Small DIY radiant bath heat

Jmichael · January 20

Hello folks,

When I built my house 20 years ago I was going to do underfloor heat. I piped 2nd floor with oxygen barrier pex. I also did my Primary bath encased in 2" mortar covered with granite. I then discovered Geothermal from a friend and changed to that because of the complexity of in-floor and ease of install of Geo. So here 20 years later I have a cold bath floor. Its still plumbed for radiant. Could I run the small single loop from my hot water heater with a mini type system or is it similar cost to do a small are verses large area? I came across the Taco radiant mixing block, which could be the answer if not for the price. I can live with floors as is, I just new there was a genius here to tell me what is possible.

Regards, Mike

hot_rod · January 20

A small electric water heater can work well for a small room. It may be less $$ than a HX block?

With the small 6 gallon tank, you can select the element wattage. They come with around a 1300- 1650W 120V, but you can downsize to slow down the cycling.

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Jmichael · January 20

Thanks for the answer, the cost of the mixing block is about $2000.00. It does everything with just 4 connections, that's why it looked interesting. What would be approx. cost of systems you show?

GroundUp · January 20

The mixing block doesn't do everything. You still need an air eliminator, expansion tank, purge valve(s), etc so if you have the space, I'd agree with Bob that a standalone water heater would be a better option financially than the mixing block. The tanks are only a few hundred dollars and can be purchased at any big box home improvement store

Mad Dog_2 · January 20

Keep it very simple....Mad Dog

hot_rod · January 20

To be honest I didn't put expansion tanks on those small systems.

8 gallons of water going from 65°- 100°= .0048 X 8G= .0384 g of expanded water

Fill it to 5 psi, it may go up less than 10psi. With a 30lb relief you have plenty of room.

If you use just the T+P in the tank, at 150 psi you have a lot of safety room.

LWC is another piece that could be eliminated, the heater has a temperature safety. I used a lwc if the heater was above the piping.

A manual air vent on top of the tank is sufficient also.

It's fairly easy to find scratch and dent small heaters at plumbing wholesalers or big box stores. $150, or 1/2 of new price typically.

You need.

Tank

Pump

T&P gauge

Webstone dual purge valve

Setpoint control, use a digital like Ranco or Johnson Controls, Honeywell, etc.

Mics fittings

Depending on where you shop 500 bucks or less

Too bad you can't find these Laing units anymore. The heater, pump, temperature and safeties were all built in. You could literally connect the pex in and out of them.

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Jmichael · January 20

Hot_rod

The Laing unit sounds like the Taco mixing block but the Taco doesn't heat water its self, it uses hot water heater. but they are $2000.00 plus. I like your idea for the other option with mini hot water heater. Could I just use my regular hot water heater? I could use a plate heat exchanger? I can get 2 for $100.00 on marketplace.

Would a Hot water recirculating pump work? I has setpoint and thermostat. How ever it could contaminate water heater with "legionnaires disease" possibly.

Jmichael · January 20

Here is a short blurb about Taco MIxing Block.

The RMB-1 is a complete injection mixing system, combining a variable speed injection mixing control, injection circulator, system circulator and air elimination all in a single unit.

Kaos · January 20

What is the hot water source? Some systems that use a desuperheater don't make all that much hot water, so you have to be careful with tapping it for heat.

hot_rod · January 20

What temperature is the water heater kept at? You may not need the mixing device included in that pump block. Those are nice to mix down supply from a system running 180F

Heat Link and others sell basic HX isolation modules.

Adding a HX to your tank is not too hard either.

Tee into the drain valve on the WH and into the hot out. A stainless pump with a check valve inside.

On the radiant side, a pump, a pressure relief, and a means to fill and purge. You could adjust the WH pump rate to get a pretty accurate outlet temperature for the radiant.

Or add a mix valve bottom example, if you want exact radiant temperature or the HW tank runs hot 140 or above

If you use a plate HX on a water heater you need to leave a way to descale it occasionally.

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Jmichael · January 21

I keep the water heater at 120. I am getting a new one soon so I am also deciding weather or not to get a heat pump. Although I don't know where all this money is coming from… I intend to do this all and move the water heater to a new location.

Jmichael · January 21

Would something like this work if I could get one?

https://ww

w.xylem.com/de-at/brands/lowara/lowara-produkte/ecocirc/#close

hot_rod · January 21

that looks like a Euro pump based on the union connections, if so it is probably a 230 V pump

mattmia2 · January 22

A second circulator and fittings for the hx add up fast. The second, small water heater if you fill it with a hose is probably the cheapest option.

Kaos · January 22

https://forum.heatinghelp.com/discussion/comment/1836698#Comment_1836698

You can't use a heat pump water heater for space heat. The heat pumps on the those are very small (~4000BTU) and it would be running way more than intended. Even if it is enough heat, It won't last long like that.

DCContrarian · January 22

https://forum.heatinghelp.com/discussion/comment/1836957#Comment_1836957

More crucially, a HPWH pulls heat from inside the building. Using it for space heating is like a perpetual motion machine.

Small DIY radiant bath heat

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