heat pump backup options...

[maverick06]

All,
Long story short, I heat mostly with wood, and have a trane XR14 hear pump (2007 install 3 ton, 3.5 ton, i forget, single zone forced hot air). The heat pump works down to 20F and requires a backup fuel option for deicing, and for below 20F.

I do not have natural gas service where i am. I currently am using my old oil burner as the backup heat option. The burner is old (80's?) but only uses a few gallons a year (20 gallons or so).

The oil tank is a 250 gallon tank in the basement from 1950.

So the system is old, and I feel like having an oil tank of that size is a liability, and the system is definitely on its last legs. So i was trying to explore what options there are for backup. Resistance electric heat is an option, but not a cheap one. I could end up just replacing the oil burner when it goes, but thats not a good solution, I still have the tank. I would love an air source heat pump that could be sole source for me in philadelphia, probably needs to run to -15F.

I like the XR14 heat pump. As I use the stove primarily, I dont want a huge investment (geothermal). I would just like to get rid of the oil.

Any thoughts on good options?

 

[maple1]

There are a few.

One would be to investigate having the Trane upgraded to something new and more efficient. I think heat pumps have improved a lot the last 10 years.

Another would be to replace your oil tank with something newer & smaller and have the boiler inspected & serviced. Well, likely the inspection first, as long as you can find someone reliable to do it. Then plan from inspection results. Just wondering what makes you think it is on its last legs? They can last a looong time - and a new tank & burner (if needed) might not be a huge expense if the boiler itself is still solid.

I got rid of all our oil stuff when I redid our heating system almost 6 years ago. It was great to get the oil out of the house along with all the related liablities. Put in an electric boiler for backup - but I would not want to use that for anything more than very infrequent backup, they are the most expensive way to heat I think, fuel cost wise. I think my next step if I couldn't keep the wood boiler going all winter would be to put something oil back in, all new. Or keep what is here & put in some new ductless heat pumps.

What is the propane situation there? That might be a possibility if your oil boiler is really done for or if you just want to be rid of oil?

 

[woodgeek]

You would never size a HP to -15F here. More like 10-15°F maybe, Then just electric strips below that. You'd get a few days a year that might cost a few extra bucks, but that's it.

One question...

Is your system set up as 'dual fuel', where it switches back and forth with an external thermostat....or is the oil called as a second stage that runs together with the HP?

That is, does your HP shut down at 20°F? I keep mine running no matter how cold it gets....I have seen -1°F for like an hour in 17 years. Mine (and most recent vintage HPs) are fine down to these temps, they just don't keep up 100% with demand.

You only need a supplement, not a standalone heat source, below 20°F.

 

[maverick06]

The manual states: (simple google search pulled up the manual if you are curious)
"Low Ambient Cooling As manufactured, this unit has a cooling capability to 55°F. The addition of an evaporator defrost control with TXV permits low ambient cooling to 20° F."

Mine was installed so that at 20F it turns off and relies completely on oil. I expect I could change that in the thermostat, but it appears that it only goes to 20F.

 

[peakbagger]

I am looking at one of these Roth "double walled tanks" to replace my oil tank. (broken link removed to http://www.roth-usa.com/products_dwt.cfmIn) my area there is no Natural Gas pretty much the standard fuel is heating oil. If I ever want to sell the house it had better have a oil furnace. I know of few folks who have had older hearing oils tanks or fuel lines fail and its an incredible hassle as the smell of diesel fuel stick around for years even in areas where the oil never touched. My elderly parents dodged a bullet on a late sixties tank, it started seeping and we had it changed quickly. There were several holes in tank just in handling it.

The Roth tanks are a lot taller so they take up less floor space. I will probably downsize to a 165 gallon unit. (I had two 275 gallons tanks). The newer oil tank is going in my garage for an off road diesel tank. The one PITA is the boiler has to be set up for suction recirc as the oil is pulled up out of the tank.

