Evaluating options: heat pumps, radiant, unit heaters, garage/shop

vtfarmer

Hello Wallies

As you regulars may recall, I became VAFarmer last year when I sold my farm in VT and moved to Virginia for family reasons. At the time I had asked about the state of the art in heat pumps. Update to today and I did indeed rip the LP furnace out and replace it with a high end Mitsubishi split system only to be disappointed with it. It just doesn't blow air that's that hot the way the LP unit did, even when it's fairly warm outside (40s). Manual J for the living area was about 50k BTU on a design day and the Mitsu is 42k, so we also had a couple of mini splits installed. To be clear: the Mitsu and minis could maintain the thermostat setpoint, it just didn't feel very comfortable with lukewarm air blowing out the vents. The minis actually seemed to blow hotter air but I hate how they look and having air blowing from up high on the wall so I would not do that again.

Due to a set of circumstances that I won't get into, I ended up selling that property (the one I just bought in VA and installed the system described above into - crazy market) and am now trying to heat a ~6000 square foot house with lots of glass and a 5 bay garage/workshop. This new place has three heat pumps all new in 2005 (when it was built) but they're equally as disappointing as the fancy new ones I put into the house that had the LP furnace. The new house has a heat loss of almost 180k on a design day by my calculations with the SlantFin app (high quality construction and good insulation, but 12 exterior doors, numerous windows and skylights, plus I want to heat the garage/workshop that I want to keep at 55). The house has hardwood floors everywhere except the bedrooms, which are carpeted.

I never thought I'd go this route, what do y'all think of radiant? Will the carpeted areas be a problem? Also, note that the higher floor load areas like hallways and transitions to exterior doors are boxed as shown in one of the attached photos, so I will not be able to get radiant loops into the whole floor area. I intend to heat the basement as well (included in 180k heat load calc), so am I correct in assuming the insulation against the floor will need to come out and stay out?

For a heat source for the radiant I was thinking of having a cast iron oil fired boiler installed on the chimney in the garage, which originally had a wood stove on it. I would have a couple of hydronic unit heaters connected for the garage, run a zone for some wall panel radiators in the finished part of the basement, and mix the water temp down to whatever the radiant loops would need. Oil because I already have a bulk tank for offroad diesel fuel for tractors and hate propane, cast iron because I like simple things and I've never had a pinner fail me - even ones older than my parents, and re-using the garage chimney because I don't want a wood stove there and also don't want the boiler in the basement where there's no flue. I will keep the pair of resistance tank type water heaters for domestic HW. We never run out and they're in good shape.

What do y'all think of this concept? What alternatives would you suggest? The cost of the project and fuel doesn't really matter, but I also don't want to spend money needlessly. The objective is comfort.

hot_rod

The heat load calc is critical for sizing and selecting components. 30 btu/ sq ft seem high. If so all the components would be oversized and you may have short cycling issues with a fixed output type boiler? Maybe the garages are in that number?

Carpet is basically insulation over a radiant flow, be careful there especially if you cannot get tube to all those joist bay

For me, radiant excels in hard surface areas like bath and kitchens, not a lot of value in bedrooms covered with furniture and not much standing around time.
A room by room load would help decide the best heat emitters for each space.

Jamie Hall

You could consider combining radiant in those areas where it makes the most sense and baseboards or panel radiators in other areas. They can both be powered by the same boiler with the right valves and pumps.

Your comment about heat pumps is telling -- and very true.

EdTheHeaterMan

Another option to consider is a duct coil. You can run 190° water thru the coil and get 145° air from the ductwork. This will be warmer than the heat pump 90° to 125° air but not as hot as an oil furnace or LP Gas furnace where duct air temperatures can reach 160° regularly. I lived in a home with HW duct coils for over 25 years and I was quite satisfied.

