Tankless hydronic heat, 1 car garage

ketchgould

I am looking for the simplest way to heat 1/2" pex in a one car new garage build. I have propane and electricity, both 120AC and 12volt DC. I would like to simply use a tankless heater, expansion tank and circ pump. Can this system work? Would electric or propane be preferred?

EdTheHeaterMan

Tankless water heaters are expensive compared to a tank type water heater. LP gas is usually less expensive for heating water compared to electricity.

I have used a small residential gas automatic tank type water heater to do a small radiant job.  The smallest burner is about 30,000 BTUh and the smallest tank is about 40 gallons.  You can pipe it as you wood a closed system and set the water temperature thermostat to 110°F or 120°F to accomplish the proper floor temperature for the project.   

Look for the lowest price tankless heater and compare it to a tank type water heater and see the difference.  Also, the tankless water heaters are problematic with a closed system.  The circulator pump needed to move the water through the tubing may not generate enough flow to operate the flow switch that opens the gas valve on the tankless water heater.      There are hundreds of folks that come on HeatingHelp.com and other sites with the problem of no heat from the water heater.  That is because the water heater is not designed for a closed system operation.  It is designed to operate on an opens system. 

Ironman

A tankless water heater is not the right tool for the job. It’s not designed, controlled or approved for space heating. And for the size of a one car garage, it would be drastically oversized.

A small mod/con boiler would be the best choice, but if you wanna do it on the cheap, a tank water heater that’s dedicated only for that could be used.

Kaos

Most tankless are rated for combi heat, but that means potable water through it. You can run plate HX and isolate the floor heat loop. Tankless are very high pressure drop and you will need a high head pump, something like a Taco 009. Even with that, you might not get more than 40000BTU out of as the flow rate is too low for the delta T you will likely see.

Lot of tank heaters are also rated for combi heat. A good quality power vent will usually run about 80% efficient for space heat, so not a bad solution either.

SuperTech

Please, don't use a tankless water heater for space heating. This website has years full of countless threads from ill informed homeowners and DIY folks who foolishly thought they can accomplish this. If it does work, it won't work well and it won't work for long. Any money saved by getting a tankless water heater instead of a boiler will be negated by cost of repairs and premature failure of the tankless water heater.

Ironman is correct. Wrong tool for the job. It's like using a snow plow to mow the lawn.…

DCContrarian

If you're considering electric, unless you use a heat pump there's no benefit to hydronic, just embed resistive wires in the concrete. The electricity usage will be the same and it's much simpler to install and control.

hot_rod

with hydronic radiant you have a wide range of options now or in the future. Oil, gas, lp, wood, pellet, coal, heat pump, solar,and future options like maybe hydrogen waste heat ??

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1814518#Comment_1814518

Not all tankless water heaters are rated Combi. if it is rated as a DHW heater only, then dont use it for space heating at all. A combi is rated for a closed system and has all the safety approvals and the manufacturers instructions to guide you. But that appliance will cost you more that 10 times the price of a 30 gallon tank with a small 30k burner.

What is correct without looking at the cost to the homeowner and the operating cost equals "You don't get the job". And if you know how to do it right with a tank type water heater, you may as well offer a price to the customer.

ketchgould

Thanks for the information. I will get the smallest LP tank water heater I can and use that.

hot_rod

Probably a 40 or 50 gallon will be the least expensive. The only downside of a tank type is if you ever want to use glycol in the system. You are looking at maybe 20 gallons or more.