 

[dleeallen]

I have a 275gal Roth oil tank. Love it. Same height as normal oval tank, just goes to the floor so it ends up shorter in length.


Sent from my iPhone using Tapatalk

 

[DBoon]

Roth makes a great tank. The gauge also makes it easy to know how much oil it has left, and when it says 98% full, I have 270 gallons of oil in a 275 gallon Roth (vertical) tank and I could never seem to get more than 240 gallons in an old steel oval tank before the whistle went off and the oil dealer stopped filling it.

 

[woodgeek]

The manual states: (simple google search pulled up the manual if you are curious)
"Low Ambient Cooling As manufactured, this unit has a cooling capability to 55°F. The addition of an evaporator defrost control with TXV permits low ambient cooling to 20° F."

Mine was installed so that at 20F it turns off and relies completely on oil. I expect I could change that in the thermostat, but it appears that it only goes to 20F.

That part of the manual is referring to cooling mode, not heating mode. I couldn't find anything about a low temp limit for heating in the manual.

Your installer probably just seat of the pants estimated that 20°F is where oil would be cheaper, and set it to switch there.

 

[Brian26]

There are a few.

One would be to investigate having the Trane upgraded to something new and more efficient. I think heat pumps have improved a lot the last 10 years.

Another would be to replace your oil tank with something newer & smaller and have the boiler inspected & serviced. Well, likely the inspection first, as long as you can find someone reliable to do it. Then plan from inspection results. Just wondering what makes you think it is on its last legs? They can last a looong time - and a new tank & burner (if needed) might not be a huge expense if the boiler itself is still solid.

I got rid of all our oil stuff when I redid our heating system almost 6 years ago. It was great to get the oil out of the house along with all the related liablities. Put in an electric boiler for backup - but I would not want to use that for anything more than very infrequent backup, they are the most expensive way to heat I think, fuel cost wise. I think my next step if I couldn't keep the wood boiler going all winter would be to put something oil back in, all new. Or keep what is here & put in some new ductless heat pumps.

What is the propane situation there? That might be a possibility if your oil boiler is really done for or if you just want to be rid of oil?

This is excellent advise. Unless the heat exchanger is cracked or something the actual oil burner assemblies are cheap, reliable and extremely well built. You can buy the most efficient Beckett AFG burner for $350. Its literally 4 bolts and 2 wire connectors to remove and replace.

I am going to look into one of those roths tanks as well. My oil tank is from 1959 but looks to be in good shape. I have read a ton of mixed things online about how long they last. Might just replace it for a peace of mind and researching those roth tanks they look like awesome tanks.

 

[coutufr]

I would not change the heat pump. I would get rid of the oil equipment. Burn with wood and put an extra woodstove if you need it. Put resistance heat for the places in your house where you can not heat with the wood stove.

 

[woodgeek]

The OP could get the manual for his thermostat (or get a new thermostat) that would operate the same equipment as a two-stage system, rather than dual fuel.

It would keep the HP going at all temps (or he could set a low lockout temp like 5°F, his current temp BTW), and then cycle the oil circulator as an assist at low temps (second stage) rather than as the sole heat source at low temp.

Unless the Trane uses a proprietary stat, the EcoBee3 would be a fine choice, and their tech support would be v helpful with the DIY install.

This would allow him to compute how much resistance backup he would need to replace the oil, figuring 30 kWh per gallon of heating oil used.

-------------------------------------

Rereading the post...the 20 gallon/year figure suggests that switching to resistance strips would only use 30*20 = 600 kWh = $75/year in electricity. The strips cost like $50, they would need to be wired to the breaker box with a heavy wire (probably 75A or 100A circuit), but that is all. If the breaker box needs to be upsized that would change the cost calculation....or he could do a sub-panel I suppose.

The 20 gallon figure is low enough that I think the system may currently be set up to stage, rather than switch. Or the OP has a smaller well insulated house with a BIG HP. Is the OP sure the HP shuts down below 20°F?

