Furnace domestic hot water temperature

[Stelcom66]

With warm weather here, my furnace has been on it's lowest setting for a while. During the cold seasons, it's at the lowest in the evening and through the weekends when I use the wood stove. My hot water is heated by and contained in the furnace. It will run randomly to maintain the hot water temperature. With oil prices the way they are, I wonder what's the lowest reasonable setting for the hot water?

The manual states the factory setting was 140 º. I set mine to 120º last year. I just lowered it to 118º. I recall there's a blend valve to combine some cold water with the hot. Maybe the fuel savings would be insignificant, but I wonder if I should reduce the temperature even more and adjust the blend valve accordingly? I just recently started doing laundry using the 'Cool' setting on the washing machine. Not sure if that, as opposed to 'Cold' heats the water a bit, or it expects a hot water feed. I have valves on the hold and cold hoses to the machine that I turn off when not in use, been only turning on cold lately.

 

[Poindexter]

Is your only hot water storage the 'loop' inside the boiler? On mine that is only about 3 gallons of water.

The wife and I are still in the five bedroom house we needed when we raising children, with a loop for DWH in the boiler, and a 50 gallon hot water tank adjacent. All the hot water fed to my house comes from the 50 gallon storage tank.

If you can really get away with only three gallons of hot water laying around an inline water heating system might work for you.

 

[Stelcom66]

I believe it's more than 3 gallons, just looked in the manual which doesn't specify, but it's a good sized tank. on the lower part of the Buderus furnace. I believe the original furnace from 1954 had that loop. There were 5 of us in the house, several showers a day and always a good supply of hot water with the Buderus. The original system wasn't cutting it - not just because of capacity, but it was about 35 years old. I heard the loop tends to get calcified on the inside effectively reducing it's diameter.

Just me now, so like you said I probably could get away with an inline system at this point.

 

[Poindexter]

Buderus is a pretty good name around here. I don't have one to talk about. On my lesser boiler, a Burnham, the hot water loop capacity is about three gallons, just installed in the last two weeks.

The original question was more or less, how low can I set the water temperature for DWH, to use less boiler fuel in the summer months. The way I read it.

I have been paying attention to this lately. The wife and I just dropped about $15k into new boiler, new hot water storage tank and little brass bits, within the last three weeks.

With essentially a 9 month heating system (6 months of winter + 3 months of shoulder) I didn't typically worry about the boiler burning a little oil in the few weeks of hot weather we have. But the new boiler sounds a little different than the old one did. It makes different noise than the old boiler, my hearing hasn't tuned the sound out as back ground noise yet, and by golly if the boiler isn't running a fair bit.

The boiler is set to maintain 160dF and 15psi in the water jacket, 24/7/365 and lights the burner when it gets down to about 130dF with usually 15psi still showing. The DWH storage tank maintains 125 dF to 118dF at about 48psi. There is a recirculating pump between the hot water loop in the boiler and the hot water storage tank.

One thing I don't like is when the DWH gets down to 118 and the DWH recirculator pump kicks on, the boiler burner lights, even when the water jacket for the boiler is at 160dF and 15psi. I would like to get a few BTUs out of the jacket into the hot water loop before the burner kicks on.

There was a thing we used to have on our old boiler that would let the boiler jacket deliver heat water to the baseboard system without kicking the burner on until the water jacket temp got down to 130. An 'economizer' I think it was called. By the time our taxes were finished for that year we got the thing delivered and installed for free. I think I want another one of those.

One of my neighbors uses her boiler to heat DHW in the winter months, but then uses electricity to heat her DHW in the summer, allowing her boiler to go cold. I don't have breaker space for that at my house, but the neighbor and I are both using off the shelf electric hot water heaters as our DHW storage tanks. Local to me oil prices are going up faster than electricity prices this month - but 'fuel surcharge' has been the single biggest line item on my electric bill for years.

The wife and I are in agreement we are not turning the set point on the DHW lower than 118dF. I readily agree keeping the boiler running to only make DHW during three months of not heating season each year is potentially wasteful, but on a cost basis per BTU, electricity, for me local, averages about 5x the price of boiler fuel.

One option for us would be, well no, that won't work. I was going to say we could not use the downstairs bathroom in the summer and use an inline water heater upstairs for that bath and kitchen in the summer months - but the laundry machines are downstairs. I think everything my wife owns needs to be washed in warm water.

I am going to stop here and go re-read the original post.

 

[Poindexter]

With warm weather here, my furnace has been on it's lowest setting for a while. During the cold seasons, it's at the lowest in the evening and through the weekends when I use the wood stove.

The settings on your thermostats, or the set points on your Buderus boiler? For the summer months I have all my thermostats around the house set to 55 dF, but the water jacket in my (not a Buderus) boiler maintains 160dF @ 15psi.

