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Solar, Generators and In-Slab Radiant

S

sjvicker

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Feb 1, 2022
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I'm starting to plan my off grid system that I intend to purchase next year and am looking for feedback on how I should plan my system for my house radiant floor heat.

I have a shed that will house the batteries, inverters and have a generator close by that will feed a shop and house. My goal is to not run any propane to the house or shop. If I had to purchase right now I'd get two of the EG4 18k complete kits from signature solar and add a propane powered generator. I think I have 2 options but I'm not sure what makes the most sense or if there's a 3rd option I'm not seeing.

Option A: The full house is electric (induction stove, electric oven, mini-split, dryer, water heater, radiant heater) and the generator recharges the batteries as necessary. I'm more comfortable with this option as I am planning to DIY and like the idea of not having to deal with exhaust gasses. I am uncertain here if this means I would need to add a 3rd inverter for those times when I'm in the shop and all of the loads hit at once.

Option B: Everything in the house is electric but the radiant is run on propane. This isn't ideal for me but given the amp draw of electric radiant, maybe this makes sense?

Other info: In the PNW my climate is mild and rarely gets below freezing or over 80deg but I do have a lot of gray days to contend with in the late fall through early spring.


What's everyone's thoughts?
 
With radiant floor heat the floor will never get to the point of felling warm, before the room is warm enough. Are you planning floor heat in the whole house or just a few small spaces like bathrooms? Using mini split heat pumps is going to be the most efficient way to heat your home. If this is a true off grid home you will want backup sources of heat, for when the sun doesn't shine, such as a wood stove, and/or propane direct vent heaters. For off grid you need to size your inverters to handle the maximum possible load, and that may require 2 or 3 inverters. You will need to make sure your batteries and propane tank are sized to you thru those grey days.
 
I would agree with pvgirl, go with a mini-split heat pump for cooling and heating, forget about electric radiant heat its very inefficient. The amount of battery storage you would need is going be $$$$. If you absolutely insist on hydronic floor heat then go with a heat pump water heater/boiler.

From an ease of installation view point, I can understand not wanting to run propane pipes around the property. However, burning propane to produce electricity with an internal combustion engine is terribly wasteful compared to using propane as a direct source of heat in a high efficiency furnace and/or tankless water heater. They run at 90 to 95% efficiency vs. the generator engine which is in the 25% to 30% range.
 
sjvicker said:
I'm starting to plan my off grid system that I intend to purchase next year and am looking for feedback on how I should plan my system for my house radiant floor heat.

I have a shed that will house the batteries, inverters and have a generator close by that will feed a shop and house. My goal is to not run any propane to the house or shop. If I had to purchase right now I'd get two of the EG4 18k complete kits from signature solar and add a propane powered generator. I think I have 2 options but I'm not sure what makes the most sense or if there's a 3rd option I'm not seeing.

Option A: The full house is electric (induction stove, electric oven, mini-split, dryer, water heater, radiant heater) and the generator recharges the batteries as necessary. I'm more comfortable with this option as I am planning to DIY and like the idea of not having to deal with exhaust gasses. I am uncertain here if this means I would need to add a 3rd inverter for those times when I'm in the shop and all of the loads hit at once.

Option B: Everything in the house is electric but the radiant is run on propane. This isn't ideal for me but given the amp draw of electric radiant, maybe this makes sense?

Other info: In the PNW my climate is mild and rarely gets below freezing or over 80deg but I do have a lot of gray days to contend with in the late fall through early spring.


What's everyone's thoughts?
Click to expand...
Radiant / hot water should be run on a heatpump...
At least that is what I do
 
I'm planning radiant heat in the slab, mini splits and a woodstove. Generally the radiant would be the primary heating source.
 
sjvicker said:
do you have one you'd recommend I research more on? Artic heat pumps pop up first on the google searches
Click to expand...
I'm in Europe , so not sure if my situation will help you ( use a European brand called nibe ) , but I am very sure some of the good folks here on the forum can steer you to a locally available brand..

When searching, look for "air to water" or "water to water" aka ground source.

