1500sqft one-zone hydronic radiant concrete slab: "New" studio/loft style apartment in New England.

lofine

Hi,
I am looking for input on the following, please:
-Electric Boilers (I've narrowed down to Slantfin, Electro, and Argo) and which excel at a system like mine.

-What to expect with one-zone heating of the space (one small bedroom, large bath, large open plan studio/loft-style overall w/kitchen.

-Experience (not just theory or instinct) with Pex (stapled down) at the bottom of 4" slab, vs zipped tied to grid and lifted during pour.

-XPS thermal break details: I'm pouring slab-on-slab (w/XPS break), want to do two layers with staggered/overlapping seams, and wondering the performance of 2" vs 3" vs 4" (2x1" and 2x1.5" vs 2x2"). Diminishing returns and price vs noticeably better performance?

-Any other details for operation, like outside controls, water temp, or anything else.

-Any wisdom/experience regarding 19th century brick building with exposed brick interior).


I am going for comfort, as it is a living space, but am anticipating high electric bills, so I want to do what I can on the initial build and set-up.

Thanks!!

Jamie Hall

I will let others comment on the radiant floor design -- but if you can manage to keep the water temperature down, you will do far better with an air to water heat pump heat source than you will with an electric boiler (although if you are in northern New England, you might want one as a backup for those very cold weeks). You say you are anticipating high electric bills -- and an electric boiler will surely give you that. A heat pump will save you a lot.

Steve Minnich

You'll need to start with:

Heat loss load calculation
Determine useable floor area for radiant panel (exclude lower cabinets, appliances, etc.
Determine necessary floor surface temp to heat the room(s)
Installation method - CHECK
Choice of tube and size based on install method
Determine finished floor R-value
Determine floor spacing (it varies)
Determine supply water temperature
Determine loop length, loop leaders, total lengths
Determine total GPM and GPM per loop
Determine head loss

There's a lot of work to it.

leonz

The only experience I have is with my fathers home and how the clowns that installed the pex from the factory that built the house with no radiant plates under the floor boards and how they did his floor and how cold it was soured me as the floor was ruined as well. In order to keep the heat in my brother nailed solid foil covered sheet insulation up against the ceiling joists in the basement to keep the heat in and added a wood pellet boiler to heat the place more effectively.

Until you have figures for the square area of each room and the windows to figure out the heat loss and do a test with a blower door and thermal camera it's not done.

A building like this will benefit from cast iron hot water radiators whether they are the tube type or the panel type and will provide more thermal mass and hold heat and shed heat slowly so keep that in mind as the climate will be cold for a long period of time and the concrete floor will hold the heat from the radiators if the slab is insulated properly with a thick one piece vapor barrier.

The tube type of hot water radiator will hold more hot water and provide more thermal mass to heat the home.

Steve Minnich

It’s not unusual for the BTU/h/sf to come in at much less than 30. 

hot_rod

mid 20 btu/ sq ft is reasonable for residential. Many new, well insulated homes come in at single digitb loads.

I'd go with 6" on center. Better recovery, more even temperature spread, and the lowest possible SWT.

Elevating the tube from the bottom will get you about a 7° lower SWT requirement and a few more btu/ ft output.
On a small job it is for sure worth the extra $$ to 6" it. The lower the SWT requirement to better suited for heat pump use.

lofine

Thanks, Jamie!
What's been your experience using an air-to-water heat pump? Have you A/B'd it with an electric boiler? Where in New England are you? What's the setup with your heatpump?

lofine

Thank you, Steve!
My plumber is using a local company who sizes/designs the systems and gathers all the supplies. I will contact them to see what calculations they are working from (or what the software is telling them).
I'm on a very small budget, but I will spend where I need to. Do you recommend I reach out to someone who can help?
Also, concrete is the finished floor, nothing on top but perhaps some jute/sisal woven area rugs (Low-R).
I'm pretty sure the loops are going under all the walls and cabinets, as I am converting a warehouse space which is totally open now. I'm doing partition walls just for the bathroom/mechanicals/bedroom. 14-16" double wythe brick walls and a cathedral R40 exterior/continuous roof/ceiling. Excellent doors and windows. Slab is the first step in building the interior...
Building built in 1883 as part of a Bottling Works.

Thanks for any and all input, folks.

Hot_water_fan

If this is a budget conscious build, I’d rethink in-floor heat. You could have electric baseboard for a few hundred vs thousands, same efficiency. 

EBEBRATT-Ed

I would be concerned with exposed brick wall that are probably not insulated. You might consider some wall mounted radiation or up the radiant tubing that runs along the walls to offset the heat loss to the large mass of brick

Jamie Hall

lofine said:

Thanks, Jamie!
What's been your experience using an air-to-water heat pump? Have you A/B'd it with an electric boiler? Where in New England are you? What's the setup with your heatpump?

Frankly, none. My information on them is mostly manufacturer's literature -- which usually isn't too bad -- and the experience of some of the other guys. I do have a fairly good sized "mini-split" air to air heat pump installed for an apartment which is part of the main structure; it works well down to about 10 or so. The backup is a vapour steam system which is for the entire structure. In general, a heat pump will use around one third to one fifth of the electricity an electric boiler would use, down to perhaps 20 Fahrenheit, then the performance drops off. If it works at all (some don't below 5 to 10, a few lower) it won't use any more power than a straight electric boiler would even so.

