Installing Radiant in my garage, I have a bunch of ? head is spinning

[jimgerken]

jimgerken,

Do you have any pics of your system by any chance?

I don't have any pics of my existing shop. However I am currently constructing a new shop on the farm we bought, and have done a pretty good job of showing that construction here in this thread:
35X60 shop design in Minnesota
No system details so far, but they will evolve in the next few months. Once complete this system will be LP fired, tankless modulating from 11000 to 200000 btu. Also supplimented by heat from an outdoor wood boiler.
Enjoy.

 

[yelbike]

He said the large thermal mass concrete/sand makes it more efficiant.


Dave

Thermal mass doesn't reflect efficiency at all. It only helps in recovery time.

Here are two exaggerated examples. Garage one has infloor heat. Its turned on initially from cold to room temperature. The boiler works full out to heat the concrete pad ( thermal mass) and surrounding materials, it takes 24 hours running to settle the temperature.

Garage two has forced air with associated ducting. Initial start up is done from cold to room temperature. It take two hours total running time. Which one is more efficient? Force air in this scenario. Wait add another scenario.

Middle of winter, both garage 1 and 2 open the over head door for one minute then close. Which one recovers to room temperature first? In floor heat because thermal mass. Does that mean its more efficient? No. When the door was open both systems lost the same amount of btuhs. They both need to replace the lost btuh.

Does that mean infloor heat is not really all that good? No, it has its place. Its known for poor air circulation(relies on convection only) which is not an issue in a garage or shop. Also you can't add air conditioning or air filtration.

Also using a hwt to heat the water as a boiler will work, it just will not last.

 

[jimgerken]

(trimmed)Also using a hwt to heat the water as a boiler will work, it just will not last.

A standing tank hot water heater does indeed "last" very well in my experience, compared to normal residential domestic hot water use. First, the system is closed loop, with virtually no new water ever added, so virtually no mineral buildup occurs. Second, the oxygen content is also low and never refreshed so less corrosion occures. Third, it is running at lower set point than most residences set their domestic water to, if set up properly for RFH. Fourth, the pressure is 12 psi or so, never spikes to 60 or 80, there is a pressure tank to keep it there and so very little stress on the tank.
My experience shows the tank type wter heater works well, and does last well. I had a controller fail, Robertshaw model of course, replaced it with Honeywell brand controller. Thats it for water heater maintenance since 1996 when I put the system together.
Once I questioned about the heat escaping from the standing water tank affecting my overall efficiency. My expert assured me that, since the heat was escaping into the space I wanted heated anyway, I was losing virtually nothing. Made sense.
On the other hand, my new shop will use a tankless, because the new shop is 2100 square feet so the 40,000 btu powervent water heater does not have the btu capacity to heat the space. Even at a conservative 25 btu per square foot specification for well-insulated workshop space in southern MN, I need 53,000 btu. Another nice feature is floor space improvement with the tankless. All the plumbing including the tankless goes on the wall. Mounted higher, it is also safer (allowing time for people to smell fumes from flammables before the fumes reach the ignition source of the heater), than the tank-type setting a couple feet off the floor on a stand.

 

[Raspy]

Water heaters do last as radiant heaters for the reasons stated by Jim. However, there is a lot more to the story than lasting or efficiency. Radiant is, by far, the most comfortable method of heating. It's also not a disadvantage that radiant doesn't stir the air, as Yelbike stated. It's an advantage. Radiant doesn't pump kitchen smells into the bedrooms or stir up dust that aggravates allergies, etc. It is ideal for people with air born health problems. Also, as in his example of the garage door opened for a minute he fails to mention that a radiant garage floor is WAY more comfortable than a cold floor with forced air heat.

There is a lot more to overall efficiency than recovery time. Boiler efficiency can be as high as 96% and radiant is very easy to zone control. So you only heat the areas you need to, at the lowest delivery temp of any system. Not blowing the air around makes the whole house more efficient.

But even if efficiencies are similar, radiant has the clear comfort advantage and that's worth a lot.