For the record, this is how I switched my house over. I had the HP installed (as a small upcharge on getting a central AC installed) with the backup strips and wiring, but that breaker switched off. I then had my previous oil boiler called as a second stage (I think my installer set it up as dual fuel switching at 40°F, and I nixed that). Back then my house was super drafty, and called 1100 gallons of oil per year, and the HP dropped that to 400 or so. I then tightened the house up until the oil backup calls get less and less, then had it ripped out and switched on the resistance strips.

 

[begreen]

Our system has similar specs. The HP lockout temp is 25º. It will try for a bit lower than that but has to cycle continuously to defrost then back. Below 25º it will go to resistance coils. We've only used resistance heat a few times in the past 11 yrs.. Most of the time below 45º outside we are heating 24/7 with wood.

 

[woodgeek]

Facing a very cold weekend (for us, averaging 10-12°F for 48 hours), and the prospect of using ~500 kWh of electricity in two days....I fired up my stove.

Low on wood, I found that the Tractor Supply not too far from my home was selling RedStone bricks for $3 per 20lb 6-pack, so I Bolted over there and picked up a bunch.

My goal was to burn most of the weekend at a level sufficient to prevent the strips from coming on, while keeping the house a little warmer than usual.

Mission accomplished.

 

[georgepds]

The split duct heat pumps work down to -15F

" The Extra Low Temperature Heating (XLTH) Series features outdoor condensing units engineered to operate in temperatures down to -15ºF, lower than any other mini-split available today."

http://www.fujitsu-general.com/us/residential/technology/xlth-low-temp-heating.html

I have two non XLTH, I think they work to -5F.. For the past couple of nights the temp is down to ~0F, and my RLS3 (normal) units were still pumping heeat

 

[begreen]

The split duct heat pumps work down to -15F

" The Extra Low Temperature Heating (XLTH) Series features outdoor condensing units engineered to operate in temperatures down to -15ºF, lower than any other mini-split available today."

http://www.fujitsu-general.com/us/residential/technology/xlth-low-temp-heating.html

I have two non XLTH, I think they work to -5F.. For the past couple of nights the temp is down to ~0F, and my RLS3 (normal) units were still pumping heeat

They keep on getting better. I was wondering how much power does that base heater take over say a week of single digit temps? I've read 80 watts for the RLS2. 2KW/day or 60KW/mo for any time the outside temps are below 36F.

 

[georgepds]

They keep on getting better. How much power does that base heater take over say a week of single digit temps?

Well.. in my house, which is a fishbowl ( something like 25 windows), the two heat pumps ( 2 x 12 kbtu/hr) can keep the house at 63 F when it is 0 F outside and the winds are howling.

I light up the WPH wood stove and bring the house to a toasty 75

 

[georgepds]

Opps.. I answered the wrong question.. can't say exactly because I have not lookd, but I can tell you not much. When I looked at the seasonal rantings (SEER and HSPF), it turns out they have and average COP of 4 ( for each kwh of electricity I put in, I get out 4 kwh of heat on average over the winter)


I've got electric meters on both units... The downstairs unit, which has been in use for 4 years , has used ~1800 kwh. The upstairs unit, which has been in use for this season only, has used ~100 kwh on the meter

IIRC, I set the downstairs one to 50 F when I went on vacation last February. It took ~ 1 kwh/day, but I do not recall the HDD for that period. The house is located in NE Ma, and it is cold now.. it's so cold in the wind sometimes you cannot breathe.. that's cold

The useage is so low, I don't even bother looking at the meters any more. My roof solar puts out ~6000 kwh/year, the shed expansion solar puts out ~4000 kwh/year, or a total of 10,000 kwh/year. I'm swimming in grid tied energy. Now I'm sorry I did not buy bigger units to heat the house to higher temperature in the bitter cold. The concern was, the greater the BTU rating, the (slightly) less the efficiency.

