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No Slab Insulation - ModCon Boiler, WarmBoard, Abandon and Go Forced Air?

Pollymath
Pollymath Member Posts: 6
I've got a 1550sqft single level house on slab in Northern Arizona. I'm at elevation, so we get a significant amount of heating days and snow days. I'd say we have the heat running October thru April.

My slab is uninsulated on both the perimeter and under slab. I know because I tore it up for a plumbing change in my bathroom, and was disappointed to find cinders 8' away from the perimeter wall. Then I met with a concrete contractor who knew my neighborhood well, and confirmed "yep, you likely don't have any insulation under the slab, we didn't do that very often in the late 90's."

Currently, I've got radiant heat via hydronic PEX, powered by a 50 gallon Apollo hot water heater pumping up 68,000 BTUs. Single pump pushing through 4 loops. My gas bills are disappointingly high.

I'm going to need to replace the Apollo at some point, and I'm torn between the costs of these three options:

1) ModCon Boiler with heat exchanger or indirect tank, something like a Lochinvar or Navien.

1-A) Or, I could use a conventional tank type hot water heater and a heat exchanger. Nice thing about this would be that I could still get some benefit from the existing system without spending loads of money on a ModCon Boiler.

2) WarmBoard retrofit. This would add some insulation to floor so I wouldn't bleed as much heat into the earth under my house.

3) Forced Air Conversion. I've got a lot of attic space that does nothing, and I've got relatively easy access into and across the space. It'd be pretty easy to run ducts around. MiniSplits are coming down in cost, and my city is getting hotter, with A/C being a selling point of many newer homes.


I'd like to compare the pros and cons of these on a more general basis. From a brief search, I see that the install of HVAC system with A/C would probably cost the same amount as a ModCon Boiler install. The WarmBoard would be significantly more expensive, because it would require flooring across the entire home to be pulled up, trim redone, etc, but, once completed it might allow for added efficiency of future radiant systems.

Thanks for any advice.

Comments

  • JUGHNE
    JUGHNE Member Posts: 8,689
    Does the snow melt away from the edges of the house?

    IIWM, before doing anything inside, I would excavate around the exterior perimeter of the house down to the footings and install at least 2" foam board (water proof).
    This would have to be protected from damage above the grade.
    It would look like oversized baseboard trim around the house.

    Regardless of what you do inside this will help with the heat loss.
    If you have a FLIR viewing gun ($400 or so) you can see the heat loss inside and outside. Pretty well a winter heating thing to look at.

    Your water heater (boiler) is probably not as efficient as even a standard cast iron type and certainly not close to a ModCon design.....if you can run low temps.

    What temp do you run the infloor tubing at now?

    After having warm floors you may be very disappointed with forced air blowing out of the ceiling at you in the wintertime.
  • GroundUp
    GroundUp Member Posts: 1,272
    A 50 gallon powervent WH and heat exchanger with SS pump for circulation would cost just as much as a mod/con boiler and use 15-20% more gas. That's not a money saver. Do you like the warm floors or even notice? What are you using for cooling?
  • Pollymath
    Pollymath Member Posts: 6
    Sorry about the delayed follow up response here.

    I've got a IR camera and yes, I know the house is bleeding heat out of the foundation. In the dead of winter it's green the whole way down the side of the house until my foundation/sill, then it's deep red.

    My Apollo 5010, 50gal commercial style water heater (for heat) is 20 years old, 65k BTU, and a huge gas hog. Back of the napkin math by Richard McGrath said it was actually a bit oversized for my application too, as he estimated I probably only needed about 40,000ish BTU input for my relatively small house, although the lack of insulation may factor into those estimates. He had no doubt a modern ModCon boiler setup could save fuel, but the question of "can I make the house warmer for cheaper" is still up for debate. Especially considering the cost of a boiler.

    When it comes to "source of comfort" I don't think it really matters to me. I've lived in homes with forced air all my life, and a few with coal stoves. What does matter is my wife's comfort (happy wife, happy life, eh) - she wants it to be 80º all year everywhere (desert rat at heart). She could care less about her feet being warm.

    In a perfect world, I'd have a cheap way of retaining my hydronic setup, but something that is not only cheap to install, but cheap to run too. Something that might cost say, a 1/4 of my current gas bill in the winter months. Now, maybe this setup isn't able to properly heat the house above say...65º, but it's cheap, and then I use a supplement heat source like a centralized gas fireplace and two mini-splits. Or vice versa, I keep my current setup, and only turn it on when I need the house at its warmest - other times just relying on the mini-splits.

