Advice for slab addition

First off, Wanted to say hello and give some background on me. I am a pretty capable guy and spent my younger years framing, flashing and roofing houses so I am no stranger to any type of construction. For the record do know when to call a trade specific professional. Ok, now for the questions

I live in a small (900 SQ) house built on a slab on foundation wall and footing. I am building an addition (440SQ) this spring. I will handle the majority of the work myself. The largest problem right now is HVAC. Currently I have a newer Intertherm/Nordyne downflow unit with central air. All ductwork is under slab. I have checked with the contractor that installed my unit and they completed a manual J stating that I will be okay with the new added space.

So, what are my best options to duct the new addition?

Should I go through the foundation wall? will require some steel support and really push the space being heated by the two 8" ducts I could tap from

Can I add a duct to the downflow plenum in the utility room and duct through the attic? This sounds easy being there is room around the base of the furnace, is it?

Also woud it help to add a second col air return in the furthest end of the new space to aid the airflow?

I have called a few HVAC contractors in the area and none seem the slightest bit interested in getting involved i this. It is Winter in PA.

I welcome all advice
Thanks
Andy

Ideally, each room would have a cold air return. Depends on how open the floorplan is and if you close off rooms.

Pushing hot air down in the heating season is not particularly efficient, but works well for cooling. Some places I've seen extend the duct low and actually use two registers - one near the ceiling for cooling and then close it off and use the lower one for heating.

Running the ductwork through the attic can work - just make sure to seal and insulate the ductwork well.

I'll add to the questions since I am doing something simlar next year. Have a 900 SF house as well with a perimeter foundation and am adding a 260 SF addition.

My question is what alternatives do I have if I CAN'T extend ductwork? Electric baseboards are one, but what other options for heating do I have? I don't need A/C, just decent heat. (Wisconsin) Again, it's only 260 SF so another furnace seems impractical.

Hope I'm not really threadjacking.

Just to respond the other answer I came up with was a radiant with tankless. I however do need AC. I agree on the baseboards, I hate the fact of limiting furnature placement

low load hydronic heating

For low load hydronic heating with in floor tubing you can consider either coming off your current water heater to a flat plate heat exchanger (it is not recommended, i.e. really bad, to mix potable and heating loop water) or switch to the Bradford White Combi2 gas water heater which has a built in heat exchanger.

If you will use hydronic baseboard emitters and the water temperature required for your load is above where you will run the water heater, you can consider the Laing electric heater/circulators as an alternative. (www.Lainginc.com)

Radiant with on demand tankless heaters designed for domestic hot water can sometimes work, but often they are not really suitable for the application.

I would recommend adding under slab insulation and PEX tubbing.

It's a lot easier to add BEFORE you pour the slab.

"Under slab" ducts will work, but you need to insulate them.

I use those cheep insulated plastic ducts in the attic and they work ok.

Build for both short term (duct work) and plan long term (PEX for future heat pump)

cattledog said:

For low load hydronic heating with in floor tubing you can consider either coming off your current water heater to a flat plate heat exchanger (it is not recommended, i.e. really bad, to mix potable and heating loop water) or switch to the Bradford White Combi2 gas water heater which has a built in heat exchanger.

If you will use hydronic baseboard emitters and the water temperature required for your load is above where you will run the water heater, you can consider the Laing electric heater/circulators as an alternative. (www.Lainginc.com)

Click to expand...

Well, My water heater fits in a tiny alcove between our chimney base and our furnace. No real room to expand. It's a 30 Gal unit which has been enough for us, but there's no way we could get 50 Gal in there. MAYBE a low insulation 40. (That's the smallest heater I see that has a heat exchanger in it)

The Laing looks really interesting, but I can't find where I can buy it. Anyone know? I'd like to even just get an idea of the cost.

Electric radiant heat is $10/SF+ which is ridiculous. But the small electric hydronic system seems about perfect if the cost isn't real high.

"Micro" Radiant

Nate--

Check out the following "micro radiant" thread on "The Wall" at www.heatinghelp.com. There is an interesting post about using a 6 gallon electric water heater with a higer power replacement element.

http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=53097&mc=11

Hmm, interesting idea. Well, the Laing pump has no real reserve capacity, and 2 KW is enough per zone. So a 2 or 2.5 gallon tank should be plenty, I would think.

Check out a SpacePak mini duct system http://www.spacepak.com/ .

construct30 said:

Check out a SpacePak mini duct system http://www.spacepak.com/ .

Click to expand...

Wow, I havebeen looking at mini split ductless units and I really like that better. I will now have to research the cost of adding one of these and hydronic floor vs a new upflow forced air and new ductwork through the attic

Keep the ideas rolling in, Thanks

Hmm, doing more research and such, I'm finding cheaper electric radiant setups.

Can I use electric radiant in floor heat as my only heat source for a room?

