Ideas for backup heat in new construction (small house)

[Alan Gage]

Howdy all,

Getting ready to built a roughly 750 sq. ft. house this spring with full basement. Both basement and main level will be insulated to at least r-20 and probably r-60 in the attic. The basement will just be a work shop now but could be finished off in the future. It should be a very easy house to heat and I plan on heating 100% with wood, which I've been doing already the past few years.

What I need to decide on though is a backup heat source for when I leave for a couple days or more in the winter to keep the pipes from freezing. Either electric or propane are options. I'm hoping I can get by without any duct work and just let the heat from the basement radiate up through the floor to keep the main level above freezing. Sound plausible?

Propane would be more efficient but would require plumbing fresh air and exhaust. For the little use the heater will see I wonder if the better efficiency of propane is worth it?

I'm pretty unfamiliar with what's available out there besides your run of the mill forced air furnaces and electric baseboard heaters. What are some of you using and what would you recommend I look into? I'm in northern Iowa and our winters get pretty cold so a heat pump is out. I'll probably get some sort of air exchanger for the house so something that could take care of that as well without having to run the furnace would be a bonus.

Thanks,

Alan

 

[semipro]

How about some hydronics and an electric or propane water heater. The hyrdronics could either be under the first floor or baseboard type. I think you can even use the same standard water heater for your hot tap water.

Here's an article in Fine Homebuilding and the house sounds somewhat similar to what you're building.

http://tinyurl.com/4aq7oer

 

[Alan Gage]

I'd never considered hydronics before, I don't know anything about them. I started doing some looking around and it would seem I've got some learning to do. Guess I'll just add it to the endless list of things to research. I was hoping to start building in April but with so many things to learn about before starting it might be a couple more years!

I'll try and read the article later. I'm on a slow connection with an old computer now and I can't open it.

Thanks,

Alan

 

[jimbom]

We can leave our house for a week in the coldest winter and it does not get below 40 F. Our basement floor stays about 60 F all year. As the temperature in the basement drops past 60 F, the floor starts radiating heat into the house. Temperature differences of 20 F will radiate approximately 23 BTU/hr-ft^2 into the house from the basement floor. Keep the plumbing out of the exterior walls and you might be good to go without backup. I learned this the hard way in a week long ice storm power outage. That experience caused me to buy our wood stove. ASHRAE design temperature here is 0 F.

Our biggest problem coming home to a cold house in the winter is the long time it takes to get the joint warmed up. Just is not fun at all for a couple of days.

 

[Jeff S]

What an excellent article.I really liked how they tied solar into the system to offset fuel cost.I've checked into these Polaris water heaters before and they are offered in both NG and propane.

 

[btuser]

I second the notion about keepin the plumbing out of the exterior walls. Basboard usually wraps the walls, and is often the first to freeze when the power goes out.

 

[semipro]

I agree also that plumbing shouldn't go in the exterior walls. I don't really like it in any house. Exterior walls are for fenestrations and insulation.


It sounds like a great vacation cabin feature would be if you were able to call the place up and turn on the heat a day before you planned to be there. If you have a phone line I think that's a relatively simple thing to do.

I'd be concerned about how to keep the pipes from freezing if you run out of gas or the electricity goes out.

 

[benjamin]

I'm twenty miles on the other side of the Lansing bridge so I know your area.

In this case, keep it simple. Electricity at $.10/KWH is cheaper than propane at $3 or less depending on the efficiency. Electric baseboards are cheapest. Electric radiant heat would be nice, especially in the bathroom where you want to feel the heat instantly. Geothermal heat pumps are a good option, especially if you want AC or someday want the option of not burning wood.

Unless you want propane for cooking or hot water it's not worth the hassle just for a few weekends a year.

The article was interesting, but how do they justify all of that garbage for a small house? If I was going to live in a "styrofoam cooler" I wouldn't want to spend $10,000+ on HVAC without the AC.

Structural Insulated Panels are nice, but disposable. Insulated Concrete Forms are a waste of insulation and thermal mass.

What kind of house are you building? and what do you want to accomplish? If you design the basement right you will be able to store a lot of heat in the concrete, whether that is wood heat or passive solar, then you can make the upper floor more conventional. The heat will travel up through the floor, better if you have some air circulation and a low heat loss.

Keep the questions coming, feel free to get ahold of me if you want to hear more crazy ideas or see some examples.

 

[begreen]

I would look into the newer super-efficient mini-split heat pumps. That will give you heating and cooling with great efficiency. This will only heat down to about 10-15F, so you will need backup for deep freeze times like you are experiencing today. That can be wood or resistance electric. But it will still cover a good 90% of the heating. On the opposite spectrum, it will really be appreciated when the temps are too mild for wood burning, but still need heat. Daikin, Sanyo, Fujitsu all make good units.

