Upgrading a Heating System
Hi all – Hoping to get some help making decisions related to potentially upgrading our heating system. We’re in the middle of a pretty extensive renovation of our 1892 colonial revival near Boston (climate zone 5a). The house is just under 5000 sqft, with three levels of living space (finished attic). We currently have a high efficiency natural gas steam boiler that was put in in 2016, connected to essentially the original steam radiator system on one zone controlled by a Nest thermostat, for which we have numerous “comfort sensors” to help us control heat it specific areas (eg at night, temp is set by an upstairs comfort sensor instead of the downstairs thermostat). We are now putting in AC and doing a few other updates that have many (though not all) of our walls open. I’m trying to figure out if there are upgrades we should make to our heating system as part of this. Aside from being single zone and the drawbacks of that, the current radiator system clangs quite a bit and we have some leaky radiators that probably need to be replaced. We’re paying quite a bit for natural gas right now and we’re a bit high on electricity too. Also worth noting that we know we have some insulation gaps and are working to remedy those in the next several months as well.
edit to add: we also have all new windows put in in the last 4 years. There are certainly drafts around them from bad insulation (we’re working to fix) but the windows themselves are solid.
I’ve spoken to several contractors and the typical recommendations have been to either add heat pumps onto the HVAC system we’re putting in for AC, or to go hydro air, which would require us to trash our current steam boiler and get a wall hung water boiler unit. I’m wary of making a total heating system switch, but maybe I shouldn’t be. I’m attaching the first floor plan for our house – second and third floors are stacked right on top of the first, with the exception of the bump out on the kitchen only, as well as a few different proposals I’ve received.
Would greatly appreciate any advice/ reactions to these proposals and guidance on what we should consider with some of these decisions. Thank you!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
The hydronic air handlers are useless for your situation and can be dismissed outright: unless the air-handlers are spec-ed for lower water temperatures, a "wall hung water boiler unit" (a modulating, condensing boiler, wall-hung or otherwise) will not be more efficient than the existing steam, plus they'll require pumping and blower energy the steam does not need. Really unclear why they'd suggest those, besides wanting to upsell a new boiler. The new boiler needn't be a condensing boiler anyway, so be wary of those contractors.
The best solution would be: 1. a heat pump, which should be essentially the same installation cost as AC as they are nearly mechanically identical. If the heat pump meets your heating load, you're done. If it doesn't, you have more choices. You could use: 1. electric resistance backup integrated into the air handler, which is dirt cheap to install but expensive to run, which may or not matter based on how often it runs. 2. A furnace using the new ductwork (a gas/electric hybrid set up). This is more expensive to install but usually cheaper to run than the electric resistance and potentially cheaper than the heat pump at some outdoor temperatures. Furnaces are different efficiencies, so it may or may not be cheaper than option 3. 3. Keep the steam as the backup.
Hydronic as an option was meant to totally replace the steam. I’m not clear why they’d suggest it either but they do seem oddly keen on it. I wasn’t sure if it was a more desirable type of heat from a comfort perspective, perhaps. It could also be that my Gc was at one point thinking the current boiler was hot water, not steam and asked for hydro quotes specifically as a result.
We can keep the steam for backup and that’s what I’m inclined to do, but the pipes for the system are pretty insane. If we ever want to finish our basement, we’ll need to consider major modifications or ripping it all out. It sounds like it’ll also inhibit an ideal ductwork setup as well, but that should be surmountable. Do you see a world where the heat pump solution could be the primary source of heat? I hear mixed things about heat pumps but it seems like the negatives come from people who are not well informed/out of date.
Yeah the combination of highest upfront cost and zero efficiency gains make it a strange choice. Heat pump combined with gas or electric supplemental heat if needed is much easier.
Are your steam rads one pipe or two pipe? One pipe is pretty hard to convert to hydronic, best to leave it as is.
First step in any of these is have an independent hvac engineer run a man J on your house.
