I built a new garge this fall, it is 30 x 40' I installed all the pex tube according to an auto cad drawing from pex supply.com. I had it all hooked up buy a professional. I am using a 40 gal electric hot water tank. The highest temp I have acheived has been 70 degrees. Will this system ever come up to temp where hot water tank will cycle the way it should???

Did you do a heat loss calculation on the garage and match it to the heat output of the water heater?

As ICFHybrid mentioned a heat load calc is necessary to determine btus required. Once that information is gathered the heating source can be selected.The length of pex and flowrate will also need to be calculated. Is there any insulation under slab or at least along the perimeter edges.

I never did those calculations, I was assured buy two different installers that a 40 gal electric hot water tank would do the job. I will be buying and hooking up wood fired out door boiler for next year. I only wanted to have heat in the garage for the winter. But i was assured it would work far better than it does. Also the istaller did not put the mixing valve in the system, said it was not required right now. Would need it once wood boiler was installed. He did not install a thermostat either, has had jumper wire on it for three weeks. Should I install the thermostat???
Thanks

a 40 gal electric hot water tank would do the job

What is the rating on the tank?
And what kind of construction is the garage? Insulation? Whst size and kind of doors? Did you see acwizard's question about insulation under the slab?

A water heater is not a boiler.
no horse power, BTU capacity
Fine for a shower
Think 25-30 btu per square foot for rough btu load with out heat loss, this assumes 2 inch under slab and reasonable wall (R21) and lid insulation (R38).
Heat loss my prove more, or less. but its a good start to see if you are even close.
Dan

There is 1 inch sm board under concrete slab, with 2 inch sm board under the club footing . The walls are 2 x 6 with an r 19 insulation. The ceiling has an r 38 .
The max rating on the tank is 4500 watts. The is one 36 inch man door ,insulated steeel. and one 12 x 14' insulated garage door which cost me a small fortune.
I have been shutting off the circulating pump, letting the tank come up to temp, the turn it on for about 5 min. I have done this about 4 times last evening and more temp has come up about 2 degrees on the return side. But in saying that it has warmed up out side also. What about not having the mixing valve or thermostat installed?

Where are you located and what is the outdoor temperature?

The heat loss in your garage is a function of the temperature inside versus outside and the insulation in between. If you use Blueridge's rule of thumb, you have 25 BTU/sf X 1200 sf = 30,000 BTU per hour heat loss.

The output of the water heater, if you have a single 4500 watt element is about 4500 X 3.4 = 15,000 BTU per hour.

If that is the case, no matter how much you play with the controls, you will never get "up to temp".

As a temporary measure have your electrician pull another circut to the HWT and wire it so the second element will fire up at the same time as the other one. That will double your heat output from the tank. You can buy them this way but they are special order.

I am located in Sault ste marie ontario, only about -6 today. But calling for -36 with the wind chill on Sunday night

Shopsmith: Can i unhook the wires that feed bottom element, and run wires from top element? It would have 220 feed at same time??

The hot water tank has two 3000 watt elements, but only top one comes on. Well that is my understanding of how the tanks work

Those outside temps are in degrees C. When you say the water heater only got to "70 degrees", is that degrees F or degrees C?

I know you will have a lot of heat when you get your wood-fired boiler going, but you really need to have some heat calculations done so you can see where the energy will be going.

How warm are you hoping to keep that garage inside?

The temps out side are in F. The temps on my manifold are 80 F going in from tank, and the return is 70 F.

I would like to be able to hold about 75 F, as i work on dump trucks and equip. Would like the floor to dry up reasonbly quick, when I open the big door there is a lot of heat loss. Right now it will not recover, using propane back up to regain heat.

I am located in Sault ste marie ontario, only about -6 today. But calling for -36 with the wind chill on Sunday night

That's a little confusing, because local stations are saying the temp there is just below freezing which is closer to -6C and the forecast for Sunday night is for wind chill as low as -30C which is about -20F

when I open the big door there is a lot of heat loss

You also have a lot of heat loss just due to regular infiltration in a structure like that. Unless you took special measures to seal the building shell and have some kind of special sealing on the door, it is probably at least as leaky as a residence and as much as half the heat can go out that way. You have about 9000 heating degree days (F) in Sault Ste Marie as it is. I hope you want to keep the slab at 75F and not the room temp. If you have a design heat loss of 40,000 - 50,000 BTU/hr on that building, you might be looking at burning 10 - 15 cords or even more depending on efficiency of your wood boiler.

Howie,

The wiring on the tank/thermostate is not designed to fire both elements at the same time. You must run a second circut and install another thermostate on the the bottom element. As I said before this a a temporty measure as the tank wiring was not designed this way. You can order one from the factory this way if you deside to make this a permenate heater.

Thanks guys all info greatly appreciated, not sure what I am going to do.

We are going to put up a manufactured home this summer. It will be ranch style as my son is disabled, so 1 floor convience is a must. We are thinking about slab on grade, but witha 4 or 5 foot crawl space. I plan on using radiant in the slab and an water air heat exchanger in the furnace. The boiler I am looking at is capable of heating 8000 sq ft. The garage is 1200 and the house will be 1600, does this sound resonable?

A boiler capable of heating 8000 sq ft heating 1600 sq ft sounds over sized. Consider a frost protected shallow , slab on grade foundation (no footings).

Well the boiler would be heating garage at 1200 sq ft, house at 1600 sq ft. I want to build house slab on grade, but our city planners can not decide if i am allowed to.