From "forced air" to "hot water"

[SteveGH]

I'm taking the plunge and going to try to be carbon neutral for heat. Right now I've got a propane forced air and propane DHW. I'm going with a Garn but looking for help getting the heat into the living space. I'm figuring on using radiators, probably baseboard. I'm intrigued with the idea of floor heat and in fact might have to consider using that in the master bath as maybe only have 18" of straight run. The floor is 3/4" OSB with laminate floor above that. Alot of the rest of the first floor is carpet and figure that would act as insulation for the floor heat. Is it possible to run floor and baseboard? Any other suggestions? Also, the second floor has two bedrooms and a loft/office with a huge opening down to great room (ya, poor planning for trying to be green). My idea is to get enought heat downstairs and let the normal convection get the heat upstairs. We never have to worry about the upstairs being cold even when most of the vents are shut. In fact I'm rigging up a couple of fan/tube assemblies to move more heat downstairs. I found a heat calculator on some radiator web site but either my calculations are way off or I'm going to need some big honkin' radiators. Help???

Also, JimK, your project has been a major gift and has me giving this project total respect. I am curious though, do you have any idea how much electrical load your system needs? Thanks again for your's, and all other experience on this forum.

 

[Medman]

If the propane forced air system is working well at distributing the heat now, you could always install a water-to-air heat exchanger in the plenum of the furnace. This is how I heat, and I have found it quite efficient. It is always good to have the air movement in winter to distribute the humidity as well, preventing condensation on windows. The added bonus is that your propane furnace is a ready backup for times when you will be gone for extended periods. Using a sidearm heat exchanger for your DHW will cut your propane consumption drastically here as well.

It sounds like you have some issues with returns from your top floor to the main floor; adding returns (which I had to do) will help the air circulation and keep the top floor at a more even temp. Duct zone controls may be necessary, but that gets complicated.

You can also add radiant underfloor heat where necessary (like in the bathroom), adding the piping as a separate zone where needed. You will lose some heat with the carpet above in other areas , but if you use staple-up tubing and reflectors it will be minimal, and may just mean running the floor tubes at a higher temp than normally used for radiant floors. If you are feeding 170* water to the HX in the plenum, you will have to mix it down to 120-140* for the floors, typically. All this is fairly easy to accomplish.

I hope this helps. You may not have to run all that tubing and baseboard if your current furnace is doing the job at distributing the heat.

EDIT: Just reread your post. Do you want to be off grid as well? Then baseboard and radiant would be the way to go, and there are good 12V pumps available (Laing) for off-grid PV systems. Using the furnace blower, like I do, can be minimal electrical impact if it has a DC ECM motor in it - normally called variable speed. By installing a new furnave with an ECM blower I reduced my elec. consumption for the blower from 11 amps to less than 1 amp at 220V. I have one 80W circ on the plenum HX and one 110W circ forthe main system. The storage option will add one 80W circ. to the electric load.

Compared to the propane/elec. system I had before, my elec. consumption is now half (850 kWh per month) and I don't use any propane (except for the BBQ). Wood use is up from 3 full cords per year in the PE woodstove to 5 full cords in the EKO.

 

[Como]

You can run UFH, radiators baseboard and forced air together.

All have their pro's and con's.

I think the baseboard units, the ones with the fins, ae basically convectors, could be more applicable to your circumstances. I ruled them out as I did not want every possibly wall length to have them and I wanted more radiant that convection. We might use UFH in the bathrooms, but elsewhere it was not practical with our existing building. We also have wide temparature fluctuations and UFH woud be too slow to respond.

 

[SteveGH]

Thanks Medman. I won't be off grid but want to be as electricity efficient to be able to help my battery bank last longer during power outages. I didn't know about a more efficient blower for the furnace. Thanks for that info.

About the extra returns, there is only one, on the first level. I've found that if I run the furnace fan all the time the temp is fairly even throughout the house, so yes I know that area could be improved. I am putting in a couple of fan/tube devices to suck heat from the ceiling of the second floor and blowing it down stairs.

 

[WoodNotOil]

A plenum hx with forced air should work well in your situation and probably be the least invasive method of adapting your current system to hot water. With that said, all the other options mentioned should work too. I changed over from steam to hotwater installing an entirely new delivery system. Baseboard upstairs, staple up radiant first floor with new Myson radiators for shoulder season, really cold days, and quick response. Note that radiant floors heat the space closest to the floor and you should not expect that heat to make it upstairs, so radiators/baseboards etc would be needed on the upper levels to supply heat there.

For DHW I would suggest thinking about an indirect tank or possibly putting plate hx for charging your propane DHW tank like people do when they put in OWBs.

 

[SteveGH]

When we built our home 10 yrs ago we didn't put in central air but I did have the coil installed with the furnace. I was told I could use that as a water to air heat exchanger. Are there any thoughts on this?

 

[Medman]

I think you could use the cooling coil for a plenum hx, but I would bet that the heat transfer would be better with a proper water-to-air heat exchanger. Besides, the cooling coil is more expensive to replace than a plenum hx, if you want/need to change it in future.

Also, with the ECM motor I run my furnace fan 24x7 on the lowest speed to circulate the air. This helps keep the ducts warm since mine run in the slab. It helps filter the air better, too, and keeps the temp in the house constant. On sunny days in the winter when I am maximizing my solar gain through the south-facing windows, the system transfers the heat to other areas of the house.

 

[SteveGH]

Thanks Medman, your info has opened up possibilities. Question to you though. Do you have a HW system combined with forced air with HX? Do you know what the CFM rating is for your DC blower?

When I was using the LPG furnace I also ran the blower 24/7 to keep temps more even. Last fall I installed a couple of Procom Blueflame heaters that have done an amazing job heating our 2400sq ft. I haven't even been running the blower although the upstairs is about 7 degrees warmer. I did fabricate a blower system to suck hot air from the ceiling upstairs and blowing downstairs.

 

[mike1234]

Just wondering why you would want to make the much more expensive shift from forced air to hot water instead of just adding a forced air wood furnace? It would seem in AZ your wood needs would be minimal, in comparison to lets say Canada, and there are lots of forced air add on furnaces on the market.

I'm taking the plunge and going to try to be carbon neutral for heat. Right now I've got a propane forced air and propane DHW. I'm going with a Garn but looking for help getting the heat into the living space. I'm figuring on using radiators, probably baseboard. I'm intrigued with the idea of floor heat and in fact might have to consider using that in the master bath as maybe only have 18" of straight run. The floor is 3/4" OSB with laminate floor above that. Alot of the rest of the first floor is carpet and figure that would act as insulation for the floor heat. Is it possible to run floor and baseboard? Any other suggestions? Also, the second floor has two bedrooms and a loft/office with a huge opening down to great room (ya, poor planning for trying to be green). My idea is to get enought heat downstairs and let the normal convection get the heat upstairs. We never have to worry about the upstairs being cold even when most of the vents are shut. In fact I'm rigging up a couple of fan/tube assemblies to move more heat downstairs. I found a heat calculator on some radiator web site but either my calculations are way off or I'm going to need some big honkin' radiators. Help???

Also, JimK, your project has been a major gift and has me giving this project total respect. I am curious though, do you have any idea how much electrical load your system needs? Thanks again for your's, and all other experience on this forum.