The chances of your place having a 6 to 7 ton cooling load is pretty much zero, at best it is about half that.
The simplest AC retrofit in older houses is high velocity as you can fish the pipes through existing walls. The equipment is not cheap but would be less work than trying to hide standard ducting.
Also make sure to keep the HVAC out of the attic, this is asking for increasing your cooling load and cost by 25% for no reason plus adding a couple of additional big air leaks to an already leaky older house. A good compromise is spray foaming a knee wall section and installing the equipment there.
Our radiators are two pipe.
Our walls are pretty thick, l and we have enough of it then open right now that we aren’t worried about running ducts as currently planned. Is there any reason other than ease that we should consider high velocity (to be honest that might be part of the plan in these proposals and I just don’t know that yet)?
I should have mentioned, our attic is finished and part of the heating zone for the steam radiator system. We’re planning to have AC there too as our guest room and main family hangout/play room is up there. Would you still advise so strongly against having a unit up there?
Without doing major energy improvements to the house, it would be very hard to make a 1890's house comfortable with anything but rads or floor heat. If you are in an area with a lot of steam heat, I'm sure you can find a decent old steamer to take a look at your setup and fix your clanging and leaks. Since you already have a newish steam boiler, any kind of major rework or replacement doesn't make financial sense.
If you can fit standard ducts in the walls than high velocity is probably not worth it. Since the high velocity equipment is pretty pricey, I'm sure the HVAC contractor would have mentioned it.
When most folks refer to attic HVAC installs, it means the air handler outside of the conditioned space of the house, this is the install you want to avoid. Since you attic is finished, provided the equipment is installed inside conditioned space (ie closet/hallway/unused den) than by all means install there. Since the air handler will be close to bedrooms, make sure to get a unit with an ECM blower, besides using less power, these are also much quieter.
A better outdoor unit might also be worth it, a fully modulating or five stage compressor is typically only $1k to $2k above a budget unit. Besides being more efficient, they are also way quieter which is nice if the unit is anywhere near windows or outdoor sitting areas.
Not sure a heat pump is really worth it for such a large and leaky old structure. You would have to oversize to such an extent to heat the place that cooling would suffer. Maybe if you are looking to do some significant envelope improvements it can be made to work, but somebody should do some calculations to figure it out.
Either way, check your cooling load. Very few houses short of an all glass cube have a cooling load of 700/800 sqft/ton.
If they go with a modulating system and a steam backup, no real downside to the heat pump here since oversizing won’t be an issue. Plus steam uses convection just like a forced air system, comfort shouldn’t be that different.
Forgive me for such basic questions, but based on the attached proposals, are the systems being recommended modulating systems? When does oversizing become an issue - Akos, are you saying it’s oversized, but Paul, you’re saying because of elements of the system that won’t actually be a problem?
One thing we’re considering is just sticking with an AC add on for now, but making sure that we can add the heat pump element later. Is that inadvisable for any reason? I’m attaching the original proposal from one of our possible contractors for this approach.
There is extra costs to go for a heat pump. This would make financial sense if the steam heat is from oil or propane. Hard to get the numbers to work for natural gas unless the home owner is actively looking to go gas free.
High temperature rads are not the same a forced air. When running full tilt in the winter, they are so warm you can feel the heat radiate off it. This is even in old leaky houses with terrible windows.
I guess with good design you can make a forced air system work as well, I have yet to see this with older houses around me though. Old leaky forced air houses tend to be pretty uncomfortable. Once the place is air sealed and windows replaced, it can definitely be made to work though.
Most residential AC systems tend to be oversized by about at least a factor of 2x. This mostly comes from using rules of thumb such as 500sqft/ton instead of doing the proper homework to size.
Except for the higher equipment costs and larger ducting, there isn't too much of an issue with oversizing. A right sized unit does mean longer run times, quieter operation and better humidity removal. Keep in mind even a right sized AC unit might only run near max capacity for a couple of hours out of a year, so an oversized unit will have very short runtimes most of the time.
