heat pump via the leaky ductwork. I would have to go down and detach some of the floor vent ducts since a few of them still deliver heat).

I don't understand why this system isn't being used in radiant heating homes as it seems perfectly viable to me. Does anyone have experience with this? HVAC people like to tout that old BS about foundation venting required to alleviate moisture buildup, but modern research has indicated that it is not nearly necessary as previously thought. It does help sell those expensive hydroponic systems though. I say we end this hydroponic hegemony now and retrofit our older homes with forced air radiant heat systems... and they're already 3/4 installed :-).

Dave
Dave, I'm having trouble understanding your motives. You ask questions, get good advice and argue with knowledgeable folks trying to help you.

It's been explained why the radiant solution you offer isn't a good idea. What you believe to be a viable system is clearly not one, yet you've dug in your heels and insist otherwise.

My area of expertise is not in heating/cooling. I tend to listen to those that have first-hand experience so that I can better understand.

Maybe you'll never believe it until you try it. It is important to remember the laws, (code) state, federal, city and county still apply. The liability for your actions today can be costly tomorrow. If any mold or mildew spores or radon are present in the crawlspace or even sewer gas, it will not be reduced by adding warm air into the entire area. And, will eventually end up in the living area.

Justy my 2
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Old 10-28-2008, 08:42 PM   #15
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the Romans had stone floors, making it even more impossible to work in your book, but apparently they made it work.

"Beenthere", I think your're confusing energy with heat. Heat is defined as the average kinetic enery per molecule in a material, and in a liquid or air, the parts with the higher average KE will rise because on average, those molecules will be farther apart, I.E. the material will be lighter. I'm sure you'll want to continue splitting hairs, but trying to make me look like a fool will continue to backfire on you.

Actually, this dicussion is rapidly becoming pointless. I already determined that the air down there is too filthy to be filtered through a heat pump, it will quickly clog. I thought of putting a screen on the (outside) return duct fan compartment. This would pull in fresh outside air in, and I could add "mud flaps" to selected foundation vents to let out the air. Obviously I'd have to put a remote sensor there to shut off when desired temp. is acheived. It may sound less efficient, but the crawl space is much smaller and would heat up fast. It would not work for cooling however, which we need in summer as much as the heat is needed in winter, so I had to scrap that idea too.
But I have already seen that blocking up the foundation vents was a good idea: our space heaters now work whereas before, no amount of space heating could get this place warm (yet our county code still requires ventilated crawlspace so we could be fined for having done it. Yea, we can depend on our local government to be looking out for our best interests. Right).

I know " beenThere" is going to trash this idea, he makes his money from selling vastly more expensive hydronic, electric, and forced/air systems. This is his hidden agenda, to discredit anything that competes with his bread and butter cash cows. This is why all the HVAC contractors jump on something like this and try to discredit it right off the bat. In another group I was attacked by them like a horde of mosquito's on fresh meat. It's got nothing to do with giving me "good advice", they're so-called advice sounds like a typical sales pitch you'd get from an HVAC sales rep. That's probably what they are because they are able to respond to my posts at all times of the day, just like a sales rep. sitting at a computer, not a tech. who'd be out in the field all day. I hope that answers the question posed by "Shamus" satisfactorily.

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