Radiant - Hydroninc/Electric

[BillinOregon]

Hi,

We are building a new home/ranch in central Oregon - Redmond, Oregon. We get some cold temps at night -teens or 20's. Day could be in the high 30's or 40's if sunny. When we get storms day time temps could be between 25 and 40. It's the high desert - lot's of sun, only 9 inches of rain. Elevation is about 2500.

We are going to build a free standing garage. It has a total dimension of 32x34 feet. The garage doors will be 12w 10t. The floor will be poured concrete. We plan on insulating the heck out of it. It will be segmented as follows:

8x34 will be a laundry room, dog, well controls, domestic solar water heater controls and mud room. The remaining 24x34 space will be a standard garage. We would like to have the temp in the standard garage space above 38 - 40 F. We don't want items to freeze. In the laundry room we would like to have it in the 45 - 50F range. I would not be out there working very often - you never know.

We hare kicking around the idea of using electric radiant floor heat for the garage structure. If an added boost is required we will install propane wall units as they are fairly inexpensive. We will have a buried tank onsite. There are other structures on the site. The horse barn tack room will have electric radiant floor heat also. I am a little concerned by being so dependant on electricity. Perhaps that can be addressed down the road with PV.

I am trying to compare electric radiant to hydroninc from a "total cost" perspective and ease if use. I keep swinging between electric and hydronic radiant. I don't like the idea of combustion in the garage that's why we are "stuck" on radiant - set it and forget it. This site rocks - it has given me great info on hydronic. Any opinions on elec hydronic or direction? Sorry for the long post. Thank you very much in advance.

Bill

 

[Chris J]

I think we need to clarify some terms. If you are heating the slab (or any mass), the heat is radiant, regardless of whether it is from electric heater wire buried in the slab, or tubes with a fluid being pumped through them. And hydronic systems with an electric boiler fall under the class of "electric radiant". (Sorry, I don't mean to sound ****.)

I think the eventual use of the area will dictate the appropriate solution. If the goal is simply to keep the garage temp above freezing, I think I would insulate the heck out of everthing and use a simple gas heater to maintain the temp. The cost of either a hydronic system or electric heater system buried in the slab would be overly expensive considering the desired results.

If you think you may want to spend time in the garage and be confortable doing it, then the extra cost of the more elaborate systems is probably warranted. Personally, it is my opinion that the heating-wire based systema are only appropriate for "low-mass" systems (i.e. thin-set on a bathroom floor). A "high-mass" system (concrete slab in a garage) will require the electric heaters to be on continuously for relatively long periods of time (hours), and this is not condusive to a long-life. High-mass systems are the correct application for a hydronic system since the temps that the concrete is exposed to is MUCH lower, and components that are likely to need service are accessible and not buried in concrete.

It is also my opinion that an electric boiler should be considered in a hydronic system. In the past I have always felt that electricty was the most expensive way to generate heat, but all forms of fossil fuels have gotten so darn expensive (and I don't think they are going to get any cheaper), that electricity now is slightly less expensive. If the application is at an elevation above sea level, then you have to de-rate the efficiency any fuel burner by 3% per 1000' of elevation, so that makes the use of electricity even more attractive.

The other thing that may be a consideration is that more and more electric companies are incorporating on-peak and off-peak power costing, most frequently used with an "ETS" heater. I managed to convince my local power company that my garage slab was functionally exactly the same as their ETS heater, and could be controlled by their contact closer in their meter just as the ETS heater is. This contact closer (a relay) is controlled by THEIR time clock, and prevents the system from being able to come on during on-peak hours. The cost of off-peak power here is 40% of the standard power cost, making the use of electricity for heating the slab, by far, a more cost-effective way to generate heat.

 

[BillinOregon]

Thanks for the reply Chris. I should have used the terms "wire" and "hydroninc" to describe the type of radiant. Makes sense. The propane option worries me - unattended combustion in a garage. There is never anyone home. I will have a work bench in the structure but will spend very little time in there. The key is to keep everything from freezing. We are moving from temperate Western Oregon to Central Oregon. This freezing thing is new to us. I am really leaning in the direction of hydronic radiant heated by an electric boiler.

 

[Chris J]

It sounds as though avoiding freezing in the garage is the primary concern, and personal comfort is not a serious consideration.

While I am one to always over-build a project (which is NOT always a positive quality), as in putting the hydronic tubing, it sounds as though you might be better off with hydronic base-board radiators, or even electric base-board radiators. These are "low-mass" heaters that can respond very quickly to demands for heat, unlike a high-mass slab. A slab will take hours (or even days) to fully respond to a call for heat, and things could freeze up in the mean time. Unless you are willing to always "idle" the slab at a given temp in anticipation of a cold spell, it probably won't give you the protection you are looking for. Doing this is fine, except that you will be paying for heat that you don't need if the temp outside doesn't drop low enough to create a threat.

Using a low-mass system can start to respond to a call for heat almost immediately, and therefore only has to come on when the conditions you define are actually present, and can turn off immediately when those conditions are no longer met.

Note that low-mass systems cannot operate only during off-peak times. High-mass systems can because you can pump a lot of extra heat into the slab during the off-peak periods, and release that heat slowly during the on-peak interval without having to actually create the heat during the on-peak period.