Posted By BadgerBoilerMN on 22 Apr 2010 08:14 AM
I'm with geotek;

I have been designing and installing an increasing number of infrared gas heaters, mounted on the ceiling of garages, both commercial and a whole new line of two stage residential models. When the slab has been poured or the usage irregular, infrared is the next best thing.

Convectors are for people who can't afford to be comfortable.

I'm liking it!

Can you point me to more info (even some vendors, mayhaps?)

Contact me directly Dana.

I agree, for on-demand use, use low mass radiant with as many IR reflective surfaces as possible.

Posted By BadgerBoilerMN on 23 Apr 2010 08:13 AM
Contact me directly Dana.

Thanks- found local distributors already - I'm on it.

Hello again. I know this is the radiant heating forum, and we already decided that would not be the best choice for my shop,  but you folks seem like all-around HVAC wiz's, and my info is already here....soooooooo!

What do you think of a mini-split system like these http://www.mehvac.com/en/profession...ingle-zone Mr. Slim products from Mitsubishi? It's a single small room, and the local HVAC company says the heat pump is fine in my area. I wonder though.....the site says "These systems provide heating to -13°F and produce 100% heating capacity at 5°F (MSZ-09); 92% capacity at 5°F for MSZ-12."

What happens below -13? It gets that cold sometimes here--never for weeks on end or anything, but what do you experts think?

This would save me from having to get gas to the building, which could be $$$$. Do they run efficiently vs. a gas furnace?

Any and all opinions welcome and appreciated.

I am in the same predicament with my shop and thanks to conversations about using the earth's temps to help heat the shop on this tread it does make more sense for my own situation. However one concern I have is with the humidity emmited by the uninsulated slab. Won't it accelerate rust on whatever's in the shop? Create condensation in widows and such?

you can use a vapor barrier without insulating if you wish.

Simply putting down a super six or other vapor will eliminate condensation on the floor?
On a side note I am in the concrete buisness and don't know any floor finisher whom doesn't pucture the vapor when pouring. This would mean I'd have to be on site to ensure the seal is not broken.
Don't mean to sidetrack or take over the tread. I think were still on track!
Thanks!

it won't eliminate condensation because of cold slabs condensing moisture from your air, if you are humid and the slab is cold. however it will stop vapor from migrating from below.

Re TAGREEN:  you mention about ripping barrier when pouring, have you used Crete-Heat or the Barrier? FYI   See the video of it on http://barrett-inc.blogspot.com/  Never heard of a tear in either product.

Posted By thagreen on 07 May 2010 09:38 AM
Simply putting down a super six or other vapor will eliminate condensation on the floor?
On a side note I am in the concrete buisness and don't know any floor finisher whom doesn't pucture the vapor when pouring. This would mean I'd have to be on site to ensure the seal is not broken.
Don't mean to sidetrack or take over the tread. I think were still on track!
Thanks!

The predominate mechanism by which ground moisture gets through the slab is via capillary wicking, with vapor diffusion being a somewhat distant second.  A few nicks in the poly won't destroy it's vapor rejection much but will make point-sources for capillary wicking.  Mixing sealer products like Xypex into concrete prior to pour mitigates the capillary draw almost completely, but acrylic or silane based concrete sealers spray-applied after the fact will also make a significant reduction in draw rates (if very little impact on vapor diffusion.)

Condensation can only happen on the floor if the temperature of the slab is below the dew point of the interior air.  The dew point of 75F 60% RH air is ~60F.  The dew point of 68F 30% RH air is in the mid 30s F.   (30-60% RH is the recommend range for human health & comfort). The temperature of middle of an unheated/uncooled slab will always be somewhere between subsoil temps and room temp.  At the edges there is some daily/seasonal weather influence on the temp, but if the slab edges are insulated the effect is small.  To guesstimate what your subsoil temps are, see this, and this.

With capillary breaks & vapor barriers in the slab and air-barriers & vapor retarders in the walls & roof, the humidity of the room will rise & fall as a function of outdoor dew points and ventilation rates (and to some extent the hygric buffering capacity of the building materials.)  In most of the US unheated/uncooled slabs that are insulated at the edges will not usually fall below the dew point of human-healthy interior air in the sweet-spot of human-comfort temps, but there could be issues throwing the bay doors to an air-conditioned shop open for an hour on a muggy hot day with dew points in the 70s.  But an unsealed slab without a vapor barrier may provide sufficient ground moisture to create mold conditions for wood or cardboard placed directly on the floor for weeks/months on end.

Posted By radiantbarrier on 07 May 2010 10:19 AM
Re TAGREEN:  you mention about ripping barrier when pouring, have you used Crete-Heat or the Barrier? FYI   See the video of it on http://barrett-inc.blogspot.com/  Never heard of a tear in either product.

We also provide a similar product called Creatherm. http://www.youtube.com/watch?v=u_9Rp5UpDg8. As said in the earlier post - we have not heard of either products tearing or ripping.

Since you're only looking to heat the shop to +50F, have you considered simply using the free +55F ground temperature as your radiant heat source? Burry some PEX 8-10 feet under the building and then circulate a water/glycol mixture between that and the slab. I’d think you could pick up enough free heat to keep the slab reasonably warm, and then use a gas/electric blower unit for a quick heat up when you’re actually in the shop. In fact, if you extend the PEX into the garage floor too you could heat the garage for free.

You have to excavate for the building anyway. so going a bit deeper to burry the pipe shouldn't cost much extra.

55 degree water would only provide something like 10 BTUs/sq ft in a 50 degree garage. You might offset some energy usage that way, but it would not likely maintain the garage in cold weather.

with heat gain from other sources though, perhaps.

It all depends on the heat load doesn't now doesn't it.

I would save the trenching, burying and pumping (this is a new one) and simply insulate the perimeter. I find the "deep earth temperature" will find its way to the slab without help. Supplemental heat may me installed at the perimeter where the heat load will be.

Perhaps a little professional design help is in order.

passive house garages, amazing.

Being in northern il I would use a Rinnia l50rsi with slab temp set at 55 and a low mass radiator or fin tube for warm up. 10 btus per sq ft will keep a well insulated building above freezing around here..I almost like that idea. Very little electric heat left in Com eds service area as they have removed most incentives.

Tankless water heater make very poor boilers.

I know its no TT Prestige but way better than a 65% tank type and electric is out of the question in N IL ComEd. Rinnias' seem to be work ok when piped correctly.