The wife and I are not anxious to lower the set point on our domestic hot water below 118dF.

I can't help you with your specific laundry, but a few observations. The courtesy valve for the hot water supply to your washing machine is very likely not built to withstand frequent open/close cycles.

We noticed a damp spot under out hot water storage tank in October 21, called our plumber, blah blah phone tag. In December 2021 our water bill doubled. In Jan 2022 we got another extremely high water bill, call the plumber again, more phone tag. So we called our water company, they sent two guys in an enormous truck and got here in two hours. I came home for this one. The first guy out of the truck was fully competent, smart, asked intelligent questions, not an idiot. He wanted to see the toilets in both bathrooms (we had already tested with food coloring) and then started looking elsewhere. He finally asked to phone a friend, I said OK, he called the remaining guy in the truck in my driveway, and second not an idiot from the water company came in and wanted to look at both toilets before he looked at anything else. NAI #2 (not an idiot #2) stated sometimes valving fails inside washing machines, so I could be pumping 3k gallons per month from the supply side to the drain side inside the clothes washer.

I had an extra 3k gallons of water, per month, on my water bill for a couple months now. 100 gallons a day. 4+ gallons per hour. Turned out it was all leaking out of my hot water storage tank - and then draining out through a hidden crack in the slab leaving only a damp spot on the floor.

So if turning off the hot or cold water supply valve to your washing machine decreases your water usage, your washing machine is broken. The cute little courtesy valve sticking out of your wall is not built for wear and tear.

For my man laundry, everything I own gets washed and rinsed in cold water. Levis, Carhartts, Tshirts, flannel shirts, socks, underwear, cold cold cold. I do have a selection of clothing that is dry clean only. And I bought white scrubs to wear to work about two years ago. All the data was saying the virus which must not be named could be killed by regular soap and water, but I work for a hospital and wanted to stay one step ahead. So I switched to white scrubs, and those get laundered in hot water, with bleach, and 118 degree hot water seems to be fine for that.

I do hope some more folks will chime in, @begreen might know who to tag. Centuries of experience on tap here in all kinds of fields.

 

[begreen]

I don't have much to add, except in agreement. We wash our clothes with warm water but rinse with cold. The HW heater is set to 125º. And yes, the service valves at the washer are not meant for frequent usage.

I would not keep adjusting the system. If the goal is to save a bit on the oil bill, insulation is your friend. Insulate as much of the hot water piping as possible. Put an external layer of insulation wrap on the HW storage tank. If sun exposure is good, perhaps consider adding a solar HW loop to the storage tank?

We too have had spikes in our water bills in the past few years. The most recent one was in a copper fitting in a hot water supply line to the upstairs that developed a minuscule leak. I can't even call it a pinhole. The water was draining into the crawlspace sight unseen. Eventually, it was enough over time to spike our water bill and start darkening the woodwork in the cabinet that hid the piping.

 

[peakbagger]

I run solar hot water panels spring summer and fall so I am at the mercy of the sun for hot water temp. I do have a backup element on the tank set at 130F. I leave power off most of the time to the element. In the winter I have an Amtrol Boilermate that is typically used with oil or gas boilers to reduce standby loss. They work well except that many cast iron boilers have to always be warm or they leak. I have a cast iron boiler that does not leak when temperature cycled. System 2000 boilers are set up for "cold start" operation, my parents had a Buderus that was cold start. Its about a gallon of oil a day to keep a boiler warm. Generally its recomended to keep the boiler low setting at 140 F to keep corrosion inside the boiler under control but with low sulfur heating oil used these days, I do not think its an issue like with the older heating oils.

I heat the Amtrol with my wood boiler in winter to 180 F using left over heat at the end of charging up my storage. I have a Honeywell temperature controller that dilutes the hot water from the Amtrol or the solar hot water panels down to 140 F. I could easily run it down to 130 F. Its too bad that the initial cost of SHW system have scared away their installation, its effectively free hot water anytime the sun is out and outdoor temp is above 40 F. Even with lower temps, the SHW panels act as preheat. If I do a new house I am tempted to pick up some used panels and install them due to little of no maintenance aspect. Mine are twenty five year old and run with a DC pump off a solar panel. I changed a expansion tank and check valve and that is total maintenance and repairs for 25 years.

 

[Stelcom66]

The settings on your thermostats, or the set points on your Buderus boiler? For the summer months I have all my thermostats around the house set to 55 dF, but the water jacket in my (not a Buderus) boiler maintains 160dF @ 15psi.

The wife and I are not anxious to lower the set point on our domestic hot water below 118dF.

