Radiant heat vs conventional

[BoostAddiction]

I've seen some garages here lately, and know of another really big one that will have radiant heat (for the newbies: heat is created by running hot water through tubing buried in the floor; the floor heats up and the heat rises to heat the rest of the room).

While I think radiant has some advantages (you can work in your bare feet, the floor feels warm if you have to sit or kneel on it), for a garage, it seems to me to be a relatively poor fit.

Why? Well, in my garage, most of the time it isn't heated or cooled (and so uses no power). I only need to heat or cool it when I actually work in it. If that is three nights a week and all day one day on the weekend, then I only heat or cool it then. The time it takes to get the temp right (heating or cooling) is pretty small in my case-- maybe only 20 minutes. This is in contrast to radiant heat which takes a very long time to heat the mass in a garage floor. The clear implication is that you have to run the radiant heating system all winter long, even if you only need it for a few hours each night. How can that be more efficient?

If you work in the garage 8 hours a day, maybe it makes sense. Or, if you want to have the garage heated even when you aren't there to keep your megadollar cars all cozy and stuff, then maybe I could see it. Otherwise, it just seems wasteful to me.

Of course, it doesn't do a thing for cooling, and as such, if you have a cooling load, you can't exactly piggyback on existing ducting, for example as you might with a regular heat pump.

Perhaps I'm missing something (it wouldn't be the first time...) but if there is a way that radiant can compete with a gas heater, or an efficient heat pump, I'd like to know about it.

Otherwise, I'm sticking with the original idea: radiant only makes sense in very cold climates where you want to keep the structure heated all the time (as in a home).

For reference, I live in the MidAtlantic and use a 2-ton minisplit with a 15 SEER. Works great all the time, whatever the season, cost very little ($<4000 installed) and is very economical to run (and it doesn't get run all that often anyway).

The obligatory pic:

-Will

 

[larry4406]

I too looked at radiant floor heat for my 28x50 garage in northern va, but have punted. I will go with a traditional forced air system with a/c.

Reasons are:
1. To be effective, you need to insulate under the slab. The best foam insulation has a compressive strength of 100 psi. Concrete slabs on grade require a minimum soil bearing pressure of 2000 psi - therefore the insulation forces you to install a structural concrete slab for big $$ (in my case several thousands). Note in all the brochures for radiant tubing they tell you to zip tie the tubes to the slab rebar. Slabs do not use rebar unless they are structural slabs (slabs on grade use welded wire mesh). How convenient this information is not disclosed.
2. The insulation costs for my garage would have been about $1500
3. The in-floor tubing would have been about $1500.

Now, assuming the structural slab upgrade was $3k, then the in-slab system would have been about $6000 and I still would not have a heat source which would run at least an additional $1500 to $2000, so total cost would then be a minimum of $8000 or so after the heat source, pumps, controllers, etc.

After these costs, I would then have a heat only system, no a/c, and a system that is slow to respond and requiring that I run it all winter long so it would be ready for the days I need heat.

A single zone gas fired unit with a/c and ductwork can be installed for under $4000 (at least with my building connections - I work for a builder and I'm a registered engineer).

In conlusion, I agree with you that in-floor radiant systems are not the system of choice for the mid-atlantic region, and it will not be in my garage.

 

[cw_racefan]

Hey Boost - How big is your garage? I'm in MD near DC, so same climate and am debating on what to do in my 32x36 garage. Either 2-ton mini-split like you, or propane forced air or propane overhead radiant. The later 2 options, obviously with no A/C. Can't decide whether the a/c is worth the extra expense or not. One nice thing with the mini-splits I have looked at is they have a de-humidify only mode.

What made you decide on the mini-split? What else did you consider?

Thanks!
Craig

 

[bmwpower]

Working on your car and sweating *****. I installed forced heat/air for around $4K. I chose to go with forced air since it was cheaper and I worried about messing up the tubing when putting in my lift. The last thing you want is a leak...that's gotta ****.

One less thing in the floor gives me that much more piece of mind.

 

[BoostAddiction]

Hey Boost - How big is your garage? I'm in MD near DC, so same climate and am debating on what to do in my 32x36 garage. Either 2-ton mini-split like you, or propane forced air or propane overhead radiant. The later 2 options, obviously with no A/C. Can't decide whether the a/c is worth the extra expense or not. One nice thing with the mini-splits I have looked at is they have a de-humidify only mode.

What made you decide on the mini-split? What else did you consider?

Thanks!
Craig

Mine is a 3.5 garage, with two sides bordered by the rest of the house. The garage is well-insulated and has a 2X6 wall on the north side.

I picked the minisplit because it seemed to be the least expensive to acquire and operate. I had estimates for a conventional heat pump but the total cost was over $11,000 and there was a fair amount of disruption with ducting, etc.

I'd seen these units before in the Caribbean and in clinical labs. They did a good job there. Mine is the most efficient one I've ever seen- most of the usual Samsung or Sanyo units are only a 10 SEER.

AC was almost as important as heat for me- I'm waayy too old to get overheated working on cars anymore. I really like coming into a cool garage and starting a project.

So far mine has been flawless. You can get them (the Daiken units) at www.smarterwayinc.com .

-Will

 

[PatrickW]

What if you live in a part of the country where you never need air-conditioning?

Perhaps the option of overhead radiant heat then becomes a less expensive option for you?

- Patrick

 

[dboat]

I guess I am really cheap then.. I put up a 30k ventless natural gas heater in my garage. Keep it around 50 degrees in the winter. It cost me $180 to buy it. Then a bud of mine and I ran the gray pipe to in a couple of hours time.. nice in the winter turn off the gas to it in the spring. I live in Erie,PA and dont need the a/c in the summer.

