We are on a quest to have the best quality AIR inside our house as possible. My youngest daughter has Asthma and lots of allergies to boot so we are making every effort to control allergens and air quality in our new build. I would like to know if using all radiant heat on all three levels of our 4500 sq ft home and using mini splits for Air Conditioning in the summer months and possibly for some heat in the shoulder seasons when the radiant heat would be to warm and could overheat the house sounds crazy? I am not familiar with costs yet but I can imagine it will be more than traditional HVAC. We are doing wall to wall hard wood flooring so I am considering warmboard for the decking in the house wall to wall as well. Just wondering if there is a reason to do anything traditional HVAC or if the mini splits and radiant will be sufficient!

best quality AIR inside our house as possible:
1. Build a superinsulated, tight house with good detailing of insulation and vapor barriers around the foundation. Done properly, this can lower moisture entering the house, keep moisture at comfortable levels in cold weather and minimize the supplemental heat required.
2. Install a good heat recovery ventilation system with merv filters. This could be a Zender, or another brand.
3. Avoid "traditional" HRVs with ductwork which can hold dust. (you won't need them anyway)

So Bob what your saying is...it's possible to use the Mini Splits for A/C only and heat the house with radiant? By employing an HRV system I will be able to filter the air and benefit from some heat recovery from the exhaust air? What are your thoughts on overall cost. If I am not doing two furnaces with heat exchangers in them for the boiler heat then the increased money shouldn't be crazy high

So Bob what your saying is...it's possible to use the Mini Splits for A/C only and heat the house with radiant?

Why do you need the radiant, again?
What kind of a climate is this?

yes, or you can simply heat the house with minisplits. The big advantage of minisplits is you can eliminate your fossil fuel boilers, and as a bonus, they are more efficient and less expensive to run. Yes, I know that the high efficiency boilers are vented directly outdoors, but I'm not convinced that air quality does not improve when they are eliminated. I've built homes with radiant heat, and understand that 80o floors are comfortable, but 65-70o floors, while not significantly warmer that air temperatures, are not "cold".

ICFHybrid I need the radiant because I already own the outdoor wood boiler....I will be moving it to the new house and want to utilize it for the Domestic Hot water as well as radiant heat in the floors. I also want radiant because my daughter has Asthma and allergies and the radiant just seems like a better system for air quality. Bloomington Indiana is the climate

Bob with my situation i am using an outdoor wood boiler, it is not super high efficiency but it doesn't effect my house air quality. That being said, do you think the cost of one mini split heat pump and potentially several powerheads in the house (apprx 2900 main and upper level sq ft plus 1600 future finished basement) will be close to the radiant?
Also, when using JUST mini splits would I use the HRV for return air and replacement air? Seems like the mini splits don't do anything but heat the air or cool the air and blow it around. I am concerned that the air may end up being really dry???

I'm building a 2800 sf 5 BR colonial with a full basement. It will have (3) minisplits - two on the 1st floor & one on the 2nd. Total installed cost is less than $9,000. I doubt you can do radiant for that price. We might find that a fourth is needed, but I doubt it. As for the basement, it will stay in the high 50's, low 60's anyway, but a fourth minisplit can be installed easily when the room is finished.

The thing about a tight, superinsulated house is that it behaves very differently from the old "standard", and these are hard concepts to understand. First, the heat is constant throughout the house - you effectlvely eliminate cold spots & cold rooms. Due to the 2nd law of thermodynamics (this is admittedly a rough translation), which is "heat flows to cold", you can use point source heaters without ductwork, since normal, unforced airflow will move the heat. We've found that since moisture moves very very slowly through tight walls (as opposed to heat leaks) the house retains much more of the moisture generated by the inhabitants, and does not become "dry", like it does in a typical house in winter. The minisplit is not heating and circulating very hot air like my hot air furnace does; it is putting out heat much closer to room temperatures, so the drying isn't forced like it is with the hot air furnace. The HRV will be circulating tempered outside air, not heated indoor air, and exhausting stale indoor air. Different system entirely.

I'd recommend selling your outdoor boiler and buying a heat recovery hot water heater. If you really enjoy cutting wood and you have lots of land, sell cordwood & use the income to finance your PV system which will eliminate your heating and electrical bills. If your boiler is anywhere near your house, it affects the outdoor air quality anyway, and can affect the indoor air quality.

Where are you? It may be that there are houses like this in your area which you could visit and/or talk to the occupants.

I've been building houses for decades and find these houses solve the major problems and comfort issues I've been battling for all those years. they really work.

I'd suggest looking for Passive House builders or consultants in your area, or builders doing zero energy homes so you can see first hand what I've described. the house does not have to be build to Passive House levels, but the builder should have a thorough understanding of PH concepts.

Thanks Bob....I appreciate the insight and real world numbers. 4 mini splits and the 10K price tag is really encouraging, I am looking at way more than that just to do traditional HVAC and that is before the radiant floor heat is even included.