 

[colebrookman]

Check the latest issue of Fine Homebuilding for ideas on back up heating in well insulated homes. We cook with propane and use a direct vent propane heater when the wood stove is out. Make sure to get a pilot light so the stove will work during power outages if you aren't home. Be safe.
Ed

 

[Alan Gage]

A little more info about the house:

Their won't be any concrete in the basement other than the floor as I'll be doing a wood foundation. It's possible I could be doing SIPs instead of standard stick construction as there is a manufacturer only about 15 miles from here. I still need to talk to them though. If I go with stick construction I'll probably be doing wet blown cellulose insulation in the basement (work shop) and main level and loose blown in the attic so it should be sealed up pretty tight. I'll have an Englander 13 wood stove on the main level which will be the main heat source. It should be more than enough to heat me out of the house.

I already have a 500lb. propane tank on the property and will have it piped into the house anyway for hot water and cooking.

The backup heat source in the basement would also be used to warm the basement a little, if needed, when I want to go down there and work. Other than that it will hopefully never be on other than when I leave the place empty for a few days. I'd like to keep it contained in the basement and let the heat radiate up through the floor to keep the main level above freezing.

I've thought about heat pumps but the majority of the usage would come with temperatures below they range they can operate efficiently. Price is higher than I'd like to pay as well. The benefit would be AC in the summer but for now I think I can get by without.

Hot water heat looks interesting and I need to do some more research but I'm wondering if it's not a bit more complication and expense than I want for a backup heat source.

Electric heat would certainly be the easiest and cheapest to install but the most expensive to run. But with the small amount I'll be using them maybe it won't really matter.

A wall mounted direct vent propane unit looks promising as well. Relatively cheap ($1000 or under), would provide plenty of heat if I wanted to keep the basement warmer than normal, and would be cheaper than propane to run. No need to exhaust out the roof, just a single hole through the side of the house.

Thanks again for all the ideas.

Alan

 

[DBoon]

Hi Alan,

I've had a small 10,000 btu Monitor natural gas-fired heater in my finished basement in my condo. It heats the basement level (~300 square feet) and the entire upstairs (~1000 square feet) down to about 10 degrees F outside. There is not a lot of ability to "pick up" from a colder than desired 68 or 70 degree inside temperature, but it does well to supply heat to keep it warm. These run on propane or kerosene as well.

If by "wood" foundation you mean a pressure treated wood foundation, I would strongly urge you not to go this route. These have a forty year life and are a problem waiting to happen. Spend a few more bucks and get a good masonry foundation below grade.

 

[benjamin]

Hot water heat looks interesting and I need to do some more research but I'm wondering if it's not a bit more complication and expense than I want for a backup heat source.


Alan

Bingo! I think hot water radiant floors make sense for a main heat source even for efficient and/or small buildings, but there's no way it makes sense for a backup like you're describing, unless you wanted to use the water heater for the backup...

A water based heat pump won't lose efficiency, the outside temperature doesn't have any effect on the performance, which is based on the inside temperature and the temperature of the water. You can install one yourself for not much more than the options you're talking about, it's no more complicated than any other water system.

I wouldn't worry about the wood foundation, it's not like you're building a nuclear waste vault here. There are enough wood foundations around, anybody here of failures?

 

[Alan Gage]

As I've been researching wood foundations I've come across lots of complaints and failures. It sounds like the majority were poorly planned and executed construction though (improper drainage, poor site choice, or incorrect treatment on the lumber). I was leaning heavily to a wood foundation but wanted to check with our local building center, where I'll be buying all the lumber for the house, first. I half expected them to recommend against but they said they've been very impressed with the ones they've seen done in the area, as longs as they've been done correctly. The only ones they were aware of that had problems were done otherwise.

I'll be building on what amounts to a gravel pit with a very low water table so it should be nearly ideal conditions for a wood foundation. We're also drier than the east coast.

I talked to some people in town that have a 35 year old wood foundation and have had no problems. I know there are some others in the area that are 50 years old now and still going strong.
Alan

 

[begreen]

I've thought about heat pumps but the majority of the usage would come with temperatures below they range they can operate efficiently. Price is higher than I'd like to pay as well. The benefit would be AC in the summer but for now I think I can get by without.

Hot water heat looks interesting and I need to do some more research but I'm wondering if it's not a bit more complication and expense than I want for a backup heat source.

Electric heat would certainly be the easiest and cheapest to install but the most expensive to run. But with the small amount I'll be using them maybe it won't really matter.