Modulating units do offer some flexibility in sizing but not enough to grossly oversize. Most have a 2:1 to 2.5:1 turndown, so not a great deal.
Most modulating units will have high SEER values (Ie Keeprite VA9). A SEER13 is bargain basement unit, a modulating unit is around SEER20. There are some in-between multi stage units that are around 16 or so. You are not in an area that needs a lot of cooling, so a modulating system is probably only worth it if you are looking for quieter outdoor unit. A right sized two stage outdoor unit with an variable speed ECM air handler is probably the best value.
Asian heat pump systems tend to be significantly cheaper with better performance but installer support and knowledge is sparse. For example a 3 ton Gree Flex hyper heat system (SEER20) is less than the cost of a Goodman two stage 3 ton AC only unit, a pair of them would probably be in the ballpark to carry the house on most days without steam backup.
For the attic install, do make sure the installer does not mean installing anything (equipment or ducting) behind knee walls or above ceiling. For example of a good setup in on a 2.5 story would put the air handler into a closet near the top of stairs with the return in the stairwell. Run ducts through the floor to feed the 1/2 story plus the floor bellow.
As someone from the Boston area, if I were in your shoes, I'd opt for a higher-efficiency system. We run cooling for enough months of the year that the efficiency gains will generate a quick ROI. I'd be looking for a 16 SEER+ outdoor condenser that is multi-stage or variable speed.
Your contractor is proposing a bargain basement single-speed outdoor condenser that I imagine (it's not evident on the quote) is paired with a bargain basement single-speed PSC blower-type indoor air handler from Goodman. There are better manufacturer's and options in this space. Carrier makes some great equipment and should be available at a local wholesaler to your contractor.
Something you might consider is checking out the MassSave website and looking at the incentives available for higher-efficiency equipment. Some of the rebates may make the step-up more palatable.
Lastly, I'd recommend either choosing the heat pump option or not. That condenser is the most expensive piece of equipment in the proposed system and is not an easy thing to swap later.
Thanks, Mike. This is really helpful. Is ecoer a decent manufacturer for heat pumps? What about Concord for condensers? We are most inclined to go with the contractor who is proposing one if those setups.
Am I understanding correctly that if a heat pump is added to the system, it also serves the role of the condenser? Or is it more nuanced than that?
I’ve been working with Mass Save as well and from what I understand incentives only exist for heat pumps, when offsetting heat use from natural gas. I don’t think there are any incentives for more vs less efficient AC systems. This is one of the reasons the heat pump entered our consideration to begin with.
Thanks!
Exactly - the one quote that detailed adding an expensive modcon to a house with an existing boiler to use with an hydro air handler and Goodman AC was a confusing jumble of high end boiler, low end AC, and useless hydro air.
“ One thing we’re considering is just sticking with an AC add on for now, but making sure that we can add the heat pump element later. Is that inadvisable for any reason?”
No - the outdoor equipment is near identical, but it’s not the same. Unfortunately, it would be expensive to add on later. It would be extremely cheap to add on now - probably a few percent.
“ When does oversizing become an issue - Akos, are you saying it’s oversized, but Paul, you’re saying because of elements of the system that won’t actually be a problem?”
They don’t look like modulating ACs so yes oversizing would be an issue. Right sized would be good, right sized and modulating would be best. Having a too large AC means it’ll struggle with dehumidification and turn on and off annoyingly. Oversizing slightly to gain more heat capacity is okay if it modulates.
Akos, it depends on their electric and gas rates. At my home, a heat pump is substantially cheaper to operate than gas.
Attaching our most recent (feb) gas and electric rates and usage. Would love a gut check on these - both seemed pretty high, as if there is room to improve. Of course insulation will help, but curious if there’s less opportunity otherwise than we thought.
