Options for increasing hot water

[Thirteen]

We are a family of 9. I have a Pensotti wall hanging propane boiler with two radiant heat loops and one approx. 40 gallon indirect water heater tank.

We could use more hot water. I actually have another brand new tank. I am not sure if I can add the second tank in series or parallel as I am not sure how to ensure each one is heated to 120F and not go too hot either.

I was also thinking of adding a third heat loop for the second indirect tank. One advantage to this idea is I have two separate water supply systems and the whole house is home run plumbed with valves. Which means I can chose the water source for each fixture in the house with just a swap of valves. An advantage to this is if two people are showering with the dishwasher running and one washing machine (we have two) running, I could split it so each tank handle a half of the load. We do get a pressure drop to each fixture when a lot is running.

I don’t need information about whether this is illegal. The bottom line is where I live the public water shuts off about once per month because it is unreliable so I have a well I switch everything over to. I have a manifold for each fixture to run off either source and master valves to swap the whole thing over to either slice at any time. We run the well typically to faucets and city water to showers, toilets, and hot water. If the city would provide reliable water I wouldn’t need to do it this way, but they don’t. Any argument my two water sources is illegal falls on my deaf ears because the city fails to provide a reliable flow of water so I do whatever I want. I am not sure why it is unreliable, but I am about the 10th from last home at the end of the system. Why don’t I just run the well for everything? It is 55 ft deep and does not supply enough volume. I wish it would because it is crystal clear drinking water without a filter on it. I thought about drilling the well deeper, but we risk turning a crystal clear water supply into a regretted mineral filled supply.

I could just buy an 80 gallon indirect tank. But, if I can do this with the tank I already have, it will save money. I can’t figure out if I can add a second tank in line with the one I have in series or parallel. Any reason to avoid just adding another heat loop and doing it that way? A new electronic control to go from two loops to three is not very expensive.

Another option would be to buy another boiler and hook it up. I could put heat loops separate if I want. I could have two separate indirect water systems. This wouldn’t save me any money, but I would have plenty of water and would not have to worry about hot water priority over heat loops in January. Not that I have noticed a priority issue now. I could also plumb them so if one fails I would have the other for everything until the failed unit is repaired.

If I had a second boiler I could also add a heat exchanger to my hot tub. Electricity costs more than propane in Maine. I can’t imagine my current boiler could handle all the load of a hot tub heat exchanger.

Any thoughts?

 

[WorthFlorida]

Look into a point of use water heaters such as under the kitchen cabinet for the sink & dishwasher, another for the washing machine, etc. Essentially taking the load off the main boiler. These point of use heaters are electric so it can make an easy install just by running 120v or 240v circuits if you have a crawl space or basement. Chronomite has many choices for just about every need. Adding more tanks just increases standby loses though new tanks are very well insulated. Point of use tankless uses no power when the water is not in use. Say for the hot tub, you be heating a lot of water to be ready when you fill the tub but how often? Using electric to heat water for domestic use is not as expensive as some may think. I've had electric for 30 years in Florida but the rates are low compared to NY or MASS. There are propane fuel tankless heaters that may fit the need. Someday you'll not have 9 people in the home and you'll have a lot of capacity not needed anymore. Just something to consider when deciding.

https://www.chronomite.com/home

 

[Sponsor]

 

[Jadnashua]

A few things to look into.

First, make sure that your indirect is setup as a priority zone. If it's done that way, the entire boiler's output will go to the indirect when needed, rather than sharing the boiler's output with the heating zones. Also, the boiler should fire hotter when the indirect is calling for heat than it might for space heating if it is setup properly.

If the tank you have is capable of higher storage temperature, going up to the max and installing a tempering valve on the outlet will make the indirect 'look' like a larger tank. The unit I have says to not exceed 140F, but some can handle as much as 180. It's not a safety issue as long as the tempering valve is functioning properly, as you'd set that to 120F out, regardless of the inlet temperature. The higher the storage temperature, the more cold gets mixed in out of the tempering valve, giving you more 120-degree water.

FWIW, where I live, a tempering valve is required on the outlet of a WH, regardless of what your storage temperature setting is.

You should probably have a check valve on your water system to prevent the possibility of pushing water into the mains feeding your place. If that's the case, you also would need an expansion tank (unless your pressure tank is in the loop after you've switched from well water back to the utility's source), in order to prevent the pressure from spiking after heating water in the indirect.

 

[Dana]

In Maine (and in most places) heat pump water heater would be a better solution than an secondary or bigger indirect on a propane fired heating system. Propane is cheaper than resistance electricity, but it's not cheaper than heat leveraged by a heat pump. The typical heat pump water heater these days gets about 2/3 of it's heat from the room air, so during the heating season 2/3 of the heat will be essentially drawn from the propane boiler by slightly increasing the heat load in the room, but during the shoulder seasons and summer a large fraction of the heat is would be the "heat of vaporization" of the humidity being removed from the air, taking the load off any dehumidifers or air conditioning you might be using.

Most of the year (even in cool climate Maine) would be far cheaper than propane-fired water heating.