I would advice to use a local supplier/HVAC installer.
When shit hits the fan ( or rather ice popcicles are forming in your home), you don't want any delays in getting it fixed.

Furthermore i am contemplating adding a solar water heater to the system
 
IMO,air to water heat pumps in the US are not yet ready for prime time, there are players in the European market but to date none of the big players in the minisplit game have stepped up with US distribution. Daiken makes them but does not distribute in US. Last thing I knew Fujitsu and Mitsubishi have not stepped in. Taco is selling rebadged Euro outside unit tied their interior unit. Their are fringe players out there and at least one domestic producer but they want to sell an integrated system through a installer type distribution channel. John Seigenthaler has been hyping these for a couple of year but to date they are still a bit bleeding edge for me.

BTW in floor hydronic radiant can work and be fairly efficient if the slab is designed right but most slabs are not designed right. A proper radiant slab need to be insulated on all sides and most builders do not. Some of the passive home folks are doing it but very expensively albeit compared to properly designed and insulated basement its "cheap".

There is lot to be said for radiant wall or ceilings, far less costly to retrofit and arguably more efficient,the trade off is loss os some interior space (about 2.5" additional wall depth.
 
peakbagger said:
IMO,air to water heat pumps in the US are not yet ready for prime time, there are players in the European market but to date none of the big players in the minisplit game have stepped up with US distribution. Daiken makes them but does not distribute in US. Last thing I knew Fujitsu and Mitsubishi have not stepped in. Taco is selling rebadged Euro outside unit tied their interior unit. Their are fringe players out there and at least one domestic producer but they want to sell an integrated system through a installer type distribution channel. John Seigenthaler has been hyping these for a couple of year but to date they are still a bit bleeding edge for me.

BTW in floor hydronic radiant can work and be fairly efficient if the slab is designed right but most slabs are not designed right. A proper radiant slab need to be insulated on all sides and most builders do not. Some of the passive home folks are doing it but very expensively albeit compared to properly designed and insulated basement its "cheap".

There is lot to be said for radiant wall or ceilings, far less costly to retrofit and arguably more efficient,the trade off is loss os some interior space (about 2.5" additional wall depth.
Click to expand...
I'm actually surprised there isn't more available in the US yet. Maybe because so much of our heating is already forced air that there's little to no market for retrofits.

I have my permits in hand and am breaking ground on my shop as soon as the ground dries in the spring. The shop will be post frame on stem wall and if that build goes well the plan will be to do the same style of structure for the house. One exception being that the slab will be insulated below grade and on the perimeter.
 
I am North, Algonquin Park Ontario Canada. I designed & built my own Hyper Efficient Home with Frost Protected Slab Foundation using 2" HD-XPS (R-20) Foam underneath and up the 8" sides of the slab, it has 7/8" Radiant Pex embedded within. My heating system runs for a Grand Total of 4 hours per day when it is -30C/-22F outside in mid winter, to maintain 25C/77F inside. I have it set to allow for 2 Degree drop before start.

I love a warm floor and bed to crawl into... None of that Nasty Chill on my creaky old bones.

Best DEAL for a DIY fully designed & partly assembled setup come from http://www.radiantcompany.com/ They will assemble the manifolds & the control board with pump, expansion tank & electronics. They have various "heater" options available... dedicated heat only, or split to provide heat & hot water etc. They generally use LPG or Natural Gas On-Demand heaters (Takagi's at the best price anywhere and Damned Good) BUT you can also use HeatPumps (electric) to run a Radiant System and it IS very Efficient.

NOTE THOUGH: My Home is FAR from the norm ! My walls are 9" thick with 6" of HD-EPS-II Foam in the walls, I have a "Cool Roof" system with 8" of PolyISO and a 2" Thermal Break as do my walls. This is unsual in general terms... TIP: If looking for Foam Sheet Insulation check with Commercial Roofing Companies (they don't have 500% markup like BigBox) also ask IF they have "Take Off" Sheet Insulation which is perfectly good but removed from commercial roofs when being redone, here is by law that they have to recycle but they will sell it CHEAP as it benefits them more. Shhh I didn't say anything.

