I have a 28' x 30' shop with infloor heat. I insulated it with 3" foam under the slab and have 6" pink in the walls with 1.5" foam out side under the sidind. The shop sits on 8" cement walls with 20" footing and I added 4" foam on the insde of the walls also to the slab. I use a 40 gallon hot water tank to heat this shop at 64 deg all winter.I will change this to a tankless system for this season because of the power use.THe floor holds 10 gallons and i`am heating 40 gallons in the tank to have water to heat the slab.Takes about 6 minutes to get hot water back from the floor to the cold side of the tank. my problem is the water heater runs all the time and never recovers from the cycles of the heat needed to keep the slab hot. I will install a tankless water heater and then I will be using power only when the system calls for heat.This shoul use less elec .My bill for heat climes now in winter to 3 times more than summer $250.00 to $800.00 in winter. Good luck running a hot water tank to heat much as it will cost you if your shop is not insulated good. I have 10" pink in the attic.

 

Don,

If I understand your post correctly, you are using an electric water heater for your heat source. It's probably only 4500 watts and has a hard time raising the temp of the tons of concrete.

Using a higher output WH might make it work better, but not necessarily. Any in-slab radiant system needs some lag time and thermal mass to be efficient and comfortable. The problem comes with wanting quick response and not getting it. Sometimes I see systems that must run for hours and hours in advance of use. In this case more power is good. But a highly insulated area that us used all the time can cruise with low output and be just fine too.

Remember, it's not the gallons in the boiler that count, it's the BTUs delivered over time.

I've also had great success with setback thermostats and relatively high output boilers. A blast in the morning before getting up and a blast in the evening around sunset for the evening. Then a lower setting for the minimum acceptable during the night. It's funny how, sometimes, a lower output over a longer time can cost more and be less comfortable than a high output at specific times. Radiant is really not about steady floor temps as much as appropriate temps in various areas at various times.

Have you tried timing yours so that the floor temp is just warm enough when you arrive in the morning and then begins to coast down so that it is beginning to feel cool as you leave?

 

Raspy

I use a timer now with on and off power to the pump set at 6 minutes on 40 min off. I will be installing a temp flow valve and time with the new electric furnace. I should see less electric use to heat the Garage,(I hope).I also Have Electronic temp control that uses a probe into the slab and with a timer will be my next plan of attack. Will It work ?

 

Don,

I don't know why you are using a timer with an on and off strategy? Don't worry about sending warm enough water to the slab, if that is what you are trying to achieve. It's energy to the slab and continuous on that will deliver more.

Also the temp flow valve will hinder the performance. More flow, more flow, more flow is what you need.

A floor sensing thermostat is a strategy that I use when I have a radiant system inside a home that already has forced air throughout. That way we can control the floor temp independently of the room temp. In your case the floor temp or room temp are probably equal ways to regulate it since the radiant is the only heat source as far as I know, and the response is slow, so the floor will not run away and get too hot before the room stst turns it off. In other words, a room stat with setback capability might be the best, or will be the best.

In your considerations don't confuse tempersature with energy. Don't try to get a large differential between the hot supply to the floor and the cold return. Go for a small differential, the smaller the better. This means more energy is being delivered and being delivered evenly. More flow is better.

Make sense?

 

I have a stove in my shop that I use early fall and spring for heat or if I need my 12' x 9.6' door open for some time. when that happens I light a fire in the stove. The thermostat with the probe will keep my slab warm when i`am using the stove. I had plans to use a mixing valve to get the water at a temp just slightly higher than the room temp I wanted in the room(65 deg. This was the plan

 

Got it. Sounds like a good plan.

I do it too by setting the thermostat on the water heater to the max temp I want delivered. Sometimes the differential in the WH thermostat can be too wide and a mixing valve will be more accurate.

When I use a probe system I bury a piece of radiant tubing, taped off on one end, and extending out of the slab on the other. Slide the probe or a thermister in. Then you can always get to it later if needed.