 

[begreen]

I don't think the COP numbers take into account the base pan heater deficit. Don't get me wrong, I think the latest generation is great. I just like full accounting.

 

[georgepds]

I don't think there is a base pan heater in the rls3 unit...

They run it as an air conditioner if the outside unit gets too cold

In the very low F unit there is... but the pan heater s included in the calculation.


At the risk of too much detail.. the numbers are good for climate zone 4..Go further north to zone 5 and you deduct 15% from performance

 

[maverick06]

I appreciate the feedback.

I have changed the thermostat to run the heat pump to 10F, (baby steps, it works at 20F, adjusted to go a little lower).

The system definitely runs heatpump to 20F, then switches over to pure oil, no heatpump use. The plus side to this plan is that the thermostat will switch back to oil if the temp drops 3F below setpoint (heatpump cant keep up).

The house isnt large, 1800Ft^2 and is about as tight as i can make it, would like it to be better, but not much more i can do. I still burn about 4 cords a year, so that is why there is so little oil use. I last bought oil in 2006 and still have about 1/8 tank left.

It sounds like there isnt a clean option out there for me. But I appreciate the input. Backup electric isnt a bad idea, but the whole house is on 100 amp service, so a lot of upgrades would be needed there.

I will try to string along the oil burner for a while more i guess.

 

[georgepds]

Can I ask what stove you use. I heat a 1500 ft2 house with an epa stove.. it reduced my wood use from 4 cords down to 2 compared to the old pre epa jotul


Might help with the wood use...

 

[woodgeek]

I appreciate the feedback.

I have changed the thermostat to run the heat pump to 10F, (baby steps, it works at 20F, adjusted to go a little lower).

The system definitely runs heatpump to 20F, then switches over to pure oil, no heatpump use. The plus side to this plan is that the thermostat will switch back to oil if the temp drops 3F below setpoint (heatpump cant keep up).

The house isnt large, 1800Ft^2 and is about as tight as i can make it, would like it to be better, but not much more i can do. I still burn about 4 cords a year, so that is why there is so little oil use. I last bought oil in 2006 and still have about 1/8 tank left.

It sounds like there isnt a clean option out there for me. But I appreciate the input. Backup electric isnt a bad idea, but the whole house is on 100 amp service, so a lot of upgrades would be needed there.

I will try to string along the oil burner for a while more i guess.

OK. Without the oil-boiler, you need to have a backup on the heat-pump, and it needs to be able to carry the whole house in a max cold situation. I still think the cheapest option would be electric strips (since these would use the existing air handler and ductwork). Mine in a slightly bigger house, backing up a 4 ton unit at 15 kW, or 62.5A @ 240V. You could probably be fine with 12kW, or 50A@240V. That's 41,000 BTU/hr...you wouldn't freeze.

RE the 100A service and breaker box....I too had a 100A box and I upgraded to a 200A box (for multiple reasons) and PECO told me that the aerial wire did NOT need to be changed. That is, it was sized big enough already by their default. So I did not have '100A' service..they said 'no such thing'...just a 100A box, and PECO was aok with me upsizing to a 200A, although I did also change the wire to the weatherhead.

One cheap option would be a sub-panel. A 50A continuous load, you would want a 80A subpanel with a single 80A 240V breaker in it, and a 4 gauge wire run to the air handler. You can definitely add a 80A subpanel on a 100A main (it bypasses the panel bus). The sub-panel, breaker and wiring would not be super-expensive. If you need to upgrade the supply to the weatherhead, that would be a bit more.

Odds are your air handler already has the board for controlling strips, and wires to your thermostat that are not hooked up for calling it.

http://www.diychatroom.com/f18/100-amp-subpanel-100-amp-main-panel-336089/

On a per BTU basis, 30 kWh probably cost more than a gallon of oil, but your usage would be low enough you probably wouldn't care. And there would be no 'service call' on the boiler either.