Alan

Based on the weather history for the area I would say it is the opposite. There would be some days, like the current cold snap, where supplemental resistance heat would be needed, but for the majority of time the heat pump would handle Iowa weather fine. Des Moines shows an average January temp of 15-30F which can be handled by the units mentioned. During the nasty cold snaps, turn up the baseboard heaters or the wood stove.

The black lines are the average low/highs for Des Moines.

 

[Alan Gage]

They're a bunch of wienies down in Des Moines, that's the deep south. Our weather would be about the same as Minneapolis. While we've been below average temps this month we still haven't had any really cold weather. Usually we have a week or two in January where the lows dip to around -20 and the highs stay below zero.

I still haven't dismissed heat pumps though. My grandfather had one on a new (large) house he built and was very happy with it. He had a bunch of deals worked out with the electric company so it cost him a ridiculously low amount to run. I talked with our provider a bit and it doesn't sound like they offer as good of a deal here, more like they give a discount on the heat pump instead of lower rates.

I've also talked to a couple of the HVAC guys in town and they don't think much of them for our climate, I don't know of very many around.

What I really meant about the heat pump mostly running in too cold of temps was that when I leave for a trip in the winter I try to coincide it with the coldest weather, so a good part of that time it will probably need a backup as well. Since the unit will be installed in the basement having the ability to use it for AC in the summer isn't a big benefit either.

They really look like a slick outfit though and if I didn't have my heart set on providing as much heat as I can with wood it would be a no brainer to install one on the main level.

Alan

 

[Alan Gage]

I just checked our average temps this is what I found:

Dec Avg. (High/Low): 27/9

Jan. Avg. (High/Low): 23/4

Feb. Avg (High/Low): 29/10

Alan

 

[begreen]

You're right, that's quite a bit colder than Des Moines. The heat pump would carry the place during the day. You would need a good unit, but the place is small. Once you have the heat load calcs done you can make a more informed decision. If it can be heated with 12K btus, the Fujitsu is the one I would look at. It's only a single unit setup, but will work ok at 10 degrees. Sorry to say the US units don't come close to that.

 

[benjamin]

Air source and ground/water source heat pumps are very different in operation, even if they're similar technology. It was -20 this morning and -26 a couple of mornings ago, air source heat pumps just don't make much sense here. Begreen lives in a climate that has almost as many heating degree days even though it barely freezes there. A cool mild climate makes an air source heat pump work a lot better (so does cheap hydo power).

If you were willing to DIY, you could put a ground source heat pump in that place for $1,500-2,000 that would heat for a fraction of the price of propane, cool for much less than the highest efficiency central AC and provide some cheap/free hot water.

 

[pyper]

Given your described usage, it sounds like electric baseboard would be a pretty good option, especially if all your plumbing is pretty much in one spot. An electric baseboard heater is really cheap to buy, cheap to install, and needs no maintenance (aside from occasional vacuum). You can get them with a dial thermostat that seems to turn them on at about 50F. True they cost more to run, but if you compare how much it would cost to buy a heat pump and put it in you can buy a lot of electric.

The only thing it won't do is come on if the power is out.

 

[Alan Gage]

I'm house sitting for some people this winter who have had a ground source heat pump for quite a few years now and they've gotten along great with it. It's more than I want to tackle DIY though and more than I want to pay someone else for an install.

I did do some more research on the mini splits and they are looking pretty impressive. Still leaning towards a direct vent wall mounted propane or electric baseboard. Nice thing about the small units like the mini splits or wall mounted propane heaters is they'll still be easy to add after construction if I decide to upgrade in the future.

Alan

 

[woodsmaster]

Just for backup for a house that size I think I'd probably go with a ventless propane wall hung unit probably under $500.00 You could even be toasty when the power is out.

 

[Highbeam]

10 cents a KWH? Very occasional backup heat? Buy a silly 50$ electric wall heater from Lowes and be done with it. It's just not worth it to futz around with anything else.

 

[jebatty]

What I need to decide on though is a backup heat source for when I leave for a couple days or more in the winter to keep the pipes from freezing. Either electric or propane are options. I’m hoping I can get by without any duct work and just let the heat from the basement radiate up through the floor to keep the main level above freezing.

For backup for what you want to heat, as infrequently as your suggest, I 2nd an electric wall heater, 240V, 3000 watt (10,200 btu). Right now, although the house is heated with the wood stove, I have one of these in the basement to maintain 50F temp. Alternative would a portable unit. I have a 3500/5000 watt unit; have used it in the basement of the house, in the shop, and in an old barn when I need temporary heat. 5000 watts is about 17,000 btu, which should be plenty to heat a house your size.

 

[Highbeam]

BG, I was checking out the fujitsu site and their mini heat pumps are only rated to heat down to 45 degrees F. The specs didn't talk about what happens when you have 10-15 degree temps as you suggest.