Dana

 

[DaveL.]

Good thread. Excellant info.. I'm another cheapskate. 75,000 btu cieling mounted natural gas heater ($1500) installed and a 17,000 btu 'wall rattler' AC unit (free). I'm completely satisfied...

 

[Lu47Dan]

Insulation under slab

on this point I have some news , I would not put the insulation under the slab , for a radiant floor . all the people that I know ,now put the insulation around the perimeter of the slab , Two inches minimun , then the insulation won't crush . you can install the insulation down to frost level and it works just as well as laying it flat under the concrete . use two to four inches of clean 2B stone and a vapor barrier . the stone provides a break to isolate the vapor barrier from your fill materail . the vapor barrier stops any moisture from rising up throught the concrete . we built two identical home hobbie shops a couple of years ago one was perimeter insulated and the other was full floor insulated for two brothers . Used a fuel oil boiler in both , the difference in fuel consumption was minimal . the full floor insulated building used more fuel than the perimeter insulated . The brother that had us do the full floor insulation did want the perimeter insulation in his because he was worried about mice digging in it . he is going too place insulation around the exterior of his building this summer at a much higher cost . Remember heat raises .

 

[Louver Dude]

I have in floor heat in my garage I heat it and my house with outdoor wood boiler ..... I love it ....the point made about insulation in the floor is true the only thing it does is speeds up initial start up, heat comes up quicker but regardless of how thick the insulation is it will still heat about 3' in to the ground that's way its more important to insulate the foundation walls then the floor..... another advantage is if I do open my garage door in the middle of winter to bring something in, as soon as I shut the door the heat comes back very quickly. and I don't have as big of heat fluctuations as Burnt air. Just my .02

 

[Scott Pearson]

Here are some pic of the Radiant heat in my building.

 

[JohnZ]

My 58' x 44' x 12' garage is super-insulated (R-26 walls, R-58 ceiling, insulated under the slab and insulated doors), and when we built it six years ago I only considered heating it; have a ceiling-hung Reznor power-vented forced-air gas unit heater with electronic ignition (no pilot flame). It's 125,000 BTU, which turned out to be much larger than I needed due to the insulating job we did; 75,000 probably would have been just right.

After four summers of sweating in the garage (my "retirement office" is out here - I'm there all day long), I bit the bullet last summer and had a Mitsubishi 42,000-BTU ductless minisplit A/C unit installed, and it's terrific - maintains mid-70's and low humidity with no problem, and it's so quiet it's scary. Info at link below:

http://www.villagephotos.com/pubbrowse.asp?folder_id=1411059

 

[muddy]

My understanding with radiant floors is that you need more to worry about moisture transfer than heat/cold transfer. There are products out there that are designed for under slab insulating......check out northwest ohio foam products for some good insulating products........

 

[HoosierBuddy]

I've given this very issue a lot of thought and have now spent a lot of money on it, as I am finishing up the HVAC on my new garage this week.

I ended up going with a standard 12 seer outside unit with an air handler for A/C in my attached garage addition. The heat is 3 zoned radiant (1 garage, 2 bonus family room, 3 breezeway). Heating the water will be accomplished with a Trinity high eff. wall boiler in the garage.

As far as the slab, we compacted 11B's, but vapor barrier over that, put 2" of HD styrofoam (about $1000 for a 28 X 38 garage) and put reinforcing grid that is designed specifically for radiant heat over that. 1/2" Pex was looped over that, with zones for my lift legs kept clear of PEX. In those areas, I went in before the pour and removed about 12 SF of insulation under where the posts would be set....this meant the concrete was 2" thicker in those areas (6" total). We poured roughly 4 1/2" of concrete over that with fiber reinforcing ($7 extra per yard...figured it was probably worth it).

As far as putting insulation just under the perimiter...I would never do that unless you are looking at free fuel. With wood or solar, you can theoretically force heat into the ground under your slab and recover that heat later. This would not be an efficient activity. You're going to lose a lot of that heat to the surrounding soil. This is not an issue with "free fuel", but since I'm using a boiler, I want all my heat to go into the slab and none of it into the ground. That's the ideal...obviously there are going to be losses in the system. I also put 2" of styrofoam around the slab perimeter to insulate it from the footer. This was beveled on the edge with the beveled edge slightly under the finish level of the concrete.

This is definitely a premium system. I'd roughly estimate that it cost 60 to 80% more for this system than a standard split system. It might be as much as twice as much as a heat pump. So, the question becomes, is it worth it? Everyone must evaluate how they are going to use their shop and come to their own conclusions.

I think I'm going to end up with a more comfortable system in terms of how it feels and how it sounds. The extra cost of installation is nominal when compared to the total cost of the project. The attached garage can be heated to a lower temperature than the rest of the building with the zoning that is part of the system. The breezeway and upstairs bonus/family room has to be heated all the time anyway. It's designed to be additional square footage for the house.

I'll know more after next winter I suppose. I really think I would say radiant heat has it's place and that ISN'T in EVERY garage. If your talking about an attached garage with living space in it, OR a standalone garage that is not going to have A/C...then it may be just the ticket.

Phil

 

[xtremes]

I have radiant heat in my 27x30 garage and I love it. It's always 65 degrees in there. I went with radiant because I keep high dollar show cars in my garage. One reason being dust. Forsed hot air systems keep the dust moving. I my old garage I was dusting my cars every day. With the radiant I don't have that problem. Also keeps all the polished alumiun and such from corroding. I'm in my garage most everyday. So it was worth it to me.