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Old 10-12-15, 02:37 PM   #1
Join Date: Sep 2008
Location: SE Wisconsin
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Default Heated Garage Floor

Hi everyone,

I'm slowly trying to figure out how to HEAT my garage when I get it constructed.

I REALLY like the idea of a heated floor. A friend of mine has one, and it is SO nice to work on cars in there in the winter!

So, here's what I am thinking...

The proposed garage would be 27' x29', with a "storage area" upstairs. The storage area could be finished to be sort of a possible home-office/escape/hobby area. It would be low ceiling and less than half (maybe even only a third) of the floorspace of the garage itself, and accessed by a fold-down temporary stairs, similar to what many people use to get to their attic.

The construction would be typical - 2x4 walls and fiberglass insulation. There would be a layer of foam insulation on the outside, with siding over that, the roof would be metal standing seam.
The foundation would be a concrete slap with PEX tubing cast into it, and at least 2 inches of EPS foam insulation under it.

I think I would like to use an ELECTRIC MICRO-BOILER.

The garage is its own freestanding building. I have natural gas piping at my house, it WOULD be possible to get natural gas out to the garage, but would be a bit of a hassle (trenching, rerouting pipes, etc.)
Also, I would prefer to get away from fossil fuels as much as I can.

An electric micro-boiler could get its electricity from solar panels (proposed 5KW grid-tie) or from my regular electric connection, which could be set to time-of-day for cost savings. Because a concrete slab heats up and cools down so slowly, I think I could just run the boiler at night (Off-peak hours) to get time-of-day pricing on the electricity to heat it.

I tried making a basic heat loss calculation, and found that I would need somewhere in the neighborhood of 24,000 btus per hour.
I also found a "rule of thumb" saying that for electric heaters, watts times 3.41 = BTUs. So for 24,000 btus, I would need an 8KW electric heater.

In my area, one of the big box home improvement stores is called Menards. They have a store not too far from my house that has a pretty good selection of pumps, pex, boilers, and other components needed for a hydronic in concrete system.

I took a look through some of the equipment they have for sale, some flyers, and general info, and think I know what I need to get, but want your input.

They have a micro boiler called the Stiebel Eltron Hydro-Shark 3 Microboiler - It's available in a 7KW and 10KW version for $500 and $530 respectively. It's basically an instant water heater, only specifically designed for hydronic heat. It's 240V, and would be directly wired to a dedicated 50A circuit.

Basically, you just flow water through it, and it kicks on and heats the water (or anti-freeze) as it goes. Simple, right!?

It also looks like 1/2" Pex is typical for this type of installation, and that's what a lot of the manifolds use. Since the size of the building will be 783 square feet, and pex typically comes in 300' rolls, it seems to make sense to use three loops of 300 feet and do 12" spacing, that would cover up to 900 square feet.

So, I would want a manifold designed for 3 loops.

I've also seen panels that are pre-assembled with the pump, pump controller, fill and purge valves. They are more expensive than I thought, with the one I would be looking at costing $1600! The upside is that it is pre-plumbed and pressure-tested. The only things missing are the manifold and thermostat. That's also two pumps, for a primary/secondary setup, which is apparently what's needed when using a tankless water-heater.

Here's the pre-built panel:

Here's a pre-built panel that comes already hooked up to the 10KW version of the micro-boiler.
(In that one, I believe the image is wrong, it seems to show one of the higher output boilers.)

Here's a link to the 10K heater. The 7K is the same thing, just $30 cheaper:

Other things I would need:
Thermostat - $50
Manifold - there's several styles, but a NICE one, that's all built together and already has flow meters on it is $210.
PEX - 3 rolls of 300' each: $130/roll - $390 total.

Panel w/ boiler: $1840 and those other things, comes to right around $2500.

Does this sound about right to you folks?

What else should I be considering? Is there a particular reason to go with a 7K vs. a 10K heater? Some reason to look at some other fuel source? Other pex or concrete considerations?

Let me know! Thanks!


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