radiant floor heating starting with existing sub-floor

[RustyShackleford]

My hyper-allergic wife insists upon ripping up the berber carpet in the master bedroom of our vacation place, and replacing it with that fake-hardwood vinyl flooring. Nothing I can do about it. But it's an opportunity - to replace the existing electric baseboard heat with radiant floor heating. But I know nothing about radiant floor heating, so hoping I can be enlightened.

The first issue is where to how to run the pipes. I'll be starting with the bare subfloor (plywood or wafer board) after the carpet is removed. I'm sure it doesn't work to just lay the fake hardwood on top of the pipes. So how would it be done ? There's easy access from the basement immediately below, so does it maybe make sense to put the pipes below the sub-floor ?

The second issue is how to heat the water. Probably just electric resistance. Natural gas is not available, and around here propane is generally more expensive, per btu, than electric. Another option is a heat pump water heater; but those are quite expensive, and I don't think the installation cost versus operating cost works out for a place that's occupied maybe 10% of the time. So does it even make sense, trading electric resistance in the baseboard units for electric resistance heating of the subfloor water ? I suspect it does; the radiant effect, as we wood-burners are well aware, is much more effective at providing sense-able heat.

I'd be grateful for peoples' thoughts !

 

[EbS-P]

How many square feet? If thinking electro resistance look into ditra by Schulter. No pipes. No water. We did it in our master bathroom. It’s nice but remember until it’s really cold the floor doesn’t feel warm just not cold.

Schluter®-DITRA-HEAT | Uncoupling (DITRA) | Schluter

Schluter®-DITRA-HEAT - Uncoupling membrane for DITRA-HEAT-E-HK electric floor heating cables

www.schluter.com

The thermostat is we got in 2020 was smart home compatible but was WiFi. An average size Mather bath costs us 30$ a year to heat. It’s over a vented crawl space which had crap insulation.

The we got the insulated one. It’s a simple system but needs to be commissioned with a high voltage current leak test or mega ohm tester (something like that).

 

[RustyShackleford]

The MBR is about 260 sq-ft in size. There is also a large bathroom attached, another130 sq-ft or so. But it's tiled, which I'm not gonna rip up; so unless I put the heat below the sub-floor (in the basement between the joists) I will continue to use the electric baseboard in the bath.

 

[sneefy]

For retrofit, you can tack up tubing underneath the floor, attaching channeled metal heat spreaders, then use reflectix insulation underneath it to mitigate losses into the open basement.

On top of the subfloor, Warmboard looks like a great product. It will have thickness, so keep that in mind.

Hydronic radiant is best heated by a boiler, but other applications can be done like geothermal, I have read (rarely) about electric on-demand water heaters being used.

If electric is your best energy source, then electric mats as mentioned above may be more viable.

For flooring, LVP works great. I built a home last year. No basement, concrete slab with hydronic tubing, heated by a boiler. Did LVP in the entire house except for the bedrooms that got carpeting. Good LVP looks really nice.

 

[RustyShackleford]

For retrofit, you can tack up tubing underneath the floor, attaching channeled metal heat spreaders, then use reflectix insulation underneath it to mitigate losses into the open basement.

On top of the subfloor, Warmboard looks like a great product. It will have thickness, so keep that in mind.

I like the idea of not having the subfloor in between the heat and the floor. But Warmboard, or its competitor, Ecowarm, is roughly $10/ft^2. That's without the PEX tubing and the water-heating method

I have read (rarely) about electric on-demand water heaters being used.

If electric is your best energy source, then electric mats as mentioned above may be more viable.

I'm afraid electric resistance IS my best method. I've done calculations for HVAC load for the room, and it's about 10 Kbtu/hr. That's about 3 kW. So not that big a heater. And I can use the 20amp/240vac circuit that's driving the electric baseboard now. On-demand electric units are VERY cheap, looks like less than $200.

 

[Poindexter]

You my friend have access to very cheap electricity, and I am happy for you.

I have been in the crawlspaces of two homes up here that has the hot water tubing tacked to the underside of the subfloor. If you go that route the homeowner who is paying the bills and trying to please a woman needs to get down into that crawlspace with a flashlight, a hammer, and some extra tacks - before the insulation goes in between the floor joists. I have personally never seen under subfloor hot water tubing with too may tacks on it.

If you can keep the place warm enough with resistance baseboard I would need a compelling reason to switch to something else with the data available so far in this thread.

 

[EatenByLimestone]

If its only occupied 10% of the time, is the heat still on when you aren't there? Will radiant heat the area up fast enough if its not kept warm?

 

[RustyShackleford]

You my friend have access to very cheap electricity, and I am happy for you.

Well, it's about $0.11/kWh. But the low occupancy dramatically shifts the install-cost versus operating-cost balance.

I have been in the crawlspaces of two homes up here that has the hot water tubing tacked to the underside of the subfloor. If you go that route the homeowner who is paying the bills and trying to please a woman needs to get down into that crawlspace with a flashlight, a hammer, and some extra tacks - before the insulation goes in between the floor joists. I have personally never seen under subfloor hot water tubing with too may tacks on it.

It's a full basement, so should be easier.