I will need to get some more references for builders doing this type stuff in my area. I just haven't been able to find anything in my area like the ideas I am getting from this website. Our architect has designed a net zero home before but he is less than knowledgable about the way to actually build one. I was baffled at his lack of knowledge.

google "zero energy homes Bloomington Indiana"

"baffled at his lack of knowledge"
While there are national and regional building science experts, the introduction of Passive House into the US about a decade ago (in Urbana, Ill) kickstarted high performance building in the USA. Passive House taught many architects and builders practical ways of building these buildings. Methods that are mathematically proven and also have over twenty years of installed knowledge. The details include the importance of building a tight shell (airsealing) to a fixed standard (.6ACH50), the importance of reducing thermal bridging, the importance of triple glazed windows - both to improve overall R value, but more importantly for comfort, since the inside pane will be close to room temperature so you will not feel a chill sitting next to the window. All these details and many more have been the subject of intense discussions around the country, on this forum, on the Green Building Advisor Forum, and area forums like the monthly meetings of the Boston Passive House group and the Building Science Discussion Group in Portland, ME. So it's all "new" and we're all learning. The vast majority of builders and architects are still working without this knowledge, but the field is growing fast. you may have to look around for a team, but it'll be well worth it.

by the way, and so you don't get the impression that cost is no object. A Passive House home in europe costs only 10-15% more and uses 90% less heat than a home built to code.

Somehow "best quality AIR inside our house as possible" and "using an outdoor wood boiler" aren't super-compatible. You may not THINK it's affecting your indoor air quality, but all wood-burners are on the high-pollutant output end of the scale, and raise the air-particulates in the local environment so that even your ventilation air is bringing in those particulates, which are often too small to be filtered.

An ERV/HRV will allow you to high ventilation rates to purge indoor air pollution that originated inside the house (from cooking, cleaning, outgassing of construction & furniture materials, etc.), all without taking a huge energy hit from moving all that conditioned heated air. Designing a house to be built with a minimum of volatile organic chemicals (VOCs) may also be important for some highly-sensitive asthmatics.

Thank Bob...our architect has been less than easy to work with. Honestly I have almost walked out a couple of different times. We have spent a lot of money and do not have one single energy efficient or "NEW" technology built into the home. My architect is LEED and whatever else certified as well and has one net zero home under his belt but I have learned more from this forum than he knows with all the certificates on the wall. Hard for me to swallow. So we took our preliminary plans and walked. I will modify them and then work with our contractors to get the best product possible. The way I am approaching this process is to keep the overall construction prices down by doing what I can do cost effectively like skip the spray foam and do the exterior foam for air sealing, possibly selling the boiler and going with mini-splits and an HRV for heating and cooling. It's all about the know how and finding a confident and knowledgable contractor in my area and that has been really tough. The cost to build a home like the one I am planning can get easily up around the 115-125 per sq ft range. When a normal build to code or maybe a little better on the insulation side of things can be done for 85-100 depending on the level of finish work you want. Thos are considerable differences in price considering I am building a total of 5500 total sq feet (garage and basement included)

Well-insulated, well-sealed homes are AWESOME. Good luck in your quest to get it done.

Thanks ICFHybrid. I am really looking forward to it...just going to be a tough row to hoe. If it was easy anyone would do it!

If it was easy anyone would do it!

Well, except that many of them won't spend any extra to save energy or money down the line. It's very much an immediate gratification world out there.

Bob l...The home we are building is a farmhouse design so nothing crazy with the framing so we may be able to do what you are saying and use 3 mini splits and then put a 4th head in the basement if needed in the future. Could you maybe shoot me your contact info in a private message so I could reach out to you for some assistance. I see you are a certified PH consultant. I could use some professional assistance with this project.

Posted By Bob I on 06 Jan 2014 09:32 AM
yes, or you can simply heat the house with minisplits. The big advantage of minisplits is you can eliminate your fossil fuel boilers, and as a bonus, they are more efficient and less expensive to run. Yes, I know that the high efficiency boilers are vented directly outdoors, but I'm not convinced that air quality does not improve when they are eliminated. I've built homes with radiant heat, and understand that 80o floors are comfortable, but 65-70o floors, while not significantly warmer that air temperatures, are not "cold".

I came across this discussion on the form and the original posters thoughts are the same as mine for my upcoming build. I will be building a home with 1900sqft on main floor + full basement and an additional 600 sqft above the garage in a loft.
My plan was to heat with radiant for air quality and comfort as well as efficiency and then supplement that system with cooling from a mini split setup and HRV.
The radiant is not an obsolute must, but it can be powered by gas in our area which is extremely cheap when compared to the alternatives. I live in southern ontario, and I am wondering if a mini split system used for heating and cooling will actually be cheaper to run, and then I can save the money of a radiant system.

You'll have to figure the cost of heat. A very efficient gas heater will be 94% +/- efficient, while a minisplit will be 250% efficient when it is not super cold. that is the advantage of minisplits, but if you can figure useage of each X cost of fuel you can get closer. One concern is that if your temps routinely get down below -20F you may need supplemental heat with minisplits.

What is the best heat loss calculator that I can download and save results?

You can eliminate fossil fuel burners with a minisplit if your electricity isn't produced by burning coal or natural gas. Good luck with that.

We have both radiant floors and a minisplit in our remodeled farmhouse and wouldn't be without either.

It is usually more complicated and expensive than you are lead to believe.

We have found that local contractors are the only reliable source of what the thing is going to cost.