I can't help you with your specific laundry, but a few observations. The courtesy valve for the hot water supply to your washing machine is very likely not built to withstand frequent open/close cycles.

The settings on the thermostats. If you've been at 118º. for DHW and have been fine with that, and don't intend on going lower I'll likely keep that setting.

Now that I recently started using the 'Cool' laundry setting (don't know if it expects a hot supply for that) I just open and close the cold water supply, maybe once a week or so. Noted re: frequent usage may not be good. In fact I left it on from last night unintentionally, It may not be necessary - I probably went 30 years and never had a hose burst.

Wow - that was quite a leak you fortunately discovered, Worst of both worlds I guess having a place for the water to drain to make it not as obvious. The main goal is so save cost on oil - but then there's the electrical cost. Probably will leave things as is - I'll spend money to save money to a point.

I'd really like to do something with solar though, Just don't have the time or money right now. Again, spending money to save money - but the concept just seems to be worth it, even maybe breaking even. Knowing you're harnessing natural energy or any resource is great IMO. Kind of like the rain barrel I have, but need to repair. Had it positioned under a gutter spout - after a few rainstorms it felt like it weighed as much as a small wood stove.

 

[Stelcom66]

I don't have much to add, except in agreement. We wash our clothes with warm water but rinse with cold. The HW heater is set to 125º. And yes, the service valves at the washer are not meant for frequent usage.

I would not keep adjusting the system. If the goal is to save a bit on the oil bill, insulation is your friend. Insulate as much of the hot water piping as possible. Put an external layer of insulation wrap on the HW storage tank. If sun exposure is good, perhaps consider adding a solar HW loop to the storage tank?

Maybe I didn't describe the valves accurately - it's not part of the washer but mounted above the hot and cold faucets for the basement sink that feed the hoses to the washer.

Made note of pipe insulation - good recommendation. Not hard to do and probably not that expensive. And yes a solar system for whatever - hot water or electricity would be great. As stated best not to go crazy with frequent furnace adjustments.

 

[Stelcom66]

I run solar hot water panels spring summer and fall so I am at the mercy of the sun for hot water temp...

I heat the Amtrol with my wood boiler in winter to 180 F using left over heat at the end of charging up my storage. .

But I'll bet overall you're saving a lot. I wish my house was set up for the wood stove to heat hot water, If I knew then (37 years ago) what I'd be doing now, I'd be in a rural area on several wood acres of land!

 

[fbelec]

as said above. running a cast iron boiler under 140 is a new boiler waiting to happen. above 140 no corrosion below 140 it corrodes faster. you wood be surprised how little oil it takes to heat water to 140. don't know the size of your nozzle on the boiler but the average house is 1 to 1.25 gallons a hour meaning if your boiler run non stop for a hour you would only burn a 1 or 1.25 gallons of oil.

i used to know a house that had solar hot water and a stone lined 80 gallon storage tank with electricity backup. here in new england in the cold the system used to make enough hot water make the pressure/temperature valve blow off so many times that he piped the blow off valve into a laundry sink so that it wouldn't flood the place. and this was on 40 year old equipment

 

[Stelcom66]

I suppose that's why the Buderus system is set initially ay 140º. A few years ago I had the anode replaced in the boiler. Maybe raising the temperature will prolong it.

 

[fbelec]

most dishwashers need 140 also. their heating element is on a timed circuit. to cold of water and it can't sanitize

 

[torpesco]

One other temperature note: Many health authorities recommend at least 120F to keep bacteria from growing in a hot water system. Some even higher. A year ago, I found a couple that said 120F or 50C, so that’s what I went with.

 

[peakbagger]

Most home owners do not worry about Legionella bacteria but in some cases it can crop up particularly in Evaporative coolers (Swamp Coolers) and more rarely home water tanks. It also can form in hot water tanks that are out of service in seasonal homes. Its far more of an issue in commercial buildings with chilling plants with cooling towers. Cooling towers are ideal breeding places and reservoirs for legionella and when the towers is in operation they throw out a plume of aerosols that can sucked up by makeup air systems particularly in health care buildings that use 100% makeup air.

Expansion tanks on water systems can be a reservoir for Legionella. Ideally the system is kept over 140F which will kill it but the temperature in an uninsulated expansion tank on a system operated at 140 F will be lower.

Potable water systems in health care and hospitality industries have some pretty extensive requirements to prevent Legionella.

Catching Legionella disease is usually not an issue with healthy people but those with compromised immune systems or compromised lung function have to watch out for it as it can be fatal.

 

[Stelcom66]

Don't know if it matters - but I have well water. If I do make a hot water adjustment again, it definitely won't be going down. I had it at I think 122º for a while, then 120, now 118º. I guess the fuel savings would be marginal, if any.