Boiler setup for hydronic shop building, with optional geothermal in the future

tonkabot

I have a new 4000sqft shop with the hydronic plumbing in the concrete on my farm

I want to DIY the boiler and plumbing, economically (I am very handy). I have nat. gas.

I also want to be able to add a geothermal heat pump at some point - I have plenty of room for a horizontal coil field - i figure I could rent an excavator for a day or so and get that all done myself - I have experience with backhoes, bobcats, loaders and such. but my main questions are how to make it so I can easily switch/ add the geothermal? is it worth doing in two stages? Does a geothermal setup even need the tankless water heater that I assume I would have for the initial install?

GroundUp

This isn't exactly a DIY type of system. If you want it to work properly, you will at the very least need some sort of engineering done to assure proper sizing and piping. Perhaps the manufacturer or distributor of the boiler (NOT water heater) that you choose will be able to assist with this?

Jamie Hall

Please don't use a tankless water heater. Not meant for the job. You'd not use a front end loader to dig a two foot trench — don't use a tankless water heater to heat a building.

Find a nice inexpensive simple boiler.

Now as to adding geothermal later — First, make sure that the design and installation of the radiant tubing in the shop is right. Also, if the floor hasn't been poured yet, make sure there is a LOT of insulation under it (if it has been, and no insulation… well… too bad…)

Then from there, the hot side heat exchanger from the heatpump — whether the cold side is geothermal or air — will just pipe right in in place of the boiler, or even in parallel with it with suitable valves.

Hot_water_fan

Some terminology issues potentially afoot. When “tankless water heater” is mentioned, often people assume the OP means a domestic water heater used as a central heating appliance. Like something you could buy from Home Depot. Don’t do that. However, OP never specified what they meant! A wall hung boiler looks the same and is mostly the same so could reasonably be called a “tankless water heater” too.

Jamie Hall

True, very true, @Hot_water_fan . My main point may have gotten lost — it was that on the radiant side no special considerations for future use of a heatpump are required.

hot_rod

sounds like the slab is already done?

If not, the tighter the tube spacing the lower the required water temperature

The lower the water temperature the higher the efficiency of the GEO, boiler, etc.

Any other improvements you can make to the building shell, the less heat required. Better insulation around overhead doors can lower infiltration, lower heating costs

Kaos

Geo only really makes sense if you have local incentives to cover part of the install. You won't get these for anything DIY so I can't see it working dollars wise even if you can do the loop on the cheap. They are also hard to design well, a shallow slinkey loop setup means high pumping power and significant efficiency hit as the ground will be pretty cold.

Compared to the cost of the above, modern air to water heat pumps are pretty cheap and will do about similar seasonal COP especially when heating a slab. If you want electric heat, this is what I would go with.

As for the fuel burner, sample of a couple but I've had good experience with condensing tankless units for combi heat. With a bit of proper design they are a cheap and efficient source of heat. As with any type of space heat, they can also be installed improperly.

DCContrarian

Once the piping is in the slab really the only thing you can change is the water temperature. Check out this thread for details:

https://forum.heatinghelp.com/discussion/198653/small-radiant-heat-floor-tankless-electric-hot-water-help

The issue with any sort of heat pump is they can't put out water as hot as a boiler can. So if you want to go to a heat pump in the future you may find that your piping requires water that is hotter than a heat pump can provide. If the piping has already been laid there's not much you can do about it.

That thread is also instructive in showing the limited role that flow can play in adjusting a system once it's installed.