Ouch. Unfortunate combination of high heat loss and high rates. Using this method, https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new, your heat loss looks to be about 100,000 btu/hr. Anything to bring that down will be a good start, I'd look at air sealing first. Based on these rates, a heat pump might be about 10% cheaper to operate if you use if for milder temperatures (the economic balance point -say above 20 degrees?) It's a moving target, as efficiencies change based on outdoor temperature, plus your gas and electric rates are moving too.
The concerning part of the gas bill is the delivery charges - gas supply costs change constantly but delivery charges usually only move consistently up and yours are high.
It’s worth mention that this bill is from a period where we’ve been under construction and are less insulated in certain areas than we would be normally, and certainly less than we will be once we complete that construction. Sounds like we need to look closer at this after we complete the insulation improvements that are already in our plans?
I noticed the delivery cost as well - that’s something that is set by the gas company, correct? Not something that can be optimized for by a homeowner?
Spend some time on this site reading about air sealing. In a big old house, fixing insulation gaps alone won't do the trick. Air sealing critical areas can really improve comfort.
Since you are mid-renovations, you have a great opportunity to do some air sealing work that isn't as easy once you are done renovating. Try to bring in an energy auditor or weatherization contractor to come and do a blower door test and air sealing assessment.
Unfortunately, yes. The delivery is the cost of maintaining the infrastructure. The adjustment of $.36/therm is interesting - unclear if that's permanent or not.
I think given the energy usage indicated by those bills, there's a strong case to be made for doing some energy modeling to figure out the right cost/benefit here. There's clearly a need for a combination of air sealing, insulating, and equipment right-sizing. The question is, after you complete the air sealing / insulation what are your projected heating and cooling loads and what equipment would be best to meet your need.
There was a previous question on the suggested equipment. I've never heard of Ecoer, but checking out their website it looks like both the air handler and heat pump are higher-efficiency variable speed units.
I'm all for modern efficient systems. But I think it might be worth having a steam pro look at yours, since you're in the heart of steam heating country.
Check out https://forum.heatinghelp.com/ it's full of some very experienced steam guys.
It seems like there is no end to how people can screw steam up, but it can work quite well if done properly.
Steam heat is kinda like mini splits in that there are a lot of people out there screwing things up, but if you get the right pro it can work pretty well.
Hi there... first time poster... and a homeowner not an expert by any means. @kcchernak, I have a similar situation. 6000 sq ft leaky old house, built 1915, but hydronic radiator heat vs steam, two separate gas boilers... one from the 1960s, 170,000 BTU/hr output, one from 1930s, likely about 250,000 BTU/hr, but no marking on it. They serve different parts of the house. Live in Lander, WY. I'll be switching to a heat pump (most likely geothermal) for basement, 1st, 2nd floors, and a separate air source heat pump for 3rd floor (for heat and to get AC in 3rd floor and some of the south facing 2nd floor rooms).
I attached a recent gas bill just for your reference... we use about the same amount of therms, but gas is way cheaper out here than in Boston. I'd second the value of doing a MAnual J calc. I did online using Cool Calc. Takes about a day to gather all the measurements and enter. Showed that my house as is, has a heat load of ~165,000BTU/hr and Cooling load of ~45,000 BTU/hr. Then can use it to adjust for energy efficiency upgrades... I think I can get to ~95,000 BTH/hr heating, 25,000 BTU/hr cooling. Note that these are way lower numbers than current systems support and lower than the rules of thumb suggest (e.g. Wyoming rule of thumb is 45 BTU/sqft... which would put me at 270,000 BTU/hr heating).
Regarding Ecoer, I have a friend in Boston (Arlington) in a single family home. He had two air source heat pumps put in last year (Bosch and Ecoer) and has been happier with the Ecoer (which his installer recommended). I can get the installer info if helpful.
hello kcchernak:
are you done with your house retrofit? What path have you choose? Still using steam heating?
If you did not switched to hydronic, please check https://www.pmmag.com/articles/97633-a-new-look-at-vacuum-heating.
Please, let me know if interested - [email protected].
Igor