Number crunching

After considering both wood and pellet stoves, I am almost sure that we are going to install a single zone mini-split heat pump in our central kitchen/dining/family room open area where we spend most of our time in a house. I have considered the multi-zone system to heat the bedrooms and downstairs as well, but that would become too costly.

The one lingering question I have is how the rest of our house is going to be heated. Currently, I have a single zone central heat with hot water baseboard radiators in each room. The thing is that the thermostat is located on the wall of the central room where the new heat pump is going to be installed. Now, if the heat pump adequately heats this central kitchen/dining/family room area, then our oil boiler heater will never come on, thus the rest of the rooms will be without heat and will be very cold. If I move the thermostat to one of the rooms or downstairs then the oil boiler heat will come on, but then it will also heat the central kitchen/dining/family room area where the heat pump will be, making the heat pump not to turn on the heat, or considerably, the oil heat system may heat that room way too high such that the heat pump will come on as a cooling air conditioner in the central room, totally negating the energy saving feature.

I will have to find a way to distribute the heat pump heated air to other rooms or to install an additional thermostat in other rooms and make the current oil heating system to multi-zone heat. Both of options can be somewhat difficult due to the floor plans and costs involved.

 

Is that 15% per hour, or over some other period of time? Or is it some other scale?

I'd have to go dig up the results of my home audit (from back before the electric utility ended the program), but do remember that the result was given in ACH, Air Changes per Hour. Our figure came in somewhat below the recommended minimum, impressing the auditor as not common for houses of this age, but acceptable because I had recently installed programmable timers on the bathroom exhaust fans to force a certain amount of mechanical ventilation. I had recently gone through a second round of sealing up infiltration paths, which is why the ACH number came in as low as it did.

I don't recall the guideline number he was using at the time, but ASHRAE's recommended minimum now is 0.35 ACH, or 15 cfm (cubic feet per minute) per person, whichever is higher. For homes with common 8 foot ceilings, the crossover point would be about 320 square feet per person.

How much ventilation do I need in my home to improve indoor air quality? | US EPA

 

That is exactly what I did in 2009, and has worked quite well.

But the rest of your situation is different than mine:

My house has no central heat, but was built with zoned electric, with a separate thermostat in each zone. Before DHP, we kept most doors closed to save heating cost in the lesser used zones. With DHP, we keep all doors open to let its output flow throughout the house as best it can. That flow is enough to keep the largest adjacent space warm enough, but is not enough for the bedrooms down the hall in colder weather. We do sleep cooler, and the temperature gradient is large enough that a good amount of heat does flow to the bedrooms, enough to significantly offset their own heat needs. But it isn't enough to turn their heat off.

People who want their bedroom as warm as the main DHP zone, fuggedaboutit. There has to be a significant temperature gradient for the heat to flow.

This plan works only with all doors mostly open, just fine to a household of only two people who sleep together, but may not work with additional people. It also violates current fire safety advice of always sleeping with doors closed, but that is a personal choice. I have added more smoke detectors.

Do your hot water radiators have individual control valves that can be shut off? I believe these would be essential to make your plan work, along with moving the thermostat(s) out of the primary DHP zone.

 

Well it is 15% per hour reduction . Being in canada the measure are in SI so pressure test was done at 50Pascal

 

I understand the problem of heat flow. But if sufficient heat is present at the central location of our kitchen/dining/family room area, then heat will transfer to the other rooms on the same floor without too much effort. All I need to do is to make sure that all the doors are open. And if that is not sufficient, then placing a small circulation fan at the doorway will do the job. This is not specific to the HP problem. In the past, I have done a similar thing with a kerosene heater in a central location in our kitchen/dining/family room area to use as the main heat source most of the day. For this setup, at night time, the kerosene heater was turned off, thus the central oil heater took over the heating function for the entire house all night long. Naturally, we kept our bedrooms substantially colder than the kitchen/dining/family room area, so this worked fine. Yes, I can see the problem with this setup, if the rest of the house needs to be as warm as the kitchen/dining/family room area, as @fuzzy1 commented

The point is that for this to work, I would have to turn down the HP during the night such that the oil boiler heat will take over the heating function for the entire house during the night keeping the rest of the house warm enough so that it won't freeze. But this will make us more dependent on the oil burner. To permanently fix this problem and take full advantage of the HP even during the night, I would either have to install multi-zone HP for each room (area) or have to update the current central oil heat system to multi zones to cover the separate heating needs as suggested below. But either option is going to be very costly, so I can't do it right now.

Thanks. That's good information to know. I was thinking of the heat pump HVAC system in my PP set at "AUTO" which switches heating and cooling automatically depending on the temperature. Incidentally, this auto switch from heat to cool and vice versa happens quite often in my PP. It is very common for us to have a morning temp of 40sF turning the "heat" on when AUTO is set to 65F, but afternoon temp reaching above 70sF automatically switching the HVAC to "cool" in the afternoon. That is one of the reasons that unless my wife is driving or riding with me, I almost always keep the HVAC OFF on my car, only turning it on when I really feel the need for extra heating or cooling.

