heat pump electric water heater vs ergomax

[munkyboi]

hi all,

i bought my house (1800 sf single level ranch with 400 sf walkout basement, built in the 60's) last december and i don't have any prior experience with oil boiler. i have a weil mcclain ultra oil boiler with a beckett burner and an ergomax indirect water heater.

in the past 80 days, the heat was never on so the boiler was only used to heat my water. i just had my oil tank filled up and it used 118 gallon of oil in the past 80 days. so that's roughly 1.47 gallon of oil used just to heat the water every day. we have only 2 people in the house and we don't use hot water for the dishwasher or laundry, so we are talking about 2 showers a day. that's very high, isn't it?

the aquastat on the ergomax is set at 170F and the boiler temperature gauge shows 180F.

do you think the reason for the high oil consumption is due to short cycling too frequently?

do i turn down the ergomax aquastat setting to reduce the short cycling frequency or do i turn down both the ergomax aquastat setting and the boiler thermostat setting? i don't see any thermostat dial outside the boiler but i do see a honeywell metal box attached to the right side of the boiler, do you think the thermostat dial is inside the box? also, i read that there are 3 settings: high, low and diff and i have no idea how to set them properly.

while researching this issue, i came across the heat pump electric heater and its benefit. do you think that even if i have the ergomax/boiler setting properly, would a heat pump electric water heater (e.g. GE geospring) still give me significant saving? i pay $0.17 per kw/h and $3.449 per gallon of oil

i am thinking of getting a wood stove insert or a wood stove and my plan is to completely get off of using oil.

i know there are a lot of questions, i really appreciate your input and advice.

thanks,
m

 

[DBoon]

There are a lot of posts about how inefficient oil boiler water heaters are, especially in the non-heating season. For most, a heat pump water heater, if you had a good place to locate it, is a very effective alternative that will save you hundreds of dollars a year compared to oil. Again, there are a lot of posts on here about that. So search around, read up, and come back with more questions.

 

[woodgeek]

Been there. 1960 house. Oil boiler.

The thing is, the BTUs you need to heat hot water are prob less than 20% of what you are using in oil. That is, 80% of the BTUs are being wasted right now, up the flue and heating your house in the summertime. In comparison, a HP water heater will run about 240% efficiency (EF*100).

The 1.5 gal/day is about typical for existing oil systems, that were all engineered back when oil costs <$1/gal. The parasitic heat losses are huge.

When mine was that high, I found I had a thermosiphon....the check valve was broken and hot water was moving on its own through my radiators, heating my house a little all summer long. I found that closing a manual zone valve in the spring, and turning it back on in the winter droppied my summer usage from 1.5 gal/d to 1.1 gal/day, and dropped my AC bill 30%. Easy to diagnose....are ANY of your radiators warm to the touch when the heat has been off for a long time???

My HPWH costs me $250 a year for electricity (family of 4 with 2 teen girls), and saves me >$100/yr on a dehumidifier and >$100 on my AC.

My oil boiler was costing me ~$1000/yr even when I didn't use it for space heating.

 

[STIHLY DAN]

My oil hot water was a gallon a day for $1,200 a year. The hpwh comes out to free hot water for the year. That's with 3 teens and washing clothes and dish's. Huge savings.

 

[munkyboi]

Been there. 1960 house. Oil boiler.

The thing is, the BTUs you need to heat hot water are prob less than 20% of what you are using in oil. That is, 80% of the BTUs are being wasted right now, up the flue and heating your house in the summertime. In comparison, a HP water heater will run about 240% efficiency (EF*100).

The 1.5 gal/day is about typical for existing oil systems, that were all engineered back when oil costs <$1/gal. The parasitic heat losses are huge.

When mine was that high, I found I had a thermosiphon....the check valve was broken and hot water was moving on its own through my radiators, heating my house a little all summer long. I found that closing a manual zone valve in the spring, and turning it back on in the winter droppied my summer usage from 1.5 gal/d to 1.1 gal/day, and dropped my AC bill 30%. Easy to diagnose....are ANY of your radiators warm to the touch when the heat has been off for a long time???

My HPWH costs me $250 a year for electricity (family of 4 with 2 teen girls), and saves me >$100/yr on a dehumidifier and >$100 on my AC.

My oil boiler was costing me ~$1000/yr even when I didn't use it for space heating.

i did suspect "thermosiphon" and put my hand to the radiators in various vent and they are not warm. but i do notice the boiler cycling quite often, so i started researching on how to adjust the aquastat on both the indirect HW and the boiler and that turned out to be a lot more complicated than i expected. (hi lo diff on the boiler with reference to the setting on the ergomax) so i still haven't made any adjustment to them yet. but while i was reading up the issue, i came across the HPWH and that opened up my eyes and from what i gather, it's pretty much a no brainer to switch to HPWH from oil. thanks for your inputs. i really appreciate it.

