Oil hot water supplement?

[maple1]

How will you heat the house?

 

[woodgeek]

YES, it makes sense. In your climate your savings might be somewhat less than they look on paper, due (depending on siting details) to either low air supply temp or heat stealing in the winter. If your boiler is throwing a lot of heat into unused space (like a basement furnace room) and the HPWH is there, the the heat stealing is not really a loss. If the HPWH is in a semi-conditioned space like a v cold basement, it will not deliver the rated EF. If the HPWH is located in 100% conditioned space far from the boiler, about half of the delivered HW BTUs in the winter will come from the boiler, and the other half from the elec grid.

If the anode is described as 'powered', then non-replaceable is not an issue at all...its permanent. If not, they presumably put in a thick enough one to last the warranty period, and you are still aok, unless you know your water chem leads to premature HWH failure.

When I researched this a couple years ago, the Rheem products were inferior eff-wise to AOSmith and GE units. Since the GEs get bad reviews, you might still look for the new AOSmith 50 gallon HPWH.

 

[bemental]

How will you heat the house?

Continue to heat the house using the furnace, only utilizing the closed-loop, zoned, hot water base board heating.


I can't yet confirm if the furnace has a tank inside, primarily because I don't know HVAC systems at all, but regardless I would prefer to use it the least amount as possible (and potentially shut 'er down during the summer).

The furnace does have its own thermostat on the side, I believe dictating the boiler's water temperature.

 

[woodgeek]

A fuel burner heating water is a boiler....inside it is prob a multi-section cast iron unit resembling an oldey-style steam radiator with your water on the inside and oil-fired hot air on the outside. The control is a box called an aquastat. The poor HW service means that you likely have a tankless coil....a long coil of copper pipe inside the boiler that heats HW flowing through it. As the boiler cycles on and off, the temp can vary a lot, and delivered water can too. I lived with that for 6 years, and then ditched it. O frabjous day.

 

[bemental]

YES, it makes sense. In your climate your savings might be somewhat less than they look on paper, due (depending on siting details) to either low air supply temp or heat stealing in the winter. If your boiler is throwing a lot of heat into unused space (like a basement furnace room) and the HPWH is there, the the heat stealing is not really a loss. If the HPWH is in a semi-conditioned space like a v cold basement, it will not deliver the rated EF. If the HPWH is located in 100% conditioned space far from the boiler, about half of the delivered HW BTUs in the winter will come from the boiler, and the other half from the elec grid.

If the anode is described as 'powered', then non-replaceable is not an issue at all...its permanent. If not, they presumably put in a thick enough one to last the warranty period, and you are still aok, unless you know your water chem leads to premature HWH failure.

When I researched this a couple years ago, the Rheem products were inferior eff-wise to AOSmith and GE units. Since the GEs get bad reviews, you might still look for the new AOSmith 50 gallon HPWH.

Thanks for the speedy response, I've read similar about the GE's, and a few bad reviews about the Rheems but at this price it may be worth the risk. Again, that warranty... I'll have a look around for some AOSMith's as well.

Regarding location, unconditioned, below ground basement. Temperature around 55-60 year round so it shouldn't be an issue. Will be near the furnace so the best stealing you described isn't too big of a deal, and the dehumidifying will we welcome. Might even help to season the wood we store down there.

 

[bemental]

A fuel burner heating water is a boiler....inside it is prob a multi-section cast iron unit resembling an oldey-style steam radiator with your water on the inside and oil-fired hot air on the outside. The control is a box called an aquastat. The poor HW service means that you likely have a tankless coil....a long coil of copper pipe inside the boiler that heats HW flowing through it. As the boiler cycles on and off, the temp can vary a lot, and delivered water can too. I lived with that for 6 years, and then ditched it. Very happy day.

Described our system correctly. Doesn't look like there's a separate storage tank for additional capacity.

I did find a 'mixer valve' that was set on the colder side (120). I've bumped that up a few degrees to see if it helps - figure we'd rather control the cold water mixing at the taps and not all at once at the furnace, but I'll measure the temperature of the hot water at the faucets to make sure we're still safe.

 

[bemental]

Had a few people come look at them, but no one followed up so off to the dump they went.

Thanks anyway!

 

[woodgeek]

My old system was the same. I hate those valves. They are designed so that if the temp of the HW feeding them gets below the set temperature, they close, making the delivered water 100% cold water. (You might think they would 'pass' 100% of the undertemp HW instead, but they don't). This leads to the famous cold bursts in showers.

So, experiment. Raising the temp on the valve might make the service worse if it closes (more) when the boiler is cycling to its low temp. Conversely, dropping the valve temp might lead it to regulate the variable temp water from the boiler better.

You can also google about aquastats on the interbloobs and maybe get the boiler to run a little hotter for better HW service (at lower eff).

 

[bemental]

YES, it makes sense. In your climate your savings might be somewhat less than they look on paper, due (depending on siting details) to either low air supply temp or heat stealing in the winter. If your boiler is throwing a lot of heat into unused space (like a basement furnace room) and the HPWH is there, the the heat stealing is not really a loss. If the HPWH is in a semi-conditioned space like a v cold basement, it will not deliver the rated EF. If the HPWH is located in 100% conditioned space far from the boiler, about half of the delivered HW BTUs in the winter will come from the boiler, and the other half from the elec grid.

If the anode is described as 'powered', then non-replaceable is not an issue at all...its permanent. If not, they presumably put in a thick enough one to last the warranty period, and you are still aok, unless you know your water chem leads to premature HWH failure.

When I researched this a couple years ago, the Rheem products were inferior eff-wise to AOSmith and GE units. Since the GEs get bad reviews, you might still look for the new AOSmith 50 gallon HPWH.

After reading your comment, I dug back into the research and found this thread (https://www.hearth.com/talk/threads/my-geospring.128122/) - seems that a lot of the poor reviews are from earlier models of the GeoSpring when manufacturing was outsourced overseas.

The Rheem I was looking into only has a 1-year labor warranty, something I was ignorant about until further investigation. Now that I know that Lowes offers a $100, 9-year extension for the labor warranty making the GeoSpring 10yr/10yr parts and labor, that the GeoSpring's anode is replaceable, and Lowes is currently offering it for $200 less than the Rheem ($799 versus $999 before rebates and discounts), it seems like a no brainer.

 

[woodgeek]

Sure. But there are also bad reviews for the new unit, FWIW.

I think the essential point is that versus oil you might make back the price of the unit in a couple years. In 3-4 years you'll be ahead of the cost of a conventional cheap elec HWH. I would def do the ext warranty on parts and labor, just to sleep well at night.

Nest step: research for rebates from your local utility co. I got $300 from mine.

Also, are you sure your boiler can sit all summer without leaking, most can, but some older units drip a bit when they go cold.

 

[bemental]

Sure. But there are also bad reviews for the new unit, FWIW.

I think the essential point is that versus oil you might make back the price of the unit in a couple years. In 3-4 years you'll be ahead of the cost of a conventional cheap elec HWH. I would def do the ext warranty on parts and labor, just to sleep well at night.

Nest step: research for rebates from your local utility co. I got $300 from mine.

Also, are you sure your boiler can sit all summer without leaking, most can, but some older units drip a bit when they go cold.

$300 state rebate, 10% military discount. Agree on break even calculations, especially in heat pump only mode. We don't have natural gas or propane in the home as of yet so an electric model makes the most fiscal sense to purchase for now.

Regarding the boiler, not at all. It's a conversation I'm going to have with the plumbers who are coming to do an estimate in a few days.

If it's unable to sit cold, then a straight bypass of the boiler might not be feasible. Will instead have to discuss placing the HWHP inline as the primary, with the boiler as backup (if this is even possible). Means the boiler will be maintaining temp. all summer long, but from what I understand we'd be able to turn the temperature down to lower the inefficiencies(?).

 

[woodgeek]

Dropping the oil boiler water temp too far can lead to condensation (water vapor is a product of combustion), and that leads to sooting up of the heat exchanger and premature failure of the boiler. The boiler is likely happier sitting cold (i.e. off) than trying to maintain a low water temp with lots of low temp burns. Most are simply not designed for that.

The bad news...your oil boiler running standby at a reasonable temp in the summer will likely cost 80% as much as using it for hot water. That is, in the summer maybe 20% of oil BTUs go to heating water...the rest is just waste heat dumped up the flue and into your house. In my case I used 300 gallons of oil during the summer, and my hot water BTUs would have been maybe 50 gallons of oil equivalent.

Most boilers can sit cold, unless they are really on their last legs. To avoid rust, if the basement is damp in the summer you can run a dehumidifier or put a (incandescent) light bulb under it.

Personally, once you confirm the boiler can sit cold in the summer, I would just retire the tankless coil completely and pipe in the HPWH rather than plumb a complex primary/secondary/bypassable system.

 

[bemental]

Dropping the oil boiler water temp too far can lead to condensation (water vapor is a product of combustion), and that leads to sooting up of the heat exchanger and premature failure of the boiler. The boiler is likely happier sitting cold (i.e. off) than trying to maintain a low water temp with lots of low temp burns. Most are simply not designed for that.

The bad news...your oil boiler running standby at a reasonable temp in the summer will likely cost 80% as much as using it for hot water. That is, in the summer maybe 20% of oil BTUs go to heating water...the rest is just waste heat dumped up the flue and into your house. In my case I used 300 gallons of oil during the summer, and my hot water BTUs would have been maybe 50 gallons of oil equivalent.

Most boilers can sit cold, unless they are really on their last legs. To avoid rust, if the basement is damp in the summer you can run a dehumidifier or put a (incandescent) light bulb under it.

Personally, once you confirm the boiler can sit cold in the summer, I would just retire the tankless coil completely and pipe in the HPWH rather than plumb a complex primary/secondary/bypassable system.

Thanks for repeating yourself for my benefit, I've read you elsewhere saying that many a time and it's sound advice.

For now I believe we'll proceed as planned, just as you suggested and the conclusion I previously came to, by 'retiring' the tankless coil. Once the warmer months come along the experimentation will come with going cold and checking for leaks, maintenance, etc.


Thanks for the great advice and insight.