Your experience with a LP or any Fossil fuel furnace has ruined your perception of what a comfortable "WARM AIR" system is like. When properly installed the Fossil fuel ducted system should not blow HOT air from the registers. If it does, it is not very well designed and this leads the short cycling and fluctuating temperatures on a regular basis. You may have lived in a home with a "BUDGET DESIGN" duct system that lends itself to that HOT air from the registers. That HOT blast of air is considered normal and comforting to many. But to the craftsmen who approach HVAC system design as an art and not just a job, those homes will feel comfortable at much lower temperatures with proper IAQ controls like humidity and filtering devices that enhance the indoor environment. (as opposed to just maintaining a temperature)

That said, You will be looking for Hydronic Heat (CI BOILER) as your best option for the basic system. You can go inexpensive to start with... with HW Duct Coils, If that is only marginally satisfactory, then add towel warmers in the bathrooms, that will make those rooms toasty without overheating the entire house. Constant HW circulation (which would normally overheat a space) with TRVs set to the temperature you desire for that space is a normal design feature if completed properly.

As a last resort or as a final project before you finish off the basement ceiling, you can do the Radiant Floor Staple Up job. I used Aluminum plates and yes... you need to remove the insulation... BUT you must put the insulation back after the tubing is in place and pressure tested. You will get a great radiant ceiling job... causing the basement to overheat, if you don't put the insulation back. Radiant heat goes in all directions Like the SUN is radiant heat from above. the tubing will heat whatever is below it. A good rule is a minimum of 4 times the insulation factor of what is above the tubing. for example... Sub-floor + Hardwood floor + Carpet pad + thick pile carpet may have an R value of 3 or so. The insulation below the tubing must be R-12 or R-13. But more is better.

If you want to heat the basement with radiant ceiling heat, you can install the insulation and add bore tubing below the insulation before the sheetrock is installed. The tubing will just lay on the sheetrock and do a great job of heating the space below the ceiling. (ask me how I know. There is a divorce involved)

These ideas come from a contractor who had to deal with consumers that don't always have the unlimited funds on hand to tackle the entire project. I have had many customers with projects that were completed in stages. You just want to plan on not doing things that are unnecessary or that don't achieve your final goal. Like putting in a LP furnace for now just to tear it out in three years when your Radiant floor project is online. I'm guessing you don't plan on that by your previous post... but you get the point.

I hope this is helpful in your planning of this home project, Good luck with your project. And settle down, why don't you! LOL

Yours Truly,
Mr. Ed

vtfarmer

Thanks guys! I hadn't even considered hydro-coils for the air handlers. I might try simply replacing the heat pumps first, as according to my non-contact thermometer I'm getting ~85 degrees at the vents from two of the three heat pumps and 110 from the third one so I suspect that two aren't working well/properly. I had them "serviced" when I bought the house but the guy just said they're old and need to be replaced (16 years?!?) but didn't give any specifics other than that parts are NLA.

@hot_rod yes, the BTU calc includes a bit of a wild guess for the loss through the five overhead doors on the garage, the rest of the building would be less than 90k. Definitely wouldn't go with a boiler bigger than probably 115k (1 GPH).

@EdTheHeaterMan you hit the nail on the head: I grew up with oil fired hot air where you almost couldn't hold your skin to the metal on the vents. Every home I've owned except these two in Virginia has had hot water radiators, so lukewarm air is really not cutting it for me. Great idea on the hydro-coils and splitting the project up.

Maybe the way to approach this is: investigate replacing existing heat pumps and deploy oil CI boiler sized for the whole house initially just feeding the garage unit heaters in parallel. Then, if replacing the heat pumps doesn't render an improvement (likely given my experience with the first VA house) either add hydro coils to the air handlers or go down the radiant path at that time. I'm not sure if I will ever close in the basement ceilings - I like seeing them open, but I can add the basement heat in later (one of the things I like about hydronics).

hot_rod

If you are concerned with IAQ, then some fan coils, air handlers allow filtration, de or humidification. And of course cooling. Tight, radiant, or hydronic only homes that are tight, tend to get stale smelling without some air turns.

vtfarmer

@hot_rod yes, sorry, I meant to respond to your comments on IAQ the first time. Two of the existing air handlers have electrostatic filters as well as humidifiers, I need to dig my air quality meter out and take some measurements.

In the summer the existing setup is adequate. I'm a northerner so I don't care much for air conditioning but it does get pretty hot and muggy here. We caught the tail end of that in the new house and the existing setup worked, as much as I disliked using it.