    One thing we're going to be doing is installing some skylights in our main living area. You might say "that will reduce your efficiency" but we're at high elevation with substantial sunlight. Even after heavy multi-foot snowstorms the snow will only last on our roof for a day or two. Our past house had some skylights and during the winter, the room where they were placed was the warmest, despite being the largest with huge ceilings. It was all the "dark" rooms that we were trying to get more heat into. In our new home, that lacks any substantial south-facing windows and is even darker, more windows may be able to kill two birds with one stone - increasing quality of life while also adding solar radiant heat.
  • Jamie Hall
    Jamie Hall Member Posts: 16,609
    You would like to reduce your energy costs to a quarter of the present? Wouldn't we all? Unfortunately, the cost of a BTU of energy delivered to you, whether it's oil or gas or wood or electricity, simply doesn't permit that. In any given area, they will be within a factor of two of each other -- or closer.

    You can, in new build, reduce the cost of that imported energy considerably by going to 100% solar heat -- even in remarkably harsh climates. But that can't be retrofitted to an existing structure -- it has to be built in from the beginning.

    As to the skylights. Depends on the skylight. There are skylights which are no worse than -- to use the fashionable term -- net zero for energy use, such as those made by Velux. They aren't cheap, but I'd say to go for it. The added light is really nice. Cheap skylights, however, are indeed energy hogs.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    PC7060
  • Jon_blaney
    Jon_blaney Member Posts: 130
    I comfortably heat and cool about half my house with a high velocity air system (UNICO) using my hot water heater. It is an open system which I run at 140 deg. My heater is oil fired. Here in New England LP and electric are expensive and I do not have NG available. I would look to an air handler and small ducts in the attic. With carefully planning, the negative aspects of attic ducts can be overcome. Heat pump for ac and heat in shoulder seasons, hydronic in winter.

    Have you compared your available energy costs per btu?

    I think you are spending a lot of money heating the ground.

  • PC7060
    PC7060 Member Posts: 365
    I comfortably heat and cool about half my house with a high velocity air system (UNICO) using my hot water heater. It is an open system which I run at 140 deg. My heater is oil fired. Here in New England LP and electric are expensive and I do not have NG available. I would look to an air handler and small ducts in the attic. With carefully planning, the negative aspects of attic ducts can be overcome. Heat pump for ac and heat in shoulder seasons, hydronic in winter. Have you compared your available energy costs per btu? I think you are spending a lot of money heating the ground.
    I have similar setup described by @Jon_blaney with spacepak high velocity system serving second level and a standard unit on first floor.  Both are heat pumps which I used in shoulder season with a separate natural gas MODCON fire tube boiler for the really cold period.  The MODCON boiler with outdoor reset was installed last December does a great job delivery just right amount of heat during moderate days so the heat pump usage may be minimal.  

    Sealing the ducts is critical if outside the conditioned space.  I used mastic on all joists for large plenum. The high velocity supply tube connection has a foam gasket but I’ve found it began to loosens after several years so I’ve sealed the supply tubes connections to the plenum using Dow window foam.   

  • Pollymath
    Pollymath Member Posts: 6
    edited September 14
    Ok just to clarify:

    Ya'll are using MODCON boilers to heat water to run into a forced air system?

    Keep in mind, I have no ducts currently. I heat the floor with hydronics. I want to save space. I don't need AC.

    If I buy and install a MODCON Boiler, I'm just going to heat the floor and not worry about anything else. They are too expensive IMO to be combining them with all kinds of other units. I'm trying to avoid buying a boiler because of their expense. I'm hearing between $-$ on the low end.

    What's frustrating is that there is a big divide between boiler installs and tankless DHW installs. Local plumbers will quote me $ for a tankless, but as soon as I mention wanting a boiler, we're immediately up in 5 digits.

    What I'd like is a cheap, DIY replacement for the horribly inefficient hot water heater that could keep up with my relatively low demand for hydronic heat, and then supplement that with a cheaper way of adding heat as needed on the coldest days. My wife even is perfectly fine with our gas fireplace, if the damn thing could ever work well.

    I think my first order of business to insulate my slab skirt the whole way around the house with 2" of foam board. That'll at least keep heat in the slab. Apparently, the cinders I have under the slab are not entirely devoid of insulative properties, and they might actually be pretty good, so abandoning the hydronic system probably isn't a wise idea at this point.