I don't really know how our current central heating system is designed and how they are operating. That's a good thing to ask next time I have our boiler serviced before the start of the next heating season in the fall. I certainly have never shut off the flow of hot water at any point in the plumbing. I just know making the current system into two zones is not as easy as just installing an additional thermostat and circulation pump. It takes major updating on the entire plumbing of the house. For that reason, I was planning to wait for the update until when the current boiler is needing to be replaced, which is, as I commented before, getting very old and can happen sometime in near future.

 

... and partially defeats the purpose of getting a heat pump in the first place.

I've spent very little time temporarily sleeping in rooms with hot water or steam radiators, so haven't learned enough about such systems. Some had individual manual control valves right at the radiator itself to throttle or shut off the heat, while some had what appeared to be some form of primitive individual thermostat, and others had nothing.

If your home had a control valve at each radiator, than the quick cheap hack path to a 2-zone system would be to close the valves at the radiators in the heat pump zone only, leaving open only the ones where the heat pump won't adequately serve.

I don't know how expensive it might be to add such valves, or if such might cause stagnation problems in the plumbing. But removing radiators and capping their pipes isn't a good choice either, as you want to make tuning adjustments as needed, and may need those radiators in the coldest weather when the heat pump can't keep up.

 

Yep, you are correct. Our heating system is hot water hydronic system not a steam boiler system. It is a single zone very simple complete loop for the entire house with a single circulation pump located near the boiler. I just checked the end of the hydronic baseboard radiator pipe connection. It does not have a ballcock valve but it has some type of valve(?) at the very end which I believe to be an air bleeder valve, but not for sure.

Not sure if it can be closed and opened to isolate the section of the loop on a system like this. My feeling is that the system is a non-branching single linear loop for the entire house such that closing any section of the pipe will shut off the entire system. I will ask the plumber when he comes to service our boiler. If it can not be closed off or easily bypassed, then it is likely that he will recommend updating the entire plumbing to a multi-zone pipe configuration, which is likely to be very costly.

 

probably a bleed valve.

i have the same system, but all the rooms have a thermostat and circulator pump

 

Yeah, if ours is branching redundant loops for each room, then conversion to multi-zone would be easier. But I don't think so. The problem is that we have all of the plumbing pipes hidden in the walls and floor/ceiling. No pipes are exposed except for a very short section where they are connecting to the boiler in a very small mechanical room in the corner of the house. So, I really don't know how the pipes are connected inside of the walls.

 

agreed, mine were all done in the remodel. even with the main loop and diverter tees exposed in the basement, i don't think there was any way to isolate each room.

 

Our house is split level raised ranch with a finished base floor. It can be called a "basement" since it is completely earth bermed on one side, half under grade on the two sides, and the remaining one side at grade level for exit to our driveway. Since this "basement" is completely finished with walls and ceilings, all pipes connected to the boiler are inside of the walls or in between the floor above and basement ceiling, making access to the pipes impossible without tearing the walls and ceilings.

 

these retrofits are more difficult than i hoped

 

Just got this in the mail. I may give them a call.

My only concern is trying to insulate the roof.
It already has some kind of 1950’s insulation.
A thin layer of silver paper, and half an inch of something attached.
Idk if blown in insulation will distribute evenly because of it.

 

Loose blown-in material will fill any gaps and spaces as long as the hose can get there. More of the problem is making sure it does not cover everything and plugging all the ventilation access. If they put the blown material all the way to the eave without first installing rafter vents, you are going to have a problem with attic space ventilation.

 

this is turning into a technical nightmare

 

So, I finally got an answer from the first installer who did the site visit and gave me a single-zone Mitsubishi heat pump quote to give me an estimate if I used the Fujitsu 15,000 BTU heat pump units, ASUG/AOUG15LZAH1. The answer was surprisingly easy. It is the same price. About ~$6000 for the total. The problem is that the quote is not itemized, so I really don't know what the breakdown is.

For the same price, I think I will go with Fujitsu. But I have another contractor scheduled. So, I will wait for at least one more estimate.

 

I think you are good with Fujitsu , I have the previous generation version of this cold weather heatpump The main difference seems to be a little increase in indoor CFM with the new generation .
FYI here is a pdf you could find informative

 

Thanks. Yes, for a single zone mini-split system, the Fujitsu Halcyon has impressive spec and seems to be a leader in low temp heating capacity. I am still exploring a multi-zone option to overcome the problem of the current single-zone central heating system in the house. The efficiency drops for the muti zone unit. And I don't know how much difference in the cost of installation between a multi-zone (single outside unit) and two single zone mini-split. Ideally, I would love to get rid of our oil boiler-based heating system for good. But that is likely to be a way too expensive upgrade. To completely replace the current central heating system, a multi-zone (total 7 indoor units) with backup electric radiant heaters for each room and also a new electric preferably heat pump water heater has to be added. Our 30+ yrs old oil-burning boiler needs to be upgraded soon one way or another. I just need to do hard math on cost differences both upfront and ongoing.