hydronic garage

Scoop

I've built a very well-insulated 400 sq. ft. garage and installed PEX tubing in the floor. I'm in southern Wisconsin. I'd like to heat it with a closed-loop system. Could I use an electric water heater? 50-60 degrees would be plenty warm for me.

Gordy

You say well insulated. Did you insulate under slab, and perimeter of slab? when you installed pex was it O2 barrier pex, and reasonable loop lengths?

It's possible to do what you want, but some questions need answered, and a heatloss done. How's the electric rates up there just north of the illinois border?

Scoop

Thanks for responding. Because of the sidehill location on my lot, I ended up putting a full footing all around the building, insulated the perimeter and under the slab, and did use 02 barrier pex. I used 2 x 6 walls. I am insulating right now. I've got two big windows facing south. No windows on the north wall. It's not a car garage, so I put in a double door that should be better than a roll-up. The rates I don't know yet,

Zman

It sounds like from capacity point of view you could use a water heater. Do a quick heat loss and post the results.
I would also look into all available fuels and compare your operating costs.
Carl

SWEI

How much foam was installed under the slab? Is this building going to be regularly or intermittently occupied?

Scoop

Answering Zman , I'm a little green on this stuff, concerning a heat loss. I think my only alternative is LP, and that went crazy high last winter. That's why I was leaning toward electric. This may be related to Swei's question about how much it's going to be used. Electric may be a bit wasteful to run if I'm not going to be using it more than a couple hours a night. I still work full-time, but will retire in a couple years, I hope. And 2" of insulation, in answer to the first question. And thanks again for responding--this looks like a good forum.

Ironman

Scoop said:

"Electric may be a bit wasteful to run if I'm not going to be using it more than a couple hours a night"

Something that you may not be aware of: a radiant slab is high mass and can take several hours or even a day to bring up to temp. You don't want to use setback as it may take hours just to get the slab warm once it's been allowed to cool.

This is the most comfortable form of heating, but it's also the slowest in response. It's designed to be left at one constant temp. If you only want quick heat for a couple of hours, then look to the least comfortable, fastest response type: forced air.

KC_Jones

I am just a homeowner and this idea may sound totally nuts, but hey I am sometimes good at foot in mouth syndrome. What about putting in some kind of hydro coil for now when he just wants quick heat short term and not even hook up the slab? Later on in retirement when it will get used more switch the boiler over to the slab and leave it on all the time for comfort. Not sure about cost of a hydro coil nor boiler sizing, but it was a thought that popped into my head when I read his post.

hot_rod

A dual fuel system would be nice, right now LP is around $1.85 here in Missouri, if it goes over 4 bucks again, wood and solar for me. You might set an electric and LP tank side by side. With two 30 amp circuits and 5.5 KW elements you get around 37,000 BTU/ hr from a tank WH, about the same as gas or LP tanks.

Be aware of gas fired appliances in a shop, check the codes.

There were some solar tanks around with a coil in the bottom and the burner driving just the upper portion of the tank. If only they had an electric element or two you would have a triple fuel input, gas, electric or solar thermal.

My shop is about the same size, I get a good portion from 5 solar collectors in SW Missouri, check into renewable rebates in WI.

No question radiant is the only way to heat a slab shop if you plan on spending any time out there. cold concrete is really hard on the body

Gordy

Take your electric bill total divide it by your Kw usage see what your bottom line rate is and come back with that info.

SWEI

For an intermittently occupied building, hybrid strategies can sometimes work better than any individual heat source. One example would be using your in-slab tubing with electric resistance heat on an ODR control to maintain a constant temperature of say 50˚F inside, then firing up something like an LPG Hot Dawg when you want to actually use the space.

Does the building orientation/shading offer any passive solar gain? Do you have wood on site?

Scoop

Swei has the idea, I think. My problem is commitment, I think. I'd like to get by on the cheap for that constant heat part. But if I keep it to about 40-45 degrees, and use an LP Hot Dawg, I don't think it should be unbearable at all. And I've seen some of these small electric heaters that advertise heating a building my size for pennies a day. They don't say how many pennies.
I've got this separated into two spaces, 40% and 60%, with the sawdust in the 60%. The heat plant will be in the 40% area, but I could put a little modine in the 60% area.
One nice thing about electric rates is they go down in the off use hours, right? So I could leave it heat the mass in the night? Average temps in January here are probably 15-20 for lows, 20-25 for highs. I'll probably need to raise the indoor temp 30 degrees?

Scoop

By the way, you guys sure ask the right questions. It's like you're in the same room.

SWEI

First, do a heat loss calculation. I would suggest you look into a Thermolec TMB, which is (as far as I know) the smallest electric boiler with onboard ODR control available in North America. By the time you purchase an electric water heater and add the necessary controls, you will probably end up spending as much or more, and the TMB requires about 1/20th of the space. Their standard boiler costs a bit more, but has what they call a "Dual-Energy" option that manages off-peak rates using a signal.

Gordy

To add to Kurts last post the thermolac will not have the stand by losses of a tank water heater especially if the space has low ambient temps

Scoop

I will do so. Thanks much. Keep you posted

McMaster

Electric water heaters are expensive to operate. Gas W/H's aren't very efficient unless you go condensing ...then with gas, you have more maintenance and costs. Perhaps a heat pump water heater? Or, best of all, go with a small boiler.

Scoop

I found a Thermolec second hand, but it's over powered (34,000 btu) for my size garage, so I passed on it. I was thinking that it would burn a lot of electricity compared to a smaller unit. I don't think I need that kind of muscle, but I could be wrong. We've had mild weather, and a space heater is working well so far. I'm still finishing the interior, but I'd like to be ready when the cold hits.

SWEI

What model is the Thermolec? All of the current models are fully modulating as far as I know, so there should be no problem running one that's a bit oversized (other than needing a larger breaker and wiring to feed it.)

Scoop

It's B-10-U. I did get heavier wire and a 50 amp breaker installed, just in case. This unit was used to heat a floor temporarily, until the natural gas was installed, and worked very well.

SWEI

The B-10 draws 41.67A at full load and is supposed to be fed by a 60A breaker. Is that "heavier wire" 6ga by any chance?

Scoop

Yup. It is 6ga. Last minute choice, but I took the six just in case.

Scoop

And Sparky, my electrician, says we put in the 60A breaker.

SWEI

You're good to go on the B-10 with that.