Most economical way to heat a home
rogue8888
| Posted in General Questions on
I have a vacation home that I need to heat in the winter to prevent frozen pipes (we do not winterize because we use the house year round). When we are not there, we lower the temperature to 59 degrees. Obviously, I feel like a lot of money is wasted since we are not there all the time. I was wondering what would be the most economical heating system to put in place? Currently we are using propane. The house is located in the mid Hudson Valley of NY.
Thank in advance for any and all help!
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Energy prices vary substantially around the country. To calculate, find the cost per unit (ie, dollars per gallon or cents per kWh). Find the BTU's per unit. Find the efficiency. Multiply all three together to get the cost per delivered BTU.
Whatever the fuel you should also look into improving your insulation.
An indoor temperature of 59 sounds high to me. I could see going as low as 45F if all you care about is not freezing pipes. If you're worried that parts of the house would get below 32F at that setting, there's another argument for improving you insulation. You could also get a wifi thermostat and put wifi freeze detectors in every room with plumbing, if there is danger of freezing you can turn the thermostat up. Similarly in the spring and fall you can turn the heat off if the outside temperature is cold but above freezing.
IIRC, I think the lowest temperature setting for modern high efficiency (condensing) furnaces is higher than 45 degrees. You risk invalidating your warranty. I can't recall the exact reasons, but the condensing part is key, and I think the figure is close to 55F, not 45F. I found this most aggravating when I learned of this minimum temperature, because I used to set the furnace much lower, just enough to avoid freezing pipes. No longer.
Yeah, I have a wifi thermostat. We have pipes that go into the ceiling and have learned that when the ceiling gets into the 20s (I have a temperatures sensor up there), that the pipes will freeze, so we'll increase the heat. However, the pipes are PEX, which seem to be "resistant" to expansion in the sense that they are more flexible in my experience. Am I correct in this? My pipes in the attic have frozen before and never had the pipes burst.
Unless your electricity is above $.30/kWh, your lowest cost heat will be a decent wall mount mini split heat pump.
Just make sure the unit you select comes with a low temperature heat option (sometimes called freeze protection mode) that will allow it to heat between 45F to 50F.
Most units can also be retrofited with a relay module to take standard thermostat controls. This lets you wire it to your favorite WIFI thermostat and have it run at any setpoint you want.
In lot of cases you can also get most of your water line freeze protection with a hot water recirc setup. This does mean keeping your water heater running.
My gut feeling is that a heat pump has an even greater advantage at lower interior temperatures, as the performance is better with a smaller temperature difference between interior and exterior. I'm trying to think though if there are limits to running it outside of its usual range.
I think the bigger issue is trying to cool bellow the min setpoint of the unit. Heating doesn't create any of the issues with water that cooling would have.
The COP of the unit should be pretty decent. Looking at the table from one of the units changing the heat setpoint from 72F to 60F increases the COP at full load from 2.5 to 3 when it is 20F outside. So going even lower should help further plus the load should be less which in most (not all) cases further increases COP.
PEX is more frost resistant than other plumbing materials, but it can be damaged by freezing.
Is there a way you can get more insulation on the cold side of those pipes? Temperature in the 20's when the thermostat is at 59F is pretty cold.
Cost analysis. Cost to heat at 59 degrees vs repairs from broken pipes.
But, more seriously, how often do you find yourself in this situation? (I don't need to know, but you should figure it.) For completeness you'd have to add up all the time you're heating at this point and figure out what the cost is above whatever you believe you may be able to drop and hold temperatures to. Payback time on any heating change/expense is?
The usual minimum recommended temperature for this kind of thing is 50*F. Going lower is risky. Even at 50*F, you need to make sure that the coldest point with anything senstive isn't getting to cold. That is especially problematic for any pipes in exterior walls, which are always going to be at least a little colder than that indoor ambient temperature.
I agree with Akos that a heat pump is probably going to be your cheapest heat source to operate, especially considering that your gas source is propane and not natural gas.
Bill
There may be a more simple solution then leaving the water on and hoping it’s warm enough not to burst. Do you have access to your main water line shutoff valve? Turn the water off when not there or at least get a plumber to add a shut off valve in area where you are most concerned for a pipe burst. If you shut the water off and drain the lines the pipes can’t burst and if they did it wouldn’t be flooding the whole place while you were gone. Second put insulation around this pipes if you don’t have any. Third would be insulate better or move them away from any cold sections even if you leave your thermostat at 50 when you are not there it isn’t working too hard to maintain the temp to prevent freezing as others have said. Back to original question most economical would be to shut water off IMO. I always use my outside shut off valve and drain my outside hose in the winter because it has highest risk of freezing. Also if you do this don’t count on every day in fall or spring to be above freezing there are those random days. Best to be safe and hold off keeping water lines open when not there to summer.
Just turning off the water and opening valves is not reliable protection against freezing. You need to blow out with compressed air anything with a valve and anything with a trap needs to be filled with propylene glycol antifreeze. This is particularly important with washing machines and dryers. If you are on well water your pump may need to be drained too depending on how it's configured.
Turning off the water and opening the valves is a good insurance if you leave the heat on, if the heat fails it minimized the damage.
Water will tend to accumulate in the low areas of the piping system. A freeze can then cause that water to freeze, expand, and rupture things. In my own experience, those "things" tend to be valve bodies. It's true that a PARTIALLY filled PIPE that freezes isn't usually a problem, but in a real plumbing system, there are always some low spots that will end up COMPLETELY full and that's where you have a problem.
If you want a place to be able to be winterized, you need to carefully plumb everything with the supply lines pitched to a low point just like you'd install drains, then you install a drain valve at that low point. To winterize a system like this, you first shutoff the main, then open the drain valve, then open ALL the other valves (including things like toilet valves), to be sure all the water drains out. I personally do a third step of pressurizing the system with compressed air, then blasting out each valve in turn to make sure there is no water remaining in any of the valve bodies or pipe fittings. When I'm done, I leave the interior pipes pressurized with air as an additional safeguard against water leaking back in past the closed main shutoff valve.
I have a cottage that I winterize every year, and I follow the steps I just mentioned above. It works well, and we don't heat the place at all over the winter.
Bill