 

[munkyboi]

My oil hot water was a gallon a day for $1,200 a year. The hpwh comes out to free hot water for the year. That's with 3 teens and washing clothes and dish's. Huge savings.

time to call for a quote on installing one. thanks.

 

[woodgeek]

I spent a little time messing around with my aquastat...figure out that it was broken and running to the high limit when it wasn't supposed to, etc. Replaced it myself with a Fleabay unit, and still had 0.9 gal/day standby usage. I put a run timer on it, the works. In the end I beat down the usage a bit, but the unit started sooting up a LOT more, and became less efficient and started blowing CO before I finally scrapped it.

I now consider that all a big waste of time/effort.

 

[munkyboi]

my understanding is that if the boiler is operating more frequently during winter season to provide heat for the house, you are basically getting "free" hot water from the ergomax, is it true?

if that's the case, would it make more sense to install a traditional resistance electric water heater just for DHW during summer and switch back to oil during winter? the reason i bring up traditional electric water heater is that if i am going to only use it for the summer months, a HPWH would take longer to pay for itself.

also, i have 4 zone hydronic heating and during winter we don't use 1 zone, is it worth the trouble to shut off the zone valve, disconnect the thermostat and purge/drain the water of that particular zone to avoid frozen pipe during winter? or it is advisable to just keep the thermostat setting as low as possible?

 

[woodgeek]

True. Standby losses from the boiler are heating your house in the winter time (and your probably uninsulated basement). I did not have an indirect tank like you, but rather a sucky tankless coil, so I had low flow rate DHW that helped me ditch the system.

Since the costs are summer standby (both oil and AC), you need to verify that your boiler can go cold all summer. Most newer systems are ok, some older one might leak if left cold. Some folks put a light bulb under it if the basement is damp to prevent rust. YMMV.

As for the elec conv versus HPWH, the GE geospring costs <$1k MSRP, and there are numerous rebates from utilities/states/etc that can get the price down to close to a conv tank. Google is your friend. State with your util co and state websites. The big box stores might also have specials for things like black friday.

If you get a conv tank, it would be slightly more expensive to run in the winter, so the cheapest thing is to keep the ergomax and switch it over seasonally. More complex plumbing arrangement and two tanks.

If you get the HPWH, it would cost somewhat less even in the winter than the oil boiler (hard to say exactly without house details). It would lower the temp of your basement, but in that way it would harvest standby heat from the boiler that would otherwise get sucked into the earth. So in that case you could simply ditch the ergomax and just have one tank taking up space and requiring periodic maintenance.

Both systems will save you mucho $$ relative to oil DHW, but the HPWH will save maybe $150-200/yr more relative to the conventional, and make up the diff in up front cost in a couple years.

Be advised: online reviews of the geospring are horrible. We don't know why. Lots of folks here have had good luck with them. Get the extended parts and labor warranty.

 

[maple1]

You would no doubt save some oil by learning how your aquastats work, and how to adjust them. They shouldn't be that complicated, on a single boiler system. 180 is awful hot to keep a boiler in the off-season, and is increasing your standby losses a lot. And 170 is awful hot to keep a hot water heater, period - if I'm understanding that part right. When I had my tankless coil oil/wood boiler, I set it back to maintain a boiler temp between 140 & 150 for the summer. I still burned around 3/4 gallon a day though - but an indirect should be better than a tankless coil. How old is the boiler? With an indirect tank, the most efficient way to run the boiler is cold start - but that boiler might not be capable of that. Failing that, you should be able to drop your summer boiler temp a lot - like to 150. And back off your indirect temp, to like 130-140.

Adjusting an aquastat doesn't cost anything. Have you taken the cover off it and checked it out? (The Honeywell thing).

You'll still save more money going to electric for hot water - but how much depends on if the boiler can stand being shut off altogether for the summer. Some start dripping when they go cold - mostly around valves & fittings (in my case anyway). And something else to consider, is dehumidification - if any is used now, or would be a benefit, HPWHs also dehumidify some as they heat the water.

 

[Circus]

Anything would cost less to run than what you have. Using a 180 boiler, with constant heat loss up the chimney to heat 120 water, is mostly standby loss. You said you don't use much hot water. If that's true, even an old fashion $300 electric resistance water heater will work fine. They have almost no standby loss. Then you can shut down that energy hog (boiler) when it's warm out.