Even if I have a slab floor and insulate the heating elements from the slab and just heat tile/thinset at 15W/SF?

I'm liking the idea more and more, and it seems it may be worth the cost. Electric baseboard heat is much cheaper, but with slab floors, I worry there will always be cold feet making the room feel cold. Depends on which flooring we go with, I suppose.

15W/hr = 51.22BTU/hr. Calculate your area and see if it equals the heat loss calculation you must have before you can make any intelligent decision. Where I live, electric heat is probably the most expensive means of heating a room. A warm floor is probably the nicest heat you can have. Heating with a boiler would likely be cheaper in energy costs, but installation costs would be higher, so that should be taken into consideration.

Duh! Dunno why I didn't do that calculation already. Heat Loss calculation was rough for now, but should be very close to what the Radiant would give.

What about a ductless heatpump?

Without going thru too many hassles you could install a Ductless heat pump in less than a day and get both heat and cooling for about as much as you would have to pay for all the slab and furnace modifications. It will also give you the advantage of being independent or zoned from the central system. Look at it this way; you may have to relocate your existing thermostat to get good performance out of your existing central unit in the new addition. With a ductless you don't have to worry about that. Point the remote and dial in whatever temperature you want. Check them out at www.mrslim.com.:cool:

therinnaiguy said:

Without going thru too many hassles you could install a Ductless heat pump in less than a day and get both heat and cooling for about as much as you would have to pay for all the slab and furnace modifications. It will also give you the advantage of being independent or zoned from the central system. Look at it this way; you may have to relocate your existing thermostat to get good performance out of your existing central unit in the new addition. With a ductless you don't have to worry about that. Point the remote and dial in whatever temperature you want. Check them out at www.mrslim.com.

Click to expand...

The mrslim has intrigued me, but I can't find one to look at. Have you actually seen one live and in person working?

With the cost of energy seeming to head in only one direction, the energy cost should be a major factor in your decisions.

Floor radiant heating will always lose some heat to the earth. You need a thorough analysis of losses, preferably by someone not involved in selling the system.

Electricity is the most expensive $/BTUs form of energy but it can be converted 100% to heat. However, if you install the heater where you automatically lose some to the ground that destroys the efficiency advantage.

One solution for small additions with distribution problems is to install a small gas-fueled heater. You can use propane or or natural gas and there are direct venting units that don't require a chimney.

I am not promoting the sellers at the link but they give you ideas of what is available.
http://www.alsheating.com/PropaneHeater.htm

http://www.houseneeds.com/shop/HeatingProducts/RoomHeaters/rinnai/rinnaispaceheaterstech.htm#556

Yeah, Started narrowing down things a bit.

WarmlyYours seems to imply that radiant heat on a slab as the only heat source might be not enough in cold climates because of heat loss through the ground.

I may still pursue Electric radiant if my wife really wants it. We'll see.

Looked at electric baseboards quite a bit. If I understand correctly, they usually are 100% on or off, and that's it. Hydrosil brand has some Hydronic electric baseboards that have VARIABLE wattage. Seems like a smart way to go to me if we go electric. Variable wattage just makes more sense for more even heat, no?

I looked at gas space heaters like that. But, our proposed addition will only be connected to the existing home by a hallway. So it's basically 4 outside walls. I worry about having one heat source for a 14X18 room. I guess I see cold spots/areas being an issue. Especially since we're looking at ~25% glass area for windows and having skylights.

Right now, I'm very attracted to these: http://www.cozyheaters.com/pdfs/products/spec_sheets/DirectVentBaseboardHtrs.pdf
Direct vent baseboard GAS heaters. Pricey, but easy to install, and gas is of course cheaper than electric. And we'd only need 2. I need about 12500 BTU from what I've calculated so far. So, 2 9000 BTU (input) units would do it.

Thoughts?

A direct vent gas heater (most have small fans) will circulate enough air to heat a 14 x 18 space.

http://www.rinnai.us/.aspx/1503/5.14fbd6a/Features-Benefits

If you click on the Owners manual link below you will get a description of how it works.

http://www.rinnai.us/Rinnai/FileLib...on/865RHFE556FAIIIFTRAIIIManual52003.pdf.aspx

Bob NH said:

A direct vent gas heater (most have small fans) will circulate enough air to heat a 14 x 18 space.

Click to expand...

Based on what? Not doubting you, just wondering how one figures the largest room that something like that would handle as far as air flow, not heat loss.

I don't see anything in the manual about that.

Is the only difference between RHFE-431WTA-N and the RHFE-431FAIII-N that one has a programmable thermostat and one does not?

Hmm, that heater does look pretty attractive. Isn't huge, doesn't stick out from the wall too much. I like the proportional control it has over heat, too. Price isn't bad either. I see it online for $1225 shipped.