Depending on where you are, Heat Pumps which can be used for Radiant Heating & Hot Water can get some serious rebates which really makes a difference.

Lastly, the Folks at the Radiant Company in Vermont are AMAZING ! They help design and layout everything, ship it fast & REALLY WELL Packed + they will answer questions and advice over the phone very quickly. I had to exchange a couple of parts and they sent the stuff by air express overnight without a thought... (mind you that was pre-covid days). Also, all parts are either North American or German + they have custom made cast brass fittings for special purposes as well.

There are now several Heat Exchanger Hot Water Systems, even Clothes Dryers and more coming available. North America is slow on the uptick but finally getting there.

Hope it helps, Good Luck.
 
If you want in floor choose a ground source heat pump. With the right engineering you can achieve similar or better efficiency than mini splits. @Steve_S is right on the Vermont group. They have been around a long time and are very helpful.
 
B-Mod said:
www.eco2waterheater.com

Energy Efficient Eco Friendly Co2 Heat Pump Hot Water | Sanco2 by Eco2 Systems LLC

Eco2 Systems LLC offers a line of innovative, energy efficient, eco-friendly heat pump hot water systems for single and multi-family residential and commercial applications.
www.eco2waterheater.com www.eco2waterheater.com
Click to expand...
The heat pump is really just for hot water, for heating there are a number of restrictions:

It is permitted to use the SANCO2 system to provide some limited capacity heating (radiant, fan coil, etc.) in certain areas of North America, when combined with a minimum of 25 gallons per day usage of DHW.​
​
It is NOT permitted to use the SANCO2 system to provide heating as its only function.​
​
Sizing​
Maximum heating capacity must be less than 8,000 BTU/h.​
Minimum design ambient temperature must be above 27°F.​
Tank capacities of the 83 Gallon or 119 Gallon tank are required for performance.​
 
pvgirl said:
The heat pump is really just for hot water, for heating there are a number of restrictions:

It is permitted to use the SANCO2 system to provide some limited capacity heating (radiant, fan coil, etc.) in certain areas of North America, when combined with a minimum of 25 gallons per day usage of DHW.​
​
It is NOT permitted to use the SANCO2 system to provide heating as its only function.​
​
Sizing​
Maximum heating capacity must be less than 8,000 BTU/h.​
Minimum design ambient temperature must be above 27°F.​
Tank capacities of the 83 Gallon or 119 Gallon tank are required for performance.​
Click to expand...
Everyone needs hot water, right? And if this unit is not enough (lives in the PNW?) you can parallel multiple units. Just a suggestion of what I would look into.
 
sjvicker said:
I'm starting to plan my off grid system that I intend to purchase next year and am looking for feedback on how I should plan my system for my house radiant floor heat.

What's everyone's thoughts?
Click to expand...
I am planning on having on in slab hydronic heat in my to-be-built home as well.
Everyone I have heard who has it love having toasty warm feet.
Option A looks good to me.
I plan to use electricity for heating the water, but I am not going to be completely off grid.
I will also have propane back up to assist my PV in heating water (if needed), if the grid power fails.
Propane is quite expensive to be the primary source though.
Of course generator back-up for power, and wood heat as a back-up heat source.
My dump load (if any) will be heating water in the winter.
 
I'm a bit late to the party, but this is my heating set-up:

medium.com

#6 Heating Systems

In a cold climate, effective and efficient heating systems are paramount. Because I’m off-grid, I also want a heating system that is fail…
medium.com medium.com

In floor radiant, with insulated concrete floor slab. I use a wood burner (gasification) in winter when I have no sun, and an air-to-water heat pump (monoblock) for spring/autumn when I do have enough power but need heating. It also provides the hot water for showering, etc. - both systems are coupled to a 3000L buffer tank (all with propylene glycol) and a heat exchanger for the shower/hot water.

It's a very efficient and effective set-up, but you do have to plan well in advance and it's an investment cost wise.
 
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