If you can keep the place warm enough with resistance baseboard I would need a compelling reason to switch to something else with the data available so far in this thread.

I think you're right. If I do anything, it should be a minisplit, for the rare occasions when some cooling might be desired.

 

[EbS-P]

I like the idea of not having the subfloor in between the heat and the floor. But Warmboard, or its competitor, Ecowarm, is roughly $10/ft^2. That's without the PEX tubing and the water-heating method

I'm afraid electric resistance IS my best method. I've done calculations for HVAC load for the room, and it's about 10 Kbtu/hr. That's about 3 kW. So not that big a heater. And I can use the 20amp/240vac circuit that's driving the electric baseboard now. On-demand electric units are VERY cheap, looks like less than $200.

Really electric heat is not terrible for smaller spaces like this. Sure you could get some air to water heatpump but that system will be $20k. If you feel bad put up some solar panels. I wouldn’t say do a 3000 sq ft house with it but… you master bed and bash sure. We did the curbless shower floor too. It was my one splurge. And with wood heat when it get colds it’s nice to have not cold tile under your feet. If you leave a towel down on it you can feel how warm it is.

Double check your LVP max temp. Some of the cheap older composite flooring was like 85 degree max. Those are settings that can be set in the thermostat. It can read floor temp or room temp.

I see electric radiant floor as a luxury.

It heats up fast enough (the floor anyway). I wouldn’t hesitate to replace electric baseboards with in floor electric.

Our electric prices are going up. But again see my luxury point. On a programmable t stat they are really nice. One at 5 am no cold floors in the morning. On at 7 pm not cold floors at night. Warm floor and a cooler room is nice. The floor gets hot before the room hits set point.

As a DIY I wouldn’t mess with hydronic floor. It might be cheaper to install but it won’t be faster or easier.

 

[RustyShackleford]

As a DIY I wouldn’t mess with hydronic floor. It might be cheaper to install but it won’t be faster or easier.

So if I do any in-floor stuff, do electric ? As in, electric resistance coils IN the floor itself ?

 

[EbS-P]

So if I do any in-floor stuff, do electric ? As in, electric resistance coils IN the floor itself ?

That schulter system is slick. Staple down the mat and press the heating wire in. Your length of wire and wire spacing determines the output. Run your 240 to the t stat. Heating leads up a conduit to the t stat j box. Lay your lvp on top. I don’t know if you need an underlayment on top of the the Orange grid. Double check that. We had tile on ours. It was the first time our contractor used this system and he spent a day making sure the layout was correct. But he was impressed how simple it was.

It’s simple. For master bed and bath it’s what I would do. Really ours doesn’t get used much as it’s supplementary for the bathroom. Your use case is different. Price it out. The diy electric hydronic route just seems less turn key. It’s a big project. I would want an out of the box system that just works. If you have time to play around and make adjustments I bet you could make it work but.

Thermo 2000 Mini2 Ultra 3kW Electric Boiler

The Mini Ultra Boilers are IDEAL for heating homes, garages, and pole buildings. They are compact, easy to install, and can also be installed in. multiple configurations. These boilers are great for floor heating, baseboards or radiators.

www.menards.com

 

[EbS-P]

That schulter system is slick. Staple down the mat and press the heating wire in. Your length of wire and wire spacing determines the output. Run your 240 to the t stat. Heating leads up a conduit to the t stat j box. Lay your lvp on top. I don’t know if you need an underlayment on top of the the Orange grid. Double check that. We had tile on ours. It was the first time our contractor used this system and he spent a day making sure the layout was correct. But he was impressed how simple it was.

It’s simple. For master bed and bath it’s what I would do. Really ours doesn’t get used much as it’s supplementary for the bathroom. Your use case is different. Price it out. The diy electric hydronic route just seems less turn key. It’s a big project. I would want an out of the box system that just works. If you have time to play around and make adjustments I bet you could make it work but.

Thermo 2000 Mini2 Ultra 3kW Electric Boiler

The Mini Ultra Boilers are IDEAL for heating homes, garages, and pole buildings. They are compact, easy to install, and can also be installed in. multiple configurations. These boilers are great for floor heating, baseboards or radiators.

www.menards.com

Look into other in floor electric heat. Ditra may require pouring self leveling over the whole floor.

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[RustyShackleford]

Yah, the Schluter stuff looks intriguing. Simpler than hydronic, you're right, and doesn't seem any more expensive. They seem to lock you in to either 12.7 or 15.2 watts per sq-ft, so gonna have to think about that..

On page 28 of the instructions:

https://www.warmyourfloor.com/media/pdf/DITRA-HEAT-Installation-Manual-2019.pdf

 

[gthomas785]

I just did this. Laid down 3/8" pex on top of subfloor with 5/8" plywood sleepers. (Fun fact: 3/8" PEX and 5/8" plywood are both 1/2" thick). PEX lines were 8" on center. 4/4 wide pine planks nails down on top of that with stain and poly.

keep in mind any closed loop heating system needs at a minimum fill and drain, purge station, air removal, expansion tank, circulator, circulator zone control, PEX tubing manifold, pressure relief, and whatever you're using to heat the water. Probably around $1000 in materials. Setting that up is my next project as soon as it gets too cold to work outside.