The main limitations for them are the maximum temperature they can reach, which is around 120 to a bit higher, for the output hot water, and the minimum temperature they can function at, which is, as I note, usually somewhere around 5.

They are not a new technology, but they haven't been installed all that commonly -- yet.

The properties I manage are in the hills of Litchfield County, northwestern Connecticut.

lofine

Thank you, Steve!
My plumber is using a local company who sizes/designs the systems and gathers all the supplies. I will contact them to see what calculations they are working from (or what the software is telling them).
I'm on a very small budget, but I will spend where I need to. Do you recommend I reach out to someone who can help?
Also, concrete is the finished floor, nothing on top but perhaps some jute/sisal woven area rugs (Low-R). I won't have a blower door test, either.
I'm pretty sure the loops are going under all the walls and cabinets, as I am converting a warehouse space which is totally open now. I'm doing partition walls just for the bathroom/mechanicals/bedroom. 14-16" double wythe brick walls and a cathedral R40 exterior/continuous roof/ceiling. Excellent doors and windows. Slab is the first step in building the interior...
Building built in 1883 as part of a Bottling Works.

Thanks for any and all input, folks.

If I wasn't clearer earlier, this is a 1500 sq ft open plan studio/loft with 23' cathedral ceilings (R40).
It's hydronic radiant heat in a 4" concrete slab. I'm looking for help from people experienced with electric boilers and radiant slab floors like I am installing. Thanks so much.

KC_Jones

lofine said:

Thank you, Steve!
My plumber is using a local company who sizes/designs the systems and gathers all the supplies. I will contact them to see what calculations they are working from (or what the software is telling them).
I'm on a very small budget, but I will spend where I need to. Do you recommend I reach out to someone who can help?
Also, concrete is the finished floor, nothing on top but perhaps some jute/sisal woven area rugs (Low-R).
I'm pretty sure the loops are going under all the walls and cabinets, as I am converting a warehouse space which is totally open now. I'm doing partition walls just for the bathroom/mechanicals/bedroom. 14-16" double wythe brick walls and a cathedral R40 exterior/continuous roof/ceiling. Excellent doors and windows. Slab is the first step in building the interior...
Building built in 1883 as part of a Bottling Works.

Thanks for any and all input, folks.

Make sure the company doing the layout and installation takes those walls into consideration with the layout. If you add the walls later, they need to be secured into the concrete. It would be a shame to have them drive a fastener through a tube because the layout and installation didn't account for the wall location.

Has the company dong the layout been out to the building to measure everything? This entire process starts with a heat loss calculation and that requires them to visit the building for the critical measurements as a first step.

Don't assume they will do proper diligence in this process, I've seen way more bad contractors than good, and if you hang around this site long enough you may not trust any after a while.

Designing these systems is a very technical process, don't let them skip steps.

lofine

Thanks, KC. I worked for contractors building and working on homes, repair/renovation and new construction, for 15+ years and installed radiant floors in two builds (both wet-install in 4" slabs, zip-tied and lifted during the pour). I completely agree with what you've said...
I took what I learned from building million dollar second homes on the Outer Cape and am applying that to a humble retrofit/conversion of a building in my price range. I'm doing the rest as best I can, and am putting most of the budget into the rebuilt insulated roof, radiant slab, and doors/windows. I'm just trying to get to the CofO so I can live there, and can't do a lot of the work I could've 20 years ago.
I'm here to gather as much actual experience from others (not just reading on other forums or quoting writers of other articles. I can do that, and continue to.)
Most contractors are stapling pex down, and then they don't have to worry much about it, 3-4" below the surface. I want my pex in the middle of the slab, so we'll be putting j-bolts in where the walls will be, to secure the plates.
Most don't do two layers of XPS under the slab, but they don't know what happens under there down the road. I'll be doing two layers with seams staggered/overlapped, like I did with the ISO in the roof, so any gaps that appear (WILL probably appear to some extent, eventually) will be minimal.
I plan on talking it out with this company fully, and pushing for how they are arriving at their calculations.
Lots of stuff is talked about like people know what they are talking about, and they are merely quoting other people. "It doesn't matter if the Pex is at the bottom of the slab, the whole thing heats up" for instance.

Heat pumps are a great idea in certain climates zones, Thanks Jamie, but this building is in Western Mass, near the VT border, and I don't know how I feel about skating that close to the edge of the technology's capabilities (below 5 deg F, which WILL happen every year). I'll be doing more investigation on that. As it is, I'm way ahead of the curve for most builders/plumbers when I talk about some of the technologies I saw as commonplace when I lived/worked in Europe for a few years. Based on your comments, I went back to my reading up on that technology (it had been a few years), and even in the pat two years it seems things have progressed quite a bit in the North American market.
I'm planning to put in a wood stove as supplemental (and emergency) heatsource, and also just for basic comfort & entertainment, but I don't want to be using it because I have a system that I know won't work all Winter, even if just for a few days, so I might also look into an emergency backup electric boiler, and whether or not that would make a heat pump make sense.

Thanks again to everyone who's commented, whether or not it is specific to what I am building or working with.

-Kevin