Tankless water heaters are a very poor choice for radiant heating for a number of reasons. They must be specifically approved for that purpose, be able to take in warm water on the cold side and they must be able to operate for long periods in a throttled down setting without getting carboned up. They are also mostly only abut 84% efficient where boilers are up to 96%. Tank water heaters have standby losses out the vent pipe that do not heat the space they are in and they have those losses all during the summer unless the heater is turned off when not used. So tank water heaters are not the best choice, usually.

Boilers are the most efficient and safest, but cost a lot more than a tank water heater and may not last as long.

There are no clear answers where one appliance fits all requirements. It's best to take it on a case by case basis. But you must be honest and not just use generalities and sales pitches to make the decision.

Thermal mass does increase efficiency because it reduces boiler cycling and allows the lowest possible delivery temperature, but no system is perfect and each has it's drawbacks. Be sure to factor in comfort. Otherwise you might end up with an efficient system that is loud, unhealthy and uncomfortable. How "efficient" is that?

By the way, my new house has radiant throughout and it will also have air conditioning.

 

[Raspy]

Hi,
One thing you asked is whether radiant is the right way to go. Its a good way to go, but a couple other solar solutions you might think about --
$350 Thermosyphon Solar Air Space Heater (with 1 year payback)
This is what I use on my shop/barn -- its very effective and very cheap -- basically free if you do it on the initial construction of the building and don't put siding under the collector, use polyiso insulation as the back wall of collector, which can also be your wall insulation.
Solar Workshop or Studio
This is what I use in my attached garage/shop -- the thing I really like about it is the really nice daylighting you get along with the solar heating.

This is a pretty nice setup that uses slab floor radiant:
Green Gate Guest House: Solar Projects

edit: should have mentioned that what makes solar work well in a cold climate is lots of collector area, and the air heating collectors are simple and cheap to build large. DIY solar water heating collectors can also be pretty cheap -- about $6 per sqft.

Gary

Gary, be careful with that Green Gate information. Some of that is not applicable to other areas. It is very low efficiency and can cause tube failures with high stagnation temps. He also intends to use ethylene glycol for preheating DHW. Careful. Also his tube spacing is way to wide. 9" would be much nicer.

 

[Renze]

I asked the neighbour down the road, but they DO have a forced heat pump (cooling ground water from 6°C to 5°C thereby transferring this heat to the shop floor, like an inversed fridge) which keeps the shop floor at 17 or 18°C

 

[Redneck in training]

I asked the neighbour down the road, but they DO have a forced heat pump (cooling ground water from 6ｰC to 5ｰC thereby transferring this heat to the shop floor, like an inversed fridge) which keeps the shop floor at 17 or 18ｰC

That is what we call geothermal heat pump or in jargon geo in the States. The "efficiency" is about 350 to 400%.

 

[Ed Hill]

Here is my experience:
We built a 36 foot by 36 foot barn. The first floor has a 12 foot ceiling and three overhead doors. Concrete walls on three sides, with one window on the south side. The top story is insulated and heated with a Modine Hot Dawg propane hot air unit. So far, though we are located in the Northeast Kingdom of Vermont, the first floor has stayed above freezing all winter. There is frost on the overhead door windows at times, but the interior stays above freezing.
We have radiant heat in our house which is heated with an outside wood furnace. The core of the house is also passive solar, which means windows and skylights and a heat retention mass, so this possibly moderates the heating requirements.

 

[Renze]

That is what we call geothermal heat pump or in jargon geo in the States. The "efficiency" is about 350 to 400%.

What do you pay for such a unit ? Much more than propane heaters ?

 

[Raspy]

Renze,

I installed one about three years ago. Can't give you the exact amount, but it's way more expensive than a simple propane boiler.

The ground heat source system has a large array of tubing buried in a pit. I think we used 1600 linear feet of 1" poly buried about 10' deep. So you start out with a hole that looks like a swimming pool.

Then the heat pump is expensive and it should be connected to a desuperheater storage tank for domestic hot water preheat.

There is considerably more labor and much more expensive equipment.

The one I did is about 3000 sq feet of radiant heat and the house is all electric with no propane. It is at 5000' elevation. They spend about $350. a month in the winter for everything.

I decided not to do it on my own house and instead will be solar thermal with oil backup.

I don't like propane and will go to great lengths to avoid it for heating. But it functions just like natural gas and you can have anything from a simple wall heater to a high efficiency condensing radiant boiler.