But if you already have another 4o gallon indirect, or even a plain old electric tank, plumbing them in series with the original indirect first in line on the flow path would give you the additional volume you're seeking. The down-stream tank would almost never call for heat. Standby losses of an electric tank are miniscule- it would use almost no electricity, since the indirect is feeding it 140F or hotter water, and would only be drawing power if the indirect has also been depleted, or during very long standby periods (measured in days, not hours.) It may use a bit of power right after a hot-tub fill, but well under half the amount that a standalone plain old electric tank would, maybe less than an eighth, since the water it's taking in will nearly always be above 100F (even at the end of a soaker tub fill) , not 40F.

The BTU/hr losses of even a huge hot tub with an insulated cover are quite modest relative to a space heating boiler, unless it's outdoors and you never put the cover on it. You get to control the rate of heat going into the hot tub heat exchanger by the pumping flow rates, but even when it's -25F outside during a Polar Vortex disturbance cold snap it probably doesn't take more than 5000 BTU/hr to keep it at 105F, assuming there is an insulated cover. If it currently has an electric heater, what is the wattage of that heater?

What its the max heat rate of the Pensotti (in either BTU/hr or watts)? What is the design heat load of your house (you can estimate that based on fuel use with these methods.) Almost all hydronic boilers installed in the US are more than 2x oversized for the design load, with plenty of extra capacity for managing a hot tub's standby losses.​

 

[Fitter30]

With 9 people dishwasher and clothes washer must never shut off. With the well water could pump it in a storage tank to 80-100 gallon control well pump by level control then a pump to feed the house, bladder tank and two condensing water heaters that talked to each other. That way water heaters would give you 10-12 gpm and your heating boiler will be just for heat. Here is a hot to cold water calculator just change setting to gpm and temperature. Mixture of the two in % and gallons

https://www.spiraxsarco.com/resources-and-design-tools/calculators/water-mixing/water-mixing

 

[Thirteen]

Thank you all for suggestions. First, I wil say that eletricity will always be my last choice. I live in Maine. The electrical supply grid in Maine is both archaic/unrealiable and expensive. We lose power at my house a lot. I do have a 22kw generator and have 40 gallons of water on propane so it probably doesn't matter with a power loss, but it is expensive and keeps going up. In Maine we pay per kwh for electricity, but they also charge a delivery fee. For us, call it $.15 per kwh. Based on stupid politics it is very likely to continue to climb in price.

I did not know that heat pump water pumps existed. I looked them up and am intrigued. I will discuss them with my plumber. I have not pulled the trigger on a heat pump in Maine because the cost of electricity is high and everyone I know with one regrets the decision. Perhaps it is just a Maine thing and out harsh conditions. I continue to look into heat pumps, but I have not found a success story in Maine yet.

I have a Pensotti PCH 34/B - 116,000 BYU/h Input and the domestic hot water is the priority zone. My house is: 1,200 sq ft first floor, 1,200 sq ft second floor, and 500 sq ft third floor. It is full spray foam insulation from the top of the foundation to the peak of the roof. We have 2 heat loops for the third floor, but didn't hook them up yet. This past winter was the most mild in a very long time so we are still not sure if we need to put any heat in the third floor versus what just rises up there.

The house is efficient for heat. My propane bill for heat, hot water, gas grill outside that gets used every day, and 10 gallons of maple syrup boiled daily comes out to an average of 1,100 gallons per year. We have a four year history of propane usage. I generally pay $1.80 per gallon, but just filled up at $1.30 during the apocalypse.

I could increase the temperature on the water in the tank and add a mixing valve. That is a good idea. I could also do something similar, but add the second tank. We are changing the well tank from the tiny one to 80-100 gallons this year. That won't solve the water supply issue in the summer, we will still need to use the city water.

I have been reviewing these suggestions in what I find on the internet while wating for my plumber. It will still be a while with the apocalypse and I acknowledge my situation is not a priority for his time.

Again, to make it clear, my plumber will do things to code, then I will change them to anything he suggests after he leaves. There is no government inspection of the work where I live.

 

[Dana]

Thank you all for suggestions. First, I wil say that eletricity will always be my last choice. I live in Maine. The electrical supply grid in Maine is both archaic/unrealiable and expensive. We lose power at my house a lot. I do have a 22kw generator and have 40 gallons of water on propane so it probably doesn't matter with a power loss, but it is expensive and keeps going up. In Maine we pay per kwh for electricity, but they also charge a delivery fee. For us, call it $.15 per kwh. Based on stupid politics it is very likely to continue to climb in price.

I did not know that heat pump water pumps existed. I looked them up and am intrigued. I will discuss them with my plumber. I have not pulled the trigger on a heat pump in Maine because the cost of electricity is high and everyone I know with one regrets the decision. Perhaps it is just a Maine thing and out harsh conditions. I continue to look into heat pumps, but I have not found a success story in Maine yet.

My(fully delivered all-in) electricity is north of 20 cents/kwh, and it's still quite a bit cheaper to run a heat pump water heater than an indirect running off a propane fired boiler, comparable to a condensing gas water heater in terms of operating cost.

When the power is out a propane boiler + indirect isn't going to be making hot water any better than an electric solution.

Don't even get me started about the stupidity of ME politics... (Not that it's more than a standard deviation out of politics in other states, at least most of the time.)

Cold climate space-heating heat pumps using vapor injection scroll compressors and R410A refrigerant (the current standard for central AC systems) have been around for more than a decade now, and getting better year on year. While the COP might only be 1.5-2 when it's all the way -20F outside, they do work. In most of ME the seasonal average COP would be about 3 (about 10,000 BTU per kwh). A 95% condensing propane boiler delivers about 87,000 BTU/gallon, and uses some electricity. At 10,000 BTU/kwh that would take less than 9 kwh to deliver the same amount of heat, which at 15 cents/kwh would be equivalent to buck-thirtyfive/gallon propane, (roughly the cheapest price you've probabaly seen in over a decade.)

Check out this marketing-fluff real-world demonstration video from one lower-cost vendor. There are many competitors, with both ductless & ductless cold climate heat pumps. Even a single decent sized ductless cold climate mini-split covering one large zone would likely pay for itself on propane savings well before the warranty is up, at the recent 10 year average price of propane in ME.

The Northeast Energy Efficiency Partnerships maintains a searchable list of heat pumps suitable for use in most of New England to compare apples-to-apples capacity and efficiency at a few select temperatures (the coolest being +5F), but the manufacturers' full specs would have extended temperature capacity tables that extend to something closer to your 99% outside design temperature if needed.

There are heat pump water heaters using CO2 as the refrigerant that take the heat from the outdoor air, but they're pricey (about 4 grand just for the hardware), and need to be freeze protected in colder climates. Most standalone heat pump water heaters use R410A compressors on top of the tank, with a coil to take heat and humidity from the room air. The big box stores seem to carry the Rheem "Performance Platinum" series, which is pretty good.

Note- most heat pump water heaters also run an average COP greater than 3, so during the shoulder seasons it will be as cheap or cheaper as heating hot water at near record low COVID crisis propane pricing.

I have a Pensotti PCH 34/B - 116,000 BYU/h Input and the domestic hot water is the priority zone. My house is: 1,200 sq ft first floor, 1,200 sq ft second floor, and 500 sq ft third floor. It is full spray foam insulation from the top of the foundation to the peak of the roof. We have 2 heat loops for the third floor, but didn't hook them up yet. This past winter was the most mild in a very long time so we are still not sure if we need to put any heat in the third floor versus what just rises up there.

The house is efficient for heat. My propane bill for heat, hot water, gas grill outside that gets used every day, and 10 gallons of maple syrup boiled daily comes out to an average of 1,100 gallons per year. We have a four year history of propane usage. I generally pay $1.80 per gallon, but just filled up at $1.30 during the apocalypse.

Assuming you have about 8500 heating degree-days/year (the colder part of US climate zone 6- not coastal Maine) that's 1100/8500= 0.13 gallons per heating degree-day which at a net 87000 BTU/gallon is 11,310 BTU/ degree-day. In a 24 hour day that's (11,310/24=) 471 per degree hour, which means for every degree drop in outdoor temp below the presumptive 65 F heating/cooling balance point the heat loss is 471 BTU/F-hr larger. Assuming a 99% outside design temp of -15F (comparable to Presque Isle's design temp) it would be (65F - -15F=) 80F heating degrees, for a design heat load of about 471 BTU/F-hr x 80F= 37,680 BTU/hr.

That is barely more than the minimum output of your boiler, according to the table 2.1 Technical data on page 10 of the manual. At max fire it can deliver 114,000 BTU/hr so you have about 76,000 BTU/hr of "extra" capacity for doing things like heating domestic hot water and hot tubs. Your radiation probably doesn't deliver anywhere near the full 114K output of that boiler, and the heat exchanger in the indirect may not be able to transfer heat that fast either. It's clearly oversized for the design heat load (by about 3x), since a fraction of that fuel use went to things other than space heating. There is no way are you going to run out of boiler capacity for other uses, even if you're heating a duplicate second house that size & condition with it at the same time.

I could increase the temperature on the water in the tank and add a mixing valve. That is a good idea. I could also do something similar, but add the second tank. We are changing the well tank from the tiny one to 80-100 gallons this year. That won't solve the water supply issue in the summer, we will still need to use the city water.

I have been reviewing these suggestions in what I find on the internet while wating for my plumber. It will still be a while with the apocalypse and I acknowledge my situation is not a priority for his time.

Again, to make it clear, my plumber will do things to code, then I will change them to anything he suggests after he leaves. There is no government inspection of the work where I live.

Increasing the storage temp on the indirect and installing a (code required in most locations) tempering valve or thermstatic mixing valve on the output would improve hot water capacity for fairly low upfront costs. Most indirects are good for 180F storage temps.

What is the hot water application that seems to hit the capacity limits of the system as-is?

 

[Dana]

BTW: Efficiency Maine has had rebate programs for heat pumps targeted at reducing #2 oil & propane use (and cost) for at least a handful of years, now.