So , I've been thinking and designing this project for a few years. Getting closer (spring 2013?)... This is a carriage house, with 2 floors of living space above a 2 car garage (a bit odd, I know). About 484 ft2 on each floor = 968 total ft2 heated. Heat load for coldest temp should be around 12kbtu to 15k. I think radiant off a water heater is too expensive. I was considering maybe 2 direct-vent space heaters and electric baseboard in perimeter rooms (to meet code). Now wondering about direct-vent fireplaces (or at least one) instead for character. Seems like they should be better than a forced-air system after vent losses etc are factored in(?) Also wondering about mini-splits....? But they're kind of expensive. But you get A/C..... Any thoughts appreciated! -michael in Wisconsin

Nat gas and heat pumps have the lowest operating costs.

right now, minisplits like the Mitsubishi Hyper Heat are good to -13. Two would do your house; you could buy them both online for 3-4K, so buying from a local company will be more, but still reasonable, and they can service them. you would need some type of backup for colder temps. This is assuming a very well insulated, tight house, but it would need to be calculated by the heatng company. The cold garage will increase your heat loss as well. If your heat loss or temp range is incompatible with minisplits, I'd suggest a direct vent propane heater as the easiest & probably best option. My brother in Fairbanks heats a 1400 sf two story home on piers very comfortably with one unit in the kitchen, and the whole house stays the same temp.

Thanks, gentlemen.

My "up-front" cost needs to be around $2500 or less. I can do some of the work, if I can get away with it. So I don't think a mini-split will cut it. I think the payback might be too long(?)

What do you think about a direct-vent fireplace (or two)? I would think their efficiency (around 80%) would be close to a small 2-stage gas furnace, after duct losses etc...??

Thanks again.
and happy holidays

Pellet stove?

I haven't had a chance to look into pellet stoves. I imagine code would not consider it a main heat source(?) What are the economics? I suppose no way to know the future cost of pellets etc..

Thanks.
-m

I guess my question right now is....how does the efficiency of a 80% direct-vent gas heater, with electric baseboard in perimeter rooms (which hopefully won't be used much, if at all if the house is tight enough) compare to the typical 96% 2-stage forced air gas furnace after duct losses etc..???

Thank-you!
-m

It's hard to beat gas at $0.26/therm.

My choice for comfort would be a two-head ductless minisplit ($1700-$2300) so you could have A/C in the Summer, combined with some mat-type resistance heating ($400-$500) so as to have toasty toes under tile in the bathroom, but the utility costs would be more, particularly if gas pricing continues to behave.

How many sun days do you get? How well designed and insulated are you interested in building. Check out thermal mass building practices. http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/conclusion.html

Posted By 950ft2 on 24 Dec 2012 08:58 PM
Thanks, gentlemen.

My "up-front" cost needs to be around $2500 or less. I can do some of the work, if I can get away with it. So I don't think a mini-split will cut it. I think the payback might be too long(?)

What do you think about a direct-vent fireplace (or two)? I would think their efficiency (around 80%) would be close to a small 2-stage gas furnace, after duct losses etc...??

Thanks again.
and happy holidays

A  typical 3/4 ton minisplit puts out about 12,000 BTU/hr down to +5F, and can deliver more at higher temps.  A 1-ton would put out about 16000BTU/hr.  The internet pricing on pretty-good 3/4 ton units (HSPF>10) are ~$1500-$1600,  1-tons run only $100 more. Most of the installation is a non-rocket-science DIY project, even if you paid to have a qualified tech do load the refrigerant and do the final commissioning & test, it won't be more than $2500 with a bit of sweat-equity.  (Pros would typically hit you for $3500-4000 for a turn-key installation for these.)

For low-load gas-fired heating, use a ~$1600 condensing tank type gas HW heater designed pre-ported for hydronic heating (eg. AO Smith Vertex) and enough baseboard (80-100') to deliver the full heat with 110F average water temp. That too can come in close to $2500 for the hardware if you really scrounge (or if you can get subsidy for the HW heater), but it may run as high as $3500 with an isolating heat exchanger.

Rinnai makes some pretty nice low-output modulating wall furnaces, in the $1200-1300 price range, (with no system-design required!), that would be more comfortable than a most direct-vent fireplaces, at similar or better efficiency.

Hi guys..

Thanks for the input. If I can get away with installing a mini-split, that may be the best idea. I've installed furnaces and water heaters etc, so it should be easy. Then just have it charged by a pro...

But I also like the idea of a fireplace, as I'm trying to put some character in this design (rustic arts and crafts style).

I also need to consider all incentives/rebates available.

Thanks again!
-m

Posted By 950ft2 on 29 Dec 2012 10:32 AM
Thanks for the input. If I can get away with installing a mini-split, that may be the best idea. I've installed furnaces and water heaters etc, so it should be easy. Then just have it charged by a pro...

Many if not most of the mini-split heat pumps currently available come pre-charged with R410A for the recommended line set length (typically 15' or 25').  Some line sets come pre-charged as well with internal valves to keep the charge in and air out during the connection process.  If not, then the lines will need to be evacuated after connection to the unit and prior to opening the service valves.

The pre-charged linesets have been known to leak, and a DIYer isn't likely to be able to detect the issue if it "works mostly", but it does affect overall efficiency & capacity if it's off by very much. The manufacturers have gone out of their way to idiot-proof simple installations, but there are still some very creative idiots out there! :-)

But a reasonably competent DIYer(who has read up on it) using pre-charged linesets would probably get it right the vast majority of the time.

If you have naturally gas and need DHW, a combi-water heater is the answer. Electric baseboard is almost always the cheapest heat to install and the most expensive to operate. If you must have heat and AC the